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Radiolabelling of organic molecules with short-lived radionuclides (¹¹C, ¹⁸F) Balatoni, Julius Alexander 1994

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RADIOLABELLING OF ORGANIC MOLECULES WITHSHORT-LIVED RADIONUCLIDES (“C, 18F)Julius Alexander BalatoniB.Sc., The University of British Columbia, 1981M.Sc., The University of British Columbia, 1985A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIESDEPARTMENT OF CHEMISTRYWe accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIAAugust 1994© Julius Alexander Balatoni, 1994In presenting this thesis in partial fulfillment of the requirements for an advanced degreeat the University of British Columbia, I agree that the Library shall make it freelyavailable for reference and study. I further agree that permission for extensive copyingof this thesis for scholarly purposes may be granted by the head of my department or byhis or her representatives. It is understood that copying or publication of this thesis forfinancial gain shall not be allowed without my written permission.Department of ChemistryThe University of British Columbia2036 Main MallVancouver, CanadaDate: b. 30) jqAbstractThe primary aim of this study was to develop new methods for the introduction of short-lived radionudides (11C, 18F) into organic molecules. This was accomplished by the useof organometallic intermediates: (i) i16-arene)tricarbonylchromium complexes were usedto facilitate aromatic nucleophilic substitution of the attached arene for theincorporation of[11Cjcyanide anion, and (ii) vinyl-tin derivatives were employed forelectrophilic fluorination reactions to produce F- and 18F-labelled vinyl fluorides.A range of simple(,6-arene)tricarbonylchroniium complexes were prepared as modelsystems. Fluorine was found to be the only leaving group that was readily displaced bycyanide. Non-radioactive and 11C-labelled aryl nitriles were prepared in 10 minutes byreaction of complexes 1, 4, 5, and 6 with[12Cjcyanide and[11C]cyanide in DMSO atelevated temperature. Under the reaction conditions used, the aryl nitrile product wasliberated from the chromium tricarbonyl moiety thereby obviating the need for aseparate oxidative decomplexation step.The reactivity of (E)-vinylstannanes 30, 31, 32, 33, and 34 was studied with elementalfluorine and acetyl hypofluorite under varied conditions. Generally, gaseous CH3OOFwas found to be the most effective fluorinating agent for the electrophilic cleavage ofvinyl-tin bonds. For example, 31 was fluorinated with CH3OOF, at room temperature,to yield an isomeric mixture of 39 and 40 in 41-42% yield; fluorination with F2proceeded in 9.0% yield at best. Subsequently, 31 was radiofluorinated withCH3OO’8Fin 19% radiochemical yield (based on starting[18F]F2).11MeMe CII ICr(CO)3 Cr(CO)3 Cr(CO)3 Cr(CO)34 5 6Sn(Bu)3HOR20 O/0—Sn(Bu)3 // \c)OR’O33Sn(Bu)330 R’=R2=H31 RMe,R=HOH32 R’R2MeoO0 \\34HO HOMeO MeO39 40iiiTable of ContentsAbstract iiList of Tables viiList of Figures ixAcknowledgements xDedication xiChapter1 GENERAL INThODUCTION 11.1 Background 11.2 Aspects of Labelling with Short-lived Isotopes 31.3 Objectives and Format of this Thesis 9References 132 APPLICATION OF ORGANOCHROMIUM CHEMISTRYTO RADIOLABELLING 162.1 Introduction 162.2 Preparation of(76-Arene)tricarbonylchromium Complexes 212.2.1 Synthesis 212.2.2 Characterization 302.3 Reactions of Organochromium Compounds with Cyanide 332.4 Labelling Studies with11C-Labelled Cyanide 532.5 Summary and Conclusions 65References 68ivChapter3 DEVELOPMENT OF METHODS FOR RAPID FLUORINELABELLING 713.1 Introduction 713.2 Synthesis of Vinyl-Tin Precursors 803.3 Labelling Studies with Non-Radioactive Fluorine 853.4 Radiofluorination Work 963.5 Summary and Conclusions 101References 1044 GENERAL CONCLUSIONS 108References 1115 EXPERIMENTAL 1125.1 General Methods 1125.2 NMR Methods and Instrumentation 1155.3 Experimental for Chapter 2 1165.3.1 Sources of Materials 1165.3.2 General 1165.3.3 Preparation of(t6-Arene)tricarbonylchromiumComplexes 1185.3.4 Substitution Reactions of OrganochromiumComplexes 1255.3.5 Labelling Work with[11C]Cyanide 1355.4 Experimental for Chapter 3 1395.4.1 Sources of Materials 139VChapter5.4.2 General 1405.4.3 Preparation of Vinyl-Tin Substrates 1425.4.4 Fluorination Reactions of Vinyl-Tin Compounds 1485.4.5 Radiofluorinations with Acetyl[‘8F]Hypofluorite 153References 156viList of TablesTableCHAPTER 11.1 Characteristics of Radionuclides Used for PET 41.2 Physical Properties of Some Radionucides 71.3 Positron Emitting Radiopharmaceuticals Used Commonlyin PET Imaging Procedures 9CHAPTER 22.1 Summary of Yields Obtained for Complexes Synthesizedusing Equation 2.9 262.2 Summary of Melting Points of Organochromium Complexes 312.3 Chemical Yields Obtained for Complex 1 392.4 Chemical Yields Obtained for Complex 4 412.5 Chemical Yields Obtained for Complex 5 422.6 Chemical Yields Obtained for Complex 6 432.7 Chemical Yields Obtained for Complex 4 using 18-Crown-6 472.8 Chemical Yields Obtained for Equation 2.18 usingAcetonitrile as the Solvent 482.9 Summary of Chemical Yields 512.10 Summary of Radiochemical Yields Obtained forEquation 2.22 552.11 Summary of Radiochemical Yields Obtained forEquation 2.23. 59vi’TableCHAPTER 33.1 Yields of (E)-Vinylstannanes.833.2 Summary of Yields Obtained for the Reaction of 31with Acetyl Hypofluorite 873.3 Summary of Yields Obtained for the Reaction of 31with Fluorine 893.4 Summary of Radiochemical Yields Obtained for the Reactionof 31 with Acetyl[18F]Hypofluorite 100viiiList of FiguresFigureCHAPtER 22.1 Changes in arene reactivity when complexed to chromiumtricarbonyl 172.2 Examples of carbanions which react with(i6-ha1obenzene)tricarbonyl-chromium complexes 182.3 Examples of carbanions which react with(6-benzene)tricarbonyl-chromium 192.4 Principal fragmentation pattern of(6-arene)tricarbonyl-chromium compounds 322.5 HPLC chromatogram obtained from the analysis of the reaction ofcomplex 1 with cyanide at 135°C 402.6 Radio-HPLC chromatogram obtained from the analysis of the reactionof complex 1 with[11C]cyanide (with 0.37 equiv of carrier KCNadded) at 150°C 572.7 Radio-HPLC chromatogram obtained from the analysis of the reactionof complex 1 with[11Cjcyanide (with no carrier KCN added)at 150°C 582.8 Radio-HPLC chromatograms of[‘tC]cyanide in DMSO 61CHAPTER 55.1 Schematic of the fluorine gas handling system used to perform thefluorination reactions 141xAcknowledgementsI thank my supervisors, Dr. Laurie Hall and Dr. Mike Adam, for their invaluableguidance and helpful discussions. In particular, I am very grateful to Dr. Mike Adamfor his invaluable assistance in all aspects of the experimental development of this work,and for his helpful advice in the preparation of this thesis.I extend my thanks to Dr. Peter Legzdins and his research group for valuablediscussions and including me in their literature meetings.I am grateful to Dr. Tom Ruth and Dr. Mike Adam for the production of radionuclides (11C, 18F) used in this work. I am also thankful for the technical assistance ofSalma Jivan at TRIUMF.I gratefully acknowledge the contribution made by the Co-op students, Maurice Brulé,Dale Johnson, and Martin Dimitroff, with whom I had the pleasure of working.I greatly appreciate the service provided by the Electronics and Mechanical shops formaintenance of the NMR instrumentation, and in particular, Tom Markus, who alsoconstructed the NMR probe. I also extend my thanks to the technical staffs of thedepartmental NMR, Mass Spectrometry, and Microanalytical services.I thank my friends, Dr. Jeff Coil and Dr. Sigrid Coil, for proofreading this thesis.Finally, I especially thank my supervisors, friends, and family for their incrediblepatience, support, and encouragement through very difficult times in which it seemed thisthesis would not be completed.xDedicationTo my risen LordxiChapter 1GENERAL INTRODUCTION1.1 BackgroundOrganic molecules labelled with short-lived positron emitting nuclides have had a greatimpact on biomedical research.’ Thus, for the first time, using positron emittingradiopharmaceuticals, quantitative in vivo measurements have been made of the humanbiochemical and physiological processes of the brain, heart, and other organs.2 Forexample, it has been shown that regional brain metabolism can be correlated withfunctional activity in humans under normal circumstances,3 during somatosensorystimulation,4 and also in disease states such as schizophrenia5and senile dementia.6Other parameters of physiological function have also been measured which include bloodvolume, blood flow, oxygen- and glucose-metabolic rates, drug-receptor interactions,protein synthesis, amino acid transport, permeability of the blood-brain barrier, andtissue pH. These studies are intended to give a better understanding of disease statessuch as cancer, epilepsy, heart disease, stroke, movement disorders such as Parkinson’sdisease, and mental illness.7’8The in vivo measurement of biochemical and physiological processes, usingcompounds labelled with short-lived positron emitting nuclides, is based on the use ofPositron Emission Tomography (PET). In this technique, a positron emitting1radiopharmaceutical, with the desired biological activity, is administered to a livingsubject. Inside the body, the radiotracer decays by emitting a positron (j3, positiveelectron), which travels a few millimetres, combines with an electron, its antimatter twin,and is thereby annihilated to produce two gamma-ray photons each of 511 keV. The twogamma-rays travel in opposite directions, nearly 1800 apart, penetrating the surroundingtissue and are detected by a circular array of coincidence detectors surrounding thesubject being imaged. Only timed coincidence annihilation events registered by paireddetectors located 180° apart are recorded. From these, the spatial distribution of theradiotracer is reconstructed by computer, and is presented as a series of cross-sectionalimages.7’9The successful application of PET as a medical research tool derives from the factthat PET allows the study of physiological and biochemical processes to be done in aquantitative, non-invasive manner, within a volume element of tissue in vivo. From thetechnical viewpoint, a key ingredient of this process is the positron emitting radio-pharmaceutical itself.1° One of the cornerstones of modern medicine is the understanding that all clinical symptoms result from biochemical reactions, and as a consequence,every pathology has an underlying biochemical defect.7 Thus, the radiopharmaceuticalacts as a biochemical probe and, by virtue of the attached positron emitting nuclide, thefate of the radiopharmaceutical can be spatially mapped using PET. As a result, therange of studies that can be performed using PET depends on the availability of compounds appropriate to the study, which can be labelled with positron emitting nuclides.8’1°To date, PET has been most extensively applied to problems in neurology, cardiology,2and oncology. As a result of the successes obtained in these studies, substantial effortsare being made to expand PET into new areas of research.11”2 Therefore, to exploitthe full potential of PET, continued development of new and improved methods ofradiopharmaceutical synthesis are required.12 Aspects of Labeffing with Short-lived IsotopesThe goals of radiopharmaceutical synthesis have many elements in common with traditional synthetic organic chemistry. Both the radiochemist and organic chemist areconcerned with developing syntheses which will yield in the most direct manner, thedesired compound in the largest chemical yield possible. In addition, the radiochemistis concerned with obtaining high radiochemical yields. Radiochemical yield is definedas the amount of radioactivity incorporated into the product as a percentage of the initialquantity of radioactivity used, Both the radiochemist and organic chemist require thefinal compound to be isolated in a chemically pure state. However, radiolabelled compounds must also be radiochemically pure and free of other radionuclidic impurities.’3Furthermore, organic compounds produced as pharmaceuticals and formulated for intravenous injection, whether radiolabelled or not, must also be sterile and pyrogen free.’4In order to ensure a successful radiopharmaceutical synthesis, several additionalconsiderations hold which are not common to synthetic organic chemistry. The keyaspects that need to be addressed by the radiochemist are as follows: (i) the physicalproperties of the radionucide, (ii) the source and chemical form of the radionuclide, and(iii) the specific activity, stoichiometry, and reaction scale. These topics will now be3discussed in the above order.The most important radionuclides used in PET are ‘1C, 13N, 150, and 18F; their half-lives are listed in Table 1.1. All of these positron emitting nucides possess short half-Table 1.1: Characteristics of Radionuclides Used for PETRadionuclide Half-life % i3 Decaya Daughter(mm)11C 20.4 99.8 B, stable‘3N 9.96 100 13C, stable150 2.07 99.9 15N, stable‘8F 109.7 96.9 180, stableSOURcE: Reference 15.a13+ =positron emission.lives*,16 and emit high energy, body-penetrating radiation. These characteristics areimportant properties which make these radionudides suitable for medical use. However,these same properties also give rise to problems for radiolabelling development. Mostsignificantly, the half-life of the nuclide poses a limit on the time allowable for synthesis.The total synthesis time, beginning with the generation of the radionuclide and itsincorporation into the substrate, followed by any further chemical modifications (i.e.,removal of protecting groups, etc.) through to the final purification of theradiopharmaceutical, should be equivalent to no more than one or two half-lives of theradioisotope.17’8 Clearly, the associated manipulative problems become particularlyacute when using nudides whose half-lives are on the order of minutes. The actual* A radionucide is usually defined as short-lived when its half-life is less than 15 h.4imaging of the patient must in turn be completed within about three or four half-livesof the radionucide used.19Another problem inherent in working with positron emitting nudides is the obviousradiation hazard they pose, which unfortunately, exposes the radiochemist to apotentially serious health risk. Hence, for prudent safety reasons, it is necessary to workwith adequate levels of shielding, use remote operations whenever possible, properlymonitor the radiation level in the work area, and to work with care while handlingradioactive compounds.2°The source and chemical form in which a given radioisotope is available has asignificant impact on the development of a practical synthetic strategy. The first problemis the availability of the required positron emitting nuclide. In general, positron emittingnucides are produced by nuclear reactions performed with a charged particleaccelerator, generally a cyclotron.21 Some positron emitters are available from anuclide generator system, such as the68Ge/a (half-life of 68Ga is 68.1 mm) generator.Although such generators are very convenient as they allow shipment of radionuclidesfor long distances from the production site, unfortunately, few such generator systemsexist for positron emitting isotopes.22 Therefore, it is generally mandatory thataccelerator produced nuclides be made on site, or within relatively short travellingdistance (i.e., time) from the radiolabelling facilities.The chemical form of a given radionuclide is the second problem that has to beconsidered. Radioisotopes, as obtained from a cyclotron or generator, are usuallyavailable in a limited range of chemical forms. Although the preparation of a5radioisotope is dependant on the nuclear reaction used, target design, and cyclotroncharacteristics, the chemical form of the radioisotope is determined by a number offactors—the most crucial factor is the chemical composition of the target and the energydeposition in the target;17 this area of study is referred to as target chemistry. Therefore,if the reagent form of the radionuclide is inappropriate for a given radiolabellingprocedure, then additional chemical manipulations are required to obtain the desiredform of reagent. Since this increases the synthesis time and adds complexity to theexperimental procedure, the best approach, whenever possible, is to directly prepare theradioisotope in the specific chemical form required for the radiolabelling step.The last topic of this section is the issue of specific activity, stoichiometry, and reactionscale; these three subjects are closely related. Specific activity is defined as the quantityof radioactivity present, generally expressed in curies, per mole of compound. One curieof activity produces 3.70 x 1010 Bq (disintegrations per second); the maximum specificactivity of a radionuclide depends on its half-life (see Table 1.2), and is only attainablewhen no other isotope of the same element (i.e., carrier) is present; this ideal state isreferred to as the carrier-free (CF) state. For some radioisotopes, this CF state can beapproached only to within an order of magnitude so that some carrier is unavoidablypresent in most cases. For example, it is reported that in the production ofH11CN, theratio of 11C to ‘2C is approximately 1:3000? In light of this problem, additionalterminology is needed for specifying the extent of dilution present in aradiopharmaceutical product. The no carrier-added (NCA) state, as applied to anelement or compound, means that no carrier of the same element or compound has6Table 1.2: Physical Properties of Some RadionuclidesNucide Half-life Decay Maximum Range” MaximumModea energy (mm) specific(MeV) activity(Ci/mol)11C 20.4 mlii i3(99+%) 0.96 4.108 9.22 x iO150 207 mm 3(99 9%) 172 82 908 x 10”‘3N 9.96 mm I3(100%) 1.19 5.39 1.89 x 1010‘8F 109.7 nun i3(97%) 0.635 2.39 1.71 x iO3H 12.35 y f(l00%) 0.0186 0.0072 2.90 x 10‘4C 5730 y i31100%) 0.155 0.359 62.4SouRcE: Reference 25.aDecay modes: r =positron emission, 3 = beta particle emission.“Maximum linear range in water.been added during its preparation. The carrier-added (CA) state means a known amountof carrier has been added to the element or compound during its preparation.’7Especially when dealing with short-lived radiopharmaceuticals near their maximumspecific activity, the mass of the product is not detectable by ordinary chemical orspectroscopic means. To ifiustrate this point, consider the mass of 1 mCi of 11C ascompared to ‘4C, which is 1.5 pg (6.53 x 1010 atoms) as opposed to 0.22 mg (9.59 x 10’satoms) of 14C.26 Therefore, the production of high specific activity radiopharmaceuticalsin the CF or NCA states is highly desirable because the mass of the radiopharmaceuticals is then so small that when administered in vivo it is usually below the thresholdwhere any physiological response is invoked, yet there is adequate radioactivity present(in the order of 0.1 to 0.5 Ci/g of tissue in the case of PET instruments) to be detected7with statistical significance?4 Thus, even highly toxic molecules can be used for studiesif adequate specific activities can be achieved.’7Working with small amounts of high specific activity radionuclides usually leads toproblems regarding stoichiometry and reaction scale. When a labelling reaction isperformed, in which both labelling reagent and substrate are used in approximately oneto one ratio, everything may work well. However, when the concentration of thelabelling reagent is reduced by several orders of magnitude, as during a high specificactivity radiosynthesis, very different results may be observed. Since NCA radiosynthesesare performed on a very small scale, the amount of impurities present in the reagentsand solvents may be comparable to, or even exceed, the quantity of the radionuclideused in the synthesis. These impurities may compete with the radiolabelling reagent ina given reaction, leading either to unwanted side-products, or even to completeprevention of the formation of the desired radiolabelled product.27 If one of theimpurities present in the synthesis is carrier, this will lower the specific activity of theradiolabelled product. This can be a very serious problem when very high specificactivities are required, and as a result great care must be taken to exclude carrier fromall possible sources, such as solvents, reagents, and substrates.28In spite of the various difficulties and challenges involved in the area ofradiopharmaceutical synthesis, much progress has actually been made. A variety ofpositron emitting radiopharmaceuticals have been developed and are currently beingused in PET imaging, and some of the commonly used radiopharmaceuticals for PET8Table 1.3: Positron Emitting Radiopharmaceuticals UsedCommonly in PET Imaging ProceduresRadiopharmaceutical Application[18F]fluorodeoxyglucose Cerebral glucose metabolismMyocardial glucose metabolism[18F]fluorodopa Dopa uptake studies18F]spiperone Dopamine receptor binding[18F]-N-methylspiperone Dopamine receptor binding[18F]-16a-fluoro-17fl-estradiol Estrogen receptor binding[‘1C]carbon dioxide Tissue pH11C]-1-butanol Cerebral blood flow[11C]methionine Amino acid metabolism11Cjpalmitate Myocardial metabolism[11C]acetate Myocardial metabolism[11C]glucose Cerebral glucose metabolism11C]-N-methylspiperone Dopamine receptor binding[1501 oxygen Cerebral oxygen extractionand metabolism[15ojcarbon monoxide Cerebral blood volumeMyocardial blood volume[150]water Cerebral blood flowMyocarclial blood flow[13Nlammonia Myocardial blood flowSouRcEs: References 7,8,10,29.are summarized in Table 1.3.1.3 Objectives and Format of this ThesisWith the continuing development of PET, new and innovative synthetic methodologies9are needed to produce the required radiopharmaceuticals for future PET applications.The primary objective of this study was the exploration of new methods for theincorporation of positron emitting radionucides—specffically 11C and‘8F—into organiccompounds.Increasingly, the use of organometa.llic intermediates are providing new avenues torapidly label organic molecules. The organic derivatives of some main group metals(B,3° Si,31’2 Ge,33 Sn,34’5 Hg,36 TI,37) have been studied and utilized forradiolabelling. Generally, their prime application has been to prepare compounds thatare radiolabelled on the aromatic ring. Boron3°and silicon32 derivatives have also beensuccessfully used for the preparation of radiolabelled alkyl halides. The common featureof these reactions is the exploitation of the reactivity of the polarized carbon-metal bond,in which the metal possesses a partial positive charge and the attached carbon possessesa partial negative charge; as a result, an organometallic compound is susceptible toelectrophilic attack. This is important because the electrophilic cleavage oforganometallic precursors can potentially be performed under mild conditions with shortreaction times. Therefore, radionuclides that can be prepared in electrophilic reagentform, can in turn be used for the radiolabelling of organometallic precursors, in aregioselective manner.Previous studies in this laboratory focussed on the development of labelling vinyl-tinderivatives with radioactive bromine(82Br) and iodine (1231 and 1311).38 The use of vinyl-tin reagents was found to be very successful. This experience prompted our interest inextending the utility of vinyl-tin reagents to radiofluorinations with 18F.10The organic derivatives of transition metals, however, exhibit very different patternsof reactivity as compared to those of the main group metals.39 The fundamental reasonfor this is the presence of partly filled d or f orbitals. This leads to a variety of bondinginteractions with organic ligands.4° Transition metals are able to form complexes inwhich the metal is bonded to unsaturated organic molecules such as ethylene,cyclobutadiene, or beuzene. The normal pattern of reactivity of unsaturated organicmolecules when coordinated to transition metals is changed, whereby the unsaturatedmoieties can be attacked by a wide range of nucleophiles. The more electron-withdrawing the metal centre, the more facile is the nucleophific addition.4’ This modeof reactivity could have significant potential for the application of radiolabelling. It wasdecided to explore the labelling of aromatic rings with ‘1C using(i16-arene)tricarbonyl-chromium complexes as synthetic intermediates.The format of this thesis is as follows. Chapter 2 is devoted to the evaluation ofarene)tricarbonylchromium compounds as synthetic intermediates for the incorporationof ‘1C, in the form of [“C]cyanide, onto aromatic rings. At the beginning of the chapter,some introductory background information is presented regarding organochromiumchemistry. Then, the preparation of(6-arene)tricarbonylchromium complexes used forthis study will be described. This will be followed by an examination of the reactivityof the prepared chromium tricarbonyl complexes with non-radioactive cyanide. Lastly,radiolabelling studies with “C-labelled cyanide will be presented.Chapter 3 is devoted to the development of electrophilic fluorination methodology thatis applicable to vinyl-tin compounds with both non-radioactive fluorine and radiofluorine.11The chapter begins with an introduction to selective fluorination of organic molecules.This will be followed by a presentation of the synthesis of the vinyl-tin derivativesemployed for this present study. Next, fluorination studies of the vinyl-tin precursorswith elemental fluorine and acetyl hypofluorite will be described. Finally, radio-fluorination with 8F of a selected vinyl-tin derivative will be presented.In Chapter 4, the general conclusions developed from the studies described inChapters 2 and 3 will be presented, along with suggestions for future work.In Chapter 5, the experimental details are given for the work performed for this thesis.The general methods are described first, followed by the specific experimentaldescriptions for Chapters 2 and 3, respectively.12References1. Positron Emission Tomography; Reivich, M., Alavi, A., Eds.; Alan R. Liss: New York,1985; Positron Emission Tomography andAutoradiography: Principles andApplicationsfor the Brain and Heart; Phelps, M. E., Mazziotta, J. C., Schelbert, H. R., Eds.;Raven: New York, 1986.2. Kellersohn, C. Brit. J. Radio!. 1981, 54, 91-102; Wagner, H. N. J. Am. Med. Assoc.1986, 256, 2096-2097.3. Reivich, M.; Kuhl, D.; Wolf, A. P.; Greenberg, J. H.; Phelps, M. E.; Ido, T.; Casella,V.; Fowler, J. S.; Hoffman, E. J.; Alavi, A.; Som, P.; Sokoloff, L. Circ. Res. 1979, 44,127-137; Phelps, M. E.; Huang, S. C.; Hoffman, E. J.; Selin, C.; Sokoloff, L.; Kuhi,D. E. Ann Neurol. 1979, 6, 371-388.4. Alavi, A.; Reivich, M.; Greenberg, 3. H.; Hand, P.; Rosenquist, A.; Wolf, A. P.Semin. Nuci. Med. 1981, 11, 24-31; Greenberg, J. H.; Reivich, M.; Alavi, A.; Hand,P.; Rosenquist, A.; Rintelman, W.; Stein, A.; Tusa, R.; Dann, R.; Christman, D.;Fowler, J. S.; MacGregor, B.; Wolf, A. P. Science 1981, 212, 678-680.5. Farkas, T.; Reivich, M.; Alavi, A.; Greenberg, J. H.; Fowler, J. S.; MacGregor, R.R.; Christman, D. R.; Wolf, A. P. In Cerebral Metabolism and Neural Function;Passonneau, J. V., Hawkins, R. A., Lust, W. D., Welsh, R. A., Eds.; Williams andWilkins: Baltimore, 1980; pp 403-408.6. Ferris, S. H.; deLeon, M. J.; Wolf, A. P.; Farkas, T.; Christman, D. R.; Reisberg, B.;Fowler, 3. S.; MacGregor, R.; Goldman, A.; George, A. E.; Rampal, S. Neurobiol.of Aging 1980, 1, 127-131.7. Ter-Pogossian, M. M.; Raichie, M. E.; Sobel, B. E. Sci. Am. 1980, 243, 170-181.8. Dagani, R. Chem. Eng. News 1981, 59(45), 30-37.9. Links, J. M. In Nuclear Imaging in Drug Discoveiy, Development, and Approval;Burns, H. D., Gibson, R. E., Dannals, R. F., Siegl, P. K. S., Eds.; Birkhäuser: Boston,1993; pp 22-23.10. Jacobson, H. G. J. Am. Med. Assoc. 