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

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RADIOLABELLING OF ORGANICMOLECULES 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 PARTIALFULFILLMENT 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 thisthesis in partial fulfillmentof the requirementsfor an advanced degreeat the University of BritishColumbia, I agree thatthe Library shall makeit freelyavailable for reference andstudy. I further agree thatpermission for extensive copyingof this thesis for scholarlypurposes may be grantedby the head of my departmentor byhis or her representatives.It is understood thatcopying or publication of thisthesis forfinancial gain shallnot be allowed withoutmy written permission.Department of ChemistryThe University ofBritish Columbia2036 Main MallVancouver, CanadaDate:b. 30) jqAbstractThe primary aim of this studywas to develop new methodsfor the introduction of short-lived radionudides(11C, 18F) into organic molecules.This was accomplishedby the useof organometallic intermediates:(i)(i16-arene)tricarbonylchromiumcomplexes were usedto facilitate aromatic nucleophilicsubstitution of the attached arenefor theincorporation of[11Cjcyanideanion, and (ii) vinyl-tinderivatives were employedforelectrophilic fluorinationreactions to produceF- and 18F-labelled vinyl fluorides.A range of simple(,6-arene)tricarbonylchroniiumcomplexes were preparedas modelsystems. Fluorine wasfound to be the only leavinggroup that was readily displacedbycyanide. Non-radioactiveand 11C-labelled aryl nitrileswere prepared in 10 minutesbyreaction of complexes1, 4, 5, and 6 with[12Cjcyanideand[11C]cyanide in DMSOatelevated temperature.Under the reaction conditionsused, the aryl nitrile productwasliberated from thechromium tricarbonylmoiety thereby obviatingthe need for aseparate oxidativedecomplexation step.The reactivity of (E)-vinylstannanes30, 31, 32, 33, and 34was studied with elementalfluorine and acetyl hypofluoriteunder varied conditions.Generally, gaseous CH3COOFwas found tobe the most effective fluorinatingagent for the electrophiliccleavage ofvinyl-tin bonds. Forexample, 31 was fluorinatedwith CH3COOF,at room temperature,to yield an isomericmixture of 39 and40 in 41-42% yield;fluorination with F2proceeded in9.0% yield at best. Subsequently,31 was radiofluorinatedwithCH3COO’8Fin 19% radiochemicalyield (basedon starting[18F]F2).11MeMe CIIICr(CO)3 Cr(CO)3Cr(CO)3 Cr(CO)345 6Sn(Bu)3HOR20O/0—Sn(Bu)3//\c)OR’O33Sn(Bu)330 R’=R2=H31 RMe,R=HOH32R’R2MeoO0\\34HOHOMeO MeO3940iiiTable of ContentsAbstractiiList of TablesviiList of FiguresixAcknowledgementsxDedicationxiChapter1 GENERAL INThODUCTION11.1 Background11.2 Aspects of Labelling with Short-livedIsotopes 31.3 Objectives and Format of this Thesis9References132 APPLICATION OF ORGANOCHROMIUMCHEMISTRYTO RADIOLABELLING162.1 Introduction162.2 Preparation of(76-Arene)tricarbonylchromiumComplexes 212.2.1 Synthesis212.2.2 Characterization302.3 Reactions ofOrganochromium Compounds with Cyanide332.4 LabellingStudies with11C-Labelled Cyanide532.5 Summary andConclusions65References68ivChapter3 DEVELOPMENT OF METHODSFOR RAPID FLUORINELABELLING713.1 Introduction713.2 Synthesis of Vinyl-TinPrecursors803.3 Labelling Studies with Non-RadioactiveFluorine853.4 Radiofluorination Work963.5 Summary and Conclusions101References1044 GENERAL CONCLUSIONS108References1115 EXPERIMENTAL1125.1 General Methods1125.2 NMR Methods andInstrumentation1155.3 Experimental for Chapter21165.3.1 Sources of Materials1165.3.2 General1165.3.3 Preparation of(t6-Arene)tricarbonylchromiumComplexes1185.3.4 Substitution Reactionsof OrganochromiumComplexes1255.3.5 Labelling Workwith[11C]Cyanide1355.4 Experimentalfor Chapter 31395.4.1 Sources of Materials139VChapter5.4.2 General1405.4.3 Preparation of Vinyl-Tin Substrates 1425.4.4 Fluorination Reactions of Vinyl-Tin Compounds 1485.4.5 Radiofluorinations with Acetyl[‘8F]Hypofluorite153References156viList of TablesTableCHAPTER 11.1 Characteristics of RadionuclidesUsed for PET 41.2 Physical Properties of Some Radionucides71.3 Positron Emitting RadiopharmaceuticalsUsed Commonlyin PET Imaging Procedures9CHAPTER 22.1 Summary of Yields Obtained forComplexes Synthesizedusing Equation 2.9262.2 Summary of Melting Points ofOrganochromium Complexes 312.3 Chemical Yields Obtained forComplex 1 392.4 Chemical Yields Obtained forComplex 4 412.5 Chemical Yields Obtained forComplex 5 422.6 Chemical Yields Obtainedfor Complex 6 432.7 Chemical Yields Obtained for Complex 4 using18-Crown-6 472.8 Chemical Yields Obtained forEquation 2.18 usingAcetonitrile as the Solvent482.9 Summary of ChemicalYields512.10 Summary of RadiochemicalYields Obtained forEquation 2.22552.11 Summary of RadiochemicalYields Obtained forEquation 2.23. 59vi’TableCHAPTER 33.1 Yields of (E)-Vinylstannanes.833.2 Summary of Yields Obtainedfor the Reaction of 31with Acetyl Hypofluorite873.3 Summary of Yields Obtained forthe Reaction of 31with Fluorine893.4 Summary of RadiochemicalYields Obtained for the Reactionof 31 with Acetyl[18F]Hypofluorite100viiiList of FiguresFigureCHAPtER 22.1 Changes in arene reactivity whencomplexed to chromiumtricarbonyl172.2 Examples of carbanions which reactwith(i6-ha1obenzene)tricarbonyl-chromium complexes182.3 Examples of carbanionswhich react with(6-benzene)tricarbonyl-chromium192.4 Principal fragmentation pattern of(6-arene)tricarbonyl-chromium compounds322.5 HPLC chromatogramobtained from the analysis of the reactionofcomplex 1 with cyanide at 135°C402.6 Radio-HPLC chromatogram obtainedfrom the analysis of the reactionof complex 1 with[11C]cyanide (with0.37 equiv of carrier KCNadded) at 150°C572.7 Radio-HPLC chromatogram obtainedfrom the analysis of the reactionof complex 1 with[11Cjcyanide(with no carrier KCN added)at 150°C582.8 Radio-HPLC chromatogramsof[‘tC]cyanide in DMSO61CHAPTER 55.1 Schematic of the fluorinegas handling system used to performthefluorination reactions141xAcknowledgementsI thank mysupervisors, Dr. LaurieHall and Dr. MikeAdam, for their invaluableguidance and helpfuldiscussions. In particular,I am very gratefulto Dr. Mike Adamfor his invaluableassistance in all aspectsof the experimental developmentof this work,and for his helpfuladvice in thepreparation of this thesis.I extend my thanksto Dr. Peter Legzdinsand his researchgroup for valuablediscussions and includingme in their literaturemeetings.I am grateful to Dr.Tom Ruth and Dr. MikeAdam for the productionof radionuclides (11C, 18F)used in this work.I am also thankfulfor the technicalassistance ofSalma Jivan at TRIUMF.I gratefully acknowledgethe contributionmade by the Co-opstudents, MauriceBrulé,Dale Johnson, andMartin Dimitroff,with whom I hadthe pleasure of working.I greatly appreciatethe service providedby the Electronicsand Mechanical shopsformaintenance ofthe NMR instrumentation,and in particular,Tom Markus, whoalsoconstructed theNMR probe.I also extend my thanksto the technical staffsof thedepartmental NMR,Mass Spectrometry,and Microanalyticalservices.I thank my friends,Dr. Jeff Coil andDr. Sigrid Coil, forproofreading thisthesis.Finally, I especiallythank my supervisors,friends, and familyfor their incrediblepatience, support,and encouragementthrough very difficulttimes in which it seemedthisthesis wouldnot be completed.xDedicationTo my risen LordxiChapter 1GENERAL INTRODUCTION1.1 BackgroundOrganic moleculeslabelled with short-livedpositron emitting nuclideshave had a greatimpact on biomedicalresearch.’ Thus,for the first time,using positron emittingradiopharmaceuticals,quantitative in vivomeasurements havebeen made of the humanbiochemical andphysiological processesof the brain, heart, andother organs.2 Forexample, it hasbeen shown that regionalbrain metabolismcan be correlated withfunctional activity inhumans under normalcircumstances,3duringsomatosensorystimulation,4andalso in disease statessuch as schizophrenia5and senile dementia.6Other parametersof physiological functionhave also been measuredwhich include bloodvolume, blood flow,oxygen- and glucose-metabolicrates, drug-receptorinteractions,protein synthesis, aminoacid transport, permeabilityof the blood-brainbarrier, andtissue pH. Thesestudies are intendedto give a better understandingof disease statessuch as cancer, epilepsy,heart disease, stroke,movement disorderssuch as Parkinson’sdisease, and mentalillness.7’8The in vivomeasurement of biochemicaland physiologicalprocesses, usingcompounds labelledwith short-livedpositron emittingnuclides, is based onthe use ofPositron EmissionTomography(PET). In thistechnique, a positronemitting1radiopharmaceutical, withthe desired biological activity,is administered to a livingsubject. Inside the body, the radiotracerdecays by emitting a positron(j3, positiveelectron), which travels a few millimetres,combines with an electron, its antimattertwin,and is thereby annihilatedto produce two gamma-ray photons eachof 511 keV. The twogamma-rays travel in opposite directions,nearly1800apart, penetrating the surroundingtissue and are detectedby a circular array of coincidencedetectors surrounding thesubject being imaged. Only timedcoincidence annihilation eventsregistered by paireddetectors located 180° apart arerecorded. From these, the spatialdistribution of theradiotracer is reconstructedby computer, and is presented asa series of cross-sectionalimages.7’9The successful application ofPET as a medical research toolderives from the factthat PET allows the studyof physiological and biochemicalprocesses to be done in aquantitative, non-invasive manner,within a volume element of tissuein vivo. From thetechnical viewpoint, a key ingredientof this process is the positronemitting radio-pharmaceutical itself.1° One ofthe cornerstones of modern medicineis the understanding that all clinical symptomsresult from biochemical reactions,and as a consequence,every pathology hasan underlying biochemical defect.7Thus, the radiopharmaceuticalacts as a biochemical probeand, by virtue of the attachedpositron emitting nuclide,thefate of the radiopharmaceuticalcan be spatially mappedusing PET. As a result, therange of studies thatcan be performed using PETdepends on the availabilityof compounds appropriateto the study, which canbe labelled with positron emittingnuclides.8’1°To date, PET hasbeen most extensively appliedto problems in neurology,cardiology,2and oncology. Asa result of the successesobtained in thesestudies, substantial effortsare being made to expandPET into new areas of research.11”2Therefore, to exploitthe full potential of PET,continued developmentof new and improved methodsofradiopharmaceutical synthesisare required.12 Aspects of Labeffingwith Short-livedIsotopesThe goals of radiopharmaceuticalsynthesis have manyelements in common withtraditional synthetic organicchemistry. Both theradiochemist and organicchemist areconcerned with developingsyntheses which will yieldin the most direct manner,thedesired compound inthe largest chemical yieldpossible. In addition, theradiochemistis concerned with obtaininghigh radiochemicalyields. Radiochemical yieldis definedas the amount of radioactivityincorporated into the productas a percentage of the initialquantity of radioactivityused, Both the radiochemistand organic chemist requirethefinal compound tobe isolated in a chemicallypure state. However, radiolabelledcompounds must also be radiochemicallypure and free of otherradionuclidic impurities.’3Furthermore, organiccompounds produced as pharmaceuticalsand formulated for intravenous injection, whetherradiolabelled or not, mustalso be sterile and pyrogenfree.’4In order to ensurea successful radiopharmaceuticalsynthesis, severaladditionalconsiderations holdwhich are not commonto synthetic organic chemistry.The keyaspects that needto be addressedby the radiochemist areas follows: (i) the physicalproperties of theradionucide, (ii) thesource and chemical formof the radionuclide, and(iii) the specificactivity, stoichiometry,and reaction scale.These topics willnow be3discussed in the above order.The most important radionuclidesused in PET are ‘1C, 13N,150,and 18F; their half-lives are listed in Table 1.1.All of these positron emittingnucides possess short half-Table 1.1: Characteristics of RadionuclidesUsed for PETRadionuclide Half-life%i3DecayaDaughter(mm)11C 20.499.8 B, stable‘3N 9.96100 13C, stable1502.07 99.915N, stable‘8F 109.796.9180,stableSOURcE: Reference 15.a13+=positron emission.lives*,16and emit high energy, body-penetratingradiation. These characteristicsareimportant properties whichmake these radionudidessuitable for medical use. However,these same propertiesalso give rise to problems for radiolabellingdevelopment. Mostsignificantly, the half-lifeof the nuclide poses a limiton the time allowable for synthesis.The total synthesis time,beginning with the generationof the radionuclide anditsincorporation into thesubstrate, followed by any furtherchemical modifications (i.e.,removal of protectinggroups, etc.) throughto the final purificationof theradiopharmaceutical, shouldbe equivalent to no more thanone or two half-lives oftheradioisotope.17’18 Clearly,the associated manipulativeproblems become particularlyacute when using nudideswhose half-lives are onthe order of minutes.The actual*A radionucide is usuallydefined as short-livedwhen its half-life is less than15 h.4imaging of the patient mustin turn be completed withinabout three or four half-livesof the radionucideused.19Another problem inherentin working with positronemitting nudides is theobviousradiation hazard theypose, which unfortunately,exposes the radiochemistto apotentially serious healthrisk. Hence, for prudentsafety reasons, it is necessaryto workwith adequate levelsof shielding, use remoteoperations whenever possible,properlymonitor the radiation levelin the work area, andto work with care while handlingradioactive compounds.2°The source andchemical form in whicha given radioisotope is availablehas asignificant impacton the development ofa practical synthetic strategy.The first problemis the availability of the requiredpositron emitting nuclide.In general, positron emittingnucides are producedby nuclear reactions performedwith a charged particleaccelerator, generallya cyclotron.21 Somepositron emitters are availablefrom anuclide generator system,such as the68Ge/Ga(half-lifeof 68Ga is 68.1 mm) generator.Although such generatorsare very convenientas they allow shipment of radionuclidesfor long distances fromthe production site, unfortunately,few such generator systemsexist for positronemitting isotopes.22Therefore, it is generallymandatory thataccelerator producednuclides be made onsite, or within relativelyshort travellingdistance (i.e., time)from the radiolabellingfacilities.The chemical formof a given radionuclideis the second problemthat has to beconsidered. Radioisotopes,as obtained froma cyclotron or generator,are usuallyavailable in a limitedrange of chemical forms.Although thepreparation of a5radioisotope is dependanton the nuclear reactionused, target design, andcyclotroncharacteristics, the chemical formof the radioisotope isdetermined by a numberoffactors—the most crucialfactor is the chemical compositionof the target and the energydeposition in the target;17this area of study is referredto as target chemistry. Therefore,if the reagent form ofthe radionuclide is inappropriatefor a given radiolabellingprocedure, then additionalchemical manipulationsare required to obtainthe desiredform of reagent. Sincethis increases thesynthesis time and addscomplexity to theexperimental procedure,the best approach, wheneverpossible, is to directly preparetheradioisotope in the specificchemical form requiredfor the radiolabellingstep.The last topic ofthis section is the issue ofspecific activity, stoichiometry,and reactionscale; these threesubjects are closely related. Specificactivity is definedas the quantityof radioactivity present, generallyexpressed in curies, permole of compound. Onecurieof activity produces3.70 x1010Bq (disintegrations persecond); the maximumspecificactivity of a radionuclidedepends on its half-life(see Table 1.2), and is onlyattainablewhen no other isotopeof the same element(i.e., carrier) is present;this ideal state isreferred to as the carrier-free(CF) state. For someradioisotopes, this CF statecan beapproached only to withinan order of magnitudeso that some carrier isunavoidablypresent in mostcases. For example, it isreported that in the productionofH11CN, theratio of 11Cto ‘2C is approximately1:3000? In light ofthis problem, additionalterminology is neededfor specifyingthe extent ofdilution present inaradiopharmaceuticalproduct. The nocarrier-added (NCA)state, as appliedto anelement or compound,means that nocarrier of the sameelement or compoundhas6Table 1.2: PhysicalProperties of Some RadionuclidesNucide Half-lifeDecay Maximum Range”MaximumModeaenergy (mm) specific(MeV) activity(Ci/mol)11C 20.4 mliii3(99+%)0.96 4.108 9.22 xiO150207 mm 3(999%) 172 82908 x 10”‘3N 9.96 mmI3(100%) 1.19 5.39 1.89 x1010‘8F 109.7 nuni3(97%)0.635 2.39 1.71x iO3H 12.35y f(l00%) 0.0186 0.00722.90 x 10‘4C 5730yi31100%) 0.155 0.359 62.4SouRcE: Reference 25.aDecaymodes:r=positron emission,3 = beta particle emission.“Maximum linear range in water.been added during itspreparation. The carrier-added (CA)state means a known amountof carrier has beenadded to the element or compoundduring its preparation.’7Especially when dealingwith short-lived radiopharmaceuticalsnear their maximumspecific activity, themass of the product is not detectableby ordinary chemical orspectroscopic means. Toifiustrate this point, considerthe mass of 1 mCi of11C ascompared to ‘4C, whichis 1.5 pg (6.53 x1010atoms) as opposed to 0.22 mg(9.59 x 10’satoms) of 14C.26 Therefore,the production of highspecific activity radiopharmaceuticalsin the CF orNCA states is highly desirablebecause the mass of the radiopharmaceuticals is then so smallthat when administered invivo it is usually below thethresholdwhere any physiologicalresponse is invoked, yet thereis adequate radioactivitypresent(in the orderof 0.1 to 0.5 Ci/g oftissue in the case of PETinstruments) to be detected7with statisticalsignificance?4Thus, even highlytoxic molecules can be used forstudiesif adequate specific activitiescan be achieved.’7Working with small amountsof high specific activity radionuclidesusually leads toproblems regarding stoichiometryand reaction scale. When alabelling reaction isperformed, in which bothlabelling reagent and substrateare used in approximately oneto one ratio, everythingmay work well. However,when the concentration of thelabelling reagent is reducedby several orders of magnitude,as during a high specificactivity radiosynthesis, very differentresults may be observed. Since NCAradiosynthesesare performed on a verysmall scale, the amount of impuritiespresent in the reagentsand solvents may be comparableto, or even exceed, the quantityof the radionuclideused in the synthesis.These impurities may competewith the radiolabelling reagentina given reaction,leading either to unwantedside-products, or evento completeprevention of the formationof the desired radiolabelledproduct.27 If one of theimpurities present in thesynthesis is carrier, this will lowerthe specific activity of theradiolabelled product.This can be a very serious problemwhen very high specificactivities are required, andas a result great care must be takento exclude carrier fromall possible sources, suchas solvents, reagents, and substrates.28In spite of the variousdifficulties and challenges involvedin the area ofradiopharmaceuticalsynthesis, much progress hasactually been made. A varietyofpositron emittingradiopharmaceuticals havebeen developed and are currentlybeingused in PET imaging,and some of the commonlyused radiopharmaceuticals forPET8Table 1.3: Positron EmittingRadiopharmaceuticalsUsedCommonly in PET ImagingProceduresRadiopharmaceuticalApplication[18F]fluorodeoxyglucoseCerebral glucose metabolismMyocardial glucose metabolism[18F]fluorodopaDopa uptake studies18F]spiperoneDopamine receptor binding[18F]-N-methylspiperoneDopamine receptor binding[18F]-16a-fluoro-17fl-estradiolEstrogen receptor binding[‘1C]carbon dioxideTissue pH[11C]-1-butanolCerebral blood flow11C]methionineAmino acid metabolism[11CjpalmitateMyocardial metabolism[11C]acetateMyocardial metabolism[11C]glucoseCerebral glucose metabolism11C]-N-methylspiperoneDopamine receptor binding[1501oxygenCerebral oxygen extractionand metabolism[15ojcarbon monoxideCerebral blood volumeMyocardial bloodvolume[150]waterCerebral blood flowMyocarclial blood flow[13Nlammonia Myocardial bloodflowSouRcEs: References7,8,10,29.are summarizedin Table Objectives andFormat of thisThesisWith the continuingdevelopment of PET,new and innovativesynthetic methodologies9are needed to produce therequired radiopharmaceuticalsfor future PET applications.The primary objective ofthis study was the explorationof new methods for theincorporation of positron emittingradionucides—specffically11C and‘8F—into organiccompounds.Increasingly, the use of organometa.llicintermediates are providingnew avenues torapidly label organic molecules.The organic derivatives ofsome main group metals(B,3° Si,31’32 Ge,33Sn,34’35 Hg,36 TI,37) havebeen studied and utilizedforradiolabelling. Generally,their prime application has beento prepare compounds thatare radiolabelled on the aromaticring. Boron3°and silicon32derivatives have also beensuccessfully used for the preparationof radiolabelled alkyl halides.The common featureof these reactions is the exploitationof the reactivity of the polarizedcarbon-metal bond,in which the metal possessesa partial positive charge and the attachedcarbon possessesa partial negative charge;as a result, an organometallic compoundis susceptible toelectrophilic attack.This is important becausethe electrophilic cleavageoforganometallic precursors canpotentially be performed undermild conditions with shortreaction times. Therefore,radionuclides that can be preparedin electrophilic reagentform, can in turnbe used for the radiolabellingof organometallic precursors,in aregioselective manner.Previous studies in thislaboratory focussed on thedevelopment of labellingvinyl-tinderivatives with radioactivebromine(82Br) and iodine(1231and1311).38The use of vinyl-tin reagentswas found to be very successful.This experience promptedour interest inextending the utility ofvinyl-tin reagentsto radiofluorinations with 18F.10The organic derivativesof transition metals,however, exhibit very differentpatternsof reactivity as comparedto those of the main groupmetals.39 The fundamentalreasonfor this is the presenceof partly filled d orforbitals. This leadsto a variety of bondinginteractions with organicligands.4° Transition metalsare able to form complexes inwhich the metal isbonded to unsaturated organicmolecules such asethylene,cyclobutadiene, or beuzene.The normal pattern ofreactivity of unsaturated organicmolecules when coordinatedto transition metals is changed,whereby the unsaturatedmoieties can be attackedby a wide range of nucleophiles.The more electron-withdrawing the metalcentre, the more facile isthe nucleophific addition.4’Thismodeof reactivity could havesignificant potential for theapplication of radiolabelling.It wasdecided to explorethe labelling of aromatic ringswith ‘1C using(i16-arene)tricarbonyl-chromium complexesas synthetic intermediates.The format of this thesis isas follows. Chapter 2 is devotedto the evaluation ofarene)tricarbonylchromiumcompounds as synthetic intermediatesfor the incorporationof‘1C, in the formof [“C]cyanide, ontoaromatic rings. At the beginningof the chapter,some introductory backgroundinformation is presentedregarding organochromiumchemistry. Then, thepreparation of(6-arene)tricarbonylchromiumcomplexes used forthis study will be described.This will be followedby an examination of thereactivityof the prepared chromiumtricarbonyl complexes withnon-radioactive cyanide. Lastly,radiolabelling studieswith “C-labelled cyanidewill be presented.Chapter 3 is devotedto the development of electrophilicfluorination methodologythatis applicable to vinyl-tincompounds with bothnon-radioactive fluorineand radiofluorine.11The chapter begins withan introduction to selectivefluorination of organic molecules.This will be followedby a presentation of thesynthesis of the vinyl-tinderivativesemployed forthis present study. Next,fluorination studies ofthe vinyl-tin precursorswith elemental fluorineand acetyl hypofluoritewill be described. Finally,radio-fluorination with 8Fof a selected vinyl-tin derivativewill be presented.In Chapter 4, the generalconclusions developedfrom the studies describedinChapters 2 and3 will be presented, along withsuggestions for future work.In Chapter 5, the experimentaldetails are given forthe work performed forthis thesis.The general methodsare described first,followed by thespecific experimentaldescriptions for Chapters2 and 3, respectively.12References1. Positron EmissionTomography;Reivich, M., Alavi,A., Eds.; Alan R. Liss:New York,1985; Positron EmissionTomographyandAutoradiography: PrinciplesandApplicationsfor the Brainand 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. 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News 1981, 59(45),30-37.9. Links, J. M.In NuclearImaging in Drug Discoveiy,Development, andApproval;Burns, H. D.,Gibson, R. E., Dannals,R. F., Siegl, P. K.S., Eds.; Birkhäuser:Boston,1993;pp22-23.10. 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 Textof Radiophannacy: Theoiyand Practice; Sampson,C. B., Ed.;Gordon andBreach Science:New York, 1990;Chapter 16.1313. Theobald, A. E.In Textbook of Radiopharmacy.Theory and Practice; Sampson,C.B., Ed.; Gordon andBreach 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 PublishingUSA: 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;p65.16. Vaalburg,W.; Paans, A. M. J. In RadionuclidesProduction; Helus, F., Ed.;CRC:Boca Raton, 1983; Vol.2,p48.17, Fowler, J.S.; Wolf, A. P. The Synthesisof Carbon-il, Fluorine-i8,and Nitrogen-13Labeled RadiotracersforBiomedicalApplications;Nuclear Science Series,MonographNAS-NS-3201; TechnicalInformation Center,U.S. Department of Energy:Springfield, VA, 1982.18. See reference16; Vol. 2, Chapter 2.19. Adam, M. J., TRIUMF,Vancouver, BC, personalcommunication.20. Hesslewood, S.R. In Textbook of Radiophannacy.Theory and Practice; Sampson,C.B., Ed.; Gordonand Breach Science: New York,1990; Chapter 6.21. Wolf, A. P.; Schlyer,D. J. In Nuclear Imagingin 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 EmissionTomography; Reivich, M.,Alavi, A., Eds.;Alan R. Liss: NewYork, 1985; Chapter 4.23. Short, M. D. InTextbook of Radiopharmacy:Theory and Practice; Sampson,C. B.,Ed.; Gordon and BreachScience: New York,1990;p19.24. See reference17;pp28-29.25. Fowler,J. S.; Wolf, A. P. InPositron Emission Tomographyand Autoradiography:Principles and Applicationsfor the Brain and Heart;Phelps, M. E., Mazziotta,3. C.,Schelbert, H. R., Eds.;Raven: New York,1986;p393.26. See reference 17;p39.27. See reference17;pp29-30.1428. Wilbur, D.S.; Garcia, S. R.;Adam, M. J.;Ruth, T. J. J. LabelledCompd.Radiopharm. 1984,21, 767-779.29. Radiophannaceuticalsfor Positron EmissionTomography: MethodologicalAspects;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. LabelledCompd. Radiopharm.1983, 20, 619-626.33. Moerlein,S. M.; Coenen, H. H.J. Labelled Compd. Radiophann1984, 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. RadioanaLChem. 1981, 65, 107-113.38. Balatoni, J. A.M.Sc. Thesis, TheUniversity of BritishColumbia, Dec. 1985.39. Coates, 0.E.; Green, M. L.H.; Powell, P.; Wade,K. Principles of OiganometallicChemistiy; Chapmanand Hall: London,1979.40. Coliman, J. P.;Hegedus, L. S. Principlesand Applicationsof Organotransition MetalChemistiy; UniversityScience Books: MillValley, CA, 1980.41. Davies, S.0. OrganotransitionMetal Chemistiy: Applicationsto Organic Synthesis;Perganion: Toronto,1982; Chapter 4.15Chapter 2APPLICATION OF ORGANOCHROMRJMCHEMISTRY TORAIMOLABELLING2.1 IntroductionThe first(76-arene)tri.carbonylchromiumcomplex was reportedin 1957, by Fischer andOfele.1 Since that time, literallyhundreds of such complexeshave been prepared,characterized, and studiedwith respect to the structure andreactivity of the arene ringwhile complexed to themetal centre.2’3(,6-Arene)tricarbonylchromiumcompounds areair-stable, diamagnetic, crystallinesolids, generally yellow to orangein colour. They aresoluble in a variety of solvents,readily characterized byspectroscopic methods, and areeasily purified by chromatographicand recrystallization techniques.As a result of thew-coordination of an arene to chromium,its reactivity is significantly altered.4Thesechanges in arene reactivityare summarized in Figure 2.1.The most significantchange in arene reactivity is theincreased ability of thecoordinated areneto undergo nucleophilic aromaticsubstitution. It is thisreactionwhich has beenmost studied and extensively employedin synthetic chemistry.5 Toalesser degree, thesteric effect of the attachedchromium tricarbonyl moietyhas beenused for thestereoselective modificationsof the aromatic side chain.6The otherchanges in arene reactivityhave received less attentionregarding their potentialuse for16Enhanced NucleophilicEnhancedSubstitution/1SolvolysisEnhanced AcidityHC—C—StericHEnhancedHinderancecoAcidityFigure 2.1: Changesin arene reactivity whencomplexed to chromiumtricarbonyl. (Adapted fromreference 7.)synthesis.8’9During early studiesof the reactivity of(,76-arene)tricarbonylchromiumcompounds,Nicholls and Whitingfound that(i-chlorobenzene)tricarbonylchromiumreadilyunderwent substitutionof chlorine by methoxidein very high yield.1° UncomplexedMeOHK—OMeI + NaOMeI + NaC1 (2.1)Cr(CO)3 65°CCr(CO)3chlorobenzene isunreactive towardmethoxide under thesame conditions.Laterinvestigations haveshown other nucleophilesto react similarly, suchas sodiumphenoxide, aniline,11and 2-methyl-2-propanethiol.’2(,76-Fluorobenzene)tricarbonyl-chromium alsoexhibits reactivity towarda variety of nucleophiles.Successful reactionswith alkoxides,amines, thiolates,and cyanide havebeen reported.12”3 Ithas beenshown that fluorineis more readily displacedthan chlorine, duringaromatic nucleophilicsubstitution.4Of greater interestfor organic synthesis,is the reactivity of(6-arene)tricarbony1-17chromium complexes with carbanions.Indeed, a variety of carbanionshave beensuccessfully used to alkylate the chromiumtricarbonyl complexes ofchlorobenzene andfluorobenzene; see Figure 2.2for examples. Nucleophilic substitutionfor hydrogen can_____[01 /\IIRCr(CO)3 25°CCr(C0)3where X = Cl or FR = C(CH3)2CN, t(CH3)2COEt,C(CH3)2C0,tH(CO2Me),902Me.C,Figure 2.2: Examplesof carbanions which reactwith(6-halobenzene)tricarbonyl-chromium complexes.also occur directly on thei6-arene ring, which opensup additional syntheticpathways.(i76-Benzene)tricarbonylchromium,for example, reacts witha number of carbanions asshown in Figure 2.3. Furthermore,if the crude reaction intermediateis treated withexcess strong acid,prior to oxidative demetallation,substituted 1,3-cyclohexadienesareobtained.5Unfortunately, not allsynthetically importantcarbanions work well with(fl6-arene)-tricarbonylchromiumcomplexes. Grignard reagents,organocuprates, and alkylmercuricchlorides fail to reactat low temperatures, whileunidentified decompositionproductsare obtained uponheating. When stronglybasic anions are used, suchas methyl- or18R[01 /\RCr(C0)3 0°C Cr(C0)3where R = t(CH3)2CN, CH2CN,tH2COR, CH(CH3)CO2R, C(CH3)2C0R,SPh CHsCN-dH-sph t—CH3, CHC—-- , -CH3CH3SFigure 2.3: Examples of carbanionswhich 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 providingan additional route for ring modifications.5An important feature of(,76-arene)tricarbonylchromiumchemistry has been thedevelopment of several methods forboth complexing the chromium tricarbonyl grouponto aromatic rings and being able toremove that same group efficiently when desired.A number of approaches have been developedto u--complex an arene with chromiumtricarbonyl. Typically, chromium hexacarbonylis 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. Afterthe desired chemistry has been accomplished,thefinal arene product can be readilyrecovered by mild oxidation. A varietyof reagentshave been successfully usedfor oxidative demetallation; aqueous Ce(IV),iodine, andexposure to sunlight and air,being the most common.5’6”4This is avital consideration,if(6-arene)tricarbonylchromiumcomplexes are to be usefulin synthesis. The19introduction and subsequent removal of activatinggroups in organic chemistry presentsdifficult problems, not easily solved. Classicalaromatic nucleophilic substitution suffersfrom this deficiency, as activating groups likenitro require drastic conditions fornitration, and lack mild and direct methods to remove the riitrogroup once its activatingfunction is completed.’5 As a result, classical aromaticnucleophilic substitution hasfound limited application in complex organic synthesis.(6-Arene)tricarbonylchromiumcomplexes potentially offer a significant improvementas synthetic intermediates sincethe chromium tricarbonyl moiety can be readily attachedin most cases, thendecomplexed in high yield once synthetic operationsare done.The synthesis of radiopharmaceuticals labelledwith short-lived positron emittingnucides requires special synthetic methods,due to the considerations presented earlierin Chapter 1. Prompted by the unique propertiesand reactivity of(76-arene)tricarbonyl-chromium complexes, we decidedto explore the potential utility of these compounds forradiolabelling. There are about five reasonsthat would commend these organochromium compounds for radiolabellingwork.Firstly, most organic pharmaceuticals, either ofpotential interest for labelling or beingcurrently used in nuclear medicinetoday, contain arene rings in their structures.Examples include 6-fluoro-3,4-dihydroxyphenylalanine(6-fluorodopa), the butyrophenone neuroleptics, the estradiolclass of steroids, benzodiazepines, and benzamidessuch as Raclopride (S-(-)-3,5-dichloro-N-[(1-ethyl-2-pyrrolidinyl)]methyl-2-hydroxy-6-methoxybenzamide).’6”7Therefore, thepresence of an aromatic ring provides a possiblelabelling site for attaching theradionuclide of interest. Secondly, medically useful20radioisotopes are generally produced in anionic,nucleophilic form.18 Labellingreactions which can directly use the nucleophilic formof the radionucide areadvantageous, because this eliminates additional chemical manipulationsand time tomodify the reagent form of the radionuclide. Thirdly,(i6-arene)tricarbonylchromiumcomplexes facilitate nucleophffic substitution reactionson the aromatic ring. Thisestablished reactivity could allow the facile incorporationof nucleophilic radioisotopesonto aromatic rings. Fourthly, methods for complexingmost arenes to the chromiumtricarbonyl moiety, then later removing same, havebeen well established. This is incontrast to the use of traditional activating groups for nucleophilicaromatic substitution,such as nitro, which cannot be readily removedunder mild conditions. Finally, the othermodes of reactivity (seepp1-2) exhibited by(,76-arene)tricarbonylchromiumcompounds,adds additional synthetic options when designinga radiopharmaceutical synthesis.In this chapter, the synthesis of a number of(ij6-arene)tricarbonylchromiumcomplexeswill be described. This will be followed by studiesregarding the reactivity of theprepared chromium tricarbonyl compoundswith cyanide. Lastly, the reactions of“C-labelled cyanide with some chromium tricarbonylcompounds will be presented.2.2 Preparation of(q6-Arene)tricarbonylchromiumComplexes2.2.1 SynthesisThe objective for thisstudy was to prepare a rangeof simple (i6-arene)-tricarbonylchromium complexes inorder to study their suitability for radiolabelling.Toaccomplish this, commerciallyavailable arenes were selectedto produce the21corresponding chromium tricarbonyl complexes using literature methods.Five general methods have been developed for thesynthesis of(i76-arene)tricarbonyl-chromium compounds. The first method, as outlined inequation 2.2, is the directArene + Cr(CO)6snt(q6-Arene)Cr(CO)3 + 3 CO (2.2)reaction of arene with Cr(CO)6under thermolysisconditions. 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 carbonyland obtain ‘7r-complexedproduct. The majority of(i76-arene)tricarbonylchromiumcomplexes 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 replacedby more thermally labileligands (L) such as pyridine, 4-methylpyridine, CH3CN,or NH3,as shown in equation 2.3.3 L + Cr(CO)6heatCr(CO)3L + 3 CO (step 1)(2.3)Arene + Cr(CO)3Lheat(q6-Arene)Cr(CO)3+ 3 L (step 2)solventIn the next step, the prepared complex, Cr(CO)3L,is allowed to react with excess arene,using significantly lower temperatures,to obtain the desired product. The milderconditions of this methodologyhas allowed the preparation of chromium tricarbonylcomplexes not obtainableby the first method described above. The third methodis the*Formallynamed bis(2-methoxyethyl) ether.22direct reaction of arene with Cr(CO)6via photolysis. Irradiation of the reactionmixtureat room temperature accomplishes the desireddecarbonylation.(i6-Benzene)tricarbonyl-chromium and other complexes havebeen prepared using equation 2.4. The fourthArene + Cr(CO)6light(?76-Arene)Cr(C0)3+ 3 CO(2.4)solventmethod is arene exchange, whichrelies on the observation that(fl6-arene)-tricarbonylchromium complexes undergoexchange reactions in the presence ofanotherarene at elevated temperatures(ca. 200°C), as outlined in equation 2.5. Theuse ofdonor solvents has allowed theseexchange reactions to be conductedat lower6heat( -AreneA)Cr(CO)3+ AreneB (q -AreneB)Cr(CO)3+ AreneA(2.5)temperatures (ca. 140°C). However, thesynthetic utility of this method has beenlimitedby the high temperatures required,and by the low yields obtained. The finalmethodis the reaction of aikyneswith chromium pentacarbonyl carbenes,as illustrated inequation 2.6. A chromiumtricarbonyl complex is formed from the condensationof an(CO)5CrR2 CR32R2+ CO (2.6)Cr(CO)3Cr(CO)3alkyne with a metal carbene.This novel method requires no arenestarting material.A range of interesting7r-complexed naphthalene and phenanthrene derivativeshave beenprepared by this route.’4’1923Given the various synthetic optionsavailable, it was desirable to choosethe simplest,most direct synthetic procedureto prepare the desired(j6-arene)tricarbonylchromiumcomplexes. The choice was madeto prepare(,7-fluorobenzene)tricarbonylchroniium1by adapting the method of Mahaffy andPauson,2°and to prepare(6-chlorobenzene)-tricarbonylchromium 2 by the methodof Nicholls and Whiting.’