1988, 259, 1854-1860.11. Ter-Pogossian, M. M. J. Nuci. Med. 1985, 26, 1487-1498.12. Cox, P. H. In Text of Radiophannacy: Theoiy and Practice; Sampson, C. B., Ed.;Gordon and Breach Science: New York, 1990; Chapter 16.1313. Theobald, A. E. In Textbook of Radiopharmacy. Theory and Practice; Sampson, C.B., Ed.; Gordon and Breach Science: New York, 1990; Chapter 7.14. Nickoloff, E. L. In The Chemistry of Radiopharmaceuticals; Heindel, N. D., Burns,H. D., Honda, T., Brady, L. W., Eds.; Masson Publishing USA: New York, 1978;Chapter 5.15. Wolf, A. P.; Fowler, 3. S. In Positron Emission Tomography; Reivich, M., Alavi, A.,Eds.; Alan R. Liss: New York, 1985; p 65.16. Vaalburg, W.; Paans, A. M. J. In Radionuclides Production; Helus, F., Ed.; CRC:Boca Raton, 1983; Vol. 2, p 48.17, Fowler, J. S.; Wolf, A. P. The Synthesis of Carbon-il, Fluorine-i8, and Nitrogen-13Labeled RadiotracersforBiomedicalApplications; Nuclear Science Series, MonographNAS-NS-3201; Technical Information Center, U.S. Department of Energy:Springfield, VA, 1982.18. See reference 16; Vol. 2, Chapter 2.19. Adam, M. J., TRIUMF, Vancouver, BC, personal communication.20. Hesslewood, S. R. In Textbook of Radiophannacy. Theory and Practice; Sampson, C.B., Ed.; Gordon and Breach Science: New York, 1990; Chapter 6.21. Wolf, A. P.; Schlyer, D. J. In Nuclear Imaging in Drug Discovery, Development, andApproval; Burns, H. D., Gibson, R. E., Dannals, R. F., Siegi, P. K. S., Eds.;Birkhäuser: Boston, 1993; Chapter 3.22. Robinson, G. D., Jr. In Positron Emission Tomography; Reivich, M., Alavi, A., Eds.;Alan R. Liss: New York, 1985; Chapter 4.23. Short, M. D. In Textbook of Radiopharmacy: Theory and Practice; Sampson, C. B.,Ed.; Gordon and Breach Science: New York, 1990; p 19.24. See reference 17; pp 28-29.25. Fowler, J. S.; Wolf, A. P. In Positron Emission Tomography and Autoradiography:Principles and Applications for the Brain and Heart; Phelps, M. E., Mazziotta, 3. C.,Schelbert, H. R., Eds.; Raven: New York, 1986; p 393.26. See reference 17; p 39.27. See reference 17; pp 29-30.1428. Wilbur, D. S.; Garcia, S. R.; Adam, M. J.; Ruth, T. J. J. Labelled Compd.Radiopharm. 1984, 21, 767-779.29. Radiophannaceuticals for Positron Emission Tomography: Methodological Aspects;Stöcklin, G., Pike, V. W., Eds.; Kiuwer Academic: Boston, 1993.30. Kabalka, G. W. Acc. Chem. Res. 1984, 17, 215-221.31. Wilbur, D. S.; Anderson, K. W.; Stone, W. E.; O’Brien, H. A., Jr. J. Labelled Compd.Radiopharm. 1982, 19, 1171-1188.32. Wilbur, D. S.; Svitra, Z. V. J. Labelled Compd. Radiopharm. 1983, 20, 619-626.33. Moerlein, S. M.; Coenen, H. H. J. Labelled Compd. Radiophann 1984, 21, 1076-1077.34. Adam, M. J.; Ruth, T. J.; Pate, B. D.; Hall, L. D. J. Chem. Soc., Chem. Commun.1982, 625-626.35. Coleman, R. S.; Seevers, R. H.; Friedman, A. M. J. Chem. Soc., Chem. Commun.1982, 1276-1277.36. Bo-Li, L.; Yu-Tai, J.; Zhong-Yum, P.; Maeda, M.; Kojima, M. J. Labelled Compd.Radiopharm. 1982, 19, 1089-1096.37. Gilliland, D. L.; Basmadjiam, G. P.; Marchand, A. P.; Hinlcle, G. H.; Earlywine, A.;Ice, R. D. J. RadioanaL Chem. 1981, 65, 107-113.38. Balatoni, J. A. M.Sc. Thesis, The University of British Columbia, Dec. 1985.39. Coates, 0. E.; Green, M. L. H.; Powell, P.; Wade, K. Principles of OiganometallicChemistiy; Chapman and Hall: London, 1979.40. Coliman, J. P.; Hegedus, L. S. Principles and Applications of Organotransition MetalChemistiy; University Science Books: Mill Valley, CA, 1980.41. Davies, S. 0. Organotransition Metal Chemistiy: Applications to Organic Synthesis;Perganion: Toronto, 1982; Chapter 4.15Chapter 2APPLICATION OF ORGANOCHROMRJM CHEMISTRY TORAIMOLABELLING2.1 IntroductionThe first(76-arene)tri.carbonylchromium complex was reported in 1957, by Fischer andOfele.1 Since that time, literally hundreds of such complexes have been prepared,characterized, and studied with respect to the structure and reactivity of the arene ringwhile complexed to the metal centre.2’3(,6-Arene)tricarbonylchromium compounds areair-stable, diamagnetic, crystalline solids, generally yellow to orange in colour. They aresoluble in a variety of solvents, readily characterized by spectroscopic methods, and areeasily purified by chromatographic and recrystallization techniques. As a result of thew-coordination of an arene to chromium, its reactivity is significantly altered.4 Thesechanges in arene reactivity are summarized in Figure 2.1.The most significant change in arene reactivity is the increased ability of thecoordinated arene to undergo nucleophilic aromatic substitution. It is this reactionwhich has been most studied and extensively employed in synthetic chemistry.5 To alesser degree, the steric effect of the attached chromium tricarbonyl moiety has beenused for the stereoselective modifications of the aromatic side chain.6 The otherchanges in arene reactivity have received less attention regarding their potential use for16Enhanced Nucleophilic EnhancedSubstitution /1 SolvolysisEnhanced Acidity HC—C—StericHEnhancedHinderance co AcidityFigure 2.1: Changes in arene reactivity when complexed to chromiumtricarbonyl. (Adapted from reference 7.)synthesis.8’9During early studies of the reactivity of(,76-arene)tricarbonylchromium compounds,Nicholls and Whiting found that i-chlorobenzene)tricarbonylchromium readilyunderwent substitution of chlorine by methoxide in very high yield.1° UncomplexedMeOH K—OMeI + NaOMe I + NaC1 (2.1)Cr(CO)3 65°C Cr(CO)3chlorobenzene is unreactive toward methoxide under the same conditions. Laterinvestigations have shown other nucleophiles to react similarly, such as sodiumphenoxide, aniline,11 and 2-methyl-2-propanethiol.’ (,76-Fluorobenzene)tricarbonyl-chromium also exhibits reactivity toward a variety of nucleophiles. Successful reactionswith alkoxides, amines, thiolates, and cyanide have been reported.12”3 It has beenshown that fluorine is more readily displaced than chlorine, during aromatic nucleophilicsubstitution.4Of greater interest for organic synthesis, is the reactivity of(6-arene)tricarbony1-17chromium complexes with carbanions. Indeed, a variety of carbanions have beensuccessfully used to alkylate the chromium tricarbonyl complexes of chlorobenzene andfluorobenzene; see Figure 2.2 for examples. Nucleophilic substitution for hydrogen can_____[01 /\I I RCr(CO)3 25°C Cr(C0)3where X = Cl or FR = C(CH3)2N, t(CH3)2COEt, C(CH3)20,tH(CO2Me),902Me .C,Figure 2.2: Examples of carbanions which react with(6-halobenzene)tricarbonyl-chromium complexes.also occur directly on thei6-arene ring, which opens up additional synthetic pathways.(i76-Benzene)tricarbonylchromium, for example, reacts with a number of carbanions asshown in Figure 2.3. Furthermore, if the crude reaction intermediate is treated withexcess strong acid, prior to oxidative demetallation, substituted 1,3-cyclohexadienes areobtained.5Unfortunately, not all synthetically important carbanions work well with (fl6-arene)-tricarbonylchromium complexes. Grignard reagents, organocuprates, and alkylmercuricchlorides fail to react at low temperatures, while unidentified decomposition productsare obtained upon heating. When strongly basic anions are used, such as methyl- or18R [01 /\RCr(C0)3 0°C Cr(C0)3where R = t(CH3)2CN, CH2N, tH2COR, CH(CH3)CO2R, C(CH3)20R,SPh CH s CN-dH-sph t—CH3, CH C—-- , -CH3CH3 SFigure 2.3: Examples of carbanions which react with(6-benzene)tricarbonyl-chromium.butyllithium, proton abstraction results; this produces the lithiated,76-arene complex.However, this can be a useful result, as the lithiated species can then be treated withdifferent electrophiles, thus providing an additional route for ring modifications.5An important feature of(,76-arene)tricarbonylchromium chemistry has been thedevelopment of several methods for both complexing the chromium tricarbonyl grouponto aromatic rings and being able to remove that same group efficiently when desired.A number of approaches have been developed to u--complex an arene with chromiumtricarbonyl. Typically, chromium hexacarbonyl is either heated in neat arene, or withexcess arene in a solvent (e.g., 1,4-dioxane, di-n-butyl ether), which affords thecorresponding arene complex. After the desired chemistry has been accomplished, thefinal arene product can be readily recovered by mild oxidation. A variety of reagentshave been successfully used for oxidative demetallation; aqueous Ce(IV), iodine, andexposure to sunlight and air, being the most common.5’6”4This is a vital consideration,if(6-arene)tricarbonylchromium complexes are to be useful in synthesis. The19introduction and subsequent removal of activating groups in organic chemistry presentsdifficult problems, not easily solved. Classical aromatic nucleophilic substitution suffersfrom this deficiency, as activating groups like nitro require drastic conditions fornitration, and lack mild and direct methods to remove the riitro group once its activatingfunction is completed.’5 As a result, classical aromatic nucleophilic substitution hasfound limited application in complex organic synthesis.(6-Arene)tricarbonylchromiumcomplexes potentially offer a significant improvement as synthetic intermediates sincethe chromium tricarbonyl moiety can be readily attached in most cases, thendecomplexed in high yield once synthetic operations are done.The synthesis of radiopharmaceuticals labelled with short-lived positron emittingnucides requires special synthetic methods, due to the considerations presented earlierin Chapter 1. Prompted by the unique properties and reactivity of(76-arene)tricarbonyl-chromium complexes, we decided to explore the potential utility of these compounds forradiolabelling. There are about five reasons that would commend these organochromium compounds for radiolabelling work.Firstly, most organic pharmaceuticals, either of potential interest for labelling or beingcurrently used in nuclear medicine today, contain arene rings in their structures.Examples include 6-fluoro-3,4-dihydroxyphenylalanine (6-fluorodopa), the butyrophenone neuroleptics, the estradiol class of steroids, benzodiazepines, and benzamidessuch as Raclopride (S-(-)-3,5-dichloro-N-[( 1-ethyl-2-pyrrolidinyl)]methyl-2-hydroxy-6-methoxybenzamide).’6”7Therefore, the presence of an aromatic ring provides a possiblelabelling site for attaching the radionuclide of interest. Secondly, medically useful20radioisotopes are generally produced in anionic, nucleophilic form.18 Labellingreactions which can directly use the nucleophilic form of the radionucide areadvantageous, because this eliminates additional chemical manipulations and time tomodify the reagent form of the radionuclide. Thirdly,(i6-arene)tricarbonylchromiumcomplexes facilitate nucleophffic substitution reactions on the aromatic ring. Thisestablished reactivity could allow the facile incorporation of nucleophilic radioisotopesonto aromatic rings. Fourthly, methods for complexing most arenes to the chromiumtricarbonyl moiety, then later removing same, have been well established. This is incontrast to the use of traditional activating groups for nucleophilic aromatic substitution,such as nitro, which cannot be readily removed under mild conditions. Finally, the othermodes of reactivity (see pp 1-2) exhibited by(,76-arene)tricarbonylchromium compounds,adds additional synthetic options when designing a radiopharmaceutical synthesis.In this chapter, the synthesis of a number of(ij6-arene)tricarbonylchromium complexeswill be described. This will be followed by studies regarding the reactivity of theprepared chromium tricarbonyl compounds with cyanide. Lastly, the reactions of “C-labelled cyanide with some chromium tricarbonyl compounds will be presented.2.2 Preparation of(q6-Arene)tricarbonylchromium Complexes2.2.1 SynthesisThe objective for this study was to prepare a range of simple (i6-arene)-tricarbonylchromium complexes in order to study their suitability for radiolabelling. Toaccomplish this, commercially available arenes were selected to produce the21corresponding chromium tricarbonyl complexes using literature methods.Five general methods have been developed for the synthesis of(i76-arene)tricarbonyl-chromium compounds. The first method, as outlined in equation 2.2, is the directArene + Cr(CO)6snt(q6-Arene)Cr(CO)3 + 3 CO (2.2)reaction of arene with Cr(CO)6under thermolysis conditions. This reaction has beencarried out with various solvents ranging from neat arene to non-polar (e.g., decalin) topolar (e.g., diglyme*) solvents. The reaction must be conducted at relatively hightemperatures to achieve decarbonylation of the metal carbonyl and obtain ‘7r-complexedproduct. The majority of(i76-arene)tricarbonylchromium complexes have been preparedby this method. The second method involves a two-step process, in which during thefirst step Cr(CO)6has three carbon monoxide ligands replaced by more thermally labileligands (L) such as pyridine, 4-methylpyridine, CH3N, or NH3,as shown in equation 2.3.3 L + Cr(CO)6 heat Cr(CO)3L + 3 CO (step 1)(2.3)Arene + Cr(CO)3L heat (q6-Arene)Cr(CO)3 + 3 L (step 2)solventIn the next step, the prepared complex, Cr(CO)3Lis allowed to react with excess arene,using significantly lower temperatures, to obtain the desired product. The milderconditions of this methodology has allowed the preparation of chromium tricarbonylcomplexes not obtainable by the first method described above. The third method is the*Formally named bis(2-methoxyethyl) ether.22direct reaction of arene with Cr(CO)6via photolysis. Irradiation of the reaction mixtureat room temperature accomplishes the desired decarbonylation.(i6-Benzene)tr carbonyl-chromium and other complexes have been prepared using equation 2.4. The fourthArene + Cr(CO)6 light (?76-Arene)Cr(C0)3 + 3 CO (2.4)solventmethod is arene exchange, which relies on the observation that (fl6-arene)-tricarbonylchromium complexes undergo exchange reactions in the presence of anotherarene at elevated temperatures (ca. 200°C), as outlined in equation 2.5. The use ofdonor solvents has allowed these exchange reactions to be conducted at lower6 heat(-AreneA)Cr(CO)3+ AreneB (q-AreneB)Cr(CO)3+ AreneA (2.5)temperatures (ca. 140°C). However, the synthetic utility of this method has been limitedby the high temperatures required, and by the low yields obtained. The final methodis the reaction of aikynes with chromium pentacarbonyl carbenes, as illustrated inequation 2.6. A chromium tricarbonyl complex is formed from the condensation of an(CO)5r R2 CR32R2+ CO (2.6)Cr(CO)3 Cr(CO)3alkyne with a metal carbene. This novel method requires no arene starting material.A range of interesting 7r-complexed naphthalene and phenanthrene derivatives have beenprepared by this route.’4’1923Given the various synthetic options available, it was desirable to choose the simplest,most direct synthetic procedure to prepare the desired(j6-arene)tricarbonylchromiumcomplexes. The choice was made to prepare(,7-fluorobenzene)tricarbonylchroniium 1by adapting the method of Mahaffy and Pauson,2°and to prepare(6-chlorobenzene)-tricarbonylchromium 2 by the method of Nicholls and Whiting.’°+ Cr(CO) reflux /48 h + 3 CO (2.7)‘ji 6 (n-Bu)2OiTHF Cr(CO)31+ Cr(CO)6 reflux /17 h + 3 CO (2.8)diglyme Cr(CO)32Although(6-arene)tricarbonylchromium compounds are quite air-stable in solid form,their solutions are relatively air-sensitive. All preparations of these complexes, includingworkup and isolation, were conducted under inert atmosphere. Compound 1 wasprepared in 68% yield according to equation 2.7 using an 8:1 mixture of di-n-butyl etherand tetrahydrofuran (THF). Mahaffy and Pauson reported a 90% yield for the synthesisof 1 under similar conditions.2°Alternatively, 2 was obtained in an isolated yield of 47%(equation 2.8), based on the amount of Cr(CO)6 consumed. This result is comparableto that of Nicholls and Whiting who reported a yield of 52%, after a reaction time of 3h.’°When examining these initial experimental results, it became clear that working with24diglyme was less desirable, since it was very difficult to remove during workup. Thebutyl ether/THF mixture was readily removed to dryness, making workup much easier.More importantly, the method of Mahaffy and Pauson exhibited a potential forsignificantly better yields of chromium complexed product. As a consequence, it wasdecided to use the Mahaffy and Pauson reaction conditions for the preparation of other(6-arene)fficarbonylchromium compounds.A number of chromium tricarbonyl complexes were successfully synthesized accordingto the general equation 2.9. The results obtained are summarized in Table 2.1. Withreflux +Arene + Cr(CO)6 (n-Bu)20/THF Complex + 3 CO j (2.9)additional work and experience, the preparative yield of 1 was improved to 80% (seeTable 2.1). The reaction (equation 2.9) was found to be very sensitive to any traces ofoxygen present in the reaction mixture. Regardless of how carefully the reactionapparatus, reagents, and solvents were handled under inert atmosphere, it was vital toemploy freeze-pump-thaw degassing as a final step to ensure an oxygen-free environmentfor the reaction. The major drawback of the Mahaffy and Pauson procedure was theslowness of the reaction, thus requiring prolonged heating of the reactants (1-2 days)which can cause some decomposition of product complex. Unfortunately, thisdecomposition could result in further autocatalytic decomposition of any chromiumtricarbonyl product formed. Some investigators have recently reported that the primereason for decomposition of(76-arene)tricarbonylchromium during the reaction(equation 2.9) was due to the presence of impurities in the starting materials and25Table 2.1: Summary of Yields Obtained for Complexes Synthesizedusing Equation 2.9Arene Complex Reaction I YieldTimeC—F ‘ 48h 80%Cr(CO)31BrCBr I 44h 19%Cr(CO)33MeMe,—F 48h 89%Cr(CO)34MeMeF 16.5h 85%Cr(CO)35ClCVCF 23h 12%Cr(CO)36Me0?— /MeO N I 21h 70%e Cr(CO)3726solvents used, and traces of atmospheric oxygen over the reaction mixture.21A common problem with the direct reaction of arenes with Cr(CO)6 is the volatilityof Cr(CO)6 itself, which results in sublimation of the metal carbonyl from the reactionmixture. Anticipating this problem, a special reaction apparatus was constructed* thatallowed any sublimed Cr(CO)6 to be mechanically returned to the reaction mixture.However, it was found that the use of di-n-butyl ether with 10-20% of THF present,effectively washed back sublimed Cr(CO)6 to the reaction mixture. A regular Liebigcondenser could then be used with conventional glassware to perform the syntheticreactions (see Experimental for details).For our purposes, a paradoxical limitation of the Mahaffy and Pauson procedure, isthat while electron-donating groups on the arene helps the reaction, electron-withdrawing groups slow the reaction.22 It was found that fluorobenzene, 2-fluoro-toluene, and 4-fluorotoluene were successfully complexed, producing 1, 4, and 5 in highyield (80-89%). However, the corresponding complex of 4-chlorofluorobenzene (6) wasmade in only 12% yield. Persistent decomposition accompanied the preparation of 6,thereby limiting the reflux time possible—allowing the reaction to proceed longer thanovernight results in progressive decomposition and in little or no product formed. Inaddition, during the synthesis of 6, a significant amount of 1 was obtained as abyproducttwhich had to be separated using column chromatography.*The design of this reaction vessel was obtained from Dr. Peter Legzdins of theChemistry Department, U.B.C., and is described in the Experimental.1This would appear to result from a reductive dehalogenation process in which thefluorobenzene complex 1 is formed from 4-chlorofluorobemzene, probably via some27In addition to 6, the preparations of(i76-l,4-difluorobenzene)tricarbonylchromium 8and(,7-4-fluoroanisole)tricarbonylchromium 9 were attempted. In these two cases, onlyvery small quantities (tens of milligrams) were obtained at best. ExtensiveF—’—F MeO—FCr(CO)3 Cr(CO)38 9decomposition also accompanied these reactions. As a consequence of thesedisappointing results, other synthetic approaches were examined that would be moresuitable for complexing arenes with electron-withdrawing substituents.Limited trials of other synthetic methods also did not yield satisfactory results. Itbecame clear that a sustained study would be required to resolve this problem and thiswas beyond the scope of time available for this work. Therefore, the chromiumtricarbonyl complexes that could be prepared in adequate quantity were settled upon forthe desired radiolabelling studies.The direct reaction of benzonitrile with Cr(CO)6 does not yield the correspondingchromium tricarbonyl complex.’°’ However, Mahaffy and Pauson were able tosynthesize(6-bemzonitrile)tricarbonylchromium 10 indirectly by allowing thefluorobenzene complex 1 to react with a large excess of cyanide overnight in acetonitrileat 50°C. They obtained a 44% conversion of 10 from starting 1. Semmeihack has alsochromium species in solution. Similar results have been reported by Hudeèek andToma.2128reported, in a 1976 review, the successful reaction of cyanide anion with 1 at 25°C,obtaining a 94% yield.5 Unfortunately, the experimental details of this work have neverbeen published to the best of this author’s knowledge. We were able to prepare 10 in69% yield using different conditions, as outlined in equation 2.10.25°C123hI + NaCN I + NaF (2.10)Cr(CO)3 DMSO Cr(CO)31 10Of additional interest was the desire to prepare chromium tricarbonyl complexes inwhich the attached arene possessed groups of greater mobility toward aromaticnucleophilic substitution than halogen. Prompted by reports of radiolabelling studiesusing aromatics with dimethylsulfonium and trimethylammonium leaving groups,25’6it was considered whether an analogous chromium tricarbonyl complex could be made.Bunnet and Herman successfully methylated(6-thioanisole)tricarbonylchromium withtrimethyloxonium tetrafluoroborate to obtain -phenyldimethy1sulfonium)tricarbonyl-chromium tetrafluoroborate in 89% yield.27 However, they found that (6-N,N-dimethylaniline)tricarbonylchromium 7 could not be methylated by trimethyloxoniumtetrafluoroborate.27 In our efforts, we found that complex 7 can be methylated usingmethyltrifluoromethanesulfonate (commonly called methyl triflate) according to equation2.11.(,6-N,N,N-Trimethylanilinium)tricarbonylchromium trifluoromethanesulfonate 11was produced in 59% yield. In order to compare the behaviour of this new complex 11with the corresponding uncomplexed arene, N,N,N-trimethylanilinium trifluoromethane29/Me ++ 25°C/48 h CF3S0 (2.11)MelCH3SOF CH21Cr(CO)3 JCr(CO)37 Lsulfonate 12 and N,N,N-trimethylanilinium iodide 13 were also synthesized as shown inequation 2.12. Compound 12 was prepared in 83% yield, while 13 was obtained in 56%yield.Me +CH3SOF/C2125°C/30 mm [N_Me CF3SOMe12/Me(2.12)CH3I/CH2125°C/24 hMe132.2.2 CharacterizationAll of the(j6-arene)tricarbony1chromium complexes, except for 11, are knowncompounds. Their melting points were recorded and are presented in Table 2.2. Thechromium tricarbonyl complexes tended to decompose to some degree during meltingpoint determinations. The degree of decomposition would vary with the heating ratethereby making the melting points difficult to determine in some cases.30Table 2.2: Summary of Melting Points of Organochromium ComplexesComplex Observed mp Literature mp Reference(°C) (°C)1 117 116-117 272 100-101 101-102 203 101-105 120 284 71-72 73-74 295 59-60 6 1-62 296 61-62— none found7 137- 138 144 2011 120-121— none foundThe identification of the chromium tricarbonyl complexes was accomplished by massspectrometry (MS). The principal fragmentation patterns of simple (6-arene)-tricarbonylchromium compounds using electron impact MS have been well establishedand are shown in Figure 2.4.°’’ The fragmentation patterns exhibited by thesynthesized chromium tricarbonyl complexes were consistent with the scheme depictedin Figure 2.4. Also, Muller and Göser reported that all(6-halobenzene)tricarbony1-chromium compounds gave the Cr-halogen ion on fragmentation (i.e., [(C6H5X) rj —*[CrX] + + C6H5 )? This ion was observed for each of the chromium tricarbonylcomplexes with halogen-substituted aromatic rings. These characteristic features of themass spectra, exhibited by the chromium tricarbonyl compounds, made productidentification rapid and straight forward.Complex 11 was previously an unknown compound and was characterized byelemental analysis and 1H NMR spectroscopy. Compounds 12 and 13 were identified31[(Arene)Cr(CO)3][(Arene)Cr(CO)2f+ -Cr(CO) normal[(Arene)Cr(CO)] [Arenef’ Arenefragmentation-Cr normal[(Arene)Cr]+ [Arene] Arenefragmentation-Arene[Cr]Figure 2.4: Principal fragmentation pattern of(6-arene)tricarbonylchromiumcompounds.by 1H NMR spectroscopy. MS could not be employed for analysis of these saltcomplexes (11, 12, 13). A satisfactory elemental analysis for C, H, N, and S wasobtained for 11. The 1H NMR spectrum of 11 exhibited the aromatic proton resonancesat 5.77 (H-3,5), 6.07 (H-4), 6.69 (H-2,6) ppm, and a singlet for the trimethylammoniumgroup protons at 3.56 ppm. The 1H NMR spectral data for 12 and 13 were found to be32the same; the aromatic protons were observed at 7.58-7.68 (H-3,4,5) and 7.97 (H-2,6)ppm, and the trimethylammoriium group protons at 3.61 ppm. These results showed theexpected upfield shifts in proton resonances due to complexation with chromiumtricarbonyl. This is a characteristic feature of the ‘H NMR spectra of chromiumtricarbonyl complexes when compared to the uncomplexed arene.42.3 Reactions of Organochromium Compounds with CyanideThese studies began with investigating the reactivity of cyanide with(6-halobemzene)-tricarbonylchromium complexes 1, 2, and 3. All substitution reactions were performedI I ICr(CO)3 Cr(CO)3 Cr(CO)31 2 3under an argon or nitrogen atmosphere, using dried solvents. Complex 1 was allowedto react with excess sodium cyanide (ca. 10 equiv) in DMSO at 1500C* for 30 minutes.During heating, the initial yellow colour of the reaction mixture became dark red. Aftercooling, the reaction mixture was diluted with water, extracted with diethyl ether, thendried. The dried ether extracts were colourless. The ether extracts were concentratedand analyzed by gas chromatography (GC). GC analysis confirmed the presence ofbenzonitrile 14 as the only product obtained. This reaction was repeated under slightlydifferent conditions, where complex 1 was treated with about 2 equivalents of sodium*Reaction temperatures always refer to the oil bath temperature used.33cyanide at 155°C in DMSO for 20 minutes. After workup, GC analysis of the etherextracts exhibited two prominent peaks, a major peak due to 14 and a minor peak dueto fluorobenzene. For comparison, uncomplexed fluorobeuzene was allowed to reactwith sodium cyanide under the same conditions. GC analysis showed that only unreactedfluorobenzene was present.These initial results clearly demonstrated that the fluorobenzene complex 1 underwentsuccessful aromatic nucleophilic substitution with cyanide and that the reaction was rapidunder the conditions employed. The control experiment with uncomplexed fluorobenzene confirmed that free fluoroberizene failed to react with cyanide, and that intactchromium tricarbonyl species underwent the substitution reaction.The reactivity of the chlorobemzene complex 2 was examined next. Complex 2 wastreated with sodium cyanide (ca. 0.5 equiv) in DMSO at 160°C for 15 minutes. Afterworkup, the ether extracts were yellow in colour. GC analysis showed only the presenceof chlorobenzene. The ether extracts were subsequently treated with iodine todecomplex any intact chromium tricarbonyl components, and the GC analysis wasrepeated. Chlorobenzene remained the only compound detected. For comparison, thereaction of 1 with sodium cyanide was repeated under the same conditions as used for2. GC analysis showed two significant peaks, one peak due to 14 and the other due tofluorobenzene. In like manner, the ether extracts were again treated with iodine todecomplex any chromium tricarbonyl components present. GC analysis gave the sameresults as observed prior to oxidative decomplexation.Unfortunately, these results showed that 2 is either unreactive toward cyanide or is34possibly undergoing significant decomplexation under the reaction conditions used.However, 1 readily underwent substitution with cyanide using the analogous conditionsemployed for the reaction trial with 2. Though disappointing, this observation wascomplimentary to previous studies that have shown that fluorine is more easily displacedduring aromatic nucleophilic substitution than chlorine.4 Therefore, these resultssuggested that chlorine is an inappropriate leaving group to use in future studies, andwas thus abandoned.Lastly, the potential of bromine as a leaving group was investigated using thebromobenzene complex 3. Complex 3 was allowed to react with 0.5 equivalents ofpotassium cyanide in DMSO at 135°C for 10 minutes. After cooling, high pressureliquid chromatography (HPLC) was employed to directly examine the reaction mixture.HPLC analysis confirmed the absence of the desired product 14. In contrast, 1 wastreated with cyanide under identical conditions, and benzonitrile 14 was produced.HPLC analysis not only confirmed the presence of 14, but the yield was alsodetermined—these results will be presented and discussed later in this section.These results also indicated that 3 is either unreactive toward cyanide or is possiblydecomplexing under the reaction conditions employed. Bromine, as a consequence,would also appear to be an unsuitable leaving group for aromatic nucleophilicsubstitution. Therefore, the only useful halogen leaving group for reactions with cyanidewas determined to be fluorine.In order to further characterize the benzonitrile product 14, obtained from thereaction of 1 with cyanide, isolated products from several small scale reactions were35combined. This combined product sample (dissolved in diethyl ether) was subjected toGC analysis, and only one component was observed with almost 99% purity. The etherwas evaporated and the product sample was dissolved in deuterated chloroform forNMR spectroscopy. The room temperature 1H NMR spectrum was recorded at 80MHz.