°+ Cr(CO)reflux /48 h+ 3 CO (2.7)‘ji 6(n-Bu)2OiTHFCr(CO)31+ Cr(CO)6reflux /17 h+ 3 CO(2.8)diglymeCr(CO)32Although(6-arene)tricarbonylchromiumcompounds are quite air-stable insolid form,their solutions are relatively air-sensitive.All preparations of these complexes,includingworkup and isolation, wereconducted under inert atmosphere.Compound 1 wasprepared in 68% yield accordingto equation 2.7 using an 8:1 mixtureof di-n-butyl etherand tetrahydrofuran (THF).Mahaffy and Pauson reporteda 90% yield for the synthesisof 1 under similar conditions.2°Alternatively, 2 was obtained inan isolated yield of 47%(equation 2.8), basedon the amount of Cr(CO)6consumed.This result is comparableto that of Nicholls and Whitingwho reported a yield of52%, after a reaction time of3h.’°When examiningthese initial experimental results,it became clear that working with24diglyme was less desirable, since it was very difficultto remove during workup. Thebutyl ether/THF mixture was readily removed to dryness,making workup much easier.More importantly, the method of Mahaffy andPauson exhibited a potential forsignificantly better yields of chromium complexedproduct. As a consequence, it wasdecided to use the Mahaffy and Pausonreaction conditions for the preparation of other(6-arene)fficarbonylchromium compounds.A number of chromium tricarbonylcomplexes were successfully synthesized accordingto the general equation 2.9. The resultsobtained are summarized in Table 2.1. Withreflux+Arene + Cr(CO)6(n-Bu)20/THFComplex + 3 COj(2.9)additional work and experience, thepreparative yield of 1 was improved to80% (seeTable 2.1). The reaction(equation 2.9) was found to be very sensitive toany traces ofoxygen present in the reaction mixture.Regardless of how carefully the reactionapparatus, reagents, and solvents werehandled under inert atmosphere, it was vital toemploy freeze-pump-thaw degassingas a final step to ensure an oxygen-free environmentfor the reaction. The majordrawback of the Mahaffy and Pauson procedurewas theslowness of the reaction, thus requiringprolonged heating of the reactants (1-2 days)which can cause somedecomposition of product complex. Unfortunately,thisdecomposition could result in furtherautocatalytic decomposition of anychromiumtricarbonyl product formed.Some investigators have recently reported thatthe primereason for decompositionof(76-arene)tricarbonylchromiumduring the reaction(equation 2.9) was due to thepresence of impurities in the startingmaterials and25Table 2.1: Summary of Yields Obtainedfor Complexes Synthesizedusing Equation 2.9Arene ComplexReactionI YieldTimeC—F‘ 48h80%Cr(CO)31BrCBrI44h 19%Cr(CO)33MeMe,—F48h 89%Cr(CO)34MeMeF16.5h 85%Cr(CO)35ClCVCF23h 12%Cr(CO)36Me0?—/MeON I21h70%e Cr(CO)3726solvents used, and traces of atmospheric oxygenover the reaction mixture.21A common problem with the direct reactionof arenes with Cr(CO)6is the volatilityof Cr(CO)6itself, which results insublimation of the metal carbonyl from the reactionmixture. Anticipating this problem,a special reaction apparatus wasconstructed*thatallowed any sublimed Cr(CO)6to be mechanically returned to thereaction mixture.However, it was found that theuse of di-n-butyl ether with 10-20% of THF present,effectively washed back sublimedCr(CO)6to the reaction mixture. A regularLiebigcondenser could then be usedwith conventional glassware to performthe syntheticreactions (see Experimental fordetails).For our purposes, a paradoxicallimitation of the Mahaffyand Pauson procedure, isthat while electron-donatinggroups on the arene helpsthe reaction, electron-withdrawing groups slowthe reaction.22 It was found that fluorobenzene,2-fluoro-toluene, and 4-fluorotoluenewere successfully complexed, producing1, 4, and 5 in highyield (80-89%). However, thecorresponding complex of 4-chlorofluorobenzene(6) wasmade in only 12% yield. Persistentdecomposition accompanied the preparationof 6,thereby limiting the reflux timepossible—allowing the reaction to proceed longerthanovernight results in progressivedecomposition and in little orno product formed. Inaddition, during the synthesisof 6, a significant amountof 1 was obtained as abyproducttwhich hadto be separated using column chromatography.*Thedesign of this reactionvessel was obtained from Dr. PeterLegzdins of theChemistry Department, U.B.C.,and is described in the Experimental.1This would appearto result from a reductive dehalogenationprocess in which thefluorobenzene complex1 is formed from 4-chlorofluorobemzene,probably via some27In addition to 6, the preparations of(i76-l,4-difluorobenzene)tricarbonylchromium8and(,76-4-fluoroanisole)tricarbonylchromium9 were attempted. In these two cases, onlyvery small quantities (tens of milligrams)were obtained at best. ExtensiveF—’—FMeO—FCr(CO)3 Cr(CO)389decomposition also accompanied thesereactions. As a consequence of thesedisappointing results, othersynthetic approaches were examined that wouldbe moresuitable for complexing arenes withelectron-withdrawing substituents.Limited trials of other syntheticmethods also did not yield satisfactoryresults. Itbecame clear that a sustainedstudy would be required to resolve thisproblem and thiswas beyond the scope of timeavailable for this work. Therefore,the chromiumtricarbonyl complexes that couldbe prepared in adequate quantity were settledupon forthe desired radiolabelling studies.The direct reaction of benzonitrilewith Cr(CO)6does not yield thecorrespondingchromium tricarbonyl complex.’°’However, Mahaffy andPauson were able tosynthesize(6-bemzonitrile)tricarbonylchromium10 indirectly by allowing thefluorobenzene complex 1 to react witha large excess of cyanide overnight inacetonitrileat 50°C. They obtaineda 44% conversion of 10 from starting1. Semmeihack has alsochromium species in solution.Similar results have been reportedby Hudeèek andToma.2128reported, in a 1976 review, the successful reaction of cyanide anion with1 at 25°C,obtaining a 94% yield.5 Unfortunately, the experimental details ofthis work have neverbeen published to the best of this author’s knowledge. We wereable to prepare 10 in69% yield using different conditions, as outlined in equation 2.10.25°C123hI + NaCNI + NaF (2.10)Cr(CO)3 DMSOCr(CO)3110Of additional interest was the desire to prepare chromium tricarbonylcomplexes inwhich the attached arene possessed groups of greater mobilitytoward aromaticnucleophilic substitution than halogen. Promptedby reports of radiolabelling studiesusing aromatics with dimethylsulfonium and trimethylammoniumleaving groups,25’26it was considered whether an analogous chromiumtricarbonyl 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, theyfound that (6-N,N-dimethylaniline)tricarbonylchromium 7 could notbe methylated by trimethyloxoniumtetrafluoroborate.27 In our efforts, wefound that complex 7 can be methylated usingmethyltrifluoromethanesulfonate (commonly calledmethyl triflate) according to equation2.11.(,6-N,N,N-Trimethylanilinium)tricarbonylchromiumtrifluoromethanesulfonate 11was produced in 59% yield. In order to comparethe behaviour of this new complex 11with the corresponding uncomplexedarene, N,N,N-trimethylanilinium trifluoromethane29/Me++ 25°C/48 hCF3S0 (2.11)MelCH3SOCFCH2C1Cr(CO)3JCr(CO)37Lsulfonate 12 and N,N,N-trimethylanilinium iodide 13were also synthesized as shown inequation 2.12. Compound 12 was prepared in83% yield, while 13 was obtained in 56%yield.Me +CH3SOCF/CH2C125°C/30 mm[N_Me CF3SOMe12/Me(2.12)CH3I/CH2C125°C/24 hMe132.2.2 CharacterizationAll of the(j6-arene)tricarbony1chromiumcomplexes, except for 11, are knowncompounds. Their melting points were recordedand are presented in Table 2.2. Thechromium tricarbonyl complexes tendedto decompose to some degree during meltingpoint determinations.The degree of decomposition would vary with the heatingratethereby making the meltingpoints difficult to determine in somecases.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 tricarbonylcomplexes was accomplished by massspectrometry (MS). The principal fragmentation patterns of simple(6-arene)-tricarbonylchromium compounds using electron impact MS have beenwell establishedand are shown in Figure 2.4.°’’ The fragmentationpatterns exhibited by thesynthesized chromium tricarbonyl complexes were consistentwith the scheme depictedin Figure 2.4. Also, Muller and Göser reported thatall(6-halobenzene)tricarbony1-chromium compounds gave the Cr-halogen ionon fragmentation (i.e., [(C6H5X)Crj —*[CrX] + + C6H5 )? This ion was observed foreach of the chromium tricarbonylcomplexes with halogen-substituted aromatic rings.These characteristic features of themass spectra, exhibitedby the chromium tricarbonyl compounds, made productidentification rapid and straight forward.Complex 11 was previously an unknowncompound and was characterized byelemental analysis and 1H NMRspectroscopy. 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 fragmentationpattern of(6-arene)tricarbonylchromiumcompounds.by 1H NMR spectroscopy. MS couldnot be employed for analysis of thesesaltcomplexes (11, 12, 13). Asatisfactory elemental analysis for C,H, N, and S wasobtained for 11. The 1H NMRspectrum of 11 exhibited the aromaticproton resonancesat 5.77 (H-3,5), 6.07 (H-4),6.69 (H-2,6) ppm, and a singlet for thetrimethylammoniumgroup protons at 3.56ppm. The 1H NMR spectraldata for 12 and 13 were foundto be32the same; the aromatic protons were observed at7.58-7.68 (H-3,4,5) and 7.97 (H-2,6)ppm, and the trimethylammoriium group protons at 3.61 ppm. These resultsshowed theexpected upfield shifts in proton resonances due to complexation withchromiumtricarbonyl. This is a characteristic feature of the ‘H NMRspectra 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 reactionswere performedI IICr(CO)3 Cr(CO)3Cr(CO)312 3under an argon or nitrogen atmosphere, usingdried solvents. Complex 1 was allowedto react with excess sodium cyanide (ca. 10 equiv) in DMSOat1500C*for 30 minutes.During heating, the initial yellow colour of the reactionmixture became dark red. Aftercooling, the reaction mixture was diluted withwater, extracted with diethyl ether, thendried. The dried ether extracts were colourless. Theether 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 withabout 2 equivalents of sodium*Reactiontemperatures always refer to the oil bath temperatureused.33cyanide at 155°C in DMSO for 20 minutes.After workup, GC analysis of theetherextracts exhibited two prominent peaks,a major peak due to 14 and a minorpeak dueto fluorobenzene. For comparison,uncomplexed fluorobeuzene was allowedto reactwith sodium cyanide under the sameconditions. GC analysis showed that only unreactedfluorobenzene was present.These initial results clearly demonstratedthat the fluorobenzene complex 1 underwentsuccessful aromatic nucleophilic substitutionwith cyanide and that the reaction was rapidunder the conditions employed.The control experiment with uncomplexedfluorobenzene confirmed that free fluoroberizenefailed to react with cyanide, and thatintactchromium tricarbonyl species underwentthe substitution reaction.The reactivity of the chlorobemzenecomplex 2 was examined next. Complex2 wastreated with sodium cyanide (ca.0.5 equiv) in DMSO at 160°C for 15minutes. Afterworkup, the ether extracts were yellowin colour. GC analysis showed only thepresenceof chlorobenzene. The ether extractswere subsequently treated with iodine todecomplex any intact chromiumtricarbonyl components, and the GC analysis wasrepeated. Chlorobenzene remainedthe only compound detected. For comparison, thereaction of 1 with sodiumcyanide was repeated under the same conditionsas used for2. GC analysis showed twosignificant peaks, one peak due to 14and the other due tofluorobenzene. In like manner,the ether extracts were again treatedwith iodine todecomplex any chromiumtricarbonyl components present. GCanalysis gave the sameresults as observed priorto oxidative decomplexation.Unfortunately, these resultsshowed that 2 is either unreactivetoward cyanide or is34possibly undergoing significant decomplexationunder the reaction conditions used.However, 1 readily underwent substitutionwith cyanide using the analogous conditionsemployed for the reaction trial with 2. Thoughdisappointing, this observation wascomplimentary to previous studies that have shown thatfluorine is more easily displacedduring aromatic nucleophilic substitutionthan chlorine.4 Therefore, these resultssuggested that chlorine is an inappropriate leavinggroup to use in future studies, andwas thus abandoned.Lastly, the potential of bromine asa leaving group was investigated using thebromobenzene complex 3. Complex3 was allowed to react with 0.5 equivalents ofpotassium cyanide in DMSO at 135°C for10 minutes. After cooling, high pressureliquid chromatography (HPLC) was employedto directly examine the reaction mixture.HPLC analysis confirmed the absenceof the desired product 14. In contrast, 1 wastreated with cyanide under identicalconditions, and benzonitrile 14 was produced.HPLC analysis not only confirmedthe presence of 14, but the yieldwas alsodetermined—these results willbe presented and discussed later in this section.These results also indicated that 3 is either unreactivetoward cyanide or is possiblydecomplexing under the reactionconditions employed. Bromine, as a consequence,would also appear to be an unsuitableleaving group for aromatic nucleophilicsubstitution. Therefore, the only usefulhalogen leaving group for reactions with cyanidewas determined tobe fluorine.In order to furthercharacterize the benzonitrile product 14,obtained from thereaction of 1 with cyanide, isolatedproducts from several small scale reactions were35combined. This combined product sample (dissolved indiethyl ether) was subjected toGC analysis, and only one component was observed with almost99% purity. The etherwas evaporated and the product sample was dissolved in deuteratedchloroform forNMR spectroscopy. The room temperature 1H NMRspectrum was recorded at 80MHz.*In addition, the 1H NMR spectrum of authentic 14(commercially obtained) wasrecorded under the same conditions. The spectrumof the product sample exhibited amultiplet centered at 7.57 ppm that was the sameas that observed for authentic 14.Therefore, the 1H NMR spectrum clearly identified the product sample asbenzonitrile14. This is in addition to GC and HPLCstudies which readily identified 14 bycomparison of its retention time with that of authentic standard.Also, during HPLCstudies, an aliquot of reaction mixture was takenand standard 14 was added to see if theassigned product peak would correspondingly increase in size. This wasobserved, anddeemed as further evidence that the chromatographicassignment was correct.Furthermore, it was noted during the workup of thereactions of 1 with cyanide that thecharacteristic odour of 14 was present.A number of general observations were made duringthe early studies regarding thereaction of 1 with cyanide. Reactions employingapproximately 2 or more equivalentsof cyanide for 15-30 minutes exhibitedessentially a quantitative conversion of 1 to 14,as determined by GC analysis. The temperaturesused for these reactions were 150-155°C. Additional experimentswere performed in which the reaction mixtureswere*Thesespectra were obtained on a departmental BrukerWP-80 spectrometer withtetramethylsilane used as an external standard.36heated for as little as one to three minutesand 14 was still produced, as observed by GCand HPLC analyses. Other reactionsconducted 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, decomplexationof the aromatic nitrile takes placeduring the reaction under theconditions employed. This was demonstratedbyexamining a product mixtureby GC (after workup) which showedno change inbenzonitrile 14 concentration aftertreatment with iodine. Subsequently, thisobservationwas further confirmed with additionalexperimental experience, which shall be presentedat later stages of this discussion.As a consequence, no separateoxidativedecomplexation step was neededto liberate the organic product. This resultwas not toosurprising as it has been reportedthat(t6-arene)tricarbonylchromium complexescanundergo displacement of the aromaticring in donor solvents, such as pyridine,atelevated temperatures.32These results further indicatedjust how facile and rapid the substitutionreaction of1 with cyanide actually is. Since theintent was to ultimately apply this chemistryfor theincorporation of[11C]cyanide intoarenes, the studies to follow were designedto modelthis application. With excess cyanideand longer reaction times, excellent reactionyieldscould be assured. The half-lifeof 11C, however, is 20.4 minutes,which places a premiumon using the shortestreaction time possible. Also, itis highly desirable that the reactionbe eventually compatiblewith high specific activity [“Cjcyanide,for the reasonsdiscussed earlier in Chapter1. Therefore, the decision was madeto limit subsequentcyanide substitution reactionsto 10 minutes and to use cyanideas the limiting reagent37(0.5 equiv).Within these parameters, the reactivity of thechromium tricarbonyl complexes 1, 4,5, and 6 was examined. The general procedure usedis as follows. An aqueous solutionMe—-—F Cl-—FCr(CO)3 Cr(CO)3Cr(CO)3 Cr(CO)31 45 6of cyanide, containing a known amount of KCN,was dispensed into a reaction vessel,and was carefully dried under a fast flow of inertgas. (This was done to model thehandling necessary in using[‘1C]cyanide, whichis 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 quantitativelytransferred to a volumetric flaskand diluted to a known volumewith DMSO. This solution was analyzed by HPLC. Theextent of product formation wasdetermined using a calibration curve constructedusingHPLC absorbance values of standard solutionsof expected aryl nitrile product. Thechemical yields were calculatedusing KCN as the limiting reagent. In orderto optimizethe results obtained for each of thecomplexes studied, the reaction temperatures werevaried and the corresponding chemical yields weredetermined.Complex 1 was treatedwith cyanide, as shown in equation 2.13, usingreaction0.5 equiv KCN2Cr(CO)3DMSO /10 •K—CN+ KF +1 (2.13)38temperatures ranging from 105-150°C. The resultsobtained are summarized in Table2.3. The optimum temperature found for equation 2.13was 135°C, giving a best yieldof 41%. A representative HPLC chromatogram isshown in Figure 2.5. The chromatogram shows the presence of the desired product14 (peak A), along with residual startingcomplex 1 (peak C) and free fluorobenzene (peakB) which is visible only as a shoulderof an unidentified peak. Injection of a solution,consisting of fluorobemzene standardadded to an aliquot of reaction mixture, exhibitedan 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 withuncomplexed 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 Complex1Temperature Yield no. of Average(°C) runs Yield150 23-33% 228%135 40-41% 241%120 31% 131%115 32% 132%105 12% 112%Next, the reactions of complexes4, 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%) wereobserved at 105-115°C. The control reaction donewith 2-fluorotoluene (uncomplexed) using0.5 equiva39zCIBTIME (mm)The compounds are:(A, 5.4 mm), 14; (B, 10.5 mm),fluorobenzene; (C, 16.8 mm),1.The HPLC conditionsare: Waters 10JLm C-18 reverse phase RCM column;eluent:isocratic methanol/water,1:1; flow rate, 2.5 mL/min;UV detection setat 280 nm.Figure 2.5: HPLCchromatogram obtainedfrom the analysis ofthe reaction ofcomplex 1 with cyanideat 135°C. The yield of 14 wasdetermined to be40%.402iCr(CO)340.5 equiv KCNDMSO/lOmin,MeCN + KF +415(2.14)lents of cyanide at 135°C gaveno reaction; unreacted 2-fluorotoluenewas the onlycompound observed in the HPLCchromatogram. Two reaction trials (equation2.14)were performed using only 1.5mg of 4, this being about a tenth of theusual quantity ofcomplex used per reaction trial.This results in a five-fold excess of cyanidebeingTable 2.4: Chemical YieldsObtained for Complex 4Temperature Yield no.of Average(°C) runs Yield135 29-36% 432%125 28-29%2 28.5%11541% 1 41%105 41-43% 242%95 26% 126%135k58% 1 58%143&58% 1 58%aOnlya tenth of the usual quantity of 4 wasused, giving astoichiometric ratio of 5:1, of KCNto 4.present in these reactions. Yieldsof 58% were obtained at both 135and 143°C. Theseresults were significantly betterthan those obtained using 0.5equivalents of cyanide (seeTable 2.4).The reaction of 5 withcyanide, as summarized in equation 2.15,was studied over thetemperature range of 105-150°C.The chemical yields obtainedare outlined in Table41Cr(CO)350.5 equiv KCNDMSO/ 10mm-Me<)—CN+ KF +5 (2.15)2.5. The best yields(26-29%) were obtained at115°C, while the next bestresults (22-26%) were seen at 135°C.The control experiment performedusing uncomplexed 4-Table 2.5: Chemical YieldsObtained for Complex 5Temperature Yieldno. of Average(°C) runsYield150 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 unreacted4-fluorotoluene.The reaction of 6 with cyanide(equation 2.16) was examinedat 115 and 135°C.These results are summarizedin Table 2.6. The best yields (26-34%)were obtained atCl -—FCr(CO)360.5 equiv KCNDMSO/l0minCl +KF + 6(2.16)the reaction temperatureof 115°C. The controlreaction done with4-chiorofluoro-benzene (uncomplexed)using 0.5 equivalents ofcyanide at 135°C exhibited noreaction;unreacted 4-chlorofluorobenzenewas the only compoundobserved in the HPLC chromatogram. One reactiontrial (equation 2.16)was heated (115°C) for fiveminutes, and gave42Table 2.6: Chemical Yields Obtainedfor Complex 6Temperature Yieldno. of Average(°C) runsYield135 21%1 21%115 26-34%3 30%115k17% 1 17%areaction time of 5 mm was used.only about half the yieldobserved for a 10 minute reactiontime (see Table 2.6). Thisindicates that reaction timesshorter than 10 minutes wouldresult in a significantsacrifice in chemical yield.In the process of examining thechemical yields obtained forcomplexes 1, 4, 5, and6, it would be interestingto discover any trends or systematicpatterns of chemicalbehaviour. However, inspectingthe results presented in Tables2.3-2.6 indicates thatthere are no such patternsobservable. What emerges isthat each chromium tricarbonylcomplex studied exhibitsits own distinct pattern of reactionyields. The mechanism fornucleophiic substitution reactionsof(,76-arene)tricarbonylchromiumsystems is thoughtto proceed by a two-stepmechanism (equation 2.17),’analogous to classical aromatic“CoCo+Ystep 1KXCr,OCj “COCO-xstep 2Cr,,OCj “COCO(2.17)43nucleophilicsubstitution.*,34The first step is addition of thenucleophile (Y) onto thearomatic ring, on the side oppositethe chromium tricarbonyl moiety—thisresults in theexo-substituted, anionic5-cyclobexadienylcomplex. The second stepis expulsion of thehalide leaving group (X),giving the final substitution product.If this mechanism isvalid, it would be anticipated,from comparison to classicalaromatic nucleophilicsubstitution, that electron-withdrawinggroups would make thesubstitution reaction withcyanide more facile, while electron-donatinggroups would hinder same.35 Usingthefluorobenzene complex 1as the baseline standard, it may beexpected that the presenceof the additional methyl group in4 would hinder the reaction withcyanide, relative to1, and may lead to lowersubstitution yields during theshort reaction time used. Thebest average yield for 1 was41% obtained at 135°C, while 4 exhibitedits best averageyield of 42% at 105°C.As a result, 4 essentially equalledthe best yield obtainedby 1at 30 degrees lower temperature.On the other hand, the resultsobtained by 5 weremuch more surprising. Since4 and 5 are simply ortho- andpara-isomers, respectively,similar chemical yields withcyanide might be anticipated forboth complexes. However,5 gave unexpectedly low yields,with a best average yield of27.5% obtained at 115°C.In fact, the chemical yieldsobtained by 4 readily surpassedthose of 5 at all temperaturesinvestigated (see Tables 2.4and 2.5). Complex6, which bears an extra chlorinesubstituent (relative to 1),would be expected to produce thehighest chemical yieldswithcyanide—yet this wasnot observed. A best averageyield of 30% was exhibited at115 °C.tThe mechanism beingspecifically referredto here is addition-elimination,alsocalled SNAr by March.44Unfortunately, circumstances did not permitthe opportunity to conduct reactions attemperatures below 115°C. It is possible that higherchemical yields could be obtainedfor 6 at lower temperatures. Nonetheless, equalor better yields were obtained from 1and 4 at both 115 and 135°C.These results may be explained in part by the relative thermalstability of thecomplexes. Complex 6 was clearly more prone to decompositionin solution; this wasparticularly evident during its synthesis (see pages 27-28).Due to the presence of thechlorine substituent, in addition to the fluorine, there wouldbe less electron densityavailable on the aromatic ring to complex with thechromium tricarbonyl moiety, and theresulting complex would be anticipated tobe less thermally stable relative to 1.Therefore, the lower chemical yield for6 at 135°C, compared to that of 1, could stemfrom greater thermal breakdown of 6 at that temperature. Theyields resulting from 1and 6 at 115°C are quite comparable. As a result, 1 exhibitsbetter 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 and5 would be expected to besomewhat more thermally stable than 1. Complexes 4 and5 were both prepared inhigher yield than 1, and were foundto be as well behaved during storage and handling.However, as presented earlier, 4 exhibited better yieldsat lower temperatures ascompared to 1, but 5 exhibited significantlylower chemical yields at all reactiontemperatures employed when compared to thoseof 4. Since it would be reasonable toassume that both 4 and 5 would beof equivalent thermal stability, the reason for thismarked difference in chemical yieldsobtained by 4 and 5 is unknown. For each45chromium tricarbonyl complex studied,the chemical yields obtained were foundto bequite sensitive to reaction temperature,and hence must be optimizedfor each complexindividually to achieve the best resultspossible.In order to improve upon the chemicalyields obtained thus far, it wasdecided toinvestigate the use of crown ethers.The presence of crown etherswith many ionicreagents have shown increasedsolubility and anion reactivityin aprotic organic solvents.Therefore, by employing a crownether with potassium cyanide,it would be anticipatedthat the nucleophilicity of thecyanide anion would be enhanced.36’37Previously, 18-crown-6 (1,4,7,1O,13,16-hexaoxacyclooctadecane)has been successfully used to helpconvert benzyl halides38 andalkyl halides39 to their correspondingnitriles in high yield.As a result, 18-crown-6 waschosen as the crown ether touse, to examine its potentialbenefit on the reaction of 4with 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 followedas described earlier, except for the additionof approximately1.2 equivalents of 18-crown-6to the reaction mixture prior to heating.The reactionswere conducted overa temperature range of 95-135°Cand the chemical yields weredetermined by HPLC analysisas before. The results obtained are summarizedin Table2.7. The best yields(40-44%) were now observedto occur throughout the temperaturerange of 105-135°C. Theseresults did not surpass theprevious 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 threeequivalents of 18-crown-6, a slightly improvedyieldof 46% was obtained. However, theuse of 18-crown-6 did significantly improveuponearlier reaction yields thatwere obtained at 95, 125, and135°C (see Table2.4)—increases of about 30-50%over earlier average chemical yieldswere exhibited.Table 2.7: Chemical YieldsObtained for Complex 4 using 18-Crown-6Temperature Solvent Yieldno. of Average(°C)runs Yield135 DMSO 41%1 41%125p42% 1 42%11540% 1 40%10540-44% 2 42%105a46% 146%9535% 1 35%80 CH3CN3% 1 3%95b4% 1 4%aAbout3 equiv of 18-crown-6 was used.bAtthis oil bath temperature, the CH3CNwas observed to be refluxing.In addition to these results,a couple of reaction trials (equation 2.18) wereconductedusing acetonitrile as the solvent withone equivalent of 18-crown-6added; these weredone using oil bath temperaturesof 80 and 95°C. As shownin Table 2.7, very pooryields were obtained. Afterchromatographic (HPLC) analysis, thesereaction mixtureswere simply set aside withoutany further manipulations.The following day thesemixtures were reexaminedby HPLC, which showeda significant increase in theconcentration of 2-tolunitrile15 (see Table 2.8). Thesereaction mixtures wereagain set47aside for about two weeks. ThenHPLC analysis was performedagain and a furtherincrease in the concentrationof 15 was observed (see Table2.8). Initially, the resultsobtained using CH3CNas the reaction solvent looked whollyunimpressive, butunexpectedly, good yields of 15were produced with thepassage of time. Experience withTable 2.8: Chemical YieldsObtained for Equation 2.18using Acetonitrile as the SolventTemperature YieldTime elapsed after(°C) initial HPLCanalysis80 3%080 21% --18h80 50% —13.5d95 4%095 21%--16h95 46% —13.5dDMSO as the reactionsolvent has shown that after thereaction has been performed andthe reaction mixture analyzedby HPLC, no further changesin nitrile productconcentration wasobserved with subsequent reanalyses.Due to the elevatedtemperatures used for thereactions (equation 2.18) done inCH3CN, it was expectedthatthe chemical yields,determined initially, representedthe total nitrile productformed(and decomplexed) duringthe 10 minute reaction time. Whatis not clear is whethertheimproved yields shown inTable 2.8 were dueto the reaction continuingto occur at aslower rate at roomtemperature (during storage),or to the fact that the initiallyformed(6-2-to1unitrile)tricarbony1chromiumspecies only decomplexed toa small extent at first,48then continued to slowly decomplex while beingstored.*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 macrocycleto 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-chlorobenzonitrile17) werereadily identified by comparison of their respective retention times with that of authenticstandard. To further confirm the identity of the nitrile products 15, 16, and17, aseparate set of reaction trials was conducted to isolate the organicproducts and analyzethese by gas chromatography-mass spectrometry (GC-MS).These reactions wereperformed as described previously in the general procedureused for the earlier cyanidereactions (see page 38). Upon cooling, however, the reactionmixtures were diluted withwater, then extracted with diethyl ether. The ether extracts werecooled to 0°C, thentreated with iodine for two hoursto oxidatively decomplex any chromium tricarbonylspecies present. The treatment was quenched with theaddition of aqueous sodiumthiosulfate solution. The ether layer was furtherwashed (aqueous Na2SO3and saturated*Thereaction mixtures were kept in small, stopperedvolumetric flasks, but thesemixtures had been exposed to air during HPLCwork. As a result, any chromiumtricarbonyl species present couldgradually undergo oxidative decomposition.49NaC1 solutions), then dried. The ethersolution (concentrated to 1 mL) was analyzedfirst by GC and HPLC, then by GC-MS.Mixtures of authentic standards were preparedfrom the uncomplexed starting areneand corresponding aryl nitrile product(dissolvedin ether) and were also analyzedby GC-MS for direct comparisonto the reactionproducts obtained above.Comparison of the mass spectra obtainedfrom the reaction products withthose of theauthentic standards confirmedthe identity of the starting fluoroaromatics(2-fluoro-toluene, 4-fluorotoluene, 4-chlorofluoroben.zene)and the resulting nitrile products (15,16, 17). However, the reactionmixture containing 4-chlorofluorobenzeneand 17 alsocontained a third minor productwhich was identified as benzonitrile 14by its massspectrum.The formation of 14 as a side-productfrom the reaction of 6 with cyanidewas due tothe presence ofa small quantity of 1 contaminatingthe starting complex 6.Unfortunately, the chromatographicpurification of 6, during its originalpreparation, didnot completely remove 1as an impurity. As a consequence,1 also underwentsubstitution with cyanide as aside-reaction, affording benzonitrile 14.In addition, the chemical yieldsfor this set of reaction trials wereestimated from theGC analyses using the standardmixtures for calibration.These results are shown inTable 2.9. The key featureof these results is that noneof the yields surpassed thevalues reported earlier, whichwere determined without subjectingthe reaction mixturesto oxidative decomplexation.This further establishes thatall the aryl nitrile formedduring the substitutionreactions becomes decomplexedunder the reaction conditions50Table 2.9: Summary of ChemicalYieldsStarting NitrileTemperature YieldComplex Product(°C)4 15120 —32%5 16135 —26%6 17115 —24%used.Other leaving groups apartfrom halogen have been successfullyused in classicalaromatic nucleophilic substitution.41Hence, it was of additionalinterest to our studyto examine other leaving groupsthat could possess greater mobilitytoward nucleophilicsubstitution for(i6-arene)tricarbony1chromiumsystems. An obvious choicewould be toexamine nitro as a leavinggroup. Unfortunately, the attemptsmade to prepare (6-nitrobenzene)tricarbonylchronfiumwere unsuccessful.Chromium tricarbonyl complexeswith arene rings bearinga nitro substituent havebeen unknown until recently.”42However, promptedby radiolabelling studies usingaromatics with dimethylsulfonium24and trimethylammonium’26leaving groups for nucleophilicsubstitution reactions, wefound that we were ableto synthesize(,76-N,N,N-trimethylanilinium)tricarbonylchromiumtrifluoromethanesulfonate11. Preliminary experimentswere conducted in whichcomplex 11 wasallowed to react withcyanide as shown in equation 2.19.The samegeneral procedure wasused, as previouslydescribed for the earlier reactions(see page‘The successful synthesisof(6-2,4,6-trinitrotoluene)tricarbonylchromium,using(CH3CN)Cr(CO)as the precursor for complexingthe arene, has been recentlyreported. This representsthe first chromium tricarbonylcomplex ofa nitroaromatic.51+CF3S0No Reaction (2.19)LCr(CO)3]1138). The reactions were done at 100 and 120°C. Disappointingly, HPLCanalysisshowed 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 notbe identified. Complex 11 wasthen heated in DMSO for 10 minutes at 100°C. Aftercooling, the HPLC chromatogramof this solution showed the presence of a single newpeak. The retention time of thispeak was very close to that of the large peak observed from the reactionsabove. Theseresults seem to suggest that 11 is undergoingsome kind of transformation ordecomposition from the heating in solution. For comparison,a trial reaction was donewith uncomplexed N,N,N-trimethylaniliniumtrifluoromethanesulfonate 12 and cyanideat 100°C (equation 2.20). No reaction was observed,as evidenced by HPLC analysis.