* In addition, the 1H NMR spectrum of authentic 14 (commercially obtained) wasrecorded under the same conditions. The spectrum of the product sample exhibited amultiplet centered at 7.57 ppm that was the same as that observed for authentic 14.Therefore, the 1H NMR spectrum clearly identified the product sample as benzonitrile14. This is in addition to GC and HPLC studies which readily identified 14 bycomparison of its retention time with that of authentic standard. Also, during HPLCstudies, an aliquot of reaction mixture was taken and standard 14 was added to see if theassigned product peak would correspondingly increase in size. This was observed, anddeemed as further evidence that the chromatographic assignment was correct.Furthermore, it was noted during the workup of the reactions of 1 with cyanide that thecharacteristic odour of 14 was present.A number of general observations were made during the early studies regarding thereaction of 1 with cyanide. Reactions employing approximately 2 or more equivalentsof cyanide for 15-30 minutes exhibited essentially a quantitative conversion of 1 to 14,as determined by GC analysis. The temperatures used for these reactions were 150-155°C. Additional experiments were performed in which the reaction mixtures were*These spectra were obtained on a departmental Bruker WP-80 spectrometer withtetramethylsilane used as an external standard.36heated for as little as one to three minutes and 14 was still produced, as observed by GCand HPLC analyses. Other reactions conducted used a large molar excess (up to 17-fold) of complex 1 relative to cyanide. Again, benzonitrile 14 was obtained, accordingto GC and HPLC analyses. Lastly, decomplexation of the aromatic nitrile takes placeduring the reaction under the conditions employed. This was demonstrated byexamining a product mixture by GC (after workup) which showed no change inbenzonitrile 14 concentration after treatment with iodine. Subsequently, this observationwas further confirmed with additional experimental experience, which shall be presentedat later stages of this discussion. As a consequence, no separate oxidativedecomplexation step was needed to liberate the organic product. This result was not toosurprising as it has been reported that(t6-arene)tricarbonylchromium complexes canundergo displacement of the aromatic ring in donor solvents, such as pyridine, atelevated temperatures.32These results further indicated just how facile and rapid the substitution reaction of1 with cyanide actually is. Since the intent was to ultimately apply this chemistry for theincorporation of[11C]cyanide into arenes, the studies to follow were designed to modelthis application. With excess cyanide and longer reaction times, excellent reaction yieldscould be assured. The half-life of 11C, however, is 20.4 minutes, which places a premiumon using the shortest reaction time possible. Also, it is highly desirable that the reactionbe eventually compatible with high specific activity [“Cjcyanide, for the reasonsdiscussed earlier in Chapter 1. Therefore, the decision was made to limit subsequentcyanide substitution reactions to 10 minutes and to use cyanide as the limiting reagent37(0.5 equiv).Within these parameters, the reactivity of the chromium tricarbonyl complexes 1, 4,5, and 6 was examined. The general procedure used is as follows. An aqueous solutionMe—-—F Cl -—FCr(CO)3 Cr(CO)3 Cr(CO)3 Cr(CO)31 4 5 6of cyanide, containing a known amount of KCN, was dispensed into a reaction vessel,and was carefully dried under a fast flow of inert gas. (This was done to model thehandling necessary in using[‘1C]cyanide, which is obtained as an aqueous solution aftercyclotron production.) The(6-arene)tricarbonylchromium complex, dissolved in 1 mLof DMSO, was added to the dried cyanide. The mixture was heated for 10 minutes.Upon cooling, the reaction mixture was quantitatively transferred to a volumetric flaskand diluted to a known volume with DMSO. This solution was analyzed by HPLC. Theextent of product formation was determined using a calibration curve constructed usingHPLC absorbance values of standard solutions of expected aryl nitrile product. Thechemical yields were calculated using KCN as the limiting reagent. In order to optimizethe results obtained for each of the complexes studied, the reaction temperatures werevaried and the corresponding chemical yields were determined.Complex 1 was treated with cyanide, as shown in equation 2.13, using reaction0.5 equiv KCN2Cr(CO)3 DMSO /10 • K—CN + KF + 1 (2.13)38temperatures ranging from 105-150°C. The results obtained are summarized in Table2.3. The optimum temperature found for equation 2.13 was 135°C, giving a best yieldof 41%. A representative HPLC chromatogram is shown in Figure 2.5. The chromatogram shows the presence of the desired product 14 (peak A), along with residual startingcomplex 1 (peak C) and free fluorobenzene (peak B) which is visible only as a shoulderof an unidentified peak. Injection of a solution, consisting of fluorobemzene standardadded to an aliquot of reaction mixture, exhibited an increase of this shoulder (peak B)into a distinct peak at the same retention time, thereby confirming the assignment ofpeak B. Another control experiment was performed with uncomplexed fluorobenzeneusing 0.5 equivalents of cyanide at 135°C. Once again, only unreacted fluoroberizenewas observed in the HPLC chromatogram.Table 2.3: Chemical Yields Obtained for Complex 1Temperature Yield no. of Average(°C) runs Yield150 23-33% 2 28%135 40-41% 2 41%120 31% 1 31%115 32% 1 32%105 12% 1 12%Next, the reactions of complexes 4, 5, and 6 with cyanide were investigated. Thereactivity of 4 (equation 2.14) was examined over a temperature range of 95-135°C. Theresults obtained are shown in Table 2.4. The best yields (41-43%) were observed at 105-115°C. The control reaction done with 2-fluorotoluene (uncomplexed) using 0.5 equiva39zCI BTIME (mm)The compounds are: (A, 5.4 mm), 14; (B, 10.5 mm), fluorobenzene; (C, 16.8 mm), 1.The HPLC conditions are: Waters 10 JLm C-18 reverse phase RCM column; eluent:isocratic methanol/water, 1:1; flow rate, 2.5 mL/min; UV detection set at 280 nm.Figure 2.5: HPLC chromatogram obtained from the analysis of the reaction ofcomplex 1 with cyanide at 135°C. The yield of 14 was determined to be40%.402iCr(CO)340.5 equiv KCNDMSO/lOmin,MeCN + KF + 415(2.14)lents of cyanide at 135°C gave no reaction; unreacted 2-fluorotoluene was the onlycompound observed in the HPLC chromatogram. Two reaction trials (equation 2.14)were performed using only 1.5 mg of 4, this being about a tenth of the usual quantity ofcomplex used per reaction trial. This results in a five-fold excess of cyanide beingTable 2.4: Chemical Yields Obtained for Complex 4Temperature Yield no. of Average(°C) runs Yield135 29-36% 4 32%125 28-29% 2 28.5%115 41% 1 41%105 41-43% 2 42%95 26% 1 26%135k 58% 1 58%143& 58% 1 58%aOnly a tenth of the usual quantity of 4 was used, giving astoichiometric ratio of 5:1, of KCN to 4.present in these reactions. Yields of 58% were obtained at both 135 and 143°C. Theseresults were significantly better than those obtained using 0.5 equivalents of cyanide (seeTable 2.4).The reaction of 5 with cyanide, as summarized in equation 2.15, was studied over thetemperature range of 105-150°C. The chemical yields obtained are outlined in Table41Cr(CO)350.5 equiv KCNDMSO/ 10mm - Me<)—CN + KF + 5 (2.15)2.5. The best yields (26-29%) were obtained at 115°C, while the next best results (22-26%) were seen at 135°C. The control experiment performed using uncomplexed 4-Table 2.5: Chemical Yields Obtained for Complex 5Temperature Yield no. of Average(°C) runs Yield150 21% 1 21%135 22-26% 3 24%125 21% 1 21%115 26-29% 2 27.5%105 11% 1 11%fluorotoluene (0.5 equiv of KCN; 135°C) exhibited no reaction. HPLC analysis showedonly the presence of unreacted 4-fluorotoluene.The reaction of 6 with cyanide (equation 2.16) was examined at 115 and 135°C.These results are summarized in Table 2.6. The best yields (26-34%) were obtained atCl -—FCr(CO)360.5 equiv KCNDMSO/l0minCl + KF + 6 (2.16)the reaction temperature of 115°C. The control reaction done with 4-chiorofluoro-benzene (uncomplexed) using 0.5 equivalents of cyanide at 135°C exhibited no reaction;unreacted 4-chlorofluorobenzene was the only compound observed in the HPLC chromatogram. One reaction trial (equation 2.16) was heated (115°C) for five minutes, and gave42Table 2.6: Chemical Yields Obtained for Complex 6Temperature Yield no. of Average(°C) runs Yield135 21% 1 21%115 26-34% 3 30%115k 17% 1 17%a reaction time of 5 mm was used.only about half the yield observed for a 10 minute reaction time (see Table 2.6). Thisindicates that reaction times shorter than 10 minutes would result in a significantsacrifice in chemical yield.In the process of examining the chemical yields obtained for complexes 1, 4, 5, and6, it would be interesting to discover any trends or systematic patterns of chemicalbehaviour. However, inspecting the results presented in Tables 2.3-2.6 indicates thatthere are no such patterns observable. What emerges is that each chromium tricarbonylcomplex studied exhibits its own distinct pattern of reaction yields. The mechanism fornucleophiic substitution reactions of(,76-arene)tricarbonylchromium systems is thoughtto proceed by a two-step mechanism (equation 2.17),’ analogous to classical aromatic“CoCo+Ystep 1KXCr,OCj “COCO-xstep 2 Cr,,OCj “COCO(2.17)43nucleophilic substitution.*,34 The first step is addition of the nucleophile (Y) onto thearomatic ring, on the side opposite the chromium tricarbonyl moiety—this results in theexo-substituted, anionic5-cyclobexadienyl complex. The second step is expulsion of thehalide leaving group (X), giving the final substitution product. If this mechanism isvalid, it would be anticipated, from comparison to classical aromatic nucleophilicsubstitution, that electron-withdrawing groups would make the substitution reaction withcyanide more facile, while electron-donating groups would hinder same.35 Using thefluorobenzene complex 1 as the baseline standard, it may be expected that the presenceof the additional methyl group in 4 would hinder the reaction with cyanide, relative to1, and may lead to lower substitution yields during the short reaction time used. Thebest average yield for 1 was 41% obtained at 135°C, while 4 exhibited its best averageyield of 42% at 105°C. As a result, 4 essentially equalled the best yield obtained by 1at 30 degrees lower temperature. On the other hand, the results obtained by 5 weremuch more surprising. Since 4 and 5 are simply ortho- and para-isomers, respectively,similar chemical yields with cyanide might be anticipated for both complexes. However,5 gave unexpectedly low yields, with a best average yield of 27.5% obtained at 115°C.In fact, the chemical yields obtained by 4 readily surpassed those of 5 at all temperaturesinvestigated (see Tables 2.4 and 2.5). Complex 6, which bears an extra chlorinesubstituent (relative to 1), would be expected to produce the highest chemical yields withcyanide—yet this was not observed. A best average yield of 30% was exhibited at 115 °C.tThe mechanism being specifically referred to here is addition-elimination, alsocalled SNAr by March.44Unfortunately, circumstances did not permit the opportunity to conduct reactions attemperatures below 115°C. It is possible that higher chemical yields could be obtainedfor 6 at lower temperatures. Nonetheless, equal or better yields were obtained from 1and 4 at both 115 and 135°C.These results may be explained in part by the relative thermal stability of thecomplexes. Complex 6 was clearly more prone to decomposition in solution; this wasparticularly evident during its synthesis (see pages 27-28). Due to the presence of thechlorine substituent, in addition to the fluorine, there would be less electron densityavailable on the aromatic ring to complex with the chromium tricarbonyl moiety, and theresulting complex would be anticipated to be less thermally stable relative to 1.Therefore, the lower chemical yield for 6 at 135°C, compared to that of 1, could stemfrom greater thermal breakdown of 6 at that temperature. The yields resulting from 1and 6 at 115°C are quite comparable. As a result, 1 exhibits better yields at 135°C than6 simply because it is likely the more thermally robust complex, and not from anygreater intrinsic reactivity. On the other hand, both 4 and 5 would be expected to besomewhat more thermally stable than 1. Complexes 4 and 5 were both prepared inhigher yield than 1, and were found to be as well behaved during storage and handling.However, as presented earlier, 4 exhibited better yields at lower temperatures ascompared to 1, but 5 exhibited significantly lower chemical yields at all reactiontemperatures employed when compared to those of 4. Since it would be reasonable toassume that both 4 and 5 would be of equivalent thermal stability, the reason for thismarked difference in chemical yields obtained by 4 and 5 is unknown. For each45chromium tricarbonyl complex studied, the chemical yields obtained were found to bequite sensitive to reaction temperature, and hence must be optimized for each complexindividually to achieve the best results possible.In order to improve upon the chemical yields obtained thus far, it was decided toinvestigate the use of crown ethers. The presence of crown ethers with many ionicreagents have shown increased solubility and anion reactivity in aprotic organic solvents.Therefore, by employing a crown ether with potassium cyanide, it would be anticipatedthat the nucleophilicity of the cyanide anion would be enhanced.36’7 Previously, 18-crown-6 (1,4,7,1O,13,16-hexaoxacyclooctadecane) has been successfully used to helpconvert benzyl halides38 and alkyl halides39 to their corresponding nitriles in high yield.As a result, 18-crown-6 was chosen as the crown ether to use, to examine its potentialbenefit on the reaction of 4 with cyanide, as shown in equation 2.18. The same general0.5 eqv KCN2Cr(CO)3 18-Crown-6 / 10 mm + KF + 4 (2.18)procedure was followed as described earlier, except for the addition of approximately1.2 equivalents of 18-crown-6 to the reaction mixture prior to heating. The reactionswere conducted over a temperature range of 95-135°C and the chemical yields weredetermined by HPLC analysis as before. The results obtained are summarized in Table2.7. The best yields (40-44%) were now observed to occur throughout the temperaturerange of 105-135°C. These results did not surpass the previous best yields of 41-43%,obtained at 105-115°C, in the absence of 18-crown-6. When the reaction was repeated46at 105°C using approximately three equivalents of 18-crown-6, a slightly improved yieldof 46% was obtained. However, the use of 18-crown-6 did significantly improve uponearlier reaction yields that were obtained at 95, 125, and 135°C (see Table2.4)—increases of about 30-50% over earlier average chemical yields were exhibited.Table 2.7: Chemical Yields Obtained for Complex 4 using 18-Crown-6Temperature Solvent Yield no. of Average(°C) runs Yield135 DMSO 41% 1 41%125 p 42% 1 42%115 40% 1 40%105 40-44% 2 42%105a 46% 1 46%95 35% 1 35%80 CH3N 3% 1 3%95b 4% 1 4%aAbout 3 equiv of 18-crown-6 was used.bAt this oil bath temperature, the CH3N was observed to be refluxing.In addition to these results, a couple of reaction trials (equation 2.18) were conductedusing acetonitrile as the solvent with one equivalent of 18-crown-6 added; these weredone using oil bath temperatures of 80 and 95°C. As shown in Table 2.7, very pooryields were obtained. After chromatographic (HPLC) analysis, these reaction mixtureswere simply set aside without any further manipulations. The following day thesemixtures were reexamined by HPLC, which showed a significant increase in theconcentration of 2-tolunitrile 15 (see Table 2.8). These reaction mixtures were again set47aside for about two weeks. Then HPLC analysis was performed again and a furtherincrease in the concentration of 15 was observed (see Table 2.8). Initially, the resultsobtained using CH3N as the reaction solvent looked wholly unimpressive, butunexpectedly, good yields of 15 were produced with the passage of time. Experience withTable 2.8: Chemical Yields Obtained for Equation 2.18using Acetonitrile as the SolventTemperature Yield Time elapsed after(°C) initial HPLC analysis80 3% 080 21% --18h80 50% —13.5 d95 4% 095 21% --16h95 46% —13.5 dDMSO as the reaction solvent has shown that after the reaction has been performed andthe reaction mixture analyzed by HPLC, no further changes in nitrile productconcentration was observed with subsequent reanalyses. Due to the elevatedtemperatures used for the reactions (equation 2.18) done in CH3N, it was expected thatthe chemical yields, determined initially, represented the total nitrile product formed(and decomplexed) during the 10 minute reaction time. What is not clear is whether theimproved yields shown in Table 2.8 were due to the reaction continuing to occur at aslower rate at room temperature (during storage), or to the fact that the initially formed(6-2-to1unitrile)tricarbony1chromium species only decomplexed to a small extent at first,48then continued to slowly decomplex while being stored.* Unfortunately, this work wasnot followed up at the time.The preliminary results obtained using 18-crown-6 shows promise for the use of crownethers in the substitution reactions of chromium tricarbonyl complexes. In fact, othercrown ethers and cryptands are available for potential use.36’4° It is anticipated thatsome experimentation would be needed to find the optimum macrocycle to function inthese substitution reactions with cyanide.The identification of the aryl nitrile products formed from the reactions of complexes4,5, and 6 with cyanide was accomplished using chromatographic (HPLC) studies. Eachof the nitrile products (2-tolunitrile 15, 4-tolunitrile 16, 4-chlorobenzonitrile 17) werereadily identified by comparison of their respective retention times with that of authenticstandard. To further confirm the identity of the nitrile products 15, 16, and 17, aseparate set of reaction trials was conducted to isolate the organic products and analyzethese by gas chromatography-mass spectrometry (GC-MS). These reactions wereperformed as described previously in the general procedure used for the earlier cyanidereactions (see page 38). Upon cooling, however, the reaction mixtures were diluted withwater, then extracted with diethyl ether. The ether extracts were cooled to 0°C, thentreated with iodine for two hours to oxidatively decomplex any chromium tricarbonylspecies present. The treatment was quenched with the addition of aqueous sodiumthiosulfate solution. The ether layer was further washed (aqueous Na2SO3and saturated*The reaction mixtures were kept in small, stoppered volumetric flasks, but thesemixtures had been exposed to air during HPLC work. As a result, any chromiumtricarbonyl species present could gradually undergo oxidative decomposition.49NaC1 solutions), then dried. The ether solution (concentrated to 1 mL) was analyzedfirst by GC and HPLC, then by GC-MS. Mixtures of authentic standards were preparedfrom the uncomplexed starting arene and corresponding aryl nitrile product (dissolvedin ether) and were also analyzed by GC-MS for direct comparison to the reactionproducts obtained above.Comparison of the mass spectra obtained from the reaction products with those of theauthentic standards confirmed the identity of the starting fluoroaromatics (2-fluoro-toluene, 4-fluorotoluene, 4-chlorofluoroben.zene) and the resulting nitrile products (15,16, 17). However, the reaction mixture containing 4-chlorofluorobenzene and 17 alsocontained a third minor product which was identified as benzonitrile 14 by its massspectrum.The formation of 14 as a side-product from the reaction of 6 with cyanide was due tothe presence of a small quantity of 1 contaminating the starting complex 6.Unfortunately, the chromatographic purification of 6, during its original preparation, didnot completely remove 1 as an impurity. As a consequence, 1 also underwentsubstitution with cyanide as a side-reaction, affording benzonitrile 14.In addition, the chemical yields for this set of reaction trials were estimated from theGC analyses using the standard mixtures for calibration. These results are shown inTable 2.9. The key feature of these results is that none of the yields surpassed thevalues reported earlier, which were determined without subjecting the reaction mixturesto oxidative decomplexation. This further establishes that all the aryl nitrile formedduring the substitution reactions becomes decomplexed under the reaction conditions50Table 2.9: Summary of Chemical YieldsStarting Nitrile Temperature YieldComplex Product (°C)4 15 120—32%5 16 135 —26%6 17 115 —24%used.Other leaving groups apart from halogen have been successfully used in classicalaromatic nucleophilic substitution.41 Hence, it was of additional interest to our studyto examine other leaving groups that could possess greater mobility toward nucleophilicsubstitution for(i6-arene)tricarbony1chromium systems. An obvious choice would be toexamine nitro as a leaving group. Unfortunately, the attempts made to prepare (6-nitrobenzene)tricarbonylchronfiumwere unsuccessful. Chromium tricarbonyl complexeswith arene rings bearing a nitro substituent have been unknown until recently.”42However, prompted by radiolabelling studies using aromatics with dimethylsulfonium24and trimethylammonium’26leaving groups for nucleophilic substitution reactions, wefound that we were able to synthesize(,76-N,N,N-trimethylanilinium)tricarbonylchromiumtrifluoromethanesulfonate 11. Preliminary experiments were conducted in whichcomplex 11 was allowed to react with cyanide as shown in equation 2.19. The samegeneral procedure was used, as previously described for the earlier reactions (see page‘The successful synthesis of(6-2,4,6-trinitrotoluene)tricarbonylchromium, using(CH3CN)r(CO) as the precursor for complexing the arene, has been recentlyreported. This represents the first chromium tricarbonyl complex of a nitroaromatic.51+CF3S0 No Reaction (2.19)L Cr(CO)3 ]1138). The reactions were done at 100 and 120°C. Disappointingly, HPLC analysisshowed the absence of the desired product 14. The HPLC chromatograms of thereaction mixtures exhibited two new prominent peaks, a large peak and a much smallerpeak with a longer retention time; these peaks could not be identified. Complex 11 wasthen heated in DMSO for 10 minutes at 100°C. After cooling, the HPLC chromatogramof this solution showed the presence of a single new peak. The retention time of thispeak was very close to that of the large peak observed from the reactions above. Theseresults seem to suggest that 11 is undergoing some kind of transformation ordecomposition from the heating in solution. For comparison, a trial reaction was donewith uncomplexed N,N,N-trimethylanilinium trifluoromethanesulfonate 12 and cyanideat 100°C (equation 2.20). No reaction was observed, as evidenced by HPLC analysis.[KMe CF3SO No Reaction (220)Unfortunately, the preliminary reactions conducted with 11 failed to produce any 14.These results suggested some chemical breakdown of complex 11 while being heated.Additional time to study this problem, and the potential reactivity of 11, was simplyunavailable.522.4 Labelling Studies with‘1C-Labelled CyanideIn this section, the substitution reactions of complexes 1, 4, 5, and 6 with radioactive[11C]cyanide will be described. Due to the short half-life of ‘1C (20.4 mm), thisradionuclide must be produced at or very close to the site where the radiolabellingchemistry is to be performed. Fortunately, 11C is produced regularly at the TRIUMFfacility for the ongoing PET program at U.B.C. The small TRIUMF/Nordion CP-42cyclotron is used to generate positron emitting nucides for PET, as well as otherradioisotopes for commercial sale. Carbon-li was produced as 11C02 by protonirradiation of N2 gas via the nuclear reaction 14N(p,a)1Cat 15 MeV. The[11C]cyanidewas produced by sequential catalytic conversion of 11C02 according to equation 2.21.l)H2 l)NH3HCO CH HCN (2.21)2)Nicatalyst/450°C 2)PtIl000 CThe H”CN was trapped in an aqueous solution of NaOH (0.1 M) to generate Na11CNfor labelling use.Although the maximum specific activity of “C is 9.22 x 106 Ci/mmol, the ubiquitouspresence of ‘2C in nature invariably dilutes the specific activity of any “C reagent tosome value less than the maximum possible specific activity. The amount of dilution of“C by 12C can vary widely depending on the production conditions used. Specific activityvalues for H11CN that can be practically obtained are in the order of 2 x i0Ci/mmol.43 Unfortunately, the specific activity of the H11CN produced at TRIUMFhas not been determined, but the specific activity value is thought to be no lower than0.5 Ci/mmol. Therefore, the specific activity of the [‘1C]cyanide used for this work53can possibly range somewhere between 0.5-2000 Ci/mmol (most likely in the lowervalues of this range). Since the quantity of actual “C-labelled product is so small,*standard chemical and spectroscopic methods of characterization, such as ‘H and “CNMR, cannot be used for direct product identification. Therefore, chromatographicmethods (e.g., HPLC and GC), using non-radioactive analogues as standards, providesthe best means of product identification available. The best suited chromatographicmethod for this purpose is HPLC.4’ For this work, product identification and analysiswas performed with HPLC instrumentation that was equipped with both a UV detectorand a radioactivity detector connected in series.The radiolabeffing studies began with investigating the reactivity of complex 1 with[“C]cyanide using different amounts of added KCN (i.e., carrier). The generalprocedure used for the radiolabelling reactions with [“Cjcyanide is as follows. After thewas trapped in aqueous NaOH solution, a portion of this solution was removedand its radioactivity measured. The time at which this measurement was taken wasrecorded and designated as the start of synthesis (SOS). A known amount of KCN wasadded to the [“C]cyanide solution, then this carrier-added (CA) solution of [“C]cyanidewas transferred to a reaction vessel and dried under a fast flow of inert gas. Thearene)tricarbonylchromium complex, dissolved in 1 mL of DMSO, was added to thedried [“Cjcyanide and the mixture was heated for 10 minutes. Upon cooling, 25-50 Lof the reaction mixture was subjected to radio-HPLC purification, and the peakwas discussed in Chapter 1, this applies only to “C and other short-livedradionuclides. For example, compounds labelled with ‘H can be analyzed by ‘H NMR.54corresponding to the[11C]nitrile was collected and assayed for radioactivity. An equalvolume of reaction mixture was also assayed at the same time, thereby determining thepercentage of radioactivity in the reaction mixture contributed by the [“C]nitrile product.The radiochemical yield was then calculated.The radiochemical yields obtained have been decay corrected back to SOS toeliminate the variation of time taken for synthesis and chromatography. Therefore, theradiochemical yields can then be compared with one another, and any differences wouldreflect the relative efficacy of the reaction conditions used.Complex 1 was treated with[11C]cyanide as outlined in equation 2.22. The results/ DMSO__ll4 (2.22)Cr(CO)3 150°C/lOmin1 18obtained are summarized in Table 2.10. The first four entries (Table 2.10) represent CATable 2.10: Summary of Radiochemical Yields Obtainedfor Equation 2.22Amount of 1 Amount of Radiochemicalused (mol) KCN added Yield65 0.49 equiv 34%41 0.37 equiv 36%43 0.35 equiv 41%65 0.11 equiv 21%65 0aTrace product was observed, but its activity was too lowto count in the Capintec well counter.55reactions, while the last entry represents a no carrier-added (NCA) reaction trial. Theseinitial results demonstrated that some cyanide carrier must be present to achievesuccessful labelling with[‘1C]cyanide, under the reaction conditions used. For the CAreactions, the addition of 0.35 equivalents of KCN afforded the highest radiochemicalyield (41%). A representative radio-HPLC chromatogram of a CA reaction is shown inFigure 2.6. The chromatogram exhibits the presence of the product, [“CCN]benzonitrile 18 (peak B), and unreacted[11C]cyanide (peak A). The radio-HPLCchromatogram of the NCA reaction trial is shown in Figure 2.7. This chromatogramshows the presence of 18 as only a small peak, indicating a very low radiochemical yieldwas obtained. The time taken for synthesis and chromatography—the synthesistime—was about 30-60 minutes (measured from SOS) depending on experimentalcircumstances. Most typically, the synthesis time was 40-45 minutes.Additional CA[‘1C]cyanide reactions were then performed with complexes 1, 4, 5, and6. Each of these complexes were treated with [“C]cyanide, using 0.5 equivalents ofcarrier, as shown in equation 2.23. The results obtained are summarized in Table 2.11.F 0.5 equiv KCNR___________________a—11CN 223Cr(CO)3 DMSO/ 135°C/lOminRThe radiochemical yields parallel fairly closely the chemical yields obtained with nonradioactive cyanide under similar reaction conditions (see Tables 2.3-2.6 for comparison).Initially, H”CN was trapped in aqueous 0.005 M NaOH solution for the first tworeaction trials in order to minimize the amount of hydroxide present in the [“Cjcyanide56zCCATIME (mm)The compounds are: (A, 2.3 mm), [‘1C]cyanide; (B, 6.5 mm), [“C-CN]bemzonitrile 18.The radio-HPLC conditions are: C-18 reverse phase Whatman Partisil 10 ODS-3 column,25 cm x 9 mm; eluent: isocratic methanol/water, 1:1; flow rate, 5.0 mL/min.Figure 2.6: Radio-HPLC chromatogram obtained from the analysis of the reaction ofcomplex 1 with [‘1C}cyariide (with 0.37 equiv of carrier KCN added) at150°C. The radiochemical yield of 18 was determined to be 36%.57C,)zC/KZ/ 0T65I I I I I0 5 10 15 20TIME (mm)The radio-HPLC conditions are: C-18 reverse phase Whatman Partisil 10 ODS-3 column,25 cm x 9 mm; eluent: isocratic methanol/water, 1:1; flow rate, 5.0 mL/min.Figure 2.7: Radio-HPLC chromatogram obtained from the analysis of the reaction ofcomplex 1 with[11C]cyariide (with no carrier KCN added) at 150°C. Onlya trace of 18 was produced, for a radiochemical yield of <1%.58Table 2.11: Summary of Radiochemical Yields Obtained forEquation 2.23Starting Complex ‘1C-Labelled Nitrile RadiochemicalProduct Yield‘CNCr(CO)31 181 34%Cr(CO)34 19Me’F 31%Cr(CO)35 2019%Cr(CO)36 21reactions. After these early experiments, it was observed that the radioactivity of thetrapped[1tCjcyanide was being lost during the drying procedure. In subsequentexperiments, 0.1 M NaOH solution was used for trapping H’1CN.However, examination of the radiolabelling results of 1 with NCA[‘1Cjcyanide andCA [“C]cyanide (using 0.11 equiv of KCN) showed that in these cases the[11C]cyanide59underwent nucleophulic substitution in low yield. It was thought that perhaps hydroxidewas interfering with the reactivity of[11C]cyanide when 11CN is present in lowconcentration (little or no carrier used). Typically, a volume of 0.5 mL of 0.1 M NaOH(containing trapped 11CN) was used—this introduces 50 mol of 0H into the radio-labelling reaction. As a result, some experiments were done using different concentrations of NaOH solution to trap H11CN, and 0.025 M NaOH was the least concentratedsolution that efficiently trapped and retained the[11Clcyanide upon drying.Next, the behaviour of [“C]cyanide alone in DMSO solution was examined by radioHPLC. The chromatograms obtained are shown in Figure 2.8. Chromatogram A wasobtained from the analysis of a solution of NCA[11C]cyanide (originally trapped in 0.025M NaOH, then dried as usual) in DMSO. Note the extra peaks, apart from the mainpeak (retention time, 4.1 mm), that are present. With the addition of 25 /Lmol of KCNto this[1tCjcyanide solution, radio-HPLC analysis was repeated and chromatogram Bwas obtained. The extra peaks were significantly reduced in size, but not eliminated.A second batch ofH11CN was trapped in 0.05 M NaOH solution and dried, followed bythe addition of 1 mL of DMSO. This solution of NCA[‘1C]cyanide was heated at 150°Cfor 10 minutes. The colourless solution became amber in colour during heating. RadioHPLC analysis of the NCA[11C]cyanide solution, after cooling, exhibited chromatogramC. The effect of heating resulted in a dramatic change in the appearance of the radioHPLC chromatogram relative to earlier results. When chromatogram A is comparedwith chromatogram C, the small extra peaks observed in A have become the dominantpeaks observed in C. These results suggested that 11CN (in low concentration) may be6011CN0z0B11CNC)flME (mm)The radio-HPLC chromatograms represent the following: (i) chromatogram A wasobtained from a solution of NCA[11C]cyanide in DMSO, (ii) chromatogram B resultedfrom the addition of carrier KCN (25 mol) to the [‘1C]cyanide solution used forchromatogram A, and (iii) chromatogram C was obtained from a second batch of NCA[‘1C]cyanide that was heated at 150°C for 10 mm in DMSO. The retention time for‘1CN’ was 4.1 mm in each chromatogram.Figure 2.8: Radio-HPLC chromatograms of[11C]cyanide in DMSO.61changing into a different chemical form, in the presence of hydroxide, that cannotundergo nucleophilic substitution.Two radiolabelling trials were done with 6, in which hydroxide concentration wasreduced. For the first trial, a batch of CA[11C]cyariide was prepared using H”CN thatwas trapped in 0.025 M NaOH, followed by the addition of 0.11 equivalents of KCN, andwas dried as usual. Complex 6 was treated with the CA[11Cjcyanide at 150°C asdescribed in the general procedure.[11C-CN]-4-Chlorobenzonitrile 21 was obtained ina radiochemical yield of 21%. For the second trial, the H”CN was trapped in adifferent manner to eliminate the presence of hydroxide from the [“C]cyanide reagent.A second production run of H11CN was trapped in a glass loop that was emersed in aCC14/C02 (-23°C) cooling bath. Any ammonia gas, from the conversion of ‘1CH4(equation 2.21), was swept through the glass ioop with helium transfer gas. Then theglass ioop was removed from the cooling bath and the H11CN was slowly added to areaction vessel containing a mixture of 6, carrier KCN (ca. 0.4-0.8 equiv*), and 1 mL ofDMSO. This mixture was heated for 10 minutes at 125-130°C. Radio-HPLC analysisof the cooled reaction mixture showed that 21 was obtained in 29% radiochemical yield.These two results suggested that some improvement of radiolabelling efficiency with[11C]cyanide is possible by limiting the hydroxide quantity in the reaction mixture.The identification of the[11C]nitrile products,[11C-CN]benzonitrile 18, [‘1C-CN]-2-tolunitrile 19,[11C-CN]-4-tolunitrile 20, and11C-CN]-4-chlorobenzoriitrile 21, was*Two small crystals of KCN were used, which were not weighed, thus the quantityindicated was estimated.62accomplished using radio-HPLC studies. The chromatographic behaviour of the[11C]nitriles was consistent with that observed for the related non-radioactive aromaticnitriles (14, 15, 16, 17). For the reaction of complex 1 with CA[‘1C]cyanide, additionalproduct identification was performed with GC. The reaction mixture of a reaction trialwas analyzed by GC (injection temperature, 250°C; oven temperature, 90°C; N2 carriergas flow, 2.0 mL/min) and found 18 to be present at a retention time (RT) of 8.1minutes. This was confirmed by the addition of standard (non-radioactive) benzonitrile14 to an aliquot of reaction mixture and the assigned product peak (RT = 8.1 mm) wouldcorrespondingly increase in size. Moreover, another portion of reaction mixture wassubjected to radio-HPLC purification and the peak containing 18 was collected. Theradio-HPLC fraction was analyzed by GC and the peak due to 18 exhibited the sameretention time as standard 14.The radiolabelling results obtained in this study are still preliminary, but theydemonstrated that aromatic nucleophilic substitution reactions with CA[‘1C]cyanide canbe successfully performed with(6-arene)tricarbonylchromium compounds. However,the use of high specific activity NCA[11Cjcyanide gave a disappointing result. Thereasons for this are not clear, but this is not an uncommon problem when labelling withradionudides; the general reasons for this phenomenon were discussed in Chapter 1.In this instance, it was thought that the presence of hydroxide, which was absent in themodel labelling studies with non-radioactive cyanide, could be the problem. Thehydroxide could affect the radiolabelling results in three different ways. The firstpossibility is that the hydroxide could be chemically changing the[11C]cyanide into a63different form, thereby reducing the already low quantity of 11CN available for reaction.Evidence for this possibility was suggested by the radio-HPLC studies of[‘1C]cyanidealone in DMSO. It was observed that 11CN underwent change to unidentified radio-products upon heating. This observation warrants additional study to determine whatis actually happening to the 11CN. The second possibility is that the hydroxide is acompeting nucleophile with 11CN. Since about 50 mol of hydroxide is present, and theactual quantity of 11CN is about one to three orders of magnitude less, the hydroxideis necessarily in significant excess. Therefore, reaction with hydroxide may become thedominant process, even if hydroxide is less reactive toward chromium tricarbonylcomplexes than cyanide. The final possibifity is that hydroxide could be hydrolysing the[“C]nitrile product to the corresponding[11C]amide and [‘1Cjcarboxylic acid. Somewater would need to be present in the reaction mixture for hydrolysis to occur.However, given the very small amount of[11C]nitrile product formed, very little waterwould be necessary. It is quite possible that the drying of the trapped [“C]cyanidesolution is not totally complete, thereby leaving sufficient moisture to allow hydrolysisto proceed. Standards of the anticipated hydrolysis products, benzarnide and benzoicacid, were subjected to HPLC analysis (using the same HPLC conditions as for thereaction mixtures) and exhibited retention times of 3.2 and 2.2 minutes, respectively.These retention times are consistent with those of the unidentified radio-peaks observedin the chromatograms presented in Figures 2.6 and 2.7.642.5 Summary and ConclusionsThe objective of this study was to explore the potential of(6-arene)tricarbony1chromiumcompounds as intermediates for the radiolabelling of arene structures. The results ofthis investigation have clearly demonstrated that chromium tricarbonyl complexes canbe used to prepare aryl[11C]nitriles in fair radiochemical yield. As a result, this studyrepresents an important first step in the development of chromium tricarbonyl complexesfor radiolabelling.A range of simple(i76-arene)tricarbonylchromium complexes were prepared in 12-89%yield from the reaction of free arene with Cr(CO)6 in a refluxing mixture of di-n-butylether and THF. Arenes bearing electron-withdrawing groups gave much lower yields ofchromium tricarbonyl product in comparison to arenes with electron-donating groups.The reactivity of(6-halobenzene)tricarbonylchromium complexes 1, 2, and 3 withcyanide anion was investigated and only 1 was found to undergo aromatic nucleophilicsubstitution successfully. Hence, both chlorine and bromine were determined to beineffective leaving groups for reactions with cyanide. Therefore, the reactivity offluorine-substituted, chromium tricarbonyl complexes 1, 4, 5, and 6 were studied indetail.Complex 1 was allowed to react with cyanide (0.5 equiv) in DMSO over a temperaturerange of 105-150°C and gave beuzonitrile 14 in 12-41% yield. The best yield (41%) wasobtained at 135°C. Control experiments with uncomplexed fluorobenzene confirmedthat no fluorine displacement by cyanide occurred with free fluorobenzene under thereaction conditions used for 1.65Complex 4 was treated with cyanide (0.5 equiv) in DMSO over a temperature rangeof 95-135°C, which afforded 15 in yields of 26-43%; the best yields (41-43%) wereproduced at 105-115°C. Complex 5 was allowed to react with cyanide (0.5 equiv) inDMSO over a temperature range of 105-150°C and obtained yields of 11-29% of 16.The best yields (26-29%) were exhibited at 115°C, while the next best results (22-26%)were observed at 135°C. The reaction of 6 with cyanide (0.5 equiv) in DMSO wasstudied at temperatures of 115 and 135°C only. The best yields of 17 (26-34%) wereobtained at 115°C. The reaction time was kept to 10 minutes for these studies. Whenthe reaction time was reduced to five minutes, the chemical yield was significantlyreduced also.The cyanide substitution reaction of 4 was also studied in the presence of 18-crown-6.These reactions were conducted over a temperature range of 95- 135°C, andimprovements in chemical yield, over earlier studies, were observed throughout thetemperature range examined. The best yield of 15 (46%) was obtained at 105°C usingthree equivalents of 18-crown-6. Clearly, the use of crown ethers shows promise towardmaximizing the yields obtained from the substitution reactions of cyanide with chromiumtricarbonyl complexes.Substitution reactions with 1, 4, 5, and 6 were performed using[11C]cyanide, and thecorresponding aryl[11C]nitriles 18, 19, 20, and 21 were obtained. Some CA reactionswere done (at 150°C) with 1 which indicated that 0.35 equivalents of carrier (KCN) wasrequired to afford the best radiochemical yield (41%). Unfortunately, the NCA reactiontrial with 1 gave only a trace of 18. These initial results suggest that some carrier must66be present to achieve successful radiolabelling with [“C]cyanide, however, continueddevelopment of this work could well enable NCA radiolabelling to be accomplished inthe future. The aryl[11C]nitriles 19, 20, and 21 were produced in 34%, 31%, and 19%radiochernical yields, respectively, using 0.5 equivalents of carrier at 135°C. Thesynthesis times, as measured from SOS, were typically 40-45 minutes in length, and areacceptable for radiolabelling with ‘1C.67References1. Fischer, E. 0.; Ofele, K. Angew. Chem. 1957, 69, 715; Chem. Ber. 1957, 90, 2532-2535.2. Zeiss, H.; Wheatley, P. J.; Winkler, H. J. S. Benzenoid-Metal Complexes: StructuralDeterminations and Chemistry; Ronald: New York, 1966.3. Silverthom, W. E. Adv. Organomet. Chem. 1975, 13, 47-137.4. Coilman, 3. P.; Hegedus, L. S. Principles and Applications of Organotransition MetalChemistry; University Science Books: Mill Valley, CA, 1980; Chapter 14.5. Semmeihack, M. F. .1. Organomet. Chem. Libr. 1976, 1, 36 1-395.6. Jaouen, G. Ann. N. Y. Acad. Sci. 1977, 295, 59-78.7. See reference 4; p 653.8. Pearson, A. J. Metallo-organic Chemistry; Wiley Interscience: New York, 1985; pp348-362.9. McQuillin, F. 3.; Parker, D. G.; Stephenson, G. R. Transition Metal Organometallicsfor Organic Synthesis; Cambridge University: Cambridge, 1991; pp 182-208.10. Nicholls, B.; Whiting, M. C. I. Chem. Soc. 1959, 551-556.11. Rosca, S. I.; Rosca, S. Rev. Chim. 1974, 25, 46 1-465.12. Alemagna, A.; Buttero, P. D.; Gorini, C.; Landini, D.; Licandro, E.; Maiorana, S.J. Am. Chem. Soc. 1983, 48, 605-607.13. Mahaffy, C. A. L.; Pauson, P. L. J. Chem. Res., Synop. 1979, 128.14. Harrington, P.3. Transition Metals in Total Synthesis; Wiley Interscience: New York,1990; pp 317-319.15. Caiy, F. A.; Sundberg, R. J. Advanced Organic Chemistry—Part B: Reactions andSynthesis; Plenum: New York, 1977; Chapter 7.16. Kilbourn, M. R. Fluorine-18 Labeling of Radiopharmaceuticals; Nuclear ScienceSeries, Monograph NAS-NS-3203; National Academy: Washington, DC, 1990.17. Radiopharmaceuticals for Positron Emission Tomography: Methodological Aspects;Stöcklin, G., Pike, V. W., Eds.; Kiuwer Academic: Boston, 1993.6818. Radionuclides Production; Helus, F., Ed.; CRC: Boca Raton, 1983; Vol. 2.19. Davis, R.; Kane-Maguire, L. A. P. In Comprehensive Organometallic Chemistiy: TheSynthesis, Reactions and Structures of Organometallic Compounds; Wilkinson, G.,Stone, F. 0. A., Abel, E. W., Eds.; Perganion: Toronto, 1982; Vol. 3, pp 1001-1021.20. Mahaffy, C. A. L.; Pauson, P. L. Inorg. Synth. 1979, 19, 154-158.21. Hudeek, M.; Toma, . .1. Organomet. Chem. 1990, 393, 115-118.22. See reference 19; p 1001.23. Mahaffy, C. A. L.; Pauson, P. L. J. Chem. Res., Miniprint 1979, 1776-1794.24. Maeda, M.; Fukumura, T.; Kojima, M. Chem. Pharm. Bull. 1985, 33, 1301-1304; .1.Labelled Compd. Radiopharm. 1986, 23, 1104-1105.25. Angelini, G.; Sperauza, M.; Wolf, A. P.; Shiue, C-Y. .1. Fluorine Chem. 1985,27, 177-191.26. Haka, M. S.; Kilbourn, M. R.; Watkins, 0. L.; Toorongian, S. A. J. Labelled Compd.Radiopharm. 1989, 27, 823-833.27. Bunnet, J. F.; Hermann, H. .1. Org. Chem. 1971, 36, 408 1-4088.28. Ofele, K. Chem. Ber. 1966, 99, 1732-1736.29. Mahaffy, C. A. L. J. Organomet. Chem. 1984, 262, 33-37.30. Gilbert, J. R.; Leach, W. P.; Miller, J. R. .1. Organomet. Chem. 1973, 49, 219-225.31. Muller, J.; Göser, P. Recent Dev. Mass Spectrosc., Proc. mt. Confi Mass Spectrosc.1969 (Pub 1970), 1175-1180.32. Carganico, G.; Buttero, P. D.; Maiorana, S.; Riccardi, G. J. Chem. Soc., Chem.Commun.. 1978, 989-990.33. See reference 4; pp 653-661.34. March, J. Advanced Organic Chemistty: Reactions, Mechanisms, and Structure, 3rded.; Wiley Interscience: New York, 1985; Chapter 13.35. See reference 34; pp 584-586.36. See reference 34; pp 77-79, 321-322 and references contained therein.37. Kriipe, A. C. .1. Chem. Ed. 1976, 53, 6 18-622.6938. Zubrick, J. W.; Dunbar, B. I.; Durst, H. D. Tetrahedron Lett. 1975, 71-74.39. Cook, F. L.; Bowers, C. W.; Liotta, C. L. .1. Org. Chem. 1974, 39, 3416-3418.40. Gokel, G. W.; Durst, H. D. Synthesis 1976, 168-184.41. Miller, J. Aromatic Nucleophilic Substitution, Elsevier: New York, 1968; Chapter 5.42. Azam, K. A.; Kabir, S. E.; Kazi, A. B.; Molla, A. H.; Ullah, S. S. Chem. Abstr. 1988,109, 23086r.43. Meyer, G.-J. Radiochim. Acta 1982, 30, 175-184.44. Ruth, T. J., TRIUMF, Vancouver, BC, personal communication.70Chapter 3DEVELOPMENT OF METHODS FOR RAPIDFLUORINE LABELLING31 IntroductionIn the early 1950s, the pioneering work of Fried and Sabo led to the first significantsuccessful application of selective fluorination to modify the biological activity of anorganic molecule.1 The fluorosteroid, 9a-fluorohydrocortisone acetate 22, that wasOAc0prepared by the Squibb Company researchers, showed approximately an 11-fold increasein glucocorticoid activity over that of cortisone acetate. This report stimulated muchnew research into developing ways of selectively introducing fluorine at specific sites incompounds of potential biological interest, in order to modify their biological activity.Since the landmark work of Fried and Sabo, the study of selectively fluorinated71molecules has resulted in a variety of useful applications in biochemistry andmedicine.2’3 These applications include the use of fluorine-containing organicpharmaceuticals as anticancer and antiviral agents, antiinflammatory drugs, antibiotics,antifungal and antiparasitic agents, general anesthetics, and therapeutic drugs for mentalillness. In addition, pharmaceuticals labelled with radioactive fluorine (18F) play animportant role in PET imaging. Perfluorinated hydrocarbons are no longer the majorfocus of study in fluorine chemistry. Currently, interest in selectively fluorinatedcompounds is continuing to increase, along with the recognition of the importance ofselective fluorination methodology.4’5The attractiveness and utility of fluorine as a substituent in biologically activemolecules are due to the unique properties of fluorine that can induce profound andunexpected effects on biological activity. Firstly, fluorine is the most electronegative ofall elements, with an electronegativity (Pauling scale) of 3.98 as compared to 3.44 foroxygen, 3.16 for chlorine, or 2.96 for bromine. It is this property which producespronounced electronic effects in a molecule after the introduction of a fluorinesubstituent. Secondly, fluorine, with its small van der Waals radius (1.35 A), closelyresembles hydrogen (van der Waals radius 1.20 A) in size. As a result, the fluorinatedanalogue will usually closely resemble the non-fluorinated molecule in size when afluorine is substituted for hydrogen. This allows, for instance, fluorinated analogues tostill meet steric requirements at enzyme receptor sites. Thirdly, fluorine forms astronger bond with carbon than does hydrogen—the carbon-fluorine bond energy is 456-486 kJ/mol, while carbon-hydrogen bond energy varies from 356 to 435 kJ/mol.72Therefore, carbon-fluorine bonds exhibit increased thermal and oxidative stabifity overthat of carbon-hydrogen bonds. Lastly, fluorine, when replacing hydrogen in a molecule,usually enhances lipophilicity which increases the rate of absorption and transport of thefluorine-containing compound in vivo. In many cases, this characteristic may be the mostimportant in improving pharmacological activity.6’7An additional feature of fluorine is the availability of the artificially preparedradionuclide, 18F, which decays by positron emission. Fluorine-18 (half-life, 109.7 mm)is one of the four key radionuclides used in PET. The other conimorily used positronemitting nuclides (11C, ‘3N, 150) possess very short half-lives (—‘2-20 mm) in comparisonto ‘8F. The longer half-life of ‘8F allows for more complex or multistep radio-pharmaceutical syntheses to be conducted, and the resulting compounds can betransported over moderate distances for use at different locations. In addition, the studyof relatively slow biological processes can be performed with‘8F-labelled agents, whichwould not be feasible with agents using nuclides with shorter half-lives. Furthermore,18F-labelled compounds have the potential to produce PET images of superior resolutiondue to the relatively low energy positron (maximum 0.635 MeV) emitted by 18F (seeTable 1.2 for comparison)—this factor will be of increasing importance as PETinstrumentation improves.8’9The utilization of 18F-labelled pharmaceuticals with PET imaging has enabled anumber of human biochemical and physiological processes to be investigated in vivo, aswas presented in Chapter 1. More recently, however, the application of PET is beingextended beyond the study and diagnosis of disease to the area of drug discovery,73development, and approval of new pharmaceuticals. Drug candidates can be labelledwith positron emitting nuclides, such as 11C and 18F, to provide information regardingdrug absorption, distribution, metabolism, and elimination in vivo (human or animalsubjects) using PET imaging. These studies can complement information obtained using3H- and‘4C-labelled analogues in animals. Alternatively, established PET imagingprotocols can be used to monitor the biological behaviour of drug candidates in vivo todetermine the therapeutic potential or efficacy of such compounds. For disease stateswhere no animal models exist, PET becomes a unique tool that still enables drugassessment to be carried out. Also, given the interest in fluorine-containing biologicallyactive molecules, it would be possible—in principle, at least—to study the in vivobiochemistry of the 18F-labelled analogues via PET.1°Underlying the continued development and application of fluorinated compounds isthe ongoing need for new and improved methods to selectively introduce fluorine intopolyfunctional molecules at specific sites. However, the mild and selective introductionof fluorine into organic molecules has been and continues to be of considerablechallenge to organic chemistry. Although elemental fluorine was first prepared byMoissan in 1886,11 the organic chemistry of fluorine developed slowly in comparison tothe other halogens. It was quickly discovered that the reaction of fluorine with organiccompounds was highly exothermic, and often resulted in explosions. These observationsunderstandably discouraged further research with fluorine for decades after Moissan’stime. In the 1930s, Bockemüller demonstrated that fluorine, when diluted with inert gas(usually nitrogen), could be used for selective fluorination of organic substrates under74controlled conditions.’2 Since that time, new fluorinating agents and reactions havebeen developed making possible the synthesis of the many organofluorine compoundsavailable today.’3”4Currently, the range of methods for introducing fluorine into organic compounds isbased on the use of either elemental fluorine, hydrogen fluoride, inorganic fluorides, orvarious organofluorine reagents. These fluorinating agents can be broadly characterizedas sources of either nucleophilic or electrophilic fluorine. With these fluorinating agents,many methods have been developed to effect the transformation of different organicfunctional groups to organofluorine derivatives, and are catalogued in multiplebooks’5”6 and reviews.4’137”8 However, many of these methods, though successfulin conventional synthetic chemistry, are not compatible with the requirements ofradiolabelling with 18F.8’9A primary limitation of radiofluorination methodology is the limited range of usefulsynthetic precursors that can be produced in‘8F-labelled form. The only reagentavailable for nucleophilic fluorination is [‘8F]fluoride anion.’9 However, [‘8F]fluoridehas seen increasing application because of continuing investigations performed studyingthe different variables involved in optimizing the reaction conditions for its use withstructurally diverse substrate molecules. Investigators have studied the influence ofreaction solvent, source of ‘8F, fluoride counterion, catalyst (e.g., crown ethers), ‘9Fcarrier levels, reaction vessel material, substrate concentration, leaving group, andtemperature on the radiochemical yields obtained with [‘FJfluoride.9” Reactionconditions have been developed such that a number of aliphatic and aromatic75compounds have now been successfully radiolabelled with 18F •9,20 As a result,[18F]fluoride has gained increased importance for radiofluorination work.In contrast to nucleophilic fluorination, a number of electrophilic fluorinating agentshave been produced in‘8F-labelled form, using [‘8F]F2 as the source of 18F in each case.A list of the various fluorinating agents prepared with 18F is presented below. However,Fluorinating Agents Labelled with 18F9’2°fluorine (F2) chlorine monofluoride (C1F)perchioryl fluoride (C1O3F) trifluoromethyl hypofluorite (CF3OF)xenon difluoride (XeF2) trifluoroacetyl hypofluorite (CF3COOF)nitrosyl fluoride (NOF) acetyl hypofluorite (CH3COOF)N-fluoro-2-pyridone N-fluoropyridinium trifiatesN-fluoro-N-alkylsulfonamides (RSO2NFR‘)N-fluoro-bis(trffluoromethylsulfonyl)imide ((CF3SO2NF)most of these reagents have not actually been evaluated as to their scope and utility forradiolabelling with 1F.9 In practical experience, the vast majority of electrophilicfluorinations are performed with [18F]F2 and CH3OO18F.21’2 Acetyl hypofluorite isa relatively new reagent that was originally developed by Rozen and co-workers in198 1,23 and then was prepared in‘8F-labelled form in 1982? Acetyl hypofluorite hasbeen found to be a milder and more selective electrophilic fluorinating agent, incomparison to elemental fluorine, for a variety of substrate molecules.25’6 Moreover,the development of a simple on-line gas-solid phase synthesis of acetyl hypofluorite27has significantly increased its utility for radiofluorinations. The other 18F-labelledfluorinating agents listed previously are not trivial to produce on a routine basis, and as76a result, have not engendered serious interest by PET research groups as yet.21 Clearly,much additional research needs to be done in order to develop the full potential ofelectrophilic fluorination methodology for radiolabelling.The requirement to develop methods to prepare‘8F-labelled aromatic compounds forthe PET program at U.B.C. prompted Adam and co-workers28’9to examine the reactivity of main group organometallic derivatives with electrophilic fluorinating agents. Itwas essential that the fluorination reaction be rapid, the fluorinating agent be readilyavailable in‘8F-labelled form for routine use, and be efficient in the incorporation ofradiofluorine. Also, it was desired that the reaction conditions be mild and theexperimental manipulations be as simple as possible to perform to accommodate futureautomation. It was known that the electrophilic halogenation of organometallicderivatives such as those of tin30 and mercury was well established. However, verylittle study had been done regarding the reactivity of carbon-metal bonds withelectrophilic fluorinating agents. As a result, the reactivity of aryl-tin, (then later) arylsilicon, -germanium, -lead, -mercury, and -thallium bonds, with elemental fluorine wasinvestigated.28’9Fluorobenzene was successfully produced from phenyltri-n-butyltin (48-70% yield), tetraphenyltin (15-56% yield), tetraphenyllead (48% yield), and diphenylmercury (26-36% yield). The other organometaffic derivatives studied gave only pooryields (2.4-12%), or no detectable product in the case of the organothallium derivative.These studies represent the first reports of the cleavage of aryl-metal bonds byelectrophilic fluorination.Since the reports of Adam et al.,28’9 the fluorination of organometallic compounds has77been under study by other researchers as well. As a result, various simple aromaticcompounds have been radiolabelled with 18F utilizing organotin,29’323 organosilicon,33’45 organogermanium,33and organomercur6’37derivatives. In addition, aryllithium38’39 and Grignard39’4°reagents have also been successfully radiofluorinated.More significantly, the strategy of electrophiic fluorination of organometallic derivativeshave been applied to the preparation of18F-labelled pharmaceuticals for PET. Aryl-tinprecursors were used to prepare both 3-O-methyl-6-[18F]fluorodopa41and 6-[’8F]fluoro-dopa42 by reaction with CH3OO18F(20% radiochemical yield) and[18F]F2 (25% radio-chemical yield), respectively. 