[KMeCF3SONo Reaction (220)Unfortunately, the preliminary reactionsconducted with 11 failed to produce any 14.These results suggested some chemicalbreakdown 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 substitutionreactions of complexes 1, 4,5, and 6 with radioactive[11C]cyanide will be described.Due to the short half-lifeof ‘1C (20.4 mm), thisradionuclide must beproduced at or very close to thesite where the radiolabellingchemistry is to be performed.Fortunately, 11C is produced regularlyat the TRIUMFfacility for the ongoing PET programat U.B.C. The small TRIUMF/NordionCP-42cyclotron is used to generatepositron emitting nucidesfor PET, as well as otherradioisotopes for commercialsale. Carbon-li wasproduced as 11C02 byprotonirradiation of N2 gas viathe nuclear reaction 14N(p,a)11Cat 15 MeV. The[11C]cyanidewas producedby sequential catalytic conversionof 11C02 according to equation2.21.l)H2 l)NH3HCOCH HCN(2.21)2)Nicatalyst/450°C2)PtIl000 CThe H”CN was trapped inan aqueous solution of NaOH(0.1 M) to generate Na11CNfor labelling use.Although the maximum specificactivity of “C is 9.22 x106Ci/mmol, the ubiquitouspresence of ‘2C in nature invariablydilutes the specific activity ofany “C reagent tosome value less than themaximum possible specific activity.The amount of dilutionof“C by 12C can vary widely dependingon the production conditionsused. Specific activityvalues for H11CN thatcan be practically obtainedare in the order of 2x i0Ci/mmol.43 Unfortunately,the specific activity ofthe H11CN produced at TRIUMFhas not been determined,but the specific activityvalue is thought to be no lowerthan0.5 Ci/mmol.Therefore, the specificactivity of the[‘1C]cyanideused for this work53can possibly range somewhere between0.5-2000 Ci/mmol (most likelyin the lowervalues of this range). Since the quantityof actual “C-labelled product issosmall,*standard chemical and spectroscopic methodsof characterization, such as ‘Hand “CNMR, cannot be used for direct productidentification. Therefore, chromatographicmethods (e.g., HPLC and GC), usingnon-radioactive analogues as standards,providesthe best means of product identificationavailable. The best suited chromatographicmethod for this purpose is HPLC.4’For this work, product identificationand analysiswas performed with HPLCinstrumentation that was equipped withboth a UV detectorand a radioactivity detectorconnected in series.The radiolabeffing studiesbegan with investigating the reactivityof complex 1 with[“C]cyanide using differentamounts of added KCN (i.e., carrier).The generalprocedure used for the radiolabellingreactions 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 measurementwas taken wasrecorded and designated asthe start of synthesis (SOS). A knownamount of KCN wasadded to the [“C]cyanidesolution, then this carrier-added (CA)solution of [“C]cyanidewas transferred to a reactionvessel and dried under a fastflow of inert gas. Thearene)tricarbonylchromium complex,dissolved in 1 mL of DMSO,was added to thedried [“Cjcyanideand the mixture was heated for10 minutes. Upon cooling, 25-50Lof the reaction mixturewas subjected to radio-HPLCpurification, and the peakwas discussed in Chapter 1,this applies only to“C and other short-livedradionuclides. For example,compounds labelled with ‘H canbe analyzed by ‘H NMR.54corresponding to the[11C]nitrile was collected andassayed for radioactivity. An equalvolume of reaction mixture was also assayedat the same time, thereby determining thepercentage of radioactivity in the reaction mixturecontributed by the [“C]nitrile product.The radiochemical yield was then calculated.The radiochemical yields obtained have beendecay corrected back to SOS toeliminate the variation of time taken forsynthesis and chromatography. Therefore,theradiochemical yields can thenbe compared with one another, and any differences wouldreflect the relative efficacy of the reactionconditions used.Complex 1 was treated with[11C]cyanide asoutlined 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) representCATable 2.10: Summary of RadiochemicalYields Obtainedfor Equation 2.22Amount of 1 Amount of Radiochemicalused (mol) KCN added Yield65 0.49 equiv 34%41 0.37 equiv36%43 0.35 equiv41%65 0.11 equiv 21%65 0aTraceproduct was observed, but its activitywas 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 cyanidecarrier must be present to achievesuccessful labelling with[‘1C]cyanide, under thereaction conditions used. For the CAreactions, the addition of 0.35 equivalents ofKCN afforded the highest radiochemicalyield (41%). A representative radio-HPLC chromatogramof a CA reaction is shown inFigure 2.6. The chromatogramexhibits the presence of the product,[“CCN]benzonitrile 18 (peak B), and unreacted[11C]cyanide (peak A). The radio-HPLCchromatogram of the NCA reaction trial isshown in Figure 2.7. This chromatogramshows the presence of 18 as only a small peak, indicatinga very low radiochemical yieldwas obtained. The time taken for synthesisand chromatography—the synthesistime—was about 30-60 minutes (measured fromSOS) depending on experimentalcircumstances. Most typically, the synthesis timewas 40-45 minutes.Additional CA[‘1C]cyanidereactions 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 Table2.11.F0.5 equiv KCNR___________________a—11CN 223Cr(CO)3 DMSO/ 135°C/lOminRThe radiochemical yields parallelfairly closely the chemical yields obtainedwith nonradioactive cyanide under similarreaction conditions (see Tables 2.3-2.6 forcomparison).Initially, H”CN was trapped inaqueous 0.005 M NaOH solution for thefirst tworeaction trials in order to minimizethe 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 conditionsare: C-18 reverse phase WhatmanPartisil 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-HPLCchromatogram obtainedfrom the analysis of the reactionofcomplex 1 with [‘1C}cyariide(with 0.37 equiv of carrier KCNadded) at150°C. The radiochemicalyield of 18 was determinedto be 36%.57C,)zC/KZ/0T65I II II0 510 1520TIME (mm)The radio-HPLCconditions are:C-18 reverse phaseWhatman Partisil10 ODS-3 column,25 cm x9 mm; eluent: isocraticmethanol/water, 1:1;flow rate, 5.0 mL/min.Figure 2.7:Radio-HPLC chromatogramobtainedfrom the analysis ofthe reaction ofcomplex 1 with[11C]cyariide (withno carrier KCNadded) at 150°C.Onlya trace of 18was produced, fora radiochemicalyield of <1%.58Table 2.11: Summary of RadiochemicalYields Obtained forEquation 2.23Starting Complex ‘1C-LabelledNitrile RadiochemicalProduct Yield‘CNCr(CO)31181 34%Cr(CO)3419Me’F31%Cr(CO)35 2019%Cr(CO)36 21reactions. After these early experiments, itwas observed that the radioactivity of thetrapped[1tCjcyanide was being lostduring the drying procedure. In subsequentexperiments, 0.1 M NaOH solutionwas used for trapping H’1CN.However, examination of the radiolabellingresults of 1 with NCA[‘1Cjcyanide andCA [“C]cyanide (using 0.11equiv of KCN) showed that in thesecases the[11C]cyanide59underwent nucleophulic substitutionin low yield. It was thought thatperhaps hydroxidewas interfering with the reactivityof[11C]cyanide when 11CNis present in lowconcentration (little orno carrier used). Typically, a volumeof 0.5 mL of 0.1 M NaOH(containing trapped 11CN) wasused—this introduces 50 molof 0H into the radio-labelling reaction. As a result,some experiments were done usingdifferent concentrations of NaOH solution to trap H11CN,and 0.025 M NaOH was the leastconcentratedsolution that efficiently trappedand retained the[11Clcyanide upon drying.Next, the behaviour of [“C]cyanidealone in DMSO solution was examinedby radioHPLC. The chromatogramsobtained are shown in Figure2.8. Chromatogram A wasobtained from the analysisof a solution of NCA[11C]cyanide(originally trapped in 0.025M NaOH, then driedas usual) in DMSO. Note the extra peaks,apart from the mainpeak (retention time, 4.1 mm),that are present. With the additionof 25 /Lmol of KCNto this[1tCjcyanide solution, radio-HPLCanalysis was repeated andchromatogram Bwas obtained. The extrapeaks were significantly reducedin size, but not eliminated.A second batch ofH11CNwas trapped in 0.05 M NaOHsolution and dried, followedbythe addition of 1 mL ofDMSO. This solution of NCA[‘1C]cyanidewas heated at 150°Cfor 10 minutes. The colourlesssolution became amber in colourduring heating. RadioHPLC analysis of the NCA[11C]cyanide solution, after cooling,exhibited chromatogramC. The effect of heatingresulted in a dramatic change inthe appearance of the radioHPLC chromatogram relativeto earlier results. When chromatogramA is comparedwith chromatogramC, the small extra peaks observedin A have become the dominantpeaks observed inC. These results suggested that11CN (in low concentration) maybe6011CN0z0B11CNC)flME (mm)The radio-HPLC chromatogramsrepresent the following: (i) chromatogramA wasobtained from a solutionof NCA[11C]cyanide in DMSO,(ii) chromatogram B resultedfrom the addition of carrierKCN (25 mol) to the [‘1C]cyanidesolution used forchromatogram A, and (iii) chromatogramC was obtained from a second batch of NCA[‘1C]cyanide that was heatedat 150°C for 10 mm in DMSO. The retentiontime for‘1CN’ was 4.1 mm in eachchromatogram.Figure 2.8: Radio-HPLC chromatogramsof[11C]cyanide in DMSO.61changing into a different chemicalform, in the presence of hydroxide,that cannotundergo nucleophilic substitution.Two radiolabelling trials weredone with 6, in which hydroxideconcentration wasreduced. For the first trial, a batchof CA[11C]cyariide was preparedusing H”CN thatwas trapped in 0.025 M NaOH, followedby the addition of 0.11 equivalentsof KCN, andwas dried as usual. Complex6 was treated with the CA[11Cjcyanideat 150°C asdescribed in the general procedure.[11C-CN]-4-Chlorobenzonitrile 21was obtained ina radiochemical yield of 21%. For thesecond trial, the H”CN was trappedin adifferent manner to eliminate the presenceof hydroxide from the [“C]cyanide reagent.A second production run of H11CNwas trapped in a glassloop that was emersed in aCC14/C02(-23°C) cooling bath.Any ammonia gas, from the conversionof ‘1CH4(equation 2.21), was swept throughthe glass ioop with helium transfergas. Then theglass ioop was removed fromthe cooling bath and the H11CNwas slowly added to areaction vessel containinga mixture of 6, carrier KCN (ca. 0.4-0.8equiv*),and 1 mL ofDMSO. This mixture washeated for 10 minutes at 125-130°C.Radio-HPLC analysisof the cooled reaction mixtureshowed that 21 was obtained in29% radiochemical yield.These two results suggestedthat some improvement of radiolabellingefficiency with[11C]cyanide is possibleby limiting the hydroxide quantityin the reaction mixture.The identification of the[11C]nitrile products,[11C-CN]benzonitrile18, [‘1C-CN]-2-tolunitrile 19,[11C-CN]-4-tolunitrile20, and11C-CN]-4-chlorobenzoriitrile21, was*Twosmall crystals of KCNwere used, which werenot weighed, thus the quantityindicated was estimated.62accomplished using radio-HPLCstudies. The chromatographicbehaviour of the[11C]nitriles was consistent with thatobserved for the related non-radioactivearomaticnitriles (14, 15, 16, 17). Forthe reaction of complex 1 with CA[‘1C]cyanide,additionalproduct identification was performedwith GC. The reaction mixtureof a reaction trialwas analyzed by GC (injection temperature,250°C; oven temperature, 90°C;N2 carriergas flow, 2.0 mL/min) andfound 18 to be present ata retention time(RT)of 8.1minutes. This was confirmedby the addition of standard (non-radioactive)benzonitrile14 to an aliquot of reactionmixture and the assigned productpeak(RT= 8.1 mm) wouldcorrespondingly increasein size. Moreover, anotherportion of reaction mixturewassubjected to radio-HPLCpurification and the peak containing18 was collected. Theradio-HPLC fraction wasanalyzed by GC and the peakdue to 18 exhibited thesameretention time as standard14.The radiolabelling resultsobtained in this study are still preliminary,but theydemonstrated that aromaticnucleophilic substitution reactionswith CA[‘1C]cyanide canbe successfully performed with(6-arene)tricarbonylchromium compounds.However,the use of high specific activityNCA[11Cjcyanide gave adisappointing result. Thereasons for this are not clear,but this is not an uncommon problemwhen labelling withradionudides; the generalreasons for this phenomenon werediscussed in Chapter 1.In this instance, it wasthought that the presence ofhydroxide, which was absentin themodel labelling studieswith non-radioactivecyanide, could be the problem.Thehydroxide could affectthe radiolabelling resultsin three differentways. The firstpossibility is that thehydroxide could be chemicallychanging the[11C]cyanideinto a63different form, thereby reducing the already lowquantity of 11CN available for reaction.Evidence for this possibility was suggestedby the radio-HPLC studies of[‘1C]cyanidealone in DMSO. It was observed that 11CN underwentchange to unidentified radio-products upon heating. This observationwarrants additional study to determine whatis actually happening to the 11CN.The second possibility is that the hydroxide isacompeting nucleophile with 11CN. Since about 50mol of hydroxide is present, and theactual quantity of 11CN is about one to three ordersof magnitude less, the hydroxideis necessarily in significant excess.Therefore, reaction with hydroxide maybecome thedominant process, even if hydroxideis less reactive toward chromium tricarbonylcomplexes than cyanide. The final possibifityis that hydroxide could be hydrolysing the[“C]nitrile product to the corresponding[11C]amideand[‘1Cjcarboxylic acid. Somewater would need to be present in the reactionmixture for hydrolysis to occur.However, given the very smallamount of[11C]nitrile product formed, very littlewaterwould be necessary. It is quite possible thatthe drying of the trapped [“C]cyanidesolution is not totally complete, therebyleaving sufficient moisture to allowhydrolysisto proceed. Standards of theanticipated hydrolysis products, benzarnide andbenzoicacid, were subjected to HPLC analysis(using the same HPLC conditions as for thereaction mixtures) and exhibited retentiontimes of 3.2 and 2.2 minutes, respectively.These retention times are consistentwith those of the unidentified radio-peaksobservedin the chromatograms presentedin 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 tricarbonylcomplexesfor radiolabelling.A range of simple(i76-arene)tricarbonylchromium complexes were prepared in12-89%yield from the reaction of free arene with Cr(CO)6in 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-donatinggroups.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 determinedto beineffective leaving groups for reactions with cyanide. Therefore, the reactivity offluorine-substituted, chromium tricarbonyl complexes 1, 4, 5, and6 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 in12-41% yield. The best yield (41%) wasobtained at 135°C. Control experiments with uncomplexedfluorobenzene confirmedthat no fluorine displacement by cyanideoccurred with free fluorobenzene under thereaction conditions used for 1.65Complex 4 was treated with cyanide (0.5 equiv) in DMSOover a temperature rangeof 95-135°C, which afforded 15 in yields of 26-43%; thebest yields (41-43%) wereproduced at 105-115°C. Complex 5 was allowedto react with cyanide (0.5 equiv) inDMSO over a temperature range of 105-150°Cand obtained yields of 11-29% of 16.The best yields (26-29%) were exhibited at 115°C, while the nextbest 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 keptto 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 studiedin the presence of 18-crown-6.These reactions were conducted over a temperaturerange of 95- 135°C, andimprovements in chemical yield, over earlierstudies, were observed throughout thetemperature range examined. The best yield of 15(46%) was obtained at 105°C usingthree equivalents of 18-crown-6. Clearly, theuse of crown ethers shows promise towardmaximizing the yields obtainedfrom 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]nitriles18, 19, 20, and 21 were obtained. Some CAreactionswere done (at 150°C) with 1which indicated that 0.35 equivalents of carrier(KCN) wasrequired to afford the best radiochemicalyield (41%). Unfortunately, the NCA reactiontrial with 1 gave only a trace of18. These initial results suggest that some carriermust66be present to achieve successful radiolabellingwith [“C]cyanide, however, continueddevelopment of this work could well enableNCA radiolabelling to be accomplished inthe future. The aryl[11C]nitriles 19, 20,and 21 were produced in34%, 31%, and 19%radiochernical yields, respectively,using 0.5 equivalents of carrier at135°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-MetalComplexes: 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. Principlesand Applications of OrganotransitionMetalChemistry; University ScienceBooks: 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;p653.8. Pearson, A. J. Metallo-organicChemistry; Wiley Interscience:New York, 1985;pp348-362.9. McQuillin, F. 3.; Parker,D. G.; Stephenson, G. R. TransitionMetal Organometallicsfor Organic Synthesis; CambridgeUniversity: Cambridge, 1991;pp182-208.10. 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 TotalSynthesis; Wiley Interscience:New York,1990;pp317-319.15. Caiy, F. A.; Sundberg,R. J. Advanced Organic Chemistry—PartB: Reactions andSynthesis; Plenum: NewYork, 1977; Chapter7.16. Kilbourn,M. R. Fluorine-18 Labelingof Radiopharmaceuticals;Nuclear ScienceSeries, MonographNAS-NS-3203; National Academy:Washington, DC, 1990.17. Radiopharmaceuticalsfor Positron EmissionTomography: MethodologicalAspects;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 Structuresof Organometallic Compounds; Wilkinson,G.,Stone, F. 0. A., Abel, E. W., Eds.; Perganion:Toronto, 1982; Vol. 3,pp1001-1021.20. 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;p1001.23. 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. RecentDev. Mass Spectrosc., Proc. mt. Confi MassSpectrosc.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;pp653-661.34. March, J. Advanced OrganicChemistty: Reactions, Mechanisms,and Structure, 3rded.; Wiley Interscience: New York,1985; Chapter 13.35. See reference 34;pp584-586.36. See reference 34;pp77-79, 321-322 and referencescontained 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; Chapter5.42. 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 3DEVELOPMENTOF METHODS FOR RAPIDFLUORINE LABELLING31 IntroductionIn the early 1950s, thepioneering work of Friedand Sabo led to the first significantsuccessful application ofselective fluorinationto modify the biological activity ofanorganic molecule.1 Thefluorosteroid, 9a-fluorohydrocortisoneacetate 22, that wasOAc0prepared by theSquibb Company researchers,showed approximately an 11-foldincreasein glucocorticoidactivity over that of cortisoneacetate. This report stimulatedmuchnew research intodeveloping ways of selectivelyintroducing fluorine atspecific sites incompounds of potentialbiological interest, in orderto modify their biological activity.Since the landmarkwork of Fried andSabo, the study of selectivelyfluorinated71molecules has resulted ina variety of useful applications in biochemistryandmedicine.2’3 These applications includethe use of fluorine-containing organicpharmaceuticals as anticancerand antiviral agents, antiinflammatorydrugs, antibiotics,antifungal and antiparasitic agents, generalanesthetics, and therapeuticdrugs for mentalillness. In addition, pharmaceuticalslabelled with radioactive fluorine (18F)play animportant role in PET imaging. Perfluorinatedhydrocarbons 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 importanceofselective fluorination methodology.4’5The attractiveness and utility of fluorineas a substituent in biologically activemolecules are due to the uniqueproperties of fluorine that can induce profoundandunexpected effects on biologicalactivity. Firstly, fluorine is the most electronegativeofall elements, with an electronegativity(Pauling scale) of 3.98 as compared to3.44 foroxygen, 3.16 for chlorine, or2.96 for bromine. It is this property whichproducespronounced electronic effects ina molecule after the introduction ofa fluorinesubstituent. Secondly, fluorine, with itssmall van der Waals radius(1.35 A), closelyresembles hydrogen (van derWaals radius 1.20A) in size. As a result, the fluorinatedanalogue will usually closelyresemble the non-fluorinated moleculein size when afluorine is substitutedfor hydrogen. This allows, for instance,fluorinated analogues tostill meet steric requirementsat enzyme receptor sites. Thirdly,fluorine forms astronger bond withcarbon than does hydrogen—thecarbon-fluorine bond energy is 456-486 kJ/mol, whilecarbon-hydrogen bond energyvaries from 356 to 435 kJ/mol.72Therefore, carbon-fluorine bondsexhibit increased thermal and oxidativestabifity overthat of carbon-hydrogen bonds. Lastly,fluorine, when replacing hydrogen ina molecule,usually enhances lipophilicity which increasesthe rate of absorption and transportof thefluorine-containing compound in vivo. Inmany cases, this characteristic may bethe mostimportant in improving pharmacologicalactivity.6’7An additional feature of fluorine isthe availability of the artificially preparedradionuclide, 18F, which decaysby positron emission. Fluorine-18 (half-life, 109.7 mm)is one of the four key radionuclidesused in PET. The other conimorilyused positronemitting nuclides (11C,‘3N,150)possess very short half-lives (—‘2-20 mm) incomparisonto ‘8F. The longer half-life of ‘8Fallows for more complex or multistep radio-pharmaceutical syntheses to be conducted, andthe resulting compounds can betransported over moderate distancesfor use at different locations. In addition,the studyof relatively slow biological processescan be performed with‘8F-labelled agents,whichwould not be feasible with agents usingnuclides with shorter half-lives. Furthermore,18F-labelled compounds have thepotential to