6-[’F]Fluorodopa has also been prepared from an arylsilicon derivative using [18F1F2 (5-10% radiochemical yield)43 and an aryl-mercuryderivative using CH3OO18F(—40% radiochemical yield).” 6-[18FjFluorometarami-no145 and4-[18F]fluoro m-tyrosine6were successfully prepared from organomercurysubstrates by reaction withCH3OO’8Fin approximately 30% and 25-30% radiochemicalyields, respectively.6-[18F]fluoroveraldehyde was readily prepared in 30% radiochemicalyield from an organotin precursor using[18F]F2,but interestingly could not be obtainedfrom the corresponding organomercury derivative.47 This case reaffirms the need forvarious synthetic options to be available to successfully synthesize a desired18F-labelledcompound.The application of electrophilic fluorination via organometallic intermediates has beenalmost exclusively focussed on introducing fluorine onto aromatic rings. This isunderstandable because of the many organic compounds of biological interest thatcontain aromatic rings in their structures. Nonetheless, other potential applications also78exist. Some alkyl fluorides have been prepared via organometallic derivatives, such ascyclohexyl fluoride48 and n-tetradecyl fluoride49 from the corresponding Grignardreagents, in low yield. Benzyl[18F]fluoride was prepared from potassium benzylpentafluorosilicate in 6% radiochemical yield.35 Generally, however, primary and secondaryalkyl fluorides have been readily obtained using nucleophilic substitution with fluorideanion. Alternatively, a number of biologically interesting molecules exist which containa vinyl function in their structures.50’12 The vinyl functionality provides a potentialsite for labelling with fluorine. Moreover, some important biomolecules specificallycontain the fluorovinyl grouping,7’534and may be of interest for 18F-labelling. Thesepotential applications prompted interest in extending the strategy of electrophilicfluorination of organometaffic derivatives as a general methodology to preparefluorovinyl compounds, and is suitable for radiofluorinations with 18F.Upon review of the fluorination studies of aryl-metal systems, it seemed that theorganotin reagents gave the highest chemical and radiochemical yields, although organomercury and -silicon derivatives gave good results also. The electrophilic fluorinationreactions of aryl-tin reagents are rapid. Previous work55 with vinyl-tin compounds havedemonstrated that they are sufficiently stable to be prepared in bulk, and then stored foruse as needed. Vinyl-tin compounds can be readily prepared by reduction of thecorresponding acetylenic compounds with tin hydride reducing agents.56’57 In addition,other methods of preparation of vinyl-tin derivatives are also available.58 These factorssuggested to us that vinyl-tin substrates offered the best potential as reagents forfluorination studies.79In this chapter, the preparation of the vinyl-tin derivatives employed for this work willbe described. This will be followed by fluorination studies of the vinyl-tin substrates withelemental fluorine and acetyl hypofluorite. Lastly, the successful radiofluorination ofa vinyl-tin derivative of a steroid will be presented.3.2 Synthesis of Vinyl-Tin PrecursorsThe vinyl-tin derivatives were prepared by hydrostannylation of the correspondingacetylenic precursors, and most of the results obtained have been described previouslyin the author’s M.Sc. Thesis.55 The acetylenic starting materials were either obtainedcommercially or prepared using literature methods, as summarized in Schemes 3.1 and3.11.The acetylenic compounds, 17a-ethynyl- 1,3,5( 10)-estratriene-3, 1713-diol 23, 3-methoxy-17a-ethynyl- 1,3,5(10)-estratriene- 17i3-ol 24, 3, 17i3-dimethoxy-17a-ethynyl-1,3,5( 10)-estratriene 25, 7,8-dideoxy-1,2:3,4-di-O-isopropylidene-D-glycero-a-D-galacto-oct-7-yno-pyranose 28, and 7,8-dideoxy-l,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-ynopyranose 29, were hydrostannylated (see Schemes 3.111 and 3.IV) by an adaptationof literature procedures.57 The acetylenic precursors were treated with approximatelytwo equivalents of tri-n-butyltin hydride and a catalytic amount of AIBN (2,2 ‘-azobis(2-methylpropionitrile)), followed by heating the mixture at 95°C overnight. The (E)vinyistannylated products were isolated by chromatographic workup of the reactionmixtures, and the chemical yields are summarized in Table 3.1. Each of the (E)vinyistannanes was characterized by their physical properties (optical rotation values,80Scheme 3.!1) KOHIDMSO2) MelScheme 3.11Cr03-2 pyCH21(py = pyridine)OHHCCMgBrThFHO_//28+L-OH/2324+2581Scheme 3.1112R’O23 R’=R2=H24 R’Me,R=H25 R’R2Me(n-Bu)3SnHAIBN/heatR20R1-Sn(Bu)330 R’=R2=H31 Me,R=H32 R’R2MeScheme 3.W/0(n-Bu)3SnHAIBN/heat(n-Bu)3SnHAIBN/heatSn(Bu)3Sn(Bu)3_0Ho\3482melting points of crystalline products), elemental analysis, and spectral data (1H NMR,mass spectrometry).The AIBN catalyzed hydrostannylation reaction was found to be quite successful forall the acetylenic precursors used. However, higher yields of (E)-vinylstannylatedTable 3.1: Yields of (E)-VinylstannanesStarting Material Product Chemical Yield23 30 59%24 31 90%25 32 94%28 33 61%29 34 59%product were obtained from the steroidal acetylenic compounds, 24 and 25, in comparison with the carbohydrate acetylenic substrates (28, 29). It is known that the hydrostannylation reaction can produce three different isomers when using terminal acetylenes,59as shown in equation 3.1. As a consequence, the chemical yield of (E)-vinylstarmane will— (Bu)3SnH (Bu)3Sn,,H ÷ H\H + H\,,Sn(Bu)3R — HR H R Sn(Bu)3 R H (3.1)regioisomer Z-isomer E-isomervary depending on the proportion of (Z)-vinylstamiane and “regioisomer” which areproduced. It was observed that the hydrostarinylation reactions of 28 and 29 producedgreater proportions of alternative isomeric products, thus giving consistently lower yieldsof (E)-vinylstannanes. The lower hydrostannylation yield of 17a-(E)-tributylstannylvinyl-831,3,5(10)-estratriene-3,17fl-diol 30 from 23 was due to significant protonolysis of vinyl-tinproduct formed during the reaction;* this was most probably due to the presence of theunprotected phenolic hydroxyl group.During a more recent preparation of 3-methoxy- 17a-(E)-tributylstamiylvinyl- 1,3,5(10)-estratriene-1713-ol 31, the isomeric product, 3-methoxy-17a-(Z)-tributylstaunylvinyl-1,3,5(10)-estratriene-17j3-ol 36, was also isolated (— 10% yield). Compound 36 has notHOMeO’1’Sn(Bu)3been fully characterized as yet. However, in the preparation of (E)-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-8-C-tributylstannyl-L-glycero-c-D-galacto-oct-7-enopyranose34, bothalternative isomeric products, (Z)-7,8-dideoxy- 1,2:3,4-di-O-isopropylidene-8-C-tributyl-Sn(Bu)3(Bu)3Sn..—stannyl-L-glycero-cx-D-galacto-oct-7-enopyranose 37 and 7,8-dideoxy- 1,2:3,4-di-O-isopro-pylidene-7-C-tributylstannyl-L-glycero-a-D-galacto-oct-7-enopyranose 38, were isolated as*A significant amount of 17a-vinyl- 1,3,5(10)-estratriene-3, 17-diol 35 was recoveredfrom the hydrostannylation of 30; see Experimental for details.84a 3:2 mixture. The chemical yields of 37 and 38 were estimated to be 15% and 10%,respectively. Compounds 37 and 38 were identified by their ‘H NMR spectral data.3.3 Labelling Studies with Non-Radioactive FluorinePrior to this study, there were some reports of vinylmetallated compounds having beenused for the synthesis of fluorovinyl compounds. There was an early report in which thedirect fluorination of a vinyl-tin compound (1,2,3,4,7,7-hexafluoro-5,6-bis(trimethyl-stannyl)bicyclo[2.2.ljhepta-2,5-diene) with F2 was studied, but the desired product wasafforded in <5% yield.6° Since then, Di Raddo and Diksic6’prepared4-[’8Fjfluoroanti-pyrine using [‘8F]F2 in 18% radiochenilcal yield from 4-(trimethylsilyl)antipyrine. Leeand Schwartz62 prepared various simple vinyl fluorides in 71-88% yield using vinyl-lithium reagents and N-tert-butyl-N-fluorobenzenesulfonamide as the source forelectrophiic fluorine. Interestingly, Flanagan et al.5’ attempted to fluorinate 6-chloromercuricholest-5-en-3j3-ol with elemental fluorine, acetyl hypofluorite, and xenondifluoride under various conditions, but without success.Our study examined the reactivity of the (E)-vinylstannanes, 30, 31, 3,17(3-dimethoxy-17a-(E)-tributylstannylvinyl-1,3,5(10)-estratriene 32, (E)-7,8-dideoxy-1,2:3,4-di-O-isopropy-lidene-8-C-tributylstannyl-D-glycero-a-D-galacto-oct-7-enopyranose 33, and 34, withelemental fluorine and acetyl hypofluorite.The fluorination of 31 was initially studied in small scale experiments using excess F2or gaseous CH3OOF, and the resulting crude reaction mixtures were analyzed by TLCand 19k’ NMR It was evident from TLC analysis that both fluorinating agents produced85multiple products, but the 17 NMR spectra indicated that the reaction of 31 withCH3OOF produced significantly more fluorovinyl product than with F2. It was alsoobserved that neither fluorinating agent consumed all of the starting material.As a result, 31 was fluorinated with CH3OOF (Scheme 3.V) on a larger scale in thefollowing manner. Compound 31 was treated with approximately 1.3 equivalents ofgaseous CH3OOF in CFC13 at room temperature. This procedure was conducted withsix portions of 31 in order to employ a sufficient amount of starting material forfluorination. The crude reaction mixtures were combined and subjected to columnchromatography. The fractions containing 3-methoxy- 17a-(E)-fluorovinyl- 1,3,5( 10)-estra-triene- 1713-0139 and 3-methoxy-l7cx-(Z)-fluorovinyl-1,3,5(10)-estratriene-1713-ol 40 weresubjected to additional purification by HPLC, whereby 39 and 40 were isolated in 29.5%and 3.8% yield, respectively.Compounds 39 and 40 were readily characterized by 1H and ‘9F NMR.Scheme 3.VHOHOMeOI T > CH3OOF_J.. L/ +CFCI3 HOMeO3186MeOHaving successfully isolated the fluorovinyl products 39 and 40, the opportunityemerged to quantitatively study the fluorination reactions of 31 under differentconditions. A number of small scale reactions with 31 were conducted using thefollowing general procedure. A solution of 31 (in a chosen solvent) was treated with asmall excess (ca. 1.2-1.4 equiv) of fluorinating agent (F2 orCH3OOF). The solvent wasevaporated and the reaction mixture was dissolved in a known volume of chloroform.This solution was analyzed by HPLC to determine the combined yield of both fluorovinylproducts 39 and 40. (A solution of 39 was used as an external standard.)Firstly, 31 was allowed to react with gaseous CH3OOF (Scheme 3.V) at both -78°Cand room temperature. The results are summarized in Table 3.2. The best yields offluorinated product were obtained at room temperature, although fewer side-productswere observed (by HPLC) when the reaction was performed at -78°C. Secondly, 31 wasTable 3.2: Summary of Yields Obtained for the Reaction of 31with Acetyl HypofluoriteSolvent Temperaturea Yieldb no. of Averageruns YieldbCFC13 -78°C 26-31% 2 29%CFC13 r.t. 41-42% 2 41%CH3O r.t. 14% 1 14%CH3N r.t. 24% 1 24%TIIF r.t. 9.3% 1 9.3%ar.t.= room temperature.bRefers to the combined yield of 39 and 40.treated with CH3OOF in alternative solvents, namely dried methanol, acetonitrile, and87tetrahydrofuran, at room temperature. The yields are summarized in Table 3.2. Noneof these solvents provided improved yields of fluorinated product. Clearly, CFC13provedto be the best solvent tested for the fluorination reaction of 31. Finally, the reaction of31 with elemental fluorine (Scheme 3M) was studied at both -78°C and roomtemperature. The results are summarized in Table 3.3. It was evident by both analyticalScheme 3.VIMeO’—Sn(Bu)30.1% F2/NeCFC13MeOF+ MeOHO7 HOMeO + MeO88Table 3.3: Summary of Yields Obtained for the Reaction of 31with FluorineTemperaturea Yield of 39 and 40 Yield of 24 Yield of 41-78°C 4.2% 2.2% 14.5%r.t. 9.0% 5.4% 7.2%ar.t.= room temperature.TLC and HPLC that 31 is less reactive toward F2 than CH3OOF as less startingmaterial is consumed by F2. However, reaction with F2 does result in the formation oftwo identified non-fluorinated side-products, 24 and 3-methoxy-17a-vinyl-1,3,5 (10)-estratriene-17/3-ol 41. The identity of these compounds was established via HPLC; bycomparison of their respective retention times with those of authentic standards. Theidentity of 41 was further confirmed by ‘H NMR spectroscopy of a preliminary reactiontrial done with F2 at -78°C. The reaction of 31 with F2 clearly gave the lowest yields offluorovinyl product (39 and 40) in comparison to the reactions performed withCH3OOF.The reactivity of 30 with fluorine and acetyl hypofluorite was investigated. Compound30 was treated with approximately 0.8 equivalents of dilute (0.1%) F2 in Ne gas mixturein CFC13 at -78°C. The TLC chromatogram of the reaction mixture exhibited theformation of a new, more polar component, along with other minor components. Thisdominant new component, as observed by TLC, was isolated by column chromatographyfor identification by NMR. The 270 MHz ‘H NMR spectrum revealed that the isolatedmaterial was 17a-vinyl-1,3,5(10)-estratriene-3,173-diol 35. No trace of fluorovinylproduct was observed in the NMR spectrum. Alternatively, 30 was treated with89HOJ5-Sn(Bu)3approximately 1.2 equivalents of gaseous CH3OOF in CFCI3 at -78°C. TLC analysisof the crude reaction mixture indicated the total consumption of starting material andthe formation of an extremely complex mixture. The 19f? NMR spectrum of the reactionmixture exhibited several weak signals of fluorinated products which could not beassigned. The corresponding 1H NMR spectrum could not provide any usefulinformation due to its extremely complex pattern.Unfortunately, no fluorovinyl product could be obtained from 30 using either F2 orCH3OOF as fluorinating agents. Since the 3-O-methylated (E)-vinylstannane 31 wassuccessfully fluorinated as described earlier, the difficulty in fluorinating 30 is most likelydue to the presence of the unprotected phenolic hydroxyl group. Therefore, thisfunctionality must be protected with an easily removed protecting group, such as teflbutyldimethylsilyl, in order to develop a synthetic route to 17a-(E)-fluorovinyl-1,3,5(1O)-estratriene-3, 17i3-diol.The reactivity of 32 was also studied with fluorine and acetyl bypofluorite. The useof elemental fluorine was investigated first. Four small scale reaction trials wereperformed in which 32. was allowed to react with approximately 0.9 equivalents of dilutefluorine at -78°C (2 trials), 0°C (1 trial), and room temperature (1 trial), in CFC. The90MeO11—Sn(Bu)3TLC analysis of each reaction trial exhibited similar results; the TLC chromatogramsshowed the consumption of some starting material and the formation of a dominant,slower migrating component amongst several other minor components. In order toisolate the dominant new component observed by TLC, the reaction mixtures werecombined and subjected to column chromatography on silica gel. Half of the originalamount of 32 used for all four trials was recovered in one portion; then the dominantnew component was isolated with continued elution. The 270 MHz 1H NMR spectrumof this isolated material revealed that a mixture of several compounds were present.The compounds were identified as 25, 3, 173-dimethoxy- 17cr-vinyl-1,3,5(10)-estratriene42, and 3,17/3-dimethoxy-17a-(E)-fluorovinyl-1,3,5(10)-estratriene 43 in an approximateratio of 71:18:11, plus another component that could not be identified was present.The use of acetyl hypofluorite, prepared in two different forms, was investigated next.Compound 32 was added to a slight excess of CH3OOF prepared in a solution ofglacial acetic acid and aninionium acetate by the method of Rozen et al?3 at roomtemperature. The reaction proceeded for about 15 minutes before the acetic acid wasremoved. The crude reaction mixture was analyzed by TLC, which revealed the consumption of some starting material and the formation of a new, more polar component91Me07-MeOMeO MeOplus some other minor components. The reaction mixture was further analyzed by 1Hand 9F NMR spectroscopy. The ‘9F NMR spectrum exhibited a few weak signals dueto unidentified products, whereas the 1H NMR spectrum indicated the presence of 25,32, and 42, but not fluorovinyl product 43.Compound 32 was then treated with excess gaseous CH3OOF in CFC13 at -78°C.The TLC chromatogram of the reaction mixture exhibited only a small degree ofconversion of starting material to a new, slower migrating component, along with otherminor components. The 270 MHz 1H NMR spectrum of the reaction mixture revealedlargely unreacted starting material and a very small amount of 25 present. However, the9F NMR spectrum showed the presence of 43.These studies of the reactivity of 32 indicate that this derivative is relatively unreactivetoward CH3OOF in comparison to 31. No fluorovinyl product 43 could be obtained92with the use of CH3OOF in acetic acid, whereas only a minute amount of 43 could beproduced with gaseous CH3OOF. The reaction of 32 with elemental fluorine producedsome 43 which could be identified in a mixture of products. These results suggested thatfluorine was the most effective fluorinating agent used with 32. However, a larger scalefluorination of 32 utilizing F2 was not pursued due to the low potential yield andanticipated separation problems.Next, the reactivity of 33 toward fluorine and acetyl hypofluorite was examined inseveral small scale experiments. In the first experiment, 33 was allowed to react withapproximately 0.9 equivalents of dilute fluorine in CFC13 at -78°C. The TLC chromatoSn(Bu)3gram of the reaction mixture revealed the formation of a new, more polar componentin addition to a few minor components. The dominant new component, as observed byTLC, was isolated by column chromatography and subjected to 1H NMR spectroscopy.This material consisted of four different compounds that were identified as 28, 7,8-dideoxy- 1,2:3,4-di-O-isopropylidene-D-glycero-a-D-galacto-oct-7-enopyranose 44, (E)-8-C-fluoro-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-D-glycero-a-D-galacto-oct-7-enopyranose45, and (Z)-8-C-fluoro-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-D-glycero-cy-D-galacto-oct-7-enopyranose 46, in which 44 was the dominant component.93HO HO/°KLo\28 44FFor the second experiment, 33 was added to approximately 0.8 equivalents ofCH3OOF prepared in a solution of glacial acetic acid and ammonium acetate at roomtemperature. The reaction was allowed to proceed for about 10 minutes, then the aceticacid was removed. The crude reaction mixture was analyzed by TLC, which showed theformation of a dominant, slower migrating component plus a few minor components.Column chromatography of the reaction mixture resulted in the isolation of thedominant new component observed by TLC. This material was examined by ‘H NMRspectroscopy, which revealed that a mixture of 44, 45, and 46 was present and 44 was themajor component.In the third experiment, 33 was treated with approximately 1.2 equivalents of gaseousCH3OOF in CFC13 at -78°C. Analytical TEC of the reaction mixture revealed the94formation of a dominant, more poiar component and a few minor components. Thedominant new component, as observed by TLC, was isolated via preparative TLC (silicagel), and analyzed by 1H and 19F NMR spectroscopy. This material was found to belargely a mixture of 45 and 46, with some unidentified impurities present.The fluorination studies of 33, though qualitative in nature, showed that gaseousCH3OOF was the most effective fluorinating agent used. This agent gave the highestdegree of conversion of 33 to fluorovinyl product (45 and 46). The use of F2 orCH3OOF in acetic acid solution produced 44 as the main product. Unfortunately, thesupply of 33—as starting material—was virtually all consumed so that further larger scalefluorination work could not be conducted. Therefore, fluorination studies werecontinued using the L-glycero-a-D-galacto epimer 34 instead.Compound 34 was fluorinated with CH3OOF (Scheme 3.VII) in the followingScheme 3.VIISn(Bu)3 F[—OH CH3OOF [—OH [—oH/ CFC13 /+/maimer. Compound 34 was treated with approximately 1.3 equivalents of gaseousCH3OOF in CFC13 at room temperature. This procedure was performed with twoportions of 34 to increase the reaction scale. The crude reaction mixtures were95combined and subjected to column chromatography. (E)-8-C-Fluoro-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-enopyranose 47 was isolated in the firstchromatography fraction, and then two fractions were collected that contained mixturesof 47, (Z)-8-C-fluoro-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-enopyranose 48, and 7,8-dideoxy-1,2:3,4-di-O-isopropylidene-L-glycero-c-D-galacto-oct-7-enopyranose 49. The ratio of components in each chromatography fraction was0ocmeasured by ‘H NMR spectroscopy. The isolated yields of 47 and 48 were determinedto be 36% and 10%, respectively. Furthermore, an additional fraction was subsequentlycollected which was found to contain a single compound, identified as (E)-8-C-acetoxy-7-deoxy-1,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-enopyranose 50 by ‘H NMR.Compound 47 was readily characterized by ‘H and ‘9F NMR.3.4 Radiofluorination WorkIn this section, the radiofluorination of (E)-vinylstannane 31 using acetyl[‘8Fjhypofluoritewill be presented. The production of 18F, like 11C, is also routinely performed at theTRIUMF facility. Fluorine-18 can be produced either using the TRIUMF 500 MeV96cyclotron, or more efficiently with the smaller TRIUMF/Nordion CP-42 cyclotron viathe2°Ne(p,2pn)18Fnuclear reaction. For this work, circumstances required that theTRIUMF 500 MeV cyclotron be utilized. Radiofluorine was produced by protonirradiation of a gas mixture of natural Ne* with approximately 0.1% F2 present using the20Ne(p,Spall)18Freaction at 500 MeV. The radiofluorine is obtained in the form of 18F-labelled F2.Unfortunately, the production of [‘8F]F2 is necessarily carrier-added. Since thecyclotron target is constructed from nickel-based alloy, it must be passivated with F2.This process creates a thin layer of nickel fluoride within the interior surface of thecyclotron target, and provides a source of carrier fluorine to be present. Moreover, asmall percentage (0. 1-2.0%) of molecular fluorine must be present in the neon target gasfor[18F]F2production. However, if the amount of carrier F2 is reduced too much in thetarget gas mixture in order to significantly increase specific activity, low yields and poorrecoveries of[18F]F2are obtained.9 As a result, the practical upper limit on the specificactivity of[18F1F2 that can be achieved is reported to be around 12 Ci/mmol.63Therefore, all electrophilic fluorinations performed with18F-labelled F2, and reagentsderived from [18F]F2, result in products of low specific activity.TM Whenever aradiofluorinated product must be produced in high specific activity, the only availablelabeffing reagent is[18Fjfluoride anion.65 Nonetheless, there has been discussion in theliterature about producing high specific activity[18F]F2. The key idea is to exploit thestabifity of the negative fluorine ion in the gas phase and attract the gaseous anionic ‘8F*Natural neon consists of 90.92% of 20Ne, 0.26% of 21Ne, and 8.82% of 22Ne.97to an electrode, then perform an electrochemical oxidation to generate[18F]F2.9 Todate, there are no reports of anyone exploiting this approach, but such a developmentwould represent a true breakthrough for high specific activity radiofluorinations.Another aspect regarding the use of18F-labelled F2 is that the maximum radiochemicalyield possible is 50%. Due to the need of carrier F2 to be present in the neon cyclotrontarget, it would be a statistical improbability that both fluorine atoms in the {18F]F2produced would be fluorine-18 (i.e., 18F—’8). Therefore, only one fluorine-18 atom isexpected to be present in a 18F-labelled F2 molecule (i.e., 18F—’9). As a result, if anelectrophilic fluorination reaction proceeded in 100% maximum chemical yield, thecorresponding radiofluorination procedure would be expected to give 50% radiochemicalyield at best, since there is only a 50% probabffity of the fluorine-18 atom becomingincorporated rather than the fluorine-19 atom. For reactions using fluorination reagentssuch as CH3OO’8F,which contain only one fluorine atom, the maximum radiochemicalyield continues to be 50% because all these reagents are prepared from[18F]F2. This isan unfortunate disadvantage of all radiofluorination methods that utilize[18F]F2 as thesource of fluorine-18.9The general procedure used for the radiofluorination reactions of 31 is as follows.The 500 MeV cyclotron gas target was filled with the desired amount of 1% F2/Ne gasmixture, then pure Ne was added to dilute the F2 gas content to approximately 0.1% F2in Ne. The target gas mixture was irradiated with the 500 MeV proton beam. (Typical18F production parameters were 10 mm of target irradiation at 69 A of beam current.)When irradiation of the cyclotron target was stopped, the time was noted and designated98as the end of bombardment (EOB). After target irradiation was completed, the contentsof the target were passed through a potassium acetate/acetic acid column to producegaseous acetyl[‘8F]hypofluorite and was added to a solution of 31 (110-120 mol) inCFC13 (20 mL). The reaction mixture was assayed for radioactivity (before and afterevaporation of CFC13), along with the ammonium acetate/acetic acid column. Afterdissolution in some chloroform, a small aliquot of reaction mixture was subjected toradio-HPLC purification and the peak corresponding to‘8F-labelled fluorovinyl productwas collected, then assayed for activity. An equal volume of reaction mixture was alsoassayed at the same time in order to determine the percentage of product that waspresent in the reaction mixture. Based on the total activity of ‘8F produced at EOB, theradiochemical yield was then determined. The resulting radiochemical yields were decaycorrected back to BOB.Compound 31 was radiofluorinated with CH3OO’8F,as outlined in Scheme 3.VIILScheme 3 VIIIHOHOCH3OO18FMeOCFC13 HOMeO31MeO3The results obtained are summarized in Table 3.4. Compound 31 was kept in excessrelative to fluorinating agent in order to minimize side-reactions and to maximize theefficiency of incorporation of radiofluorine. Using excess fluorinating agent would helpmaximize the chemical yield, but could produce lower radiochemical yields. Theradiofluorination reaction of 31 gave the highest radiochemical yields (19%) whenconducted at room temperature. The radiolabelled product that was isolated for yielddeterminations was a mixture of 3-methoxy-17-a-(E)-[8F]fluorovinyl-1,3,5( 10)-estra-Table 3.4: Summary of Radiochemical Yields Obtained for theReaction of 31 with Acetyl[18FjHypofluoriteAmount of Temperaturea RadiochemicalCH3OO18Fused Yieldb—0.74 equiv r.t. 19%—0.50 equiv r.t. 19%—0.77 equiv-78°C 9.7%—0.50 equiv -78°C 5.0%ar.t.