produce PET images of superior resolutiondue to the relatively low energy positron(maximum 0.635 MeV) emittedby 18F (seeTable 1.2 for comparison)—thisfactor will be of increasing importanceas PETinstrumentation improves.8’9The utilization of 18F-labelledpharmaceuticals with PET imaging hasenabled anumber of humanbiochemical and physiological processesto be investigated in vivo, aswas presented in Chapter1. More recently, however, theapplication of PET is beingextended beyond the studyand diagnosis of diseaseto the area of drug discovery,73development, and approval ofnew pharmaceuticals. Drug candidatescan be labelledwith positron emitting nuclides,such as 11C and 18F, to provideinformation regardingdrug absorption, distribution,metabolism, and elimination in vivo(human or animalsubjects) using PET imaging.These studies can complementinformation obtained using3H- and‘4C-labelled analoguesin animals. Alternatively, establishedPET imagingprotocols can be used to monitorthe biological behaviour of drugcandidates in vivo todetermine the therapeutic potentialor efficacy of such compounds.For disease stateswhere no animal models exist, PETbecomes a unique tool thatstill enables drugassessment to be carried out.Also, given the interest in fluorine-containingbiologicallyactive molecules, it wouldbe possible—in principle,at least—to study the in vivobiochemistry of the 18F-labelledanalogues via PET.1°Underlying the continueddevelopment and applicationof fluorinated compounds isthe ongoing need for new and improvedmethods to selectively introduce fluorineintopolyfunctional molecules at specificsites. However, the mild andselective introductionof fluorine into organicmolecules has been and continuesto be of considerablechallenge to organic chemistry.Although elemental fluorinewas first prepared byMoissan in1886,11the organic chemistry of fluorinedeveloped slowly in comparisontothe other halogens. It was quicklydiscovered that the reaction offluorine with organiccompounds was highly exothermic,and often resulted in explosions.These observationsunderstandably discouragedfurther research with fluorinefor decades after Moissan’stime. In the 1930s,Bockemüller demonstrated that fluorine,when diluted with inertgas(usually nitrogen), could beused for selective fluorinationof organic substrates under74controlled conditions.’2 Since thattime, new fluorinating agentsand reactions havebeen developed making possiblethe synthesis of the manyorganofluorine compoundsavailable today.’3”4Currently, the range of methodsfor introducing fluorine into organiccompounds isbased on the use of either elementalfluorine, hydrogen fluoride, inorganicfluorides, orvarious organofluorine reagents.These fluorinating agents canbe broadly characterizedas sources of either nucleophilicor electrophilic fluorine. Withthese fluorinating agents,many methods have beendeveloped to effect the transformationof different organicfunctional groups toorganofluorine derivatives,and are catalogued in multiplebooks’5”6 and reviews.4’1317”8However, many of thesemethods, though successfulin conventional syntheticchemistry, are not compatiblewith the requirements ofradiolabelling with 18F.8’9A primary limitation of radiofluorinationmethodology is the limited rangeof usefulsynthetic precursorsthat can be produced in‘8F-labelledform. The only reagentavailable for nucleophilic fluorinationis[‘8F]fluoride anion.’9However,[‘8F]fluoridehas seen increasing applicationbecause of continuing investigationsperformed studyingthe different variables involvedin optimizing the reaction conditionsfor its use withstructurally diverse substratemolecules. Investigatorshave studied the influenceofreaction solvent, sourceof ‘8F, fluoride counterion,catalyst (e.g., crown ethers),‘9Fcarrier levels, reactionvessel material, substrateconcentration, leavinggroup, andtemperature on theradiochemical yieldsobtained with [‘FJfluoride.9”Reactionconditions have beendeveloped such thata number of aliphatic and aromatic75compounds have now been successfully radiolabelled with18F•9,20As a result,[18F]fluoride has gained increased importance forradiofluorination work.In contrast to nucleophilic fluorination, a numberof electrophilic fluorinating agentshave been produced in‘8F-labelled form, using [‘8F]F2as the sourceof 18F in each case.A list of the various fluorinating agents preparedwith 18F is presented below. However,Fluorinating Agents Labelled with 18F9’2°fluorine (F2) chlorine monofluoride(C1F)perchioryl fluoride (C1O3F) trifluoromethylhypofluorite (CF3OF)xenon difluoride (XeF2) trifluoroacetylhypofluorite (CF3COOF)nitrosyl fluoride (NOF) acetyl hypofluorite(CH3COOF)N-fluoro-2-pyridone N-fluoropyridiniumtrifiatesN-fluoro-N-alkylsulfonamides (RSO2NFR‘)N-fluoro-bis(trffluoromethylsulfonyl)imide ((CF3SO2)NF)most of these reagents have not actually been evaluatedas to their scope and utility forradiolabelling with 1F.9 In practical experience,the vast majority of electrophilicfluorinations are performed with[18F]F2 and CH3COO18F.21’22Acetyl hypofluorite isa relatively new reagent that was originally developedby Rozen and co-workers in1981,23and then was prepared in‘8F-labelledform in 1982? Acetyl hypofluorite hasbeen found to be a milder and more selectiveelectrophilic fluorinating agent,incomparison to elementalfluorine, for a variety of substrate molecules.25’26Moreover,the development of a simple on-linegas-solid phase synthesis of acetylhypofluorite27has significantly increased itsutility for radiofluorinations. The other18F-labelledfluorinating agents listed previouslyare not trivial to produce on a routine basis,and as76a result, have not engenderedserious interest by PET researchgroups as yet.21 Clearly,much additional researchneeds to be done in orderto develop the full potentialofelectrophilic fluorinationmethodology for radiolabelling.The requirement to developmethods to prepare‘8F-labelledaromatic compoundsforthe PET program atU.B.C. prompted Adam andco-workers28’29to examinethe reactivity of main group organometallicderivatives with electrophilicfluorinating agents.Itwas essential that thefluorination reactionbe rapid, the fluorinatingagent be readilyavailable in‘8F-labelledform for routineuse, and be efficient in theincorporation ofradiofluorine. Also,it was desired thatthe reaction conditionsbe mild and theexperimental manipulationsbe as simple as possibleto perform to accommodatefutureautomation. It wasknown that the electrophilichalogenation of organometallicderivatives suchas those of tin30 and mercurywas well established.However, verylittle study had beendone regarding thereactivity of carbon-metalbonds withelectrophilic fluorinatingagents. As a result, thereactivity of aryl-tin, (thenlater) arylsilicon, -germanium,-lead, -mercury, and-thallium bonds, withelemental fluorine wasinvestigated.28’29Fluorobenzenewas successfully producedfrom phenyltri-n-butyltin(48-70% yield), tetraphenyltin(15-56% yield), tetraphenyllead(48% yield), and diphenylmercury (26-36%yield). The other organometafficderivatives studiedgave only pooryields (2.4-12%),or no detectable productin the case of the organothalliumderivative.These studies representthe first reports ofthe cleavage of aryl-metalbonds byelectrophilic fluorination.Since the reportsof Adam et al.,28’29 thefluorination of organometalliccompounds has77been under study by otherresearchers as well. Asa result, various simple aromaticcompounds have beenradiolabelled with 18Futilizing organotin,29’3233organosilicon,33’3435 organogermanium,33and organomercur6’37derivatives. In addition,aryllithium38’39 and Grignard39’4°reagents have also beensuccessfully radiofluorinated.More significantly, thestrategy of electrophiic fluorinationof organometallic derivativeshave been applied to the preparationof18F-labelled pharmaceuticalsfor PET. Aryl-tinprecursors were used toprepare both 3-O-methyl-6-[18F]fluorodopa41and 6-[’8F]fluoro-dopa42 by reaction with CH3COO18F(20% radiochemicalyield) and[18F]F2(25% radio-chemical yield), respectively.6-[’8F]Fluorodopa hasalso been prepared froman arylsilicon derivativeusing [18F1F2 (5-10% radiochemicalyield)43 and an aryl-mercuryderivative using CH3COO18F(—40% radiochemical yield).”6-[18FjFluorometarami-no145 and4-[18F]fluoro-m-tyrosine46were successfully preparedfrom organomercurysubstrates by reactionwithCH3COO’8Fin approximately30% and 25-30% radiochemicalyields, respectively.6-[18F]fluoroveraldehydewas readily prepared in30% radiochemicalyield from an organotinprecursor using[18F]F2,but interestingly couldnot be obtainedfrom the correspondingorganomercury derivative.47This case reaffirmsthe need forvarious syntheticoptions to be availableto successfully synthesizea desired18F-labelledcompound.The application ofelectrophilic fluorinationvia organometallicintermediates has beenalmost exclusivelyfocussed on introducingfluorine onto aromaticrings. This isunderstandable becauseof the many organiccompounds ofbiological interest thatcontain aromaticrings in their structures.Nonetheless, other potentialapplications also78exist. Some alkyl fluorides havebeen prepared via organometallicderivatives, such ascyclohexyl fluoride48 and n-tetradecylfluoride49 from the correspondingGrignardreagents, in low yield. Benzyl[18F]fluoride was prepared frompotassium benzylpentafluorosilicate in6% radiochemical yield.35 Generally, however,primary and secondaryalkyl fluorides have been readilyobtained using nucleophilic substitutionwith fluorideanion. Alternatively, a number ofbiologically interesting moleculesexist which containa vinyl function in their structures.50’5152The vinyl functionality providesa potentialsite for labelling with fluorine.Moreover, some importantbiomolecules specificallycontain the fluorovinylgrouping,7’5354and maybe of interest for 18F-labelling.Thesepotential applications promptedinterest in extending thestrategy of electrophilicfluorination of organometafficderivatives as a generalmethodology to preparefluorovinyl compounds, andis suitable for radiofluorinations with18F.Upon review of the fluorinationstudies of aryl-metal systems,it seemed that theorganotin reagents gave thehighest chemical and radiochemicalyields, although organomercury and -silicon derivativesgave good results also. The electrophilicfluorinationreactions of aryl-tin reagentsare rapid. Previous work55 withvinyl-tin compounds havedemonstrated that they aresufficiently stable to be preparedin bulk, and then stored foruse as needed. Vinyl-tincompounds can be readily preparedby reduction of thecorresponding acetyleniccompounds with tin hydridereducing agents.56’57 Inaddition,other methods of preparationof vinyl-tin derivatives are alsoavailable.58 These factorssuggested to us that vinyl-tinsubstrates offered the bestpotential as reagents forfluorination studies.79In this chapter, thepreparation ofthe vinyl-tin derivativesemployed for this workwillbe described. This willbe followed by fluorinationstudies of the vinyl-tinsubstrates withelemental fluorineand acetyl hypofluorite.Lastly, the successfulradiofluorinationofa vinyl-tin derivativeof a steroid willbe presented.3.2 Synthesis of Vinyl-TinPrecursorsThe vinyl-tin derivativeswere preparedby hydrostannylation ofthe correspondingacetylenic precursors,and most of theresults obtained havebeen described previouslyin the author’s M.Sc.Thesis.55 The acetylenicstarting materialswere either obtainedcommerciallyor prepared usingliterature methods,as summarized in Schemes3.1 and3.11.The acetyleniccompounds, 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, and7,8-dideoxy-l,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-ynopyranose 29, werehydrostannylated(see Schemes 3.111and 3.IV) by an adaptationof literature procedures.57The acetylenic precursorswere treated withapproximatelytwo equivalentsof tri-n-butyltin hydrideand a catalytic amountof AIBN (2,2 ‘-azobis(2-methylpropionitrile)),followed by heatingthe mixture at 95°C overnight.The (E)vinyistannylatedproducts wereisolated by chromatographicworkup of the reactionmixtures, andthe chemicalyields are summarizedin Table 3.1. Eachof the (E)vinyistannaneswas characterizedby their physical properties(optical rotation values,80Scheme 3.!1) KOHIDMSO2) MelScheme 3.11Cr03-2pyCH2C1(py= pyridine)OHHCCMgBrThFHO_//28+L-OH/2324+2581Scheme 3.1112R’O23 R’=R2=H24R’Me,R=H25 R’R2Me(n-Bu)3SnHAIBN/heatR20R1-Sn(Bu)330 R’=R2=H31 R1Me,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), elementalanalysis, and spectral data (1H NMR,mass spectrometry).The AIBN catalyzed hydrostannylation reactionwas 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 3059%24 3190%25 3294%28 3361%29 3459%product were obtained from the steroidal acetyleniccompounds, 24 and 25, in comparison with the carbohydrate acetylenicsubstrates (28, 29). It is known that thehydrostannylation reaction can produce threedifferent isomers when using terminalacetylenes,59as shown in equation 3.1. As a consequence, the chemical yieldof (E)-vinylstarmane will— (Bu)3SnH(Bu)3Sn,,H ÷ H\H + H\,,Sn(Bu)3R — HR H RSn(Bu)3 R H (3.1)regioisomer Z-isomer E-isomervary depending on the proportion of(Z)-vinylstamiane and “regioisomer” whichareproduced. It was observed thatthe hydrostarinylation reactions of 28 and 29producedgreater proportions ofalternative isomeric products, thus givingconsistently lower yieldsof (E)-vinylstannanes. The lowerhydrostannylation yield of17a-(E)-tributylstannylvinyl-831,3,5(10)-estratriene-3,17fl-diol30 from 23 was dueto significant protonolysis of vinyl-tinproduct formed duringthereaction;*this was most probably dueto the presence of theunprotected phenolichydroxyl group.During a more recentpreparation 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-ol36, was also isolated(—10% yield). Compound 36 hasnotHOMeO’1’Sn(Bu)3been fully characterizedas yet. However, in the preparationof (E)-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-8-C-tributylstannyl-L-glycero-c-D-galacto-oct-7-enopyranose34, bothalternative isomericproducts, (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-enopyranose37 and 7,8-dideoxy- 1,2:3,4-di-O-isopro-pylidene-7-C-tributylstannyl-L-glycero-a-D-galacto-oct-7-enopyranose38, were isolatedas*Asignificant amount of17a-vinyl- 1,3,5(10)-estratriene-3,17-diol 35 was recoveredfrom thehydrostannylation of 30;see Experimental fordetails.84a 3:2 mixture. The chemical yields of37 and 38 were estimated tobe 15% and 10%,respectively. Compounds37 and 38 were identified by their ‘H NMR spectraldata.3.3 Labelling Studies with Non-RadioactiveFluorinePrior to this study, there weresome reports of vinylmetallated compoundshaving 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 productwasafforded in <5% yield.6° Since then,Di Raddo and Diksic6’prepared4-[’8Fjfluoroanti-pyrine using [‘8F]F2in 18% radiochenilcalyield from 4-(trimethylsilyl)antipyrine.Leeand Schwartz62 prepared varioussimple vinyl fluorides in 71-88% yieldusing vinyl-lithium reagents and N-tert-butyl-N-fluorobenzenesulfonamideas the source forelectrophiic fluorine. Interestingly,Flanagan et al.5’ attempted tofluorinate 6-chloromercuricholest-5-en-3j3-olwith elemental fluorine, acetyl hypofluorite,and xenondifluoride under various conditions,but without success.Our study examined the reactivityof the (E)-vinylstannanes, 30, 31, 3,17(3-dimethoxy-17a-(E)-tributylstannylvinyl-1,3,5(10)-estratriene32, (E)-7,8-dideoxy-1,2:3,4-di-O-isopropy-lidene-8-C-tributylstannyl-D-glycero-a-D-galacto-oct-7-enopyranose33, and 34, withelemental fluorine and acetylhypofluorite.The fluorination of 31was initially studied in small scale experimentsusing excess F2or gaseous CH3COOF, and theresulting crude reaction mixtureswere analyzed by TLCand19k’NMR It was evidentfrom TLC analysis thatboth fluorinating agents produced85multiple products, but the17NMR spectra indicated that the reaction of 31 withCH3COOF produced significantly more fluorovinylproduct than with F2. It was alsoobserved that neither fluorinating agent consumedall of the starting material.As a result, 31 was fluorinated with CH3COOF(Scheme 3.V) on a larger scale in thefollowing manner. Compound 31was treated with approximately 1.3 equivalents ofgaseous CH3COOF in CFC13at room temperature. This procedurewas conducted withsix portions of 31 in order toemploy a sufficient amount of starting material forfluorination. The crude reaction mixtureswere combined and subjected to columnchromatography. The fractions containing3-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 purificationby HPLC, whereby 39 and 40 were isolated in 29.5%and 3.8% yield, respectively.Compounds 39 and 40 were readily characterizedby 1H and ‘9F NMR.Scheme 3.VHOHOMeOI T>CH3COOF_J..L/ +CFCI3HOMeO3186MeOHaving successfully isolatedthe fluorovinyl products 39 and 40,the opportunityemerged to quantitativelystudy the fluorination reactions of 31 underdifferentconditions. A number of small scalereactions with 31 were conducted usingthefollowing general procedure.A solution of 31 (in a chosen solvent)was treated with asmall excess (ca. 1.2-1.4 equiv) of fluorinatingagent (F2 orCH3COOF). The solvent wasevaporated and the reaction mixturewas dissolved in a known volume of chloroform.This solution was analyzed byHPLC to determine the combined yieldof both fluorovinylproducts 39 and 40. (A solutionof 39 was used as an external standard.)Firstly, 31 was allowed to react withgaseous CH3COOF (Scheme 3.V) at both-78°Cand room temperature. Theresults are summarized in Table 3.2.The best yields offluorinated product were obtainedat room temperature, although fewerside-productswere observed (by HPLC) when thereaction was performed at -78°C. Secondly,31 wasTable 3.2: Summary of Yields Obtainedfor the Reaction of 31with Acetyl HypofluoriteSolventTemperaturea Yieldbno. of AveragerunsYieldbCFC13 -78°C26-31% 2 29%CFC13 r.t.41-42% 241%CH3OH r.t.14% 1 14%CH3CN r.t.24% 1 24%TIIF r.t.9.3% 19.3%ar.t.