= room temperature.bRefers to the combined yield of 51 and 52; the radio-chemical yield was determined from the initial activityof[18FJF2produced at EOB.triene-17-o1 51 and 3-methoxy-17a-(Z)-[8F]fluorovinyl-1,3,5( 10)-estratrien.e-17i3-ol 52.The specific activity of this product mixture was not determined. However, in a separateexperiment, the specific activity of CH3OO’8F generated using 18F productionparameters described earlier was determined to be about 190 mCi/mmol. Therefore,the isolated product mixture would be of quite low specific activity, as expected.The identification of the[18F]fluorovinyl products 51 and 52 was accomplished using100radio-HPLC studies. The chromatographic behaviour of 51 and 52 was consistent withthat observed for the related non-radioactive fluorovinyl compounds (39 and 40). Inaddition, the leftover reaction mixtures (after radio-HPLC analysis), obtained from theradiofluorinations done at room temperature (first two entries of Table 3.4), wereallowed to decay to zero activity. These mixtures were then analyzed by ‘9F NMRspectroscopy. The 19J NMR spectra readily confirmed the presence of 39 and 40,thereby confirming the successful radiofluorination of 31.In this study, the fluorination reaction of 31 with gaseous acetyl hypofluorite wassuccessfully extended to accomplish the 18F-labelling of 31. The radiofluorinationreaction is essentially instantaneous upon addition of fluorinating agent. The time takenfrom EOB to the isolation of crude reaction mixture was in the order of 15-17 minutes.The additional time required thereafter was for the radio-HPLC purification work.Clearly, the synthesis time is quite short and well suited for radiolabelling with ‘8F.3.5 Summary and ConclusionsThe purpose of this study was to develop a general methodology to directly preparefluorovinyl compounds from vinyl-tin intermediates, and to utffize this synthetic approachfor radiofluorinations with ‘8F. This objective was indeed fulfilled to a large degree, asmost of the vinyl-tin substrates studied were successfully fluorinated using gaseous acetylhypofluorite. In addition, one of the vinyl-tin derivatives was radiofluorinated with acetyl[‘8F]hypofluorite in respectable radiochemical yield.The vinyl-tin substrates were readily obtained from the AIBN catalyzed hydrostamiyl101ation of the corresponding acetylenic precursors, with tri-n-butyltin hydride, in 59-94%yield. The reactivities of (E)-vinylstannanes 30, 31, 32, 33, and 34 were studied withelemental fluorine and acetyl hypofluorite under varied conditions.The most effective fluorinating agent used to fluorinate 31 was gaseous acetylhypofluorite, at room temperature, which afforded yields of 4 1-42% of 39 and 40 as anisomeric mixture (yields determined via HPLC analysis). In contrast, fluorination of 31with elemental fluorine gave 9.0% yield at best. Furthermore, (E)-fluorovinyl 39 and(Z)-fluorovinyl 40 were prepared and isolated in 29.5% and 3.8% yields, respectively,from the reaction of 31 with CH3OOF.Compound 30 could not be directly fluorinated using either F2 or CH3OOF. Thisresult is most likely due to the presence of the unprotected phenol function of 30. Byprotecting this group, it would be anticipated that 30 can be successfully fluorinated inan analogous manner to 31. Alternatively, 32 was found to be relatively unreactivetoward fluorination as compared to 31. Reaction of 32 with gaseous CH3OOFproduced only a trace of (E)-fluorovinyl product 43. Better results were observedemploying elemental F2 as some 43 could be obtained as a minor component in amixture of products.Compound 33 was readily fluorinated using gaseous CH3OOF. Treatment of 33 withCH3OOF (prepared in acetic acid solution) or with F2 also generated fluorinatedproduct, but gave 44 as the main product. However, the stock of 33 had been virtuallyall consumed, so that further larger scale reactions with gaseous CH3OOF could notbe performed. Therefore, fluorination studies were continued with L-glycero-a-D-galacto102epimer 34 instead. Compound 34 was allowed to react with gaseous CH3OOF (atroom temperature) and (E)-fluorovinyl 47 and (Z)-fluorovinyl 48 were obtained in 36%and 10% yield, respectively.Compound 31 was radiofluorinated using gaseous acetyl[18F]hypofluorite in 19%radiochemical yield. The radiolabelled product consists of a mixture of (E)[‘8F]fluorovinyl 51 and (Z)-[18Fjfluorovinyl 52 of low specific activity. The reaction timeswere of the order of 15-17 minutes (measured from EOB) which is well suited forradiolabelling with 18F.103References1. Fried, 3.; Sabo, E. F. .1 Am. Chem. Soc. 1954, 76, 1455-1456.2. Ciba Foundation Symposium in Carbon-Fluorine Compounds: Chemistiy, Biochemistiyand Biological Activities; Elsevier: New York, 1972.3. BiomedicinalAspects ofFluorine Chemistiy; Filler, R., Kobayashi, Y., Eds.; KodanshaLtd.: Tokyo, 1982.4. Furin, G. G. Soy. Sci. Rev., Sect. B: 1991, 16, 1-140.5. Selective Fluorination in Organic and Bioorganic Chemistiy; Welch, J. T., Ed.; ACSSymposium Series 456; American Chemical Society: Washington, DC, 1991.6. Filler, R.; Naqvi, S. M. In Biomedicinal Aspects of Fluorine Chemistiy; Filler, R.,Kobayashi, Y., Eds.; Kodansha Ltd.: Tokyo, 1982; Chapter 1.7. Welch, J. T. In Selective Fluorination in Organic and Bioorganic Chemistiy; Welch,J. T., Ed.; ACS Symposium Series 456; American Chemical Society: Washington,DC, 1991; Chapter 1.8. Fowler, J. S.; Wolf, A. P. The Synthesis of Carbon-li, Fluorine-i 8, and Nitrogen-i3LabeledRadiotracersforBiomedicalApplications; Nuclear Science Series, MonographNAS-NS-3201; Technical Information Center, U.S. Department of Energy:Springfield, VA, 1982.9. Kilbourn, M. R. Fluorine-i8 Labeling of Radiopharmaceuticals; Nuclear ScienceSeries, Monograph NAS-NS-3203; National Academy: Washington, DC, 1990.10. Nuclear Imaging in Dnsg Discoveiy, Development, and Approval; Burns, H. D.,Gibson, R. E., Dannals, R. F., Siegi, P. K. S., Eds.; Birkhäuser: Boston, 1993.11. Moissan, H. Compt. Rend. 1886, 102, 1543-1544; 103, 202-205.12. Bockmüller, W. Liebigs Ann. Chem. 1933, 506, 20-59.13. Purrington, S. T.; Kagen, B. S.; Patrick, T. B. Chem. Rev. 1986, 86, 977-1018.14. Banks, R. E.; Tatlow, J. C. In Fluorine: The First Hundred Years (1886-1986); Banks,R. E., Sharp, D. W. A., Tatlow, J. C., Eds.; Elsevier Science: New York, 1986;Chapter 4.15. Hudlicky, M. Chemistiy of Organic Fluorine Compounds: A Laboratoiy Manual withComprehensive Literature Coverage, 2nd ed.; John Wiley and Sons: New York, 1976.10416. New Fluorinating Agents in Organic Synthesis; German, L., Zemskov, S., Eds.;Springer-Verlag: Berlin, 1989.17. Sharts, C. M.; Sheppard, W. A. Org. React. (N Y.) 1974, 21, 125-406.18. Gerstenberger, M. R. C.; Haas, A. Angew. Chem., mt. Ed. Engl. 1981, 20, 647-667.19. Nickles, R. J.; Gatley, S. J.; Votaw, J. R.; Kornguth, M. L. mt. J. App!. Radial. Isot.1986, 37, 649-66 1.20. Berridge, M. S.; Tewson, T. J. mt. .1. App!. Radiat. Isot. 1986, 37, 685-693.21. Adam, M. J., TRIUMF, Vancouver, BC, personal communication.22. See reference 9; pp 70-90.23. Rozen, S.; Lerman, 0.; Kel, M. .1. Chem. Soc., Chem. Commun. 1981, 443-444.24. Fowler, J. S.; Shiue, C.-Y.; Wolf, A. P.; Salvador, P. A.; MacGregor, R. R. J.Labelled Compd. Radiopharm. 1982, 19, 1634-1636.25. Rozen, S.; Lerman, 0.; Kol, M.; Hebel, D. I. Org. Chem. 1985, 50, 4753-4758.26. Adam, M. J. .1. Chem. Soc., Chem. Commun. 1982, 730-73 1; Adam, M. 3.; Pate, B.D.; Nesser, J.-R.; Hall, L. D. Carbohydr. Res. 1983, 124, 215-224.27. Jewett, D. M.; Potocki, 3. F.; Ehrenkaufer, R. E. J. Fluorine Chem. 1984,24,477-484.28. Adam, M. J.; Pate, B. D.; Ruth, T. 3.; Berry, 3. M.; Hall, L D. .1. Chem. Soc., Chem.Commun. 1981, 733.29. Adam, M. J.; Berry, 3. M.; Hall, L. D.; Pate, B. D.; Ruth, T. 3. Can. .1. Chem. 1983,61, 658-660.30. Ingham, R. K.; Rosenberg, S. D.; Gilman, H. Chem. Rev. 1960, 60, 459-539.31. Larock, R. C. Tetrahedron 1982, 38, 1713-1754.32. Adam, M. J.; Ruth, T. J.; Jivan, S.; Pate, B. D. .1. Fluorine Chem. 1984, 25, 329-337.33. Coenen, H. H.; Moerlein, S. M. J. Fluorine Chem. 1987, 36, 63-75.34. Di Raddo, P.; Diksic, M.; Jolly, D. J. Chem. Soc., Chem. Commun. 1984, 159-160.35. Speranza, M.; Shiue, C.-Y.; Wolf, A. P.; Wilbur, D. S.; Angelini, G. J. Chem. Soc.,Chem. Commun. 1984, 1448-1449.10536. Visser, G. W. M.; Halteren, B. W. v.; Herscheid, J. D. M.; Brinlcman, G. A.;Hoekstra, A. .1. Chem. Soc., Chem. Commun. 1984, 655-656.37. Visser, G. W. M.; Bakker, C. N. M.; Halteren, B. W. v.; Herscheid, J. D. M.;Brinkman, G. A.; Hoekstra, A. .1. Org. Chem. 1986, 51, 1886-1889.38. Ehrenkaufer, R. E.; MacGregor, R. R. mt. .1. Appi. Radiat. Isot. 1983, 34, 613-615.39. Satyamurthy, N.; Bida,, G. T.; Barrio, J. R.; Phelps, M. E. J. Nucl. Med. 1984, 25,P23.40. Oberdorfer, F.; Hofman, E.; Maier-Borst, W. J. Labelled Compd. Radiopharm. 1988,25, 999-1005.41. Adam, M. J.; Lu, J.; Jivan, S. J. Labelled CompcL Radiopharm. 1994, 34, 565-570.42. Namavari, M.; Bishop, A.; Satyamurthy, N.; Bida, G.; Barrio, J. R. mt. J. Appi.Radiat. Isot. 1992, 43, 989-996.43. Diksic, M.; Farrokhzad, S. J. Nuci. Med. 1985, 26, 1314-1318.44. Luxen, A.; Barrio, 3. R.; Bida, G. T.; Satyamurthy, N. J. Labelled Compd.Radiopharin. 1986, 23, 1066-1067.45. Mislankar, S. G.; Gildersleeve, D. L.; Muiholland, G. K.; Massin, C. C.; Toorongian,S. A.; Wieland, D. M. .1 Nucl. Med. 1987, 28, 624.46. Barrio, 3. R.; Perimutter, M. M.; Luxen, A.; Melega, W. P.; Grafton, S. T.; Huang,S. C.; Hoffman, J. M.; Van Moffaert, G.; Mazziotta, J. C.; Phelps, M. E. J. Nuci.Med. 1989, 30, 752; Gildersleeve, D. L.; Van Dort, M. E.; Rosenspire, K. C.;Toorongian, S.; Wieland, D. M. .1. Nucl. Med. 1989, 30, 752.47. Luxen, A.; Perimutter, M. M.; Barrio, J. R. J. Labelled CompcL Radiophwm. 1989,26, 1-2.48. Purrington, S. T.; Jones, W. A. J. Fluorine Chem. 1984, 26, 43-46.49. Barnette, W. E. .1. Am. Chem. Soc. 1984, 106, 452-454.50. Knapp, F. F., Jr.; Goodman, M. M.; Kabalka, G. W.; Sastry, K. A. R. J. Med. Chem.1984, 27, 94-97; Penman, M. E.; Watanabe, K. A.; Schinazi, R. F.; Fox, J. J. .1. Med.Chem. 1985, 28, 74 1-748.51. Flanagan, R. 3.; Charleson, F. P.; Synnes, E. I.; Wiebe, L. I.; Theriault, Y. X.;Nakashima, T. T. Can. J. Chem. 1985, 63, 2853-2860.10652. Franke, L. A.; Hanson, R. N. J. Nucl. Med. 1984, 25, 1116-1121.53. Bey, P.; McCarthy, 3. R.; McDonald, I. A. In Selective Fluorination in Organic andBioorganic Chemistry; Welch, J. T., Ed.; ACS Symposium Series 456; AmericanChemical Society: Washington, DC, 1991; Chapter 8.54. Ailmendinger, T.; Felder, E.; Hungerbuehler, E. In Selective Fluorination in Organicand Bioorganic Chemistiy; Welch, J. T., Ed.; ACS Symposium Series 456; AmericanChemical Society: Washington, DC, 1991; Chapter 13.55. Balatoni, J. A., M.Sc. Thesis, The University of British Columbia, Dec. 1985.56. van der Kerk, G. J. M.; Noltes, J. C. J. App!. Chem. 1959, 9, 106-113.57. Jung, M. E.; Light, L. A. Tetrahedron Left. 1982, 23, 385 1-3854; Ensley, H. E.;Buescher, R. R.; Lee, K. .1. Org. Chem. 1982, 47, 404-408.58. Omae, I. J. Organomet. Chem. Libr. 1989, 21, 1-341.59. Poller, R. C. The Chemzstiy of Organotin Compounds; Academic: New York, 1970;pp 112-113.60. Banks, R. E.; Haszeldine, R. N.; Prodgers, A. J. Chem. Soc., Perkin Trans. 1 1973,596-598.61. Di Raddo, P.; Diksic, M. mt. J. App!. Radiat. Isot. 1985, 36, 953-956.62. Lee, S. H.; Schwartz, J. J. Am. Chem. Soc. 1986, 108, 2445-2447.63. See reference 9; p 5.64. See reference 9; pp 22-24.65. See reference 9; p 37 and 43.107Chapter 4GENERAL CONCLUSIONSThe investigation presented in Chapter 2 demonstrated that(6-arene)tricarbony1-chromium complexes can be used as synthetic intermediates for the radiolabelling of theattached arene ring with “C via nucleophilic substitution with[11C]cyanide. This resultrepresents the first application of chromium tricarbonyl complexes for radiolabelling withshort-lived nucides. From a broader perspective, however, this accomplishment couldbe the first step to a range of new radiolabelling methods based on the utilization oforganotransition metal complexes. A number of transition metal systems facilitate theaddition of various nucleophiles onto unsaturated organic molecules while complexedto the metal centre.’ This pattern of reactivity needs to be explored further withnucleophilic forms of medically useful radioisotopes,2such as ‘8F, 75Br, 77Br, and 123jThe application of chromium tricarbonyl complexes could be significantly advancedwith additional studies. A further exploration of reaction conditions should be conductedto improve radiochemical yields, particularly with NCA [“Cjcyanide. This could includean investigation of various crown ether and other catalysts, employment of microwavedrying of the [“C]cyanide solution and microwave heating of the radiolabeffing reaction,and the use of smaller volumes of reaction solvent to concentrate the reactants. Also,a study of alternative ways of trappingH11CN in the absence of hydroxide may result in108significantly improved labelling yields. Furthermore, other potentially effective leavinggroups should be explored to complement or supersede fluorine. Lastly, the substitutionreactions of F-, Br, and 1 with chromium tricarbonyl complexes warrant study becauseof the importance of radiohalogens in nuclear medicine.2The investigation described in Chapter 3 revealed that vinyl-tin derivatives can bedirectly fluorinated with gaseous acetyl hypofluorite, in most cases, to produce stable and‘8F-labelled vinyl fluorides. This result represents another extension of the use oforganotin compounds for electrophilic fluorinations, including radiofluorinations with‘8F.Very recently, other researchers have reported using vinyl-tin compounds to preparevinyl fluorides. Tius and Kawakami3fluorinated a number of simple vinyl-tin derivativeswith XeF2 (in the presence of AgPF6)in 24-52% yield, however, reaction times rangedfrom 3-18 hours. Hodson and co-workers4used cesium fluoroxysulfate to fluorinatesome vinyl-tin compounds which produced vinyl fluorides in 25-56% yield, and in somecases, a-fluoroketones were unexpectedly made in 47-75% yield (reactions were runovernight). Matthews et al.5 reported the electrophilic fluorination of several(fluorovinyl)stannanes with 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2joctanebis(tetrafluoroborate) affording difluoro olefins in 35-74% yield (30 mm reaction timeat 80°C). Each of these reports provides new methods for fluorinating vinyl-tincompounds which is very positive, however, each of these methods, for various reasons,would appear to be incompatible for radiolabelling with ‘8F. What is gratifying is thatseveral years after choosing vinyl-tin intermediates for our fluorination studies, otherresearch groups are also selecting tin reagents for the preparation of vinyl fluorides.109Undoubtedly, the application of organotin compounds will continue to be extended asinterest in selectively fluorinated organic molecules remains.Nonetheless, the following suggestions for future work can be made. The explorationof alternative fluorinating agents for use with vinyl-tin substrates would be very prudent.Also, the reactivity of fluorine and acetyl hypofluorite should be further examined witha wider range of structurally diverse vinylstannylated derivatives. Moreover, thefluorination of vinyl-silicon and -mercury derivatives warrant some additional study.In retrospect, it is pleasing to see that although a few years have unfortunately elapsedsince the experimental work was performed and the writing of this thesis completed, theresults obtained are still new and currently relevant, and have not been duplicated in theliterature. Even though various aspects of the specific experimental studies could havebeen done differently, the studies pursued for this thesis were well worthwhile andexhibit significant future potential. The application of organometallic compounds assynthetic intermediates for radiolabelling is only in the early stages of development still,but will continue to expand with future research.110References1. Davies, S. G. Organotransition Metal Chemistiy: Applications to Organic Synthesis;Pergamon: Toronto, 1982; Chapter 4.2. Nozaki, T. In Radionuclides Production; Helus, F., Ed.; CRC: BocaRaton, 1983; Vol.2, Chapter 3.3. Tius, M. A.; Kawakami, J. K. Synth. Commun. 1992, 22, 1461-1471.4. Hodson, H. F.; Madge, D. 3.; Widdowson, D. A. Synlett 1992, 831-832.5. Matthews, D. P.; Miller, S. C.; Jarvi, E. T.; Sabol, J. S.; McCarthy, J. R. TetrahedronLett. 1993, 34, 3057-3060.111Chapter 5EXPERIMENTAL5.1 General MethodsSolutions were concentrated under reduced pressure with a Büchi rotary evaporator,except for solutions of organochromium complexes, which were concentrated in vacuousing a high vacuum, rotary vacuum pump assembly. Melting points were taken incapillaries (in air) using a Büchi 510 oil bath melting point apparatus, or were obtainedon a Fisher-Johns melting point apparatus, and are uncorrected. Optical rotations weredetermined using a Perkin-Elmer model 141 polarimeter.Tetrahydrofuran (THF) and diethyl ether were distilled from calcium hydride orsodium benzophenone ketyl.’ Dimethyl sulfoxide (DMSO) was distilled under reducedpressure from calcium hydride, then carefully stored under nitrogen. Di-n-butyl etherwas distilled from sodium under nitrogen, while hexane, dichioromethane, andacetonitrile were distilled from calcium hydride. Methanol was distified from magnesiummethoxide prepared in situ by reaction of methanol with magnesium turnings. For highpressure liquid chromatography (HPLC) work, singly distilled water, HPLC gradeacetonitrile and methanol, and reagent grade hexanes and diethyl ether were used, whichwere filtered (0.45 m Millipore brand Durapore membrane) before use. All othersolvents used were of spectro or reagent grade, and were used without further treatment.112Thin-layer chromatography (TLC) was performed on pre-coated silica gel plates(Baker-flex Silica gel 1B2-F or E. Merck Silica gel 60, No. 5534). Visualization waseffected either by (a) spraying with 30% sulfuric acid in ethanol, then heating, (b) withshort-wavelength UV light, or (c) by visual inspection (for coloured, organochromiumcompounds). The TLC solvent systems used were very similar to those listed for thecolumn chromatography of the individual compounds. Column chromatography wasperformed using Silica gel 60 (E. Merck, 70-230 mesh). Flash chromatography wasperformed using Silica gel 60 (E. Merck, 230-400 mesh) by the method of Still et al.2HPLC was done with a system consisting of a Spectro-Physics SP 8700 solvent deliverysystem, a Rheodyne 7126 injector, an ISCO (model V4) variable wavelength UV detectoroperated at 254-280 nm, and a Spectro-Physics SP 4270 integrator recorder, using oneof the following columns, either (a) a Waters 10 Lm C-18 reverse phase RCM column(column A), (b) two Waters 10 m C-18 reverse phase RCM columns connected inseries (column B), (c) a C-18 reverse phase Whatman Partisil 10 ODS-3 column, 25 cmx 9 mm, equipped with a Waters C-18 guard column (column C), or (d) normal phasePhenomenex Ultremex 5 Silica column, 25 cm x 10 mm (column D). The followingsolvent mixtures were used for HPLC: (i) methanol/water, 1:1 (solvent A), (ii)water/acetoriitrile, 1:1 (solvent B), (iii) water/acetonitrile, 3:2 (solvent C), and (iv)hexanes/diethyl ether, 4:1 (solvent D). The following gradient solvent programs werealso used for HPLC: (i) from 0 to 10 mm, an isocratic mixture of methanol/water(85:15) was used, followed by a systematic increase to 100% methanol during 10 to 12mm, and a constant composition of 100% methanol was maintained from 12 to 20 mm113(solvent program A), and (ii) from 0 to 18 mm, an isocratic mixture of methanol/water(75:25) was used, followed by a systematic increase to 100% methanol during 18 to 21mm, and a constant composition of 100% of methanol was maintained from 21 to 30 mm(solvent program B). Radio-HPLC analysis and purification was performed with thesame HPLC system fitted with a NaI(Tl) scintillation detector system and a dual channelstrip chart recorder. Radioactive samples were assayed with either a Capintec wellcounter (model CRC-543X) or a Beckman 8000 scintillation counter.Analytical gas chromatography (GC) was performed with a Hewlett-Packard model5840A GC, equipped with an FID detector, using a 30 m x 0.75 mm i.d. wide bore(Supelco SPB-1) capillary column. Unless otherwise stated, GC analyses were performedisothermally using the following conditions: injection temperature, 200°C; oventemperature, 120°C; N2 carrier gas flow, 2.0 mt/mm.Low resolution electron impact mass spectra were recorded with either a Kratos/AEIMS902 or a Kratos/AEI MS5O mass spectrometer. An ionization potential of 70 eV wasused for the mass spectra obtained. Spectra are quoted as m/z values, while selectedion fragmentations are reported as percentages of the base peak. High resolution massmeasurements were determined using the Kratos/AEI MS5O mass spectrometer. Gaschromatography-mass spectrometry (GC-MS) was performed using a Delsi Nermag RiO1OC quadruple mass spectrometer interfaced with a Varian 6000 GC or a Kratos MS8Ocoupled to a Carlo Erba 4160 GC.All microanalyses were performed by Mr. P. Borda, Microanalytical Laboratory,University of British Columbia.1145.2 NMR Methods and Instrumentation1H NMR spectra were measured at room temperature at 270 and 400 MHz. The 270MHz spectra were obtained with a home-built spectrometer based on a Bruker WP-60console, a Nicolet 1180 computer (32K), a Nicolet 293B pulse programmer, a oneMegabyte Diablo disk drive (model 31), and an Oxford Instruments Superconductingsolenoid magnet. In addition to this spectrometer, a separate data processing system,consisting of another Nicolet 1180 computer (32K), one Megabyte Diablo disk drive(model 31) and a digital plotter, was available for processing and plotting of NMR data.Standard NTCFTB software was used on the spectrometer and data station.Furthermore, some of the 270 MHz data was transferred from the Nicolet 1180 datastation to a newer Nicolet 1280 computer, for processing with increased computermemory and digital plotting.The 400 MHz spectra were obtained with a Bruker WH-400 high-resolutionspectrometer equipped with an Aspect 3000 computer. Along with this spectrometer,a separate Bruker data processing system, comprised of an Aspect 3000 computer, digitalplotter and dot matrix printer, was available for data processing and plotting. FactoryBruker software was used on the spectrometer and data station.‘9F NMR spectra were measured at 188 and 254 MHz, also at room temperature. The188 MHz spectra were obtained with a Bruker AC-200E spectrometer. The NMR datafrom this spectrometer was transferred to and processed on the Bruker data station,described above. The 254 MHz spectra were obtained using the previously describedhome-built spectrometer (controlled by the Nicolet 1180 computer) with a home-built,11519F-tuned probe.*5.3 Experimental for Chapter 25.3.1 Sources of MaterialsChemicals and reagents were purchased from suppliers as follows. Chromiumhexacarbonyl was obtained from Pressure Chemical Co. Fluorobenzene, 2- and 4-fluorotoluene, 4-chiorofluorobeuzene, 4-chlorobenzonitrile, methyltrifluoromethanesulfonate, and 18-crown-6 were purchased from Aldrich Chemical Co. Eastman KodakCo. supplied the benzonitrile and 4-tolunitrile, and ICN Pharmaceuticals Inc. suppliedthe 2-tolunitrile. HPLC grade methanol and acetonitrile were obtained from FisherScientific Ltd., or BDH Chemicals.5.3.2 GeneralAll manipulations for the preparation and purification of the(6-arene)tricarbonyl-chromium complexes were performed so as to maintain all chemicals under anatmosphere of nitrogen or argon using conventional bench-top techniques for themanipulation of air-sensitive compounds.3The(6-arene)tHcarbonylchromium complexes, that were synthesized from Cr(CO)6,were prepared either using a 200-mL, round-bottom, three-neck flask fitted with anitrogen inlet, a magnetic stir bar, and a condenser equipped with a mineral oil-bubblerThe probe construction and electronics was done by Tom Markus (Electronics shop,Chemistry Department, U.B.C.).116(glassware A), or a specially constructed reaction apparatus (glassware B) that consistsof a 250-mL, round-bottom flask fused to a 3 in. long condenser which is joined to anadditional 3 in. long glass tube (1 in. o.d.) equipped with a central ST* 24 ground glassjoint and two angled ST 19 ground glass joints. This glassware is fitted with a glass rodthat is placed through the central ST 24 joint and reaches to a dimple at the bottom ofthe flask and has a small paddle near the bottom of the flask (to stir the reactionmixture) plus a 3 in. long screw paddle which closely fits the interior wall of thecondenser region (to scrap and return sublimed Cr(CO)6to the reaction mixture). Theglass rod is rotated by a variable speed, overhead stirrer motor. The assembledglassware is also equipped with a nitrogen inlet and mineral oil bubbler. With eitherset-up, the glassware was wrapped with aluminum foil to protect the reaction from light.Silica gel 60 (E. Merck, 70-230 mesh) was used for the filtration of organochromiumsolutions to remove any decomposition.All substitution reactions were carried out in oven-dried Pierce Reactivials®(Rockford, IL) equipped with magnetic stir bars and screw caps that were fitted withTeflon-lined, silicone septa.tH”CN was produced via the catalytic conversion of “CO2. The “CO2 was producedon the TRIUMF/Nordion CP-42 cyclotron using the‘4N(p,a)11Creaction at 15 MeV.The “CO2 in the N2 target gas was converted to “CH4 by mixing the target gas with*sT denotes standard taper.1These septa provided an excellent seal to maintain the exclusion of air andmoisture, and to prevent the loss of volatile components.117H2(g) then passing the mixture over a Ni cata]yst at 450°C. Thereafter, the 11CH4 wascombined with NH3(g) and passed over Pt at 1000°C, thus obtaining H”CN.4 TheH’1CN was trapped in an aqueous solution of NaOH (1 mL, 0.1 M) to produce Na”CN.5.3.3 Preparation of(,6-Arene)tricarbonylchromium ComplexesPreparation of -fluorobenzene)tricarbonylchromium 1.Chromium hexacarbonyl (1.0 g, 4.54 mmol) and fluorobenzene (5.0 mL, 53 mmol)were dissolved in a mixture of (n-Bu)20/THF (80 mL/10 mL) in glassware A. Thereaction mixture was degassed by performing three freeze-pump-thaw cycles. Uponreintroducing a nitrogen atmosphere into the reaction vessel, the stirred reaction mixturewas heated to reflux for 48 h. The reaction mixture was cooled to room temperatureand filtered through a short pad of silica gel to remove any greyish-green decomposition.The bright yellow filtrate was evaporated to dryness in vacuo. The residue was dissolvedin diethyl ether, and the resulting solution was transferred by canula filtration into aSchlenk tube. The undissolved residue was then washed with some hexane and thesewashings were likewise added to the ether solution. Solvent was slowly removed underreduced pressure until yellow crystals began to appear. The ether/hexane mixture waswarmed gently until all crystals redissolved, then was placed in the freezer forcrystallization. Bright yellow crystals were isolated and dried under a flow of N2,initially, then under a high vacuum overnight. Two additional crops of crystals wereobtained from the mother liquor, affording a total yield of 0.84 g (80%) of 1, mp 117°C{lit.5 mp 116-117°C}. Mass spectrum, m/z: 232 (M, 38), 204 (M-CO, 3), 176 (M1182(CO), 9), 148 (M-3(CO), 54), 96 (M-Cr(CO)3,21), 71(33), 52 (100).Preparation of(,6-ch1orobenzene)tricarbony1chromium 2.Chromium hexacarbonyl (1.86 g, 8.45 mmol) and chlorobenzene (25 mL, 0.25 mol)were added to diglyme (30 mL) in glassware B. The stirred reaction mixture was heatedto reflux for 16.5 h. The reaction mixture was cooled to room temperature, then filteredthrough a short pad of Celite using some diethyl ether to rinse and facilitate the transferof the reaction vessel contents. The yellow filtrate was concentrated via distillationunder reduced pressure, then some petroleum ether was added to induce crystallization.Even with cooling, no crystals had formed. Therefore, some ethyl acetate was added tothis solution and was then evaporated in vacuo. This process was repeated several timesand the volume of diglyme was successfully reduced. Once again, petroleum ether wasadded to the concentrated solution till a small amount of precipitation occurred, thenwas placed in a fridge for cooling. A single large, yellow crystal was obtained, which wasremoved and washed with cold petroleum ether, then dried under a flow of argon. Thefiltrate was heated and filtered hot, to