= room temperature.bRefersto the combined yield of39 and 40.treated with CH3COOFin alternative solvents, namelydried methanol, acetonitrile,and87tetrahydrofuran,at room temperature.The yields aresummarized inTable 3.2.Noneof these solventsprovided improvedyields of fluorinatedproduct. Clearly, CFC13provedto be the best solventtested for the fluorinationreaction of 31.Finally, the reactionof31 with elementalfluorine (Scheme3M) was studiedat both -78°C androomtemperature.The results aresummarized inTable 3.3. It was evidentby both analyticalScheme 3.VIMeO’—Sn(Bu)30.1% F2/NeCFC13MeOF+ MeOHO7HOMeO+ MeO88Table 3.3: Summary of YieldsObtained for the Reaction of 31with FluorineTemperatureaYield of 39 and 40Yield 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 lessreactive toward F2 thanCH3COOF as less startingmaterial is consumed by F2. However,reaction with F2 does result in theformation oftwo identified non-fluorinatedside-products, 24 and3-methoxy-17a-vinyl-1,3,5 (10)-estratriene-17/3-ol 41. The identityof these compounds was establishedvia HPLC; bycomparison of their respectiveretention times with those of authenticstandards. Theidentity of 41 was further confirmedby ‘H NMR spectroscopy of a preliminaryreactiontrial done with F2 at -78°C.The reaction of 31 withF2 clearly gave the lowest yieldsoffluorovinyl product(39 and 40) in comparisonto the reactions performed withCH3COOF.The reactivity of 30with fluorine and acetyl hypofluoritewas investigated. Compound30 was treated withapproximately 0.8 equivalents ofdilute (0.1%) F2 in Negas mixturein CFC13 at -78°C.The TLC chromatogram ofthe reaction mixture exhibitedtheformation of a new, morepolar component, alongwith other minor components.Thisdominant new component,as observed by TLC, wasisolated by column chromatographyfor identificationby NMR. The 270 MHz‘H NMR spectrumrevealed that the isolatedmaterial was 17a-vinyl-1,3,5(10)-estratriene-3,173-diol35. No trace of fluorovinylproduct was observedin the NMR spectrum.Alternatively,30 was treated with89HOJ5-Sn(Bu)3approximately 1.2 equivalentsof gaseous CH3COOF in CFCI3at -78°C. TLC analysisof the crude reactionmixture indicated the totalconsumption of starting materialandthe formation of an extremelycomplex mixture. The19f?NMR spectrum of the reactionmixture exhibited severalweak signals of fluorinatedproducts which could not beassigned. The corresponding1H NMR spectrum could not provideany usefulinformation due to its extremelycomplex pattern.Unfortunately, no fluorovinylproduct could be obtainedfrom 30 using either F2 orCH3COOF as fluorinatingagents. Since the 3-O-methylated(E)-vinylstannane 31 wassuccessfully fluorinatedas described earlier, the difficultyin fluorinating 30 is most likelydue to the presence ofthe unprotected phenolichydroxyl group. Therefore, thisfunctionality must beprotected with an easily removedprotecting group, such as teflbutyldimethylsilyl, inorder to develop a syntheticroute to 17a-(E)-fluorovinyl-1,3,5(1O)-estratriene-3,17i3-diol.The reactivity of32 was also studied with fluorineand acetyl bypofluorite. Theuseof elemental fluorinewas investigated first. Foursmall scale reaction trialswereperformed in which 32.was allowed to react withapproximately 0.9 equivalentsof dilutefluorine at -78°C(2 trials), 0°C (1 trial),and room temperature (1trial), in CFC. The90MeO11—Sn(Bu)3TLC analysis of each reactiontrial exhibited similar results;the TLC chromatogramsshowed the consumptionof some starting material andthe formation of a dominant,slower migrating componentamongst several other minorcomponents. In order toisolate the dominant newcomponent observed by TLC, thereaction mixtures werecombined and subjectedto column chromatographyon silica gel. Half of the originalamount of 32 used forall four trials was recoveredin one portion; then the dominantnew component was isolated withcontinued elution. The270 MHz 1H NMR spectrumof this isolated material revealedthat a mixture of severalcompounds were present.The compounds were identifiedas 25, 3, 173-dimethoxy-17cr-vinyl-1,3,5(10)-estratriene42, and3,17/3-dimethoxy-17a-(E)-fluorovinyl-1,3,5(10)-estratriene43 in an approximateratio of 71:18:11, plus anothercomponent that could notbe identified was present.The use of acetyl hypofluorite,prepared in two differentforms, was investigatednext.Compound 32 was addedto a slight excess of CH3COOFprepared in a solutionofglacial acetic acid andaninionium acetateby the method of Rozen et al?3at roomtemperature. The reactionproceeded for about 15minutes before the aceticacid wasremoved. The crude reactionmixture was analyzedby TLC, which revealed theconsumption of somestarting material and theformation of a new, more polarcomponent91Me07-MeOMeOMeOplus some other minorcomponents. The reactionmixture was furtheranalyzed by 1Hand 9F NMR spectroscopy.The ‘9F NMR spectrum exhibiteda few weak signals dueto unidentified products,whereas the 1H NMR spectrumindicated the presenceof 25,32, and 42,but not fluorovinyl product43.Compound 32 wasthen treated withexcess gaseous CH3COOFin CFC13 at -78°C.The TLC chromatogramof the reaction mixtureexhibited only asmall degree ofconversion of startingmaterial to a new,slower migrating component,along with otherminor components.The 270 MHz 1H NMRspectrum of thereaction mixture revealedlargely unreactedstarting material anda very small amount of 25present. However, the9F NMR spectrumshowed the presenceof 43.These studiesof the reactivity of32 indicate that thisderivative is relativelyunreactivetoward CH3COOFin comparisonto 31. No fluorovinylproduct 43 couldbe obtained92with the use of CH3COOFin acetic acid, whereasonly a minute amountof 43 could beproduced withgaseous CH3COOF. Thereaction of 32 withelemental fluorine producedsome 43 which couldbe identified in a mixtureof products. Theseresults suggested thatfluorine was themost effective fluorinatingagent used with 32.However, a larger scalefluorination of 32utilizing F2 wasnot pursued due tothe low potential yieldandanticipated separationproblems.Next, the reactivityof 33 toward fluorineand acetyl hypofluoritewas examined inseveral small scaleexperiments. In thefirst experiment,33 was allowed to reactwithapproximately0.9 equivalents of dilutefluorine in CFC13at -78°C. The TLC chromatoSn(Bu)3gram of the reactionmixture revealed theformation of a new,more polar componentin addition toa few minor components.The dominant new component,as observed byTLC, was isolatedby column chromatographyand subjected to 1HNMR spectroscopy.This materialconsisted of fourdifferent compoundsthat were identifiedas 28, 7,8-dideoxy-1,2:3,4-di-O-isopropylidene-D-glycero-a-D-galacto-oct-7-enopyranose44, (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, inwhich 44 was the dominantcomponent.93HO HO/°KLo\2844FFor the secondexperiment, 33 was addedto approximately0.8 equivalents ofCH3COOF prepared ina solution of glacial aceticacid and ammonium acetateat roomtemperature. Thereaction was allowedto proceed for about 10 minutes,then the aceticacid was removed.The crude reaction mixturewas analyzed by TLC, whichshowed theformation of a dominant,slower migrating componentplus a few minor components.Column chromatographyof the reactionmixture resulted in theisolation of thedominant new componentobserved by TLC. Thismaterial was examinedby ‘H NMRspectroscopy, whichrevealed that a mixtureof 44, 45, and 46 was presentand 44 was themajor component.In the third experiment,33 was treatedwith approximately 1.2equivalents of gaseousCH3COOF inCFC13 at -78°C.Analytical TEC ofthe reaction mixture revealedthe94formation of a dominant,more poiar componentand a few minorcomponents. Thedominant new component,as observed by TLC, wasisolated via preparative TLC (silicagel), and analyzedby 1H and 19F NMR spectroscopy.This material was foundto belargely a mixture of 45 and46, with some unidentifiedimpurities present.The fluorinationstudies of 33, thoughqualitative in nature,showed that gaseousCH3COOF was themost effective fluorinatingagent used. This agentgave the highestdegree of conversionof 33 to fluorovinyl product(45 and 46). Theuse of F2 orCH3COOF in acetic acidsolution produced 44as the main product. Unfortunately,thesupply of 33—as startingmaterial—was virtuallyall consumed so that further largerscalefluorination workcould not be conducted.Therefore, fluorinationstudies werecontinued using theL-glycero-a-D-galacto epimer 34instead.Compound 34was fluorinated with CH3COOF(Scheme 3.VII) in the followingScheme 3.VIISn(Bu)3F[—OHCH3COOF[—OH [—oH/CFC13/+/maimer. Compound34 was treated with approximately1.3 equivalents of gaseousCH3COOF inCFC13 at room temperature.This procedure was performedwith twoportions of 34to increase the reactionscale. The crude reactionmixtures were95combined and subjectedto column chromatography.(E)-8-C-Fluoro-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-enopyranose47 was isolated in thefirstchromatography fraction,and then two fractionswere collected that containedmixturesof 47,(Z)-8-C-fluoro-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-enopyranose 48, and7,8-dideoxy-1,2:3,4-di-O-isopropylidene-L-glycero-c-D-galacto-oct-7-enopyranose 49.The ratio of componentsin each chromatographyfraction was0ocmeasured by ‘H NMRspectroscopy. The isolatedyields of 47 and 48 weredeterminedto be 36% and10%, respectively. Furthermore,an additional fractionwas subsequentlycollected which was foundto 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-enopyranose50 by ‘H NMR.Compound 47was readily characterizedby ‘H and ‘9F NMR.3.4 RadiofluorinationWorkIn this section,the radiofluorinationof (E)-vinylstannane31 using acetyl[‘8Fjhypofluoritewill be presented.The productionof 18F, like 11C, is alsoroutinely performedat theTRIUMF facility.Fluorine-18 can be producedeither usingthe TRIUMF 500 MeV96cyclotron, or more efficientlywith the smallerTRIUMF/Nordion CP-42 cyclotronviathe2°Ne(p,2pn)18Fnuclear reaction.For this work, circumstancesrequired that theTRIUMF 500 MeVcyclotron be utilized.Radiofluorine was producedby protonirradiation of a gas mixtureof naturalNe*with approximately0.1% F2 present using the20Ne(p,Spall)18Freactionat 500 MeV. Theradiofluorine is obtained inthe form of 18F-labelled F2.Unfortunately, the productionof [‘8F]F2 is necessarilycarrier-added. Sincethecyclotron target is constructedfrom nickel-basedalloy, it must be passivatedwith F2.This process createsa thin layer of nickel fluoridewithin the interior surfaceof thecyclotron target,and provides a sourceof carrier fluorine to bepresent. Moreover, asmall percentage(0. 1-2.0%) of molecular fluorinemust be present in the neon targetgasfor[18F]F2production.However, if the amountof carrier F2 is reducedtoo much in thetarget gas mixturein order to significantlyincrease specific activity, lowyields and poorrecoveries of[18F]F2areobtained.9 As a result,the practical upper limiton the specificactivity of[18F1F2that can be achieved isreported to be around12 Ci/mmol.63Therefore, all electrophilicfluorinations performedwith18F-labelledF2, and reagentsderived from [18F]F2,result in products oflow specific activity.TM Wheneveraradiofluorinated productmust be produced inhigh specific activity,the only availablelabeffing reagent is[18Fjfluoride anion.65 Nonetheless,there has been discussionin theliterature about producinghigh specific activity[18F]F2.The key ideais to exploit thestabifity of the negativefluorine ion in thegas phase and attractthe gaseous anionic ‘8F*Naturalneon consists of90.92% of 20Ne, 0.26% of21Ne, and 8.82%of 22Ne.97to an electrode, then performan electrochemical oxidationto generate[18F]F2.19 Todate, there are no reports of anyoneexploiting this approach,but such a developmentwould represent a true breakthroughfor high specific activity radiofluorinations.Another aspect regardingthe use of18F-labelled F2 is thatthe maximum radiochemicalyield possible is 50%. Dueto the need of carrier F2to be present in the neon cyclotrontarget, it would be a statisticalimprobability that both fluorineatoms in the {18F]F2produced would be fluorine-18(i.e., 18F—’8F). Therefore,only one fluorine-18 atomisexpected to be present ina 18F-labelled F2 molecule (i.e.,18F—’9F). As a result, ifanelectrophilic fluorinationreaction proceeded in100% maximum chemical yield, thecorresponding radiofluorinationprocedure would be expectedto give 50% radiochemicalyield at best, since thereis only a 50% probabffityof the fluorine-18 atom becomingincorporated rather than thefluorine-19 atom. For reactionsusing fluorination reagentssuch as CH3COO’8F,whichcontain only one fluorine atom,the maximum radiochemicalyield continues to be50% because all these reagents are preparedfrom[18F]F2.This isan unfortunate disadvantageof all radiofluorination methodsthat utilize[18F]F2 as thesource of fluorine-18.9The general procedureused for the radiofluorinationreactions of 31 is as follows.The 500 MeV cyclotrongas target was filled withthe desired amount of1% F2/Ne gasmixture, then pure Newas added to dilute the F2gas content to approximately0.1% F2in Ne. The targetgas mixture was irradiatedwith the 500 MeV protonbeam. (Typical18F productionparameters were 10 mmof target irradiationat 69 A of beam current.)When irradiationof the cyclotron targetwas stopped, the time wasnoted and designated98as the end of bombardment(EOB). After target irradiationwas completed, the contentsof the target werepassed through a potassium acetate/aceticacid column to producegaseous acetyl[‘8F]hypofluoriteand was added to a solutionof 31 (110-120 mol) inCFC13 (20 mL). Thereaction mixture was assayedfor radioactivity (before andafterevaporation of CFC13), alongwith the ammonium acetate/aceticacid column. Afterdissolution in some chloroform,a small aliquot of reaction mixturewas subjected toradio-HPLC purificationand the peak correspondingto‘8F-labelled fluorovinyl productwas collected, then assayedfor activity. An equal volumeof reaction mixture was alsoassayed at the same time inorder to determine the percentageof product that waspresent in the reaction mixture.Based on the total activity of ‘8Fproduced at EOB, theradiochemical yield wasthen determined. Theresulting radiochemical yields weredecaycorrected back to BOB.Compound 31 was radiofluorinatedwith CH3COO’8F,as outlinedin Scheme 3.VIILScheme 3 VIIIHOHOCH3COO18FMeOCFC13HOMeO31MeO3The results obtained are summarizedin Table 3.4. Compound31 was kept in excessrelative to fluorinatingagent in order to minimizeside-reactions and to maximizetheefficiency of incorporation ofradiofluorine. Using excessfluorinating agent would helpmaximize the chemical yield,but could produce lower radiochemicalyields. Theradiofluorination reaction of31 gave the highest radiochemicalyields (19%) whenconducted at room temperature.The radiolabelled productthat was isolated for yielddeterminations wasa mixture of 3-methoxy-17-a-(E)-[18F]fluorovinyl-1,3,5(10)-estra-Table 3.4: Summary of RadiochemicalYields Obtained for theReaction of 31 with Acetyl[18FjHypofluoriteAmount ofTemperatureaRadiochemicalCH3COO18Fused Yieldb—0.74 equiv r.t.19%—0.50 equivr.t. 19%—0.77 equiv-78°C 9.7%—0.50 equiv-78°C5.0%ar.t.= room temperature.bRefersto the combined yield of 51 and52; the radio-chemical yield wasdetermined from the initialactivityof[18FJF2producedat EOB.triene-17-o1 51and 3-methoxy-17a-(Z)-[18F]fluorovinyl-1,3,5( 10)-estratrien.e-17i3-ol 52.The specific activity ofthis product mixture wasnot determined. However,in a separateexperiment, thespecific activity of CH3COO’8Fgenerated using 18Fproductionparameters describedearlier was determinedto be about 190 mCi/mmol.Therefore,the isolated productmixture wouldbe of quite low specificactivity, as expected.The identificationof the[18F]fluorovinylproducts 51 and 52was accomplishedusing100radio-HPLC studies. Thechromatographic behaviourof 51 and 52 was consistent withthat observed for the relatednon-radioactive fluorovinylcompounds (39 and 40). Inaddition, the leftover reactionmixtures (after radio-HPLCanalysis), obtained from theradiofluorinations done at roomtemperature (firsttwo entries of Table 3.4), wereallowed to decay to zero activity.These mixtures were then analyzedby ‘9F NMRspectroscopy. The19JNMR spectra readily confirmedthe presence of 39 and 40,thereby confirming thesuccessful radiofluorination of31.In this study, the fluorinationreaction of 31 withgaseous acetyl hypofluorite wassuccessfully extendedto accomplish the 18F-labelling of31. The radiofluorinationreaction is essentially instantaneousupon addition of fluorinatingagent. The time takenfrom EOB to the isolationof crude reaction mixturewas in the order of 15-17 minutes.The additional time requiredthereafter was for the radio-HPLCpurification work.Clearly, the synthesistime is quite short and wellsuited for radiolabelling with ‘8F.3.5 Summary and ConclusionsThe purpose of thisstudy was to develop a generalmethodology to directly preparefluorovinyl compoundsfrom vinyl-tin intermediates,and to utffize this synthetic approachfor radiofluorinationswith ‘8F. This objectivewas indeed fulfilled toa large degree, asmost of the vinyl-tin substratesstudied were successfullyfluorinated using gaseousacetylhypofluorite. In addition,one of the vinyl-tin derivativeswas radiofluorinated withacetyl[‘8F]hypofluorite inrespectable radiochemicalyield.The vinyl-tinsubstrates were readily obtainedfrom the AIBNcatalyzed hydrostamiyl101ation of the corresponding acetylenic precursors,with tri-n-butyltin hydride, in 59-94%yield. The reactivities of (E)-vinylstannanes30, 31, 32, 33, and 34 were studied withelemental fluorine and acetyl hypofluorite undervaried conditions.The most effective fluorinating agent usedto fluorinate 31 was gaseous acetylhypofluorite, at room temperature, whichafforded yields of 4 1-42% of 39 and 40 as anisomeric mixture (yields determined viaHPLC analysis). In contrast, fluorination of 31with elemental fluorine gave9.0% yield at best. Furthermore, (E)-fluorovinyl39 and(Z)-fluorovinyl 40 were prepared andisolated in 29.5% and 3.8% yields, respectively,from the reaction of 31 with CH3COOF.Compound 30 could not be directlyfluorinated using either F2 or CH3COOF. Thisresult is most likely due to the presenceof the unprotected phenol function of 30. Byprotecting this group, it wouldbe anticipated that 30 can be successfully fluorinated inan analogous manner to 31. Alternatively,32 was found to be relatively unreactivetoward fluorinationas compared to 31. Reaction of 32 withgaseous CH3COOFproduced only a trace of (E)-fluorovinylproduct 43. Better results wereobservedemploying elemental F2 as some 43could be obtained as a minor componentin amixture of products.Compound 33 was readilyfluorinated using gaseous CH3COOF. Treatmentof 33 withCH3COOF (prepared inacetic acid solution) or with F2also generated fluorinatedproduct, but gave 44as the main product. However, thestock of 33 had been virtuallyall consumed, so that furtherlarger scale reactions withgaseous CH3COOF could notbe performed. Therefore, fluorinationstudies were continued withL-glycero-a-D-galacto102epimer 34 instead. Compound 34 wasallowed to react with gaseous CH3COOF(atroom temperature) and (E)-fluorovinyl 47 and(Z)-fluorovinyl 48 were obtained in36%and 10% yield, respectively.Compound 31 was radiofluorinatedusing gaseous acetyl[18F]hypofluorite in19%radiochemical yield. The radiolabelledproduct consists of a mixture of (E)[‘8F]fluorovinyl 51 and (Z)-[18Fjfluorovinyl52 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 inCarbon-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 BioorganicChemistiy; Welch, J. T., Ed.; ACSSymposium Series 456; American Chemical Society:Washington, DC, 1991.6. Filler, R.; Naqvi, S. M. In Biomedicinal Aspectsof Fluorine Chemistiy; Filler, R.,Kobayashi, Y., Eds.; Kodansha Ltd.: Tokyo, 1982;Chapter 1.7. Welch, J. T. In Selective Fluorinationin Organic and Bioorganic Chemistiy; Welch,J. T., Ed.; ACS Symposium Series 456; American ChemicalSociety: Washington,DC, 1991; Chapter 1.8. Fowler, J. S.; Wolf, A. P. The Synthesisof Carbon-li, Fluorine-i8, and Nitrogen-i3LabeledRadiotracersforBiomedicalApplications; Nuclear ScienceSeries, MonographNAS-NS-3201; Technical Information Center,U.S. Department of Energy:Springfield, VA, 1982.9. Kilbourn, M. R. Fluorine-i8 Labeling of Radiopharmaceuticals; NuclearScienceSeries, Monograph NAS-NS-3203; NationalAcademy: 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. LiebigsAnn. 