remove some greenish decomposition, then wasplaced back in the fridge for crystallization. Yellow crystals (400 mg) were isolated anddried in vacuo. The large single crystal, obtained initially, was recrystallized from hotpetroleum ether. This afforded 265 mg of additional yellow crystals, which gave a totalyield of 47% (665 mg) of 2 (based on Cr(CO)6 consumed*), mp 100-101°C {lit.6 mp*Unreacted Cr(CO)6remaining in the reaction vessel was recovered by sublimationunder high vacuum; this gave 0.60 g of recovered Cr(CO)6.119101-102°C}.Preparation of(6-bromobenzene)tricarbony1chromium 3.Chromium hexacarbonyl (4.00 g, 18.2 mmol) and bromobenzene (10.0 mL, 95.2 mmol)were added to a mixture of (n-Bu)20/THF (100 mL/10 mL) in glassware B. Thereaction mixture was degassed by performing a single freeze-pump-thaw cycle. Uponreintroducing an N2 atmosphere over the reaction mixture, it was heated, with stirring,to reflux for 44 h. The cooled reaction mixture was filtered through a short pad of silicagel and the yellow filtrate was reduced to dryness in vacuo. Compound 3 was obtainedas dark yellow crystals, in a yield of 992 mg (19%), mp 101-105°C {lit.7 mp 120°C}.Mass spectrum, m/z: 294 (81Br: M, 31), 292 (79Br: M, 34), 266 (81Br: M-CO, 3), 264(79Br: MtCO, 3), 238 (81Br: M-2(CO), 6), 236 (79Br: M-2(CO), 6), 210 (81Br: M3(CO), 26), 208 (79Br: Mt3(CO), 28), 158 (81Br: M-Cr(CO)3,5), 156 (79Br: MCr(CO)3,4), 133 (81Br: 5), 131 e9Br: 7), 52 (100).Preparation of(i6-2-fluorotoluene)tricarbonylchromium 4.Chromium hexacarbonyl (1.0 g, 4.54 rninol) and 2-fluorotoluene (5.8 mL, 53 mmol)were dissolved in a mixture of (n-Bu)20/THF (80 mL/10 mL) in glassware A. Allsubsequent steps were essentially identical to the preparation of compound 1.Compound 4 was obtained as yellow crystals, in a total yield of 0.99 g (89%), mp 71-72°C {lit.8 mp 73-74°C}. Mass spectrum, m/z: 246 (M, 15), 218 (M-CO, 1), 190 (M2(CO), 4), 162 (Mt3(CO), 25), 110 (M-Cr(CO)3,26), 109 (44), 71(12), 52 (100).120Preparation of(i76-4-fluorotoluene)tricarbonylchromium 5.Chromium hexacarbonyl (4.00 g, 18.2 mmol) and 4-fluorotoluene (10.0 mL, 91 mmol)were added to a mixture of (n-Bu)20/THF (100 mL/10 mL) in glassware B. Thereaction mixture was degassed by performing a single freeze-pump-thaw cycle. Uponreintroducing an N2 atmosphere over the reaction mixture, it was heated, with stirring,to reflux for 16.5 h. The cooled reaction mixture was filtered through a short pad ofsilica gel and the yellow filtrate was reduced to dryness under reduced pressure. Afterfurther drying in vacuo, compound 5 was obtained as bright yellow crystals, in a yield of3.79 g (85%), mp 59-60°C {lit.8 mp 61-62°C}. Mass spectrum, m/z: 246 (M, 11), 218(M-CO, 1), 190 (M-2(CO), 3), 162 (M-3(CO), 23), 110 (M-Cr(CO)3,17), 109 (31),71(16), 52 (100).Preparation of (q’-4-chlorofluorobenzene)tricarbonylchromium 6.Chromium hexacarbonyl (4.00 g, 18.2 mmol) and 4-chlorofluorobenzene (10.0 mL, 93.9nimol) were added to a mixture of (n-Bu)20/THF (100 mL/10 mL) in glassware A. Thestirred reaction mixture was heated to reflux for 23 h. Upon cooling to roomtemperature, the reaction mixture was concentrated to about 10 mL under reducedpressure and a plug of sublimed Cr(CO)6(1.1 g) was recovered from the condenser. Theconcentrated reaction mixture was chromatographed on neutral alumina (Fisher, 80-200mesh) with hexane as the eluent. A single yellow band was collected and the solvent wasremoved in vacuo. TLC analysis, on alumina (eluent: hexane), of the yellow residueshowed the presence of two components. Column chromatography was repeated on the121two-component mixture using silica gel with hexane/ether (5:1). The first fraction, aftersolvent removal, afforded 0.42 g of 6 as yellow crystals, mp 6 1-62°C {lit. mp: nonefound}. TLC analysis on silica gel (eluent: hexane/ether, 1:1), indicated the presenceof only one component. Mass spectrum, m/z: 268 (37C1: M, 6), 266 (35C1: M, 17), 240(37C1: M-CO, 2), 238 (35C1: M-CO, 3), 212(37C1: M-2(CO), 2), 210 (35C1: M-2(CO),5), 184 (37C1: M-3(CO), 9), 182 (35C1: M-3(CO), 25), 132 (37C1: M-Cr(CO)3,10), 130(35C1: M-Cr(CO)3,29), 95 (22), 89 (37C1: 3), 87 (35C1: 9), 71 (14), 52 (100).A second fraction (0.12 g) was collected, which contained a mixture of 1 and 6, with6 being the dominant component as determined by ThC analysis (silica gel; eluent:hexane/ether, 1:1). This material unfortunately underwent partial decomposition andwas discarded.A final fraction was collected, and after the eluate was evaporated to dryness in vacuo,0.11 g of yellow crystals were isolated, mp 97-100°C. TLC analysis (silica gel; eluent:hexane/ether, 1:1) showed this material to be a mixture of 1 and 6, with 1 being themajor component present. Mass spectrometric analysis of this mixture gave the followingresults; mass spectrum, m/z: compound 1, 232 (M, 22), 204 (M-CO, 3), 176 (M2(CO), 5), 148 (Mt3(CO), 27), 96 (M-Cr(CO)3,40); compound 6, 268 (37C1: M, 0.6),266(35C1: M, 2.0), 240(37C1: MtCO, 0.1), 238(35Cl: M-CO, 0.3), 212(37C1: M-2(CO),0.2), 210(35C1: M-2(CO), 0.4), 184(37C1: M-3(CO), 1.1), 182(35C1: M-3(CO), 3.7), 132(37Cl: MtCr(CO)3,1.8), 130 (35C1: M-Cr(CO)3,6.9).The isolated yield of 6 (obtained from the first fraction) was 12%, based on theamount of Cr(CO)6consumed.122Preparation of(q6-N,N-dimethylaniline)tricarbonylchromium 7.Chromium hexacarbonyl (4.00 g, 18.2 mmol) and N,N-dimethylaniline (20 mL, 0.16mol) were dissolved in a mixture of (n-Bu)20/THF (60 mL/5 mL) in glassware A. Thestirred reaction mixture was heated to reflux for 21 h. After cooling to roomtemperature, the volume of the reaction mixture was concentrated under reducedpressure and a large crop of yellow crystals deposited. The remaining supernatant wasthen canula transferred to another flask. The crystals were collected on a glass frit andwashed repeatedly with cold hexane, then dried in vacuo. Compound 7 was isolated asyellow crystals, for a yield of 3.30 g (70%), mp 137-138°C {lit.6 mp 144°C}.Preparation of ((-benzonitri1e)tricarbony1chromium 10.DMSO (2 mL) was added to compound 1 (44.8 mg, 0.193 mmol) and NaCN (21.4 mg,0.437 minol) contained in a 5-mL Reactivia1® under argon. The reaction mixture wasstirred for 23 h at ambient temperature. The reaction mixture was then added to water(20 mL) and subsequently extracted with diethyl ether (3 x 15 mL). The ether extractswere washed with aqueous, saturated sodium chloride solution and dried over anhydrousmagnesium sulfate. The dried ether extracts were filtered through a short pad of silicagel and the solvent wasjaken to dryness under reduced pressure. Compound 10 wasisolated as yellow crystals, in a yield of 32 mg (69%).123Preparation of(6-N,N,N-trimethy1aniIinium)tricarbony1chromium trifluoromethanesulfonate 11.Compound 7 (1.00 g, 3.89 rnmol) was added to CH21 (25 mL) and stirred at roomtemperature until dissolved. Methyltrifluoromethanesulfonate (1.1 mL, 9.7 rnmol) wasadded by syringe and the mixture was stirred overnight. Yellow crystals had depositedand the supernatant was canula transferred to another flask. This solution was stirredovernight. The yellow crystals were dried in vacuo, then dissolved in acetonitrile. Theresulting solution was transferred by canula filtration into a Schienk tube. The volumeof CH3N was reduced by a third under reduced pressure, then diethyl ether was addeduntil the solution became slightly cloudy. This mixture was placed in the freezerovernight.The previous solution, in which the reaction was allowed to continue, afforded anothercrop of yellow crystals. These were isolated and recrystallized as described for the firstbatch of crystals. Both batches of crystals were isolated, and dried under a flow of N2initially, then under high vacuum. Compound 11 was obtained as yellow crystals, in atotal yield of 0.97 g (59%). An analytical sample was obtained by performing twosequential recrystallizations of a portion of 11 from acetonitrile/diethyl ether, mp 120-121°C (dec.).* Anal. calcd. forC,3H4rFNO6S:C 37.06, H 3.35, N 3.32, S 7.61; found:C 37.40, H 353, N 3.49, S 7.44. ‘H NMR (270 MHz, DMSO-d6)& 3.56 (s, 9H,N(CH3),5.77 (t, 2H, H-3,5), 6.07 (t, 1H, H-4), 6.69 (d, 2H, H-2,6).*Performed in capillaries that were packed and sealed under nitrogen.124Preparation of N,N,N-trimethylanilinium trifluoromethanesulfonate 12.N,N-Dimethylaniline (1.00 mL, 7.89 mmol) and methyltrifluoromethanesulfonate (1.1mL, 9.7 mmol) were added sequentially by syringe to CH21 (25 mL) while under anitrogen atmosphere. The reaction mixture was allowed to stir at room temperature.After 30 mm, TLC analysis indicated that all the N,N-dimethylaniline present wasconsumed. The copious quantities of white crystals that deposited, were collected anddried in vacuo. These crystals were recrystallized from dichloromethane/diethyl ether,which afforded a total yield of 1.87 g (83%) of 12, mp 82-83°C {lit. mp: none found}.1H NMR (270 MHz, DMSO-d6)&: 3.61 (s, 9H, N(CH3),7.58-7.67 (m, 3H, H-3,4,5), 7.97(d, 2H, H-2,6).Preparation of N,N,N-trimethylanilinium iodide 13.N,N-Dimethylaniline (1.00 mL, 7.89 mmol) and iodomethane (0.54 mL, 8.67 mmol)were added to CH21 (25 mL) under a nitrogen atmosphere. The reaction mixture wasallowed to stir overnight at room temperature. The resulting white crystals which haddeposited were collected, washed with diethyl ether and dried under reduced pressure.Compound 13 was obtained in a yield of 1.16 g (56%). 1H NMR (270 MHz, DMSO-d6)& 3.61 (s, 9H, N(CH3),7.58-7.68 (m, 3H, H-3,4,5), 7.97 (d, 2H, H-2,6).5.3.4 Substitution Reactions of Organochromium ComplexesSubstitution reactions with stable cyanide.General Procedure: An aliquot (200 L, 10 mg/mL) of aqueous KCN (32 mo1) was125injected into a 5-mL Reacti-vial under inert atmosphere. The water was evaporatedto dryness, using a block heater, under a rapid flow of nitrogen or argon. The (,-arene)tricarbonylchromium complex (65 mol) was taken up in DMSO (1 mL), thenadded by syringe to the Reacti-vial®. The stirred mixture was heated at the desiredtemperature in a thermostated silicone oil bath for 10 minutes. After cooling (ice/waterbath) to room temperature, the reaction mixture was quantitatively transferred to avolumetric flask and diluted to a known volume with DMSO. This solution was analyzedby HPLC, which was standardized with known solutions of expected aryl nitrile product,to determine the extent of product formation. The chemical yields were calculated usingKCN as the limiting reagent.A separate set of reactions were performed to isolate the organic products and identifythese by GC-MS, therefore, the workup of these reaction mixtures, after cooling, wasconducted as follows. The reaction mixture was diluted with water or saturated NaC1solution (3 mL), and extracted with diethyl ether (1 x 6 mL, 2 x 3 mL). The combinedether extracts were washed with water or saturated NaC1 solution (2 x 3 mL). Thestirred ether solution was treated with iodine (146 mo1) at 0°C for 2 hours to ensurecomplete decomplexation. The treatment was quenched with the addition of aqueoussodium thiosulfate solution (5 mL, 0. 1M) and the ether layer was washed further withsodium thiosulfate solution (4 mL, 0.1M), then with saturated NaC1 solution (2 x 4 mL)and was dried over anhydrous magnesium sulfate. The dried ether layer was filtered andconcentrated under reduced pressure to 1 mL. The concentrated ether solution wasanalyzed initially by GC and HPLC, then by GC-MS.126Reaction of 1 with cyanide.A typical reaction trial was performed as follows. Compound 1 (15.6 mg, 67.21Lmol)was allowed to react with KCN (2.10 mg, 32.2 mol), at 135°C, as described in thegeneral procedure above. The final DMSO mixture was analyzed by HPLC (column A;eluent: solvent A; flow rate, 2.5 mL/min; UV detection, 280 nm) and it was determinedthat 1.34 mg of benzonitrile 14 (RT* = 5.4 mm) was present, for a yield of 40%.Other reaction trials were conducted at 105, 115, 120, and 150°C, which gave yieldstof 12, 32, 31, and 33%, respectively.Reaction of 4 with cyanide.A typical reaction trial was performed as follows. Compound 4 (16.2 mg, 65.8 mol)was allowed to react with KCN (2.10 mg, 32.2 jmol), at 105°C, as described in thegeneral procedure. The final DMSO mixture was analyzed by HPLC (column B; eluent:solvent C; flow rate, 2.5 mL/min; UV detection, 270 rim) and it was determined that1.62 mg of 2-tolunitrile 15 (RT= 12.1 mm) was present, for a yield of 43%.Other reaction trials were conducted at 95, 115, 125, and 135°C, which gave yieldstof 26, 41, 29, and 36%, respectively.Two reaction trials were performed using 1.5 mg (6.1 1Lmol) of 4 with KCN (2.00 mg,30.7 mol), at 135 and 143 °C, using the general procedure. In each case, 0.41 mg of 15‘RT denotes retention time.1These results represent the best chemical yields obtained where more than onereaction trial was performed.127was obtained, for a yield of 58% based on 4 as the limiting reagent.A separate reaction trial was done to identify the organic products by GC-MS.Compound 4 (16.2 mg, 65.8 mol) was allowed to react with cyanide, at 120°C, asdescribed in the general procedure. The concentrated ether solution was analyzed byGC and only two significant peaks were observed, which were identified as 2-fluorotoluene (RT=3.2mm) and 2-tolunitrile 15 (RT=5.7 mm). This sample was furtheranalyzed by HPLC (column A; eluent: solvent C; flow rate, 2.5 mL/min; UV detection,270 nm) and found that 15 eluted first (RT=7.3 mm), followed by 2-fluorotoluene(RT 16.2 nun). Identification of the above products was accomplished by thecomparison of the GC and HPLC retention times with those of authentic samples. Theidentity of the products was further confirmed by GC-MS, using for comparison the massspectra (acquired under very similar instrumental conditions) obtained from a premadesolution of authentic samples. Mass spectra, m/z: 2-fluorotoluene, 110 (M, 48), 109(M-H, 100), 108 (M-2H, 15), 89 (3), 83 (15), 74 (12), 59 (15), 57 (6); compound 15,117 (M, 100), 116 (M4-H, 85), 115 (M4-2H, 13), 90 (44), 89 (47), 63 (16).Reaction of 5 with cyanide.A typical reaction trial was performed as follows. Compound 5 (16.1 mg, 65.4 ILmol)was allowed to react with KCN (2.10 mg, 32.2 /Lmol), at 115°C, as described in thegeneral procedure. The final DMSO mixture was analyzed by HPLC (column B; eluent:solvent C; flow rate, 2.5 mL/min; UV detection, 270 nm) and it was determined that1.11 rng of 4-toluriitrile 16 (RT= 12.2 mm) was present, for a yield of 29%.128Other reaction trials were conducted at 105, 125, 135, and 150°C, which gave yields*of 11, 21, 26, and 21%, respectively.A separate reaction trial was done to identify the organic products by GC-MS.Compound 5 (16.5 mg, 67.0 mo1) was allowed to react with cyanide, at 135 °C, asdescribed in the general procedure. The concentrated ether solution was analyzed byGC and only two prominent peaks were observed, which were identified as 4-fluorotoluene (RT=3.2mm) and 4-tolunitrile 16 (RT=6.3 mm). This sample was furtheranalyzed by HPLC (column A; eluent: solvent C; flow rate, 2.5 mL/min; UV detection,270 mm) and found that 16 eluted first (RT=7.mm), followed by 4-fluorotoluene(RT= 15.9 mm). Identification of the above products was performed by the comparisonof the GC and HPLC retention times with those of authentic samples. The identity ofthe products was further confirmed by GC-MS, using for comparison the mass spectra(acquired under very similar instrumental conditions) obtained from a premade solutionof authentic samples. Mass spectra, m/z: 4-fluorotoluene, 110 (M, 66), 109 (M-H,100), 89 (2), 83 (21), 57 (3); compound 16, 117 (M, 100), 116 (M-H, 52), 90 (38), 89(30), 63 (7).Reaction of 6 with cyanide.A typical reaction trial was performed as follows. Compound 6 (18.2 mg, 68.3 1mol)was allowed to react with KCN (2.10 mg, 32.2 Mmol), at 115°C, as described in the‘These results represent the best chemical yields obtained where more than onereaction trial was performed.129general procedure. The final DMSO mixture was analyzed by HPLC (column B; eluent:solvent C; flow rate, 2.5 mL/min; UV detection, 270 urn) and it was determined that1.53 mg of 4-chlorobenzonitrile 17 (RT= 12.5 mm) was present, for a yield of 34%.A reaction trial was also conducted at 135°C, which gave a yield of 21%.An additional reaction trial was performed at 115°C that was heated only for 5 mm(instead of 10 mm) and gave a chemical yield of 17%.A separate reaction trial was done to identify the organic products by GC-MS.Compound 6 (17.7 mg, 66.3 mo1) was allowed to react with cyanide, at 115°C, asdescribed in the general procedure. The concentrated ether solution was analyzed byGC and two major peaks were observed, which were identified as 4-chlorofluorobenzene(RT = 3.5 mm) and 4-chlorobenzonitrile 17 (RT = 7.1 mm), and also a smaller unknownpeak was observed that was identified eventually (by GC-MS) as benzonitrile 14 (RT 4.5mm). This sample was further analyzed by HPLC (column A; eluent: solvent A; flowrate, 2.5 niL/mill; UV detection, 270 nni) and found that 14 eluted first (RT = 4.6 mm),followed by 17 (RT = 7.6 mm) and an unidentified peak (RT = 10.1 mm), then finally 4-chlorofluorobenzene (RT = 18.3 mm) appeared last. Identification of the principalproducts was performed by the comparison of the GC and HPLC retention times withthose of authentic samples. The identification of the products was completed by GCMS, using for comparison the mass spectra (acquired under very similar instrumentalconditions) obtained from a premade solution of authentic samples in the case of theprincipal products, and by inspection of the mass spectrum obtained for 14. Massspectra, m/z: 4-chlorofluorobenzene, 132(37C1: M, 32), 130 (35C1: M, 100), 95 (M.-Cl,13058), 94 (M-HCl, 11), 69 (13), 68 (13), 65 (8), 51(11), 50 (36); compound 17, 139 (37C1:M, 31), 137 (35C1: M, 100), 112 (37C1: M-HCN, 1), 110(35C1: M-HCN, 3), 102 (MCl, 36), 76 (14), 75 (25), 74 (11), 68 (4), 51(19), 50 (35); compound 14, 103 (M, 100),102 (M-H, 2), 77 (M-CN, 8), 76 (M-HCN, 40), 63 (4), 52 (9), 51 (21), 50 (26).Reaction of 4 with cyanide in the presence of 18-crown-6 and DMSO.A typical reaction trial was performed as follows. Compound 4 (16.0 mg, 65.01Lmol)was allowed to react with KCN (2.10 mg, 32.2 1Lmol), at 105°C, as described in thegeneral procedure except that about 1.2 equivalents of 18-crown-6 (9.8 mg, 371.mol) wasadded to the reaction mixture before heating. The final DMSO mixture was analyzedby HPLC (column B; eluent: solvent C; flow rate, 2.5 mL/min; UV detection, 270 nm)and it was determined that 1.65 mg of 2-tolunitrile 15 (RT= 14.3 mm) was present, fora yield of 44%.Other reaction trials were conducted at 95, 115, 125, and 135°C, which gave yields of35, 40, 42, and 41%, respectively.An additional reaction trial was performed using 16.2 mg (65.8 1.mol) of 4 with KCN(2.10 mg, 32.2 mol), at 105°C, which used approximately 3 equivalents of 18-crown-6(26 mg, 98 1Lmol) and afforded a chemical yield of 46%.Reaction of 4 with cyanide in the presence of 18-crown-6 and CH3N.Two reaction trials were performed as follows. In the first trial, 4 (16.2 mg, 65.81Lmol) was allowed to react with KCN (2.10 mg, 32.2 Mmol), at 80°C, as described in the131general procedure except that 1 equivalent of 18-crown-6 (8.5 mg, 321mol) was addedto the reaction mixture and CH3N was used as the reaction solvent. The final CH3Nmixture was analyzed by HPLC (column B; eluent: solvent C; flow rate, 2.5 mL/min; UVdetection, 270 nm) and it was determined that 0.094 mg of 2-tolunitrile 15 (RT= 13.8mm) was present, for a yield of 3%. This mixture was stored and reanalyzedapproximately 18 hours later by HPLC; it was found that 0.81 mg of 15 was now present,which represents a yield of 21%. The mixture was stored again, then reanalyzed 13.5days after the initial HPLC analysis. At this time, 1.90 mg of 15 was determined to bepresent, for a final yield of 50%.The second reaction trial was performed in the same way as the first, except that anoil bath temperature of 95°C was used (it was noted that the reaction mixture wasrefluxing). A chemical yield of 4% was obtained, as determined by HPLC. The mixturewas stored, and upon reanalysis about 16 hours later, the yield was found to be increasedto 21%. This mixture was stored again, then reanalyzed 13.5 days after the initial HPLCanalysis. The final yield of 15 was found to be 46%.Attempted reaction of 11 with cyanide.Two reaction trials were performed as follows. In the first trial, 11 (27 mg, 64 mo1)was allowed to react with KCN (2.10 mg, 32.2 mo1), at 100°C, as described in thegeneral procedure. The final DMSO mixture was analyzed by HPLC (column A; eluent:solvent C; flow rate, 2.5 mL/min; UV detection, 270 nm) and the chromatogramexhibited a large peak (RT=7.9 mm) and a much smaller peak (RT= 18.2 mm), but132neither peak could be identified. Under these HPLC conditions, benzonitrile 14 wasexhibiting a retention time of 4.4 mm. Therefore, HPLC analysis confirmed the absenceof any desired 14 in the product mixture.The second reaction trial was performed in the same way as the first, except thereaction temperature used was 120°C. The same essential results were obtained asreported in the first trial above.Heating of 11 in DMSO without cyanide present.Compound 11 (27 mg, 64 mol) was heated in DMSO (1 mL) for 10 mm at 100°C,in the same fashion as described in the general procedure; the addition of aqueous KCNand its associated drying was not done. The resulting DMSO solution was analyzed byHPLC (column A; eluent: solvent C; flow rate, 2.5 mL/min; UV detection, 270 nm) andthe chromatogram exhibited a single large peak (RT=8.1 mm) which could not beidentified.Attempted reaction of fluorobenzene with cyanide.Fluorobenzene (5.7 1.L, 60 mo1) was allowed to react with KCN (2.00 mg, 30.7 !mo1),at 135°C, as described in the general procedure. The final DMSO mixture was analyzedby HPLC (column A; eluent: solvent B; flow rate, 2.5 mL/min; UV detection, 270 urn)and the chromatogram exhibited a single peak (RT = 4.2 mm) which was identified asfluorobenzene. Under these HPLC conditions, benzouitrile 14 had a retention time of2.8 mm, thereby confirming the absence of 14 in the product mixture.133Attempted reaction of 2-fluorotoluene with cyanide.2-Fluorotoluene (6.6 L, 60 mol) was allowed to react with KCN (2.00 mg, 30.7mol), at 135°C, as described in the general procedure. The final DMSO mixture wasanalyzed by HPLC (column A; eluent: solvent B; flow rate, 2.5 niL/mm; UV detection,270 nm) and the chromatogram exhibited a single peak (RT = 7.2 mm) which wasidentified as 2-fluorotoluene. Under these HPLC conditions, 2-tolunitrile 15 had aretention time of 3.9 miii, thereby confirming the absence of 15 in the product mixture.Attempted reaction of 4-fluorotoluene with cyanide.4-Fluorotoluene (6.6 L, 60 mo1) was allowed to react with KCN (2.00 mg, 30.7,Lmol), at 135°C, as described in the general procedure. The final DMSO mixture wasanalyzed by HPLC (column A; eluent: solvent B; flow rate, 2.5 mL/min; UV detection,270 mn) and the chromatogram exhibited a single peak (RT = 7.3 mm) which wasidentified as 4-fluorotoluene. Under these HPLC conditions, 4-tolunitrile 16 had aretention time of 4.1 mm, thereby confirming the absence of 16 in the product mixture.Attempted reaction of 4-chiorofluorobeuzene with cyanide.4-Chlorofluorobenzene (6.4 L, 60 mol) was allowed to react with KCN (2.00 mg,30.7 mol), at 135°C, as described in the general procedure. The final DMSO mixturewas analyzed by HPLC (column A; eluent: solvent B; flow rate, 2.5 mL/min; UVdetection, 270 mm) and the chromatogram exhibited a single peak (RT=7.6 miii) whichwas identified as 4-chlorofluorobenzene. Under these HPLC conditions, 4-134chlorobenzonitrile 17 had a retention time of 4.6 mm, thereby confirming the absenceof 17 in the product mixture.Attempted reaction of 12 with cyanide.Compound 12 (18 mg, 63 .4mol) was allowed to react with KCN (2.10 mg, 32.2 pmol),at 100°C, as described in the general procedure. The final DMSO mixture was analyzedby HPLC (colunm A; eluent: solvent C; flow rate, 2.5 mL/min; UV detection, 270 am)and no product peaks were observed in the chromatogram (12 is not observable by UVdetection at 270 mu). Under these HPLC conditions, benzonitrile 14 had a retentiontime of 4.1 mm, thereby confirming the absence of 14 in the product mixture.5.3.5 Labelling Work with [“C] CyanideSubstitution reactions with [“C] cyanide.General Procedure: After the H11CN was generated and trapped in aqueous NaOHsolution (1 mL, 0.1 M), 0.5-1.0 mL of this radioactive stock solution was taken (thesolution was counted at this stage and the time was notedD and a known amount ofnon-radioactive KCN (carrier) was added, then this mixture was added to a 5-mL Reactivial® (which contained an inert atmosphere). The [“C]cyanide solution was rapidlyevaporated to dryness (using a block heater) under a fast flow of nitrogen or argon. Asolution of(,6-arene)tricarbonylchromium (40-65 mol) in DMSO (1 mL) was added bysyringe to the Reacti-vial®. The stirred mixture was heated at the desired temperatureThis point in time was designated as the start of synthesis (SOS).135in a thermostated silicone oil bath for 10 minutes. Upon cooling (ice/water bath) toambient temperature, a small portion of the reaction mixture was subjected to radioHPLC purification and the peak corresponding to the[11C]nitrile product was collectedand counted to determine the decay corrected radiochemical yield.Reaction of 1 with [“C]cyanide.A representative reaction trial was performed as follows. Compound 1 (9.5 mg, 41mol) was treated with a mixture of 27.8 mCi (SOS) of[11C]cyanide and 0.37 equivalentsof carrier KCN (0.98 mg, 15 mol), then heated at 150°C, as described in the generalprocedure. HPLC analysis (column C; eluent: solvent A; flow rate, 5.0 mL/min; UVdetection, 254 mn) of the reaction mixture determined that 9.93 mCi (decay correctedto SOS) of[11C-CN]benzonitrile 18 (RT = 6.5 mm) was produced for a radiochemical yieldof 36%.Other reaction trials were conducted at 150°C which used varying amounts of carrierKCN (0.11, 0.35, 0.49 equiv) and gave 21%, 41%, and 34% radiochemical yields,respectively.An additional reaction trial was performed at 135 °C, which used 0.51 equivalents ofcarrier KCN, and afforded a radiochemical yield of 35%.Reaction of 1 with no carrier-added [11Cjcyanide.Compound 1 (15 mg, 65 mol) was treated with 22.8 mCi (SOS) of [“Cjcyariide (withno carrier KCN added), then heated at 150°C, as described in the general procedure.136HPLC analysis (column C; eluent: solvent A; flow rate, 5.0 mL/min; UV detection, 254nm) of the reaction mixture determined that only a trace of [“C-CN]benzonitrile 18(RT = 6.5 mm) was present—the activity of the collected product fraction was too low tobe counted with the Capintec well counter.Reaction of 4 with [“C] cyanide.Compound 4 (14.8 mg, 60.1 mol) was treated with a mixture of 8.50 mCi (SOS) of[“Cjcyanide and 0.51 equivalents of carrier KCN (2.00 mg, 30.7 mol), then heated at135 °C, as described in the general procedure. HPLC analysis (column A; eluent: solventB; flow rate, 2.5 mL/min; UV detection, 270 urn) of the reaction mixture determinedthat 2.93 mCi (decay corrected to SOS) of[11C-CN]-2-tolunitrile 19 (RT = 4.0 mm) wasproduced for a radiochemical yield of 34%.Reaction of 5 with [“C]cyanide.Compound 5 (14.8 mg, 60.1 mol) was treated with a mixture of 7.84 mCi (SOS) of[‘1C]cyanide and 0.51 equivalents of carrier KCN (2.00 mg, 30.7 mol), then heated at135 °C, as described in the general procedure. HPLC analysis (column A; eluent: solventB; flow rate, 2.5 mE/mm; UV detection, 270 mu) of the reaction mixture determinedthat 2.39 mCi (decay corrected to SOS) of[‘1C-CN]-4-tolunitrile 20 (RT=4.l mm) wasproduced for a radiochemical yield of 31%.137Reaction of 6 with [“C]cyanide.Compound 6 (12.3 mg, 46.1 mol) was treated with a mixture of 16.73 mCi (SOS) of[‘1C]cyariide (in this case the H11CN was trapped in 0.025 M NaOH solution) and 0.11equivalents of carrier KCN (0.33 mg, 5.0 mol), then heated at 150°C, as described inthe general procedure. HPLC analysis (column C; eluent: solvent A; flow rate, 3.0mL/min; UV detection, 254 mn) of the reaction mixture determined that 3.54 mCi(decay corrected to SOS) of[11C-CN]-4-chlorobenzonitrile 21 (RT = 12.0 mm) wasproduced for a radiochemical yield of 21%.Another reaction trial was performed at 135°C, which used 0.51 equivalents of carrierKCN, and afforded a radiochemical yield of 19%.Reaction of 6 with [‘1C]cyanide in the absence of base.An experiment was done to eliminate the presence of base (both ammonia andhydroxide) from the labelling[11C]cyauide reagent. TheH11CN/NH3gas stream waspassed through a glass loop, which was emersed in a CC14/C02(-23°C) cooling bath, andtrapped out the H11CN, while sweeping away the NH3 with helium gas flow. The glassioop was removed from the cooling bath and H’1CN was slowly purged into a Reactivial® which contained a mixture of 6 (10.0 mg, 37.5 mo1), carrier KCN (1-2 mg, 15-31mol*), and DMSO (1 mL) under N2 atmosphere. When the H11CN transfer wascomplete, the radioactive mixture was counted (3.87 mCi, SOS). This mixture wasTwo small crystals of KCN were used, which were not weighed, thus the quantityindicated was estimated.138heated for 10 minutes at 125-130°C. After cooling, HPLC analysis (column C; eluent:solvent A; flow rate, 3.0 mL/min; UV detection, 254 nm) of the reaction mixturedetermined that 1.11 mCi (decay corrected to SOS) of [“C-CN]-4-chlorobenzonitrile 21(RT= 14.9 mm) was produced for a radiochemical yield of 29%.5.4 Experimental for Chapter 35.4.1 Sources of Materialsl7cr-Ethynylestradiol 23 was obtained from Sigma Chemical Co. Tri-n-butyltin hydridewas purchased from the Aldrich Chemical Co. and Alfa Products, and 2,2 ‘-azobis- (2-methylpropionitrile), commonly referred to as AIBN, was supplied by Aldrich ChemicalCo.The O-methylated estradiols, 3-methoxy- l7cr-ethynyl- 1,3,5( 10)-estratriene- 17f3-ol 24and 3, 17fl-dimethoxy-17a-ethynyl- 1,3,5( 10)-estratriene 25, were prepared by adapting themethod of Johnstone and Rose.9 Compound 23 was treated with powdered potassiumhydroxide in DMSO, followed by the addition of iodomethane. Flash chromatographyof the crude product mixture on silica gel with hexanes/diethyl ether (2:1) afforded 24and 25 in 67% and 31% yields, respectively. 3-Methoxy-l7cr-vinyl-1,3,5(10)-estratriene-17fl-ol 41 was also prepared by an adaptation of the procedure of Johnstone and Rose.9A mixture of 23 and 17a-vinyl-1,3,5(10)-estratriene-3,17f3-diol 35, obtained from thehydrostarinylation of 23 (see Subsection 5.4.3), was treated with potassium hydroxide inDMSO, and then with iodomethane. Flash chromatography on silica gel with hexanes/diethyl ether (1:1) gave pure 41 in 52% yield (based on the amount of 35 used).139The acetylenic sugars, 7,8-dideoxy- l,2:3,4-di-O-isopropylidene-D-glycero-a-D-galacto-oct-7-ynopyranose 28 and its L-glycero-a-D-galacto epimer 29, were prepared according topublished procedures in two steps. First, 1,2:3,4-di-O-isopropylidene-a-D-galacto-hexodialdo- 1,5-pyranose 27 was prepared by oxidation of 1,2:3,4-di-O-isopropylidene-a-D-galactopyranose 26 (Koch-Light Laboratories Ltd.) using either chromium trioxidedipyridine complex (in 52% yield) as described by Arrick and co-workers,’° or thechromium trioxide-pyridine complex in the presence of acetic anhydride (in 68% yield)according to Garegg and Samuelsson.” Then 27 was treated with ethynylmagnesiumbromide according to the procedure of Hems et al.12 and a mixture of 28 and 29 wasobtained (85% yield) in a ratio of 62:38 (determined by ‘H NMR), respectively. Thismixture was separated using column chromatography on silica gel with dichloromethane/hexanes/diethyl ether (6:2:1).Research grade Ne and 1% F2 in Ne gas mixture were specially prepared in ultra-highpurity (suitable for 18F production) by either Matheson Gas Products (Edmonton, AB)or Canadian Liquid Air Ltd. (Vancouver, BC).Freon-li (CFC13)was purchased from Matheson Gas Products.5.4.2 GeneralFluorine gas is toxic, highly corrosive, and generally dangerous, and therefore requireshandling with great care.’3”4 Hence, a specialized fluorine gas handling system wasused to perform all studies involving elemental fluorine and acetyl hypofluorite, and isshown in Figure 5.1. This gas handling system was constructed from components, such140CYCLOTRONSHIELDING ventmetering( valvepressure pressuretransducer transducerreactionFigure 5.1: Schematic of the fluorine gas handling system used to perform thefluorination reactions.as stainless steel and Teflon, that are compatible with reactive fluorine gas. The fluorinetank and gas handling system are stationed in a fume hood specifically designed for usewith radionucides. The gas handling system is connected via 1/8 in. o.d. stainless steeltubes to the gas targets used on the TRIUMF/Nordion CP-42 cyclotron and the largerTRIUMF 500 MeV cyclotron. The cyclotron gas targets are essentially gas-tightcylinders, fabricated from nickel (for the CP-42 cyclotron)’5or Inconel 600, a nickel-based alloy (for the 500 MeV cyclotron).’6 The gas handling system was connected tothe reaction vessel with Teflon tubing (1/16 or 1/8 in. o.d.) using Swagelok fittings141(Crawford Fitting Co., Salon, OH) and Teflon ferrules.Gaseous CH3OOF was produced by passing a dilute mixture of F2 (—0.1%) in Nethrough a column containing a solid mixture of potassium acetate/acetic acid in a molarratio of 2:3. TheCHOOK/CHOH mixture was prepared according to the methodof Jewett et al.17The quantification of the amount of F2 or CH3OOF used for fluorinationexperiments was accomplished by iodometric titration.18”9 Prior to performing actualfluorination reactions with vinyl-tin substrates, one or two “dummy” trials would be donein which the fluorinating agent was added to an aqueous solution of excess KI, and theliberated 12 was then titrated with standardized 0.1 M sodium thiosulfate solution.[‘8F1F2was produced by the20Ne(p,Spall)’8Freaction with a target gas mixture of 0.1%F2 in natural neon that was irradiated with 500 MeV protons from the TRIUMFcyclotron.16Gaseous CH3OO’8Fwas prepared by venting the [‘8F]F2 produced after targetirradiation through the solidCH3OOK/CHOHcolumn17that was described earlier.5.4.3 Preparation of Vinyl-Tin SubstratesGeneral procedures for hydrostannylation of acetylenic compounds.Procedure A: Under an N2 atmosphere, a solution of acetylenic compound in 1,4-dioxane was prepared. To this stirred solution, five equivalents of tri-n-butyltin hydridewas added by syringe, then the mixture was refluxed overnight. The solvent wasremoved and the crude mixture was chromatographed on a silica gel column to obtain142the stannylated product.Procedure B: Under an N2 atmosphere, a mixture of acetylenic compound, a catalyticamount of AIBN, and two equivalents of tri-n-butyltin hydride were combined, and thestirred mixture was heated overnight (thermostated silicone oil bath, 95°C). Aftercooling, the entire reaction mixture was chromatographed on a silica gel column toisolate the stannylated product.General: In all cases, the vinyl-tin products after chromatographic isolation werethoroughly dried under high vacuum, then stored in vacuo over sodium hydroxide pellets.Vinyl-tin compounds are sufficiently air-stable so that they can be easily handled in theopen under normal conditions, however, prolonged exposure to the atmosphere willresult in gradual decomposition. Proper storage, therefore, is very important.Preparation of l7cr-(E) -tributylstannylvinyl-1,3,5(10)-estratriene-3,1713-diol 30 and l7a-vinyl-1,3,5(10)-estratriene-3,17j3-diol 35.Method A: Compound 23 (1986 mg, 6.70 mmol) in 1,4-dioxane (10 mL) was hydrostannylated as described in procedure A. Flash chromatography of the crude mixturewas performed on silica gel (3.5 cm x 15 cm) with dichloromethane/hexanes/diethylether (6:2:1). The first fraction contained 30 as the dominant product plus twounidentified byproducts, while further elution isolated a mixture of 23 and 35 (1090 mg)in a ratio of 29:71 as determined by ‘H NMR. Therefore, 774 mg of 35 was estimatedto be present in the second fraction for a yield of 38%. The first fraction was furtherpurified by column chromatography on silica gel (150 mg) with dichloromethane/143hexanes /ether (6:4:1) which afforded 780 mg of 30 (20% overall isolated yield) as a veryviscous syrup, and upon drying overnight in vacuo, crystallized as an off-white solid. Ananalytical sample was obtained by flash chromatography on silica gel withdichioromethane/hexanes/ether (6:4:1), mp 86-87.5°C, [a]4 + 19.00 (c 1.7, 1,4-dioxane).Anal. calcd. forC32H5O2Sn: C 65.43, H 8.92; found: C 65.60, H 8.78. 1H NMR (270MHz, CDC13)& 0.81-0.97 (m, 18H, 18-CH3andSn(CHCH3),1.20-2.37 (severalm, 26H, 17-OH, Sn(CH2CH3)CH and CH2 of steroid nucleus), 2.80 (m, 2H,CH2 of steroid nucleus), 5.30 (s, 1H, 3-011), 6.07 (d,J2021 = 19.4 Hz, 2JSn,H 70 Hz, 1H,H-21), 6.20 (d, 3JSn,H = 66 Hz, 1H, H-20), 6.57 (d, 24 = 2.9 Hz, 1H, H-4), 6.62 (dd, J1,2= 8.8 Hz, 1H, H-2), 7.13 (d, 1H, H-i). Mass spectrum, m/z: 531(120Sn: M-C4H9,100).In an attempt to separate 35 from 23 for characterization, column chromatography ofa portion of the mixture of 23 and 35 was performed on silica gel with dichloromethane/hexanes/ether (6:4:1). Unfortunately, complete separation was not achieved as 23 coeluted with all fractions containing 35, with the largest percentage of 23 being presentin the early fractions. Therefore, a sample was obtained by combining several of the latefractions that contained the lowest percentage of 23. This sample was recrystallized frombenzene/hexanes, then analyzed by HPLC (column C; eluent: methanol/water, 3:1; flowrate, 6.0 mL/min; UV detection, 280 nm) and found that a ratio of 23 (RT=.6mm) to35 (R.=5.0 mm) of 19:81 was present. As a result, to effectively isolate 35 an HPLCseparation was carried out by injecting this sample (dissolved in THF) in several portionsonto column C and eluting 35 using the same conditions (flow rate was changed to 3.0mL/min) employed for HPLC analysis. The peaks corresponding to 35 were collected,144but due to a minute amount of 23 still present, the isolated material was subjected toadditional HPLC purification. The material obtained from the second HPLCpurification was recrystallized from benzene/hexanes, which afforded 35 as whitecrystals, mp 169.5-170°C, [a15 + 58.5° (c 1, 1,4-dioxane). Anal. calcd. forC20H60:C80.50, H 8.78; found: C 80.54, H 8.72. ‘H NMR (270 MHz, CDC13)ô: 0.95 (s, 3H, 18-CH3), 1.24-2.37 (several m, 14H, 17-OH, CH and CH2 of steroid nucleus), 2.80 (m, 2H,CH2 of steroid nucleus), 4.68 (hr s, 1H, 3-OH), 5.15 (dd,J2021a 10.8 Hz, ‘21a,21b 1.2Hz, 1H, H-21a), 5.20 (dd,2O,lb = 17.3 Hz, 1H, H-21b), 6.11 (dd, 1H, H-20), 6.56 (d, J24= 2.8 Hz, 1H, H-4), 6.62 (dd, J12 = 8.2 Hz, 1H, H-2), 7.14 (d, 1H, H-i). Mass spectrum,m/z: 298 (M, 51), 280 (M-H2O, 15). Exact mass calcd. forC20H60:298.1934; found:298.1934.Method B: Compound 23 (1.00 g, 3.37 mmol) was hydrostannylated as described inprocedure B. Column chromatography on silica gel (100 g) with dichloromethane/hexanes/diethyl ether (6:4:1) afforded in one portion 1.17 g (59%) of 30. Physical andspectral (‘H NMR) properties of this material were identical with those reported earlier.TLC analysis of the reaction mixture confirmed the presence of 35, but the compoundwas not eluted off the column.Preparation of 3-methoxy-17o&(E)-tributyIstanny1vinyI-1,3,5(10)-estratriene-173-o1 31.Compound 24 (492 mg, 1.59 mmol) was bydrostannylated as described in procedureB. Column chromatography on silica gel (100 g) with hexanes/diethyl ether (5:1) yieldedin the first fraction 114 mg of crude 3-methoxy-17a-(Z)-tributylstannylvinyl-1,3,5(10)-145estratriene-17fl-ol 36, and in the following two fractions, 860 mg of 31. Compound 31was isolated as a colourless oil in 90% yield, [Qf]4 + 17.1° (c 1.2, 1,4-dioxane). Anal.calcd. forC33H54O2Sn: C 65.90, H 9.05, 0 5.32; found: C 65.83, H 9.00, 0 5.28. Massspectrum, m/z: 602 (‘20Sn: M, 0.2), 545 (‘20Sn: M-C4H9,100).Preparation of 3,173-dimethoxy-17o-(E)-tributy1stanny1viny1-1,3,5(1O)-estratriene 32.Compound 25 (1.00 g, 3.08 minol) was hydrostannylated as described in procedure B.Column chromatography on silica gel (200 g) with hexanes/diethyl ether (20:1) yieldedin the first fraction 0.23 g of 32 plus a minute amount of unidentified byproduct, and inthe second fraction 1.56 g of pure 32. Compound 32 was isolated in an overall yield of94% as an oil, and after drying in vacuo for 15-30 minutes, crystallized as a white solid.The material from the second fraction exhibited mp 50-52.5°C, [a]4 +44.1° (c 1.2,CHC13). Anal. calcd. forC34H56O2Sn: C 66.35, H 9.17, 0 5.20; found: C 66.37, H 9.18,0 5.35. ‘H NMR (270 MHz, C6D) ô: 0.93 (t, J 7.3 Hz, 9H, Sn(CHCH3),1.01 (m, 6H, Sn(CHCH3),1.12 (s, 3H, 18-CH3), 1.21-2.29 (several m, 25H,Sn(CH2CH3),CH and CH2 of steroid nucleus), 2.63-2.86 (m, 2H, CH2 of steroidnucleus), 3.23 (s, 3H, 17-OCH3),3.39 (s, 3H, 3-OCH), 6.23 (d,J2021 = 19.7 Hz, 2JSn,H =75 Hz, 1H, H-21), 6.37 (d, 3Sn,H = 69 Hz, 1H, H-20), 6.68 (d, J2,4 = 2.6 Hz, 1H, H-4),6.75 (dd, J,,2 = 8.6 Hz, 1H, H-2), —7.16 (d, 1H, H-i). Mass spectrum, m/z: 616(120Sn:M, 1), 601(120Sn: M-CH3,5), 559 (‘20Sn: M-C4H9,66).146Preparation of (E)-7,8-dideoxy- 1,2:3,4-di-O-isopropylidene-8-C-tributylstannyl-n-glyce-ro-a-D-galacto-oct-7-enopyranose 33.Compound 28 (884 mg, 3.11 mmol) was hydrostannylated as described in procedureB. Column chromatography on silica gel (200 g) with dichioromethane/hexanes/diethylether (6:6:1) afforded in one fraction 1093 mg (6 1%) of 33. Compound 33 was isolatedas a colourless syrup, [a]3 -36.1° (c 1, CHC13). Anal. calcd. forC26H48O6Sn: C 54.28, H8.41; found: C 54.21, H 8.52. 1H NMR (270 MHz, CDC13) & 0.81-0.97 (m, 15H,Sn(CH2CH3),1.21-1.55 (2 m, 24H, 2 x C(CH3)2and Sn(CH2CH3),2.81 (d,J6,OH = 7.0 Hz, 1H, 6-011), 3.68 (dd, J5,6 = 6.5 Hz, J4,5 = 1.7 Hz, 1H, H-5), 4.32(dd, J1,2 = 5.0 Hz,J23 = 2.3 Hz, 1H, H-2), 4.34 (m, J6,7 = 4.4 Hz, J6,8 = 1.4 Hz, 1H, H-6),4.45 (dd, J3,4 = 8.0 Hz, 1H, H-4), 4.61 (dd, 1H, H-3), 5.59 (d, 1H, H-i), 6.18 (dd, J78 =19.2 Hz, 3Sn,H = 64 Hz, 1H, H-7), 6.38 (dd, 2Sn,H = 70 Hz, 1H, H-8). Mass spectrum,m/z: 561 (120Sn: M-CH3,3), 519(120Sn: M-C4H9,100).Preparation of (E)-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-8-C-tributylstannyl-L-glyce-ro-oc-D-galacto-oct-7-enopyranose 34.Compound 29 (898 mg, 3.16 mmol) was hydrostannylated as described in procedureB except that after 19 hours of heating, 0.50 mL of tri-n-butyltin hydride (0.54 g, 1.86nimol) was added and heating was continued for another three hours. Columnchromatography on silica gel (200 g) with hexanes/diethyl ether (4:1) yielded in the firstfraction 444 mg of a mixture of (Z)-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-8-C-tributylstanny1-L-glycero-c-D-galacto-oct-7-enopyranose 37 and 7,8-dideoxy- 1,2:3,4-di-O-147isopropylidene-7-C-tributylstannyl-L-glycero-cr-D-galacto-oct-7-enopyranose 38 in a ratioof 3:2 as determined by 1H NMR. As a result, 266 mg of 37 and 178 mg of 38 wasestimated to be present in the mixture, for chemical yields of 15% and 10%, respectively.Further elution afforded 1076 mg of 34 in a second fraction, for a 59% yield.Compound 34 was isolated as a colourless syrup, [a]4 -37.0° (c 1.3, CHC1). Anal. calcd.forC26H48O6Sn: C 54.28, H 8.41, 0 16.68; found: C 54.57, H 8.47, 0 16.55. Massspectrum, m/z: 561 (120Sn: M-CH3,2), 519(120Sn: M-C4H9,100).5.4.4 Fluorination Reactions of Vinyl-Tin CompoundsFluorination of vinyl-tin substrates with elemental F2 or gaseous CH3OOF.General Procedure: A solution of vinyl-tin compound (60-200 1mol) was prepared(different solvents were employed) and placed in a glass reaction vessel (oven dried)under inert atmosphere. A stream of inert gas was passed through the vinyl-tin solutionvia a 1/16 in. o.d. Teflon tube, positioned at the bottom of the solution, which wascontrolled by the fluorine gas handling system (see Figure 5.1). To conduct fluorinationsat 0 or -78°C, the vinyl-tin solution was cooled with either an ice/water (0°C) bath oraC02/2-propanol (-78°C) cooling bath.The desired quantity of 1% F2/Ne gas mixture (60-230 mol F2) was loaded intoeither the CP-42 or 500 MeV gas target using the fluorine gas handling system, and thenpure Ne was added to dilute the F2 concentration to approximately 0.1% in Ne. Toperform fluorinations with F2, the dilutedF2/Ne gas mixture was then added directly tothe vinyl-tin solution after the inert gas flow was turned off. However, to perform148fluorinations with gaseous CH3OOF, the dilutedF2/Ne gas mixture was instead passedthrough a solidCH3OOK/CHOH column and the effluent added to the vinyl-tinsolution. Both fluorinating agents (F2 or CH3OOF) were added at a flow rate of - 50mL/min to the vinyl-tin solution. After the addition of fluorinating agent was completed,the reaction mixture was transferred to a round-bottom flask and the solvent wasremoved in vacuo. The residue was analyzed by TLC, then worked up as consideredappropriate.Preparation of 3-methoxy-17a-(E)-fluorovinyl-1,3,5(1O) -estratriene-1713-ol 39 and 3-methoxy-17a-(Z)-fluorovinyl-1,3,5(10)-estratriene-173-ol 40.Compound 31 (92.7 mg, 154 mol) was dissolved in CFC13 (20 mL) and added to aglass reaction vessel (2.0 cm o.d. x 10 cm length). This solution was treated withapproximately 1.3 equivalents of CH3OOF, at room temperature, as described in thegeneral procedure. Five additional fluorinations of compound 31 were conducted in thesame manner, employing a total of 554.6 mg of 31 (922 mol).The reaction mixtures obtained were combined, then subjected to column chromatography on silica gel (100 g) with hexanes/diethyl ether (4:1) as the eluent. The firstfraction (55 mg) collected contained 39 in 96% purity as indicated by HPLC analysis(column D; eluent: solvent D; flow rate, 3.5 mL/min; UV detection, 280 nm). Withcontinued elution, a second fraction (66 mg) was obtained which contained a mixture of39 (RT= 17.8 mm) and 40 (RT=26.2 mm) in a ratio of 79:21 by HPLC analysis. Both ofthe isolated chromatography fractions were subjected to further purification via HPLC.149Each fraction was dissolved in a minimum of ether, and then was injected in severalportions onto the HPLC silica gel column and eluted using the same conditionsemployed for HPLC analysis. The peaks corresponding to 39 and 40 were collected,whereby all of 39 was isolated in one batch (90.0 mg) and all of 40 was isolated inanother batch (11.5 mg). The isolated yields of 39 and 40 were 29.5% and 3.8%,respectively.Quantification of yields for the reaction of 31 with gaseous CH3OOF.Compound 31 (76.4 mg, 127 mol) was dissolved in CFC13 (20 mL) and added to aglass reaction vessel (2.0 cm o.d. x 10 cm length). This solution was treated withapproximately 1.3 equivalents of CH3OOF, at room temperature, as described in thegeneral procedure. After solvent removal, the residue was dissolved in a known volumeof CHC13. The product mixture was analyzed by HPLC (column C; solvent program A;flow rate, 6.0 mL/min; UV detection, 280 urn) using a standard solution of 39 as anexternal standard. It was determined that 17.0 mg of 39 and 40 (both co-elute, RT=S.Omm) was present, for a yield of 41% based on the amount of 31 used.Additional fluorination trials were conducted using alternative reaction solvents.Compound 31 (74.1 mg, 123 mo1) was dissolved in dried CH3O (20 mL) and treatedwith approximately 1.3 equivalents ofCH3OOF as described above. It was determinedby HPLC analysis that 5.59 mg of 39 and 40 was obtained, for a yield of 14%.Compound 31 (80.7 mg, 134 mol) was dissolved in dried CH3N (20 mL), whichrequired about 0.5 mL of CHC13 to help solubilize 31, and was treated with150approximately 1.2 equivalents of CH3OOF as described above. It was determined byHPLC analysis that 10.4 mg of 39 and 40 was obtained, for a yield of 24%.Compound 31 (71 mg, 118 mo1) was dissolved in dried THF (20 mL) and treatedwith approximately 1.4 equivalents ofCH3OOF as described above. It was determinedby HPLC analysis that 3.62 mg of 39 and 40 was obtained, for a yield of 9.3%.Quantification of yields for the reaction of 31 with elemental F2.Compound 31 (103.2 mg, 172 mol) was dissolved in CFC13 (20 mL) and added to aglass reaction vessel (2.0 cm o.d. x 10 cm length). This solution was treated withapproximately 1.25 equivalents of F2, at room temperature, as described in the generalprocedure. After solvent removal, the residue was dissolved in a known volume ofCHC13. The product mixture was analyzed by HPLC (column C; solvent program A;flow rate, 6.0 mL/min; UV detection, 280 nm) using a standard solution of 39 as anexternal standard. It was determined that 5.10 mg of 39 and 40 (both co-elute, RT=4.97mm) was present, for a yield of 9.0% based on the amount of 31 used. In addition, twoside-products that were present in significant amounts were identified as 3-.methoxy-l7a-ethynyl- 1,3,5 ( 10)-estratriene- 173-ol 24 (RT = 4.39 mm) and 3-methoxy- 17a-vinyl- 1,3,5(10)-estratriene-173-ol 41 (RT = 5.70 mm). Standard solutions of 24 and 41 were prepared foruse as external standards. HPLC analysis indicated that 2.89 mg of 24 and 3.85 mg of41 were present, for yields of 5.4% and 7.2%, respectively.An additional fluorination experiment was done using 95.9 mg (159 ILmol) of 31 inCFC13 (20 mL), which was treated with approximately 1.35 equivalents of F2 at -78°C,151as described above. It was determined by HPLC analysis that 2.23 mg of 39 and 40 wasobtained, for a yield of 4.2%. Furthermore, the side-products 24 and 41 were obtainedin 2.2% (1.11 mg) and 14.5% (7.23 mg) yields, respectively.Preparation of (E)-8-C-fluoro-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-enopyranose 47 and (Z)-8-C-fluoro-7,8-dideoxy-1,2:3,4-di-O-isopropyli-dene-L-glycero-a-D-galacto-oct-7-enopyranose 48.Compound 34 (83.6 mg, 145 mol) was dissolved in CFC13 (20 mL) and added to aglass reaction vessel (2.0 cm o.d. x 10 cm length). This solution was treated withapproximately 1.3 equivalents of CH3OOF, at room temperature, as described in thegeneral procedure. A second fluorination of compound 34 (80.9 mg, 141 mol) wasperformed as outlined above. The reaction mixtures obtained were combined, thensubjected to column chromatography on silica gel (60 g) with dichloromethane/hexanes/diethyl ether (6:2:1) as the eluent.The first fraction (29.5 mg) collected contained 47 in —98% purity as indicated by ‘HNMR. The second fraction (4.0 mg) contained a mixture of 47, 48, and 7,8-dideoxy-1,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-enopyranose 49 in a ratio of43:36:21 as determined by ‘H NMR. The third fraction (9.0 mg) contained a mixtureof 47, 48, and 49 in a ratio of 6:83:11. The final fraction (5.4 mg) contained a singlecompound that was identified as (E)-8-C-acetoxy-7-deoxy-1,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-enopyranose 50.The chemical yield of 47, as contained in the first three chromatography fractions, was152determined to be 36% (32 mg). The yield of 48, as contained in the second and thirdfractions, was determined to be 10% (9 mg).A larger scale synthesis of 47 and 48 was carried out as follows. Compound 34 (81.9mg, 142 mol) was dissolved in CFC13 (20 mL) and added to a glass reaction vessel (2.0cm o.d. x 10 cm length). This solution was treated with approximately 1.35 equivalentsof CH3OOF, at room temperature, as described in the general procedure. Threeadditional fluorinations of compound 34 were performed in the same manner, employinga total of 326.5 mg of 34 (567 mol). The reaction mixtures were combined, thensubjected to column chromatography on silica gel (140 g) with dichioromethane/hexanes/diethyl ether (6:2:1) as the eluent.5.4.5 Radiofluorinations with Acetyl[18F]HypofluoriteGeneral procedure for radiofluorination with gaseous CH3OO’8F.A solution of vinyl-tin compound (110-120 mol) in CFC13 (20 mL) was prepared ina glass reaction vessel (2.0 cm o.d. x 12.5 cm length) under inert atmosphere. The 500MeV gas target was filled with 4 or 6 psi (0.27 or 0.41 atm) of 1% F2/Ne gas mixture,then pure Ne was added until 100 psi (6.8 atm) was reached. For a typical ‘8Fproduction run, the target gas mixture was irradiated for 10 minutes at 69 1A. Whenthe irradiation of the target gas was stopped, this time was noted and designated as theend of bombardment (EOB). After irradiation, the radioactive gas mixture was passedthrough a solidCH3OOK/CHOH column and into the reaction vessel at a flowrate of —50 mL/min. With the addition ofCH3OO18Fcompleted, the reaction mixture153was transferred to a round-bottom flask, then assayed for radioactivity. TheCH3OOK/CH3OOH column was also assayed for activity. The reaction mixture was evaporatedto dryness in vacuo and reassayed for activity, then dissolved in a small amount ofCHC13. An aliquot of this mixture was subjected to radio-HPLC purification and thepeak corresponding to the18F-labelled product was collected, then counted to determinethe percentage of product present in the reaction mixture. The decay correctedradiochemical yield was calculated by dividing the total activity due to product (in thereaction mixture) with the total activity of 18F produced in the cyclotron target at EOB.Reaction of 31 with CH3OO18Fat room temperature.Compound 31 (72.1 mg, 120 mol) was radiofluorinated using approximately 0.74equivalents ofCH3OO’8F(produced with 6 psi of 1%F2/Ne), at room temperature, asdescribed in the general procedure. HPLC analysis (column C; solvent program A; flowrate, 6.0 mL/min; UV detection, 254 mn) of the reaction mixture determined that 3.68mCi (decay corrected to EOB) of 3-methoxy-l7cy-(E)-[’8F]fluorovinyl-1,3,5( 10)-estra-triene- 173-o1 51 and 3-methoxy-17a-(Z)-[’8Fjfluorovinyl-1,3,5 ( 10)-estratriene- 17i3-ol 52(both co-elute, RT=5.5 mm) was produced for a radiochemical yield of 19%.An additional radiofluorination trial was conducted using a greater excess of vinyl-tin31. Compound 31 (71.0 mg, 118 1Lmol) was radiofluorinated using approximately 0.5equivalents of CH3OO’8F(produced with 4 psi of 1%F2/Ne), at room temperature,as described in the general procedure. HPLC analysis (column C; solvent program B;flow rate, 6.0 mL/min; UV detection, 254 mu) of the reaction mixture determined that1543.79 mCi (decay corrected to EOB) of 51 and 52 (both co-elute, RT 11.0 mm) wasproduced for a radiochemical yield of 19%.Reaction of 31 with CH3OO18Fat -78°C.Compound 31 (69.0 mg, 115 1mol) was radiofluorinated using approximately 0.77equivalents of CH3OO’8F(produced with 6 psi of 1%F2/Ne), at -78°C, as describedin the general procedure. HPLC analysis (column C; solvent program A; flow rate, 6.0mL/min; UV detection, 254 am) of the reaction mixture determined that 1.72 mCi(decay corrected to EOB) of 51 and 52 (both co-elute, RT=S.4 mm) was produced fora radiochemical yield of 9.7%.An additional radiofluorination trial was conducted using a greater excess of vinyl-tin31. Compound 31 (71.7 mg, 119 mo1) was radiofluorinated using approximately 0.5equivalents of CH3OO18F(produced with 4 psi of 1%F2/Ne), at -78°C, as describedin the general procedure. HPLC analysis (column C; solvent program B; flow rate, 6.0mL/min; UV detection, 254 nm) of the reaction mixture determined that 1.65 mCi(decay corrected to EOB) of 51 and 52 (both co-elute, RT = 10.7 mm) was produced fora radiochemical yield of 5.0%.155References1. Gordon, A. 3.; Ford, R. A. The Chemist’s Companion: A Handbook ofPractical Data,Techniques and References; Wiley Interscience: New York, 1972; p 439.2. Still, W. C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923-2925.3. Shriver, D. F.; Drezdzon, M. A. The Manipulation ofAir-sensitive Compounds, 2nded.; Wiley Interscience: Toronto, 1986.4. Adam, M. J.; Grierson, J. R.; Ruth, T. J.; Pedersen, K.; Pate, P. D. J. Nuci. Med.1987, 28, 1599-1603.5. Bunnet, J. F.; Hermann, H. J. Org. Chem. 1971, 36, 408 1-4088.6. Mahaffy, C. A. L.; Pauson, P. L. Inorg. Synth. 1979, 19, 154-158.7. Ofele, K. Chem. Ber. 1966, 99, 1732-1736.8. Mahaffy, C. A. L. .1. Organomet. Chem. 1984, 262, 33-37.9. Johnstone, R. A. W.; Rose, M. E. Tetrahedron 1979, 35, 2169-2173.10. Arrick, R. B.; Baker, D. C.; Horton, D. Carbohydr. Res. 1973, 26, 441-447.11. Garegg, P. J.; Samuelsson, B. Carbohydr. Res. 1978, 67, 267-270.12. Hems, R.; Horton, D.; Nakadate, M. Carbohydr. Res. 1972, 25, 205-216.13. Hudlick, M. Chemistiy of Organic Fluorine Compounds: A Laboratoiy Manual withComprehensive Literature Coverage, 2nd ed.; John Wiley and Sons: New York, 1976;pp 13-14.14. Matheson Gas Data Book, 5th ed.; Matheson Gas Prducts: East Rutherford, NJ,1971; pp 261-265.15. Ruth, T. J. mt. .1. Appl. Radiat. Isot. 1985, 36, 107-110.16. Ruth, T. J.; Adam, M. J.; Burgenjon, J. J.; Lenz, J.; Pate, B. D. mt. J. AppL Radiat.Isot. 1985, 36, 93 1-933.17. Jewett, D. M.; Potocki, J. F.; Ehrenkaufer, R. E. J. Fluorine Chem. 1984,24, 477-484.18. Skoog, D. A.; West, D. M. Fundamentals of Analytical Chemistiy; Holt, Rhinehartand Winston: New York, 1965; pp 462 and 485-490.15619. Casella, V.; Ido, T.; Wolf, A. P.; Fowler, J. S.; MacGregor, R. R.; Ruth, T. 3. .1. Nuci.Med. 1980, 21, 750-757.157

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