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, 2nded.; John Wiley and Sons: New York, 1976.10416. New Fluorinating Agents in OrganicSynthesis; 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 reference9;pp70-90.23. 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. FluorineChem. 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. FluorineChem. 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. LabelledCompd. 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. LabelledCompcL 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 OrganicandBioorganic 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 Fluorinationin 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 Universityof 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 Chemzstiyof Organotin Compounds; Academic: New York,1970;pp112-113.60. 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;p5.64. See reference 9;pp22-24.65. See reference 9;p37 and 43.107Chapter 4GENERAL CONCLUSIONSThe investigation presentedin Chapter 2 demonstratedthat(6-arene)tricarbony1-chromium complexescan be used as synthetic intermediatesfor the radiolabelling of theattached arene ring with“C via nucleophilic substitutionwith[11C]cyanide. This resultrepresents the first applicationof chromium tricarbonyl complexesfor radiolabelling withshort-lived nucides. Froma broader perspective, however,this accomplishment couldbe the first step to a rangeof new radiolabelling methodsbased on the utilization oforganotransition metal complexes.A number of transition metal systemsfacilitate theaddition of various nucleophilesonto unsaturated organic molecules whilecomplexedto the metal centre.’This pattern of reactivity needsto be explored further withnucleophilic forms of medicallyuseful radioisotopes,2suchas ‘8F, 75Br, 77Br, and 123jThe application of chromiumtricarbonyl complexes could besignificantly advancedwith additional studies.A further exploration of reactionconditions should be conductedto improve radiochemicalyields, particularly with NCA [“Cjcyanide.This could includean investigation ofvarious crown ether andother catalysts, employmentof microwavedrying of the [“C]cyanidesolution and microwave heatingof the radiolabeffingreaction,and the use of smallervolumes of reaction solventto concentrate the reactants.Also,a study of alternativeways of trappingH11CNin the absence of hydroxidemay result in108significantly improved labelling yields. Furthermore,other potentially effective leavinggroups should be explored to complementor supersede fluorine. Lastly, the substitutionreactions of F-, Br, and 1 with chromiumtricarbonyl complexes warrant study becauseof the importance of radiohalogens innuclear medicine.2The investigation described in Chapter3 revealed that vinyl-tin derivatives can bedirectly fluorinated with gaseous acetylhypofluorite, in most cases, to produce stable and‘8F-labelled vinyl fluorides. This resultrepresents another extension of the use oforganotin compounds for electrophilicfluorinations, including radiofluorinations with‘8F.Very recently, other researchershave reported using vinyl-tin compoundsto 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 whichproduced vinyl fluorides in 25-56% yield, and insomecases, a-fluoroketones were unexpectedlymade in 47-75% yield (reactions were runovernight). Matthews et al.5 reportedthe electrophilic fluorination of several(fluorovinyl)stannanes with 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2joctanebis(tetrafluoroborate) affording difluoroolefins in 35-74% yield (30 mm reaction timeat 80°C). Each of these reportsprovides new methods for fluorinating vinyl-tincompounds which is very positive, however,each of these methods, for various reasons,would appear to beincompatible for radiolabelling with ‘8F. Whatis gratifying is thatseveral years after choosing vinyl-tinintermediates for our fluorination studies, otherresearch groups are alsoselecting tin reagents for the preparationof vinyl fluorides.109Undoubtedly, the application of organotincompounds will continue to be extendedasinterest in selectively fluorinated organicmolecules remains.Nonetheless, the following suggestionsfor future work can be made. The explorationof alternative fluorinating agents foruse with vinyl-tin substrates would be veryprudent.Also, the reactivity of fluorine andacetyl hypofluorite should be further examined witha wider range of structurally diversevinylstannylated derivatives. Moreover, thefluorination of vinyl-silicon and -mercuryderivatives warrant some additionalstudy.In retrospect, it is pleasing to see thatalthough a few years have unfortunatelyelapsedsince the experimental workwas performed and the writing of this thesis completed, theresults obtained are still new and currentlyrelevant, and have not been duplicatedin theliterature. Even though various aspectsof the specific experimental studiescould havebeen done differently, the studies pursuedfor this thesis were well worthwhile andexhibit significant future potential. Theapplication of organometallic compoundsassynthetic intermediates for radiolabellingis only in the early stages of developmentstill,but will continue to expand with futureresearch.110References1. Davies, S. G. Organotransition MetalChemistiy: Applications to OrganicSynthesis;Pergamon: Toronto, 1982; Chapter4.2. Nozaki, T. In RadionuclidesProduction; 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. Synlett1992, 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 underreduced pressure with aBüchi rotary evaporator,except for solutions of organochromiumcomplexes, which were concentratedin vacuousing a high vacuum,rotary vacuum pump assembly.Melting points were taken incapillaries (in air) usinga Büchi 510 oil bath melting pointapparatus, or were obtainedon a Fisher-Johns meltingpoint apparatus, and are uncorrected. Opticalrotations weredetermined using a Perkin-Elmermodel 141 polarimeter.Tetrahydrofuran (THF)and diethyl ether were distilled fromcalcium hydride orsodium benzophenone ketyl.’ Dimethylsulfoxide (DMSO) was distilledunder reducedpressure from calcium hydride,then carefully stored undernitrogen. Di-n-butyl etherwas distilled from sodiumunder nitrogen, while hexane,dichioromethane, andacetonitrile were distilledfrom calcium hydride. Methanolwas distified from magnesiummethoxide prepared insitu by reaction of methanolwith magnesium turnings. Forhighpressure liquid chromatography(HPLC) work, singly distilledwater, HPLC gradeacetonitrile and methanol,and reagent grade hexanes and diethylether were used, whichwere filtered (0.45m Millipore brand Duraporemembrane) before use. Allothersolvents used were ofspectro or reagent grade,and were used without further treatment.112Thin-layer chromatography(TLC) was performedon pre-coated silica gelplates(Baker-flex Silica gel 1B2-For E. Merck Silica gel 60,No. 5534). Visualizationwaseffected eitherby (a) spraying with 30% sulfuricacid in ethanol, then heating,(b) withshort-wavelength UV light,or (c) by visual inspection(for coloured, organochromiumcompounds). TheTLC solvent systems usedwere very similar to thoselisted for thecolumn chromatographyof the individualcompounds. Column chromatographywasperformed using Silicagel 60 (E. Merck, 70-230mesh). Flash chromatographywasperformed using Silicagel 60 (E. Merck, 230-400mesh) by the method ofStill et al.2HPLC was done witha system consistingof a Spectro-Physics SP 8700 solventdeliverysystem, a Rheodyne 7126injector, an ISCO (modelV4)variable wavelengthUV detectoroperated at 254-280 nm,and a Spectro-PhysicsSP 4270 integrator recorder,using oneof the following columns,either (a) a Waters 10Lm C-18 reverse phase RCMcolumn(column A),(b) two Waters 10 m C-18reverse phase RCM columnsconnected inseries (column B),(c) a C-18 reversephase Whatman Partisil10 ODS-3 column, 25 cmx 9 mm, equipped witha Waters C-18 guard column(column C), or (d) normalphasePhenomenex Ultremex5 Silica column, 25 cmx 10 mm (column D). Thefollowingsolvent mixtureswere 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/diethylether, 4:1 (solvent D).The following gradientsolvent programs werealso used for HPLC:(i) from 0 to 10mm, an isocratic mixtureof methanol/water(85:15) wasused, followedby a systematic increaseto 100% methanol during 10to 12mm, and a constantcomposition of100% methanol was maintainedfrom 12 to 20 mm113(solvent program A), and (ii) from 0 to18 mm, an isocratic mixture of methanol/water(75:25) was used, followed by a systematicincrease to 100% methanol during 18to 21mm, and a constant composition of100% of methanol was maintained from 21 to 30 mm(solvent program B). Radio-HPLCanalysis and purification was performed with thesame HPLC system fitted with a NaI(Tl) scintillationdetector system and a dual channelstrip chart recorder. Radioactive sampleswere assayed with either a Capintec wellcounter (model CRC-543X) or a Beckman8000 scintillation counter.Analytical gas chromatography (GC)was performed with a Hewlett-Packard model5840A GC, equipped with an FIDdetector, using a 30 m x 0.75 mm i.d. widebore(Supelco SPB-1) capillary column. Unless otherwisestated, GC analyses were performedisothermally using the followingconditions: injection temperature, 200°C; oventemperature, 120°C; N2 carrier gas flow,2.0 mt/mm.Low resolution electron impactmass spectra were recorded with either a Kratos/AEIMS902 or a Kratos/AEI MS5Omass spectrometer. An ionization potential of70 eV wasused for the mass spectra obtained.Spectra are quoted as m/z values,while selectedion fragmentations are reportedas percentages of the base peak. High resolution massmeasurements were determined usingthe Kratos/AEI MS5O mass spectrometer.Gaschromatography-mass spectrometry(GC-MS) was performed using a Delsi Nermag RiO1OC quadruple mass spectrometerinterfaced with a Varian 6000GC or a Kratos MS8Ocoupled to a Carlo Erba4160 GC.All microanalyses wereperformed by Mr. P. Borda, MicroanalyticalLaboratory,University of British Columbia.1145.2 NMR Methods and Instrumentation1H NMR spectra were measured at room temperature at 270and 400 MHz. The 270MHz spectra were obtained with a home-builtspectrometer based on a Bruker WP-60console, a Nicolet 1180 computer (32K),a Nicolet 293B pulse programmer, a oneMegabyte Diablo disk drive (model 31), and anOxford 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 forprocessing and plotting of NMR data.Standard NTCFTB software wasused on the spectrometer and data station.Furthermore, some of the 270 MHzdata was transferred from the Nicolet 1180 datastation to a newer Nicolet 1280 computer, forprocessing with increased computermemory and digital plotting.The 400 MHz spectra were obtained witha Bruker WH-400 high-resolutionspectrometer equipped with an Aspect3000 computer. Along with this spectrometer,a separate Bruker data processingsystem, comprised of an Aspect 3000 computer, digitalplotter and dot matrix printer, wasavailable for data processing and plotting. FactoryBruker software was used on thespectrometer and data station.‘9F NMR spectra were measuredat 188 and 254 MHz, also at room temperature. The188 MHz spectra wereobtained with a Bruker AC-200E spectrometer.The NMR datafrom this spectrometer was transferredto and processed on the Bruker data station,described above. The 254 MHz spectrawere obtained using the previouslydescribedhome-built spectrometer (controlledby the Nicolet 1180 computer) with a home-built,11519F-tunedprobe.*5.3 Experimental for Chapter 25.3.1 Sources of MaterialsChemicals and reagents were purchasedfrom suppliers as follows. Chromiumhexacarbonyl was obtained fromPressure Chemical Co. Fluorobenzene, 2-and 4-fluorotoluene, 4-chiorofluorobeuzene,4-chlorobenzonitrile, methyltrifluoromethanesulfonate, and 18-crown-6 were purchasedfrom Aldrich Chemical Co. Eastman KodakCo. supplied the benzonitrile and 4-tolunitrile,and ICN Pharmaceuticals Inc. suppliedthe 2-tolunitrile. HPLCgrade methanol and acetonitrile were obtainedfrom FisherScientific Ltd., or BDH Chemicals.5.3.2 GeneralAll manipulations for the preparationand purification of the(6-arene)tricarbonyl-chromium complexes were performedso as to maintain all chemicals under anatmosphere of nitrogen or argon usingconventional bench-top techniquesfor themanipulation of air-sensitivecompounds.3The(6-arene)tHcarbonylchromiumcomplexes, that were synthesizedfrom Cr(CO)6,were prepared either usinga 200-mL, round-bottom, three-neck flaskfitted with anitrogen inlet, a magnetic stirbar, and a condenser equipped witha mineral oil-bubblerThe probe constructionand electronics was done by TomMarkus (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 3in. long condenser which is joined to anadditional 3 in. long glass tube (1 in. o.d.) equippedwith a centralST*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 reachesto a dimple at the bottom ofthe flask and has a small paddle near thebottom of the flask (to stir the reactionmixture) plus a 3 in. long screw paddle whichclosely fits the interior wall of thecondenser region (to scrap and return sublimedCr(CO)6to the reaction mixture). Theglass rod is rotated by a variablespeed, overhead stirrer motor. The assembledglassware is also equipped with a nitrogen inletand mineral oil bubbler. With eitherset-up, the glassware was wrapped with aluminumfoil to protect the reaction from light.Silica gel 60 (E. Merck, 70-230 mesh) wasused for the filtration of organochromiumsolutions to remove any decomposition.All substitution reactions were carriedout in oven-dried Pierce Reactivials®(Rockford, IL) equipped with magnetic stirbars and screw caps that were fitted withTeflon-lined, silicone septa.tH”CN was produced via the catalyticconversion of “CO2.The “CO2 was producedon the TRIUMF/Nordion CP-42cyclotron using the‘4N(p,a)11Creaction at 15MeV.The “CO2 in the N2 targetgas was converted to “CH4 by mixing the targetgas with*sTdenotes standard taper.1These septa provided an excellentseal to maintain the exclusion ofair andmoisture, and to preventthe loss of volatile components.117H2(g) then passing themixture over a Ni cata]ystat 450°C. Thereafter,the 11CH4 wascombined with NH3(g)and passed over Pt at1000°C, thus obtainingH”CN.4 TheH’1CN was trapped inan aqueous solution ofNaOH (1 mL, 0.1 M)to produce Na”CN.5.3.3 Preparation of(,6-Arene)tricarbonylchromiumComplexesPreparation of(i-fluorobenzene)tricarbonylchromium1.Chromium hexacarbonyl(1.0g, 4.54 mmol) and fluorobenzene(5.0 mL, 53 mmol)were dissolved in amixture of (n-Bu)20/THF(80 mL/10 mL) in glasswareA. Thereaction mixture wasdegassed by performingthree freeze-pump-thaw cycles.Uponreintroducing a nitrogenatmosphere into the reactionvessel, the stirred reactionmixturewas heated to refluxfor 48 h. The reactionmixture was cooled toroom temperatureand filtered througha short pad of silica gelto remove any greyish-greendecomposition.The bright yellow filtratewas evaporated to drynessin vacuo. The residuewas dissolvedin diethyl ether, andthe resulting solutionwas transferred by canulafiltration into aSchlenk tube.The undissolved residuewas then washed withsome hexane and thesewashings werelikewise added to theether solution. Solventwas slowly removedunderreduced pressure untilyellow crystals beganto appear. The ether/hexanemixture waswarmed gentlyuntil all crystalsredissolved, then was placedin the freezerforcrystallization. Brightyellow crystals wereisolated and dried undera flow of N2,initially, then undera high vacuum overnight.Two additionalcrops of crystals wereobtained fromthe mother liquor,affording a total yieldof 0.84g (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 (1.86g, 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 cooledto room temperature, then filteredthrough a short pad of Celite using some diethyl etherto rinse and facilitate the transferof the reaction vessel contents. The yellow filtrate wasconcentrated via distillationunder reduced pressure, then some petroleumether 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 processwas repeated several timesand the volume of diglyme was successfully reduced.Once again, petroleum ether wasadded to the concentrated solution till a small amount of precipitationoccurred, thenwas placed in a fridge for cooling. A single large,yellow crystal was obtained, which wasremoved and washed with cold petroleum ether, thendried under a flow of argon. Thefiltrate was heated and filtered hot,to remove some greenish decomposition, then wasplaced back in the fridge for crystallization. Yellowcrystals (400 mg) were isolated anddried in vacuo. The large singlecrystal, obtained initially, was recrystallized from hotpetroleum ether. This afforded 265mg of additional yellow crystals, which gave a totalyield of 47% (665 mg) of 2(based on Cr(CO)6consumed*),mp 100-101°C {lit.6 mp*UnreactedCr(CO)6remaining in the reaction vessel was recoveredby sublimationunder high vacuum; this gave0.60 g of recovered Cr(CO)6.119101-102°C}.Preparation of(6-bromobenzene)tricarbony1chromium3.Chromium hexacarbonyl(4.00 g, 18.2 mmol) and bromobenzene (10.0mL, 95.2 mmol)were added to a mixture of(n-Bu)20/THF (100 mL/10 mL)in glassware B. Thereaction mixture was degassedby performing a single freeze-pump-thawcycle. Uponreintroducing an N2 atmosphereover the reaction mixture, it washeated, with stirring,to reflux for 44 h. The cooled reactionmixture was filtered through a shortpad of silicagel and the yellow filtrate was reducedto dryness in vacuo. Compound3 was obtainedas dark yellow crystals, ina yield of 992 mg (19%), mp 101-105°C {lit.7mp 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), 131e9Br: 7), 52 (100).Preparation of(i6-2-fluorotoluene)tricarbonylchromium4.Chromium hexacarbonyl (1.0g, 4.54 rninol) and 2-fluorotoluene (5.8 mL, 53 mmol)were dissolved in a mixtureof (n-Bu)20/THF (80 mL/10mL) in glassware A. Allsubsequent steps wereessentially identical to thepreparation of compound 1.Compound 4 was obtainedas yellow crystals, in a total yield of0.99 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)tricarbonylchromium5.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 degassedby performing a single freeze-pump-thaw cycle.Uponreintroducing an N2 atmosphereover the reaction mixture, it was heated,with stirring,to reflux for 16.5 h. The cooled reactionmixture was filtered through ashort pad ofsilica gel and the yellow filtrate was reducedto dryness under reduced pressure. Afterfurther drying in vacuo,compound 5 was obtained as bright yellowcrystals, in a yield of3.79 g (85%), mp 59-60°C {lit.8 mp61-62°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)tricarbonylchromium6.Chromium hexacarbonyl (4.00g, 18.2 mmol) and 4-chlorofluorobenzene (10.0 mL, 93.9nimol) were added to a mixtureof (n-Bu)20/THF (100 mL/10 mL)in glassware A. Thestirred reaction mixturewas heated to reflux for 23 h. Uponcooling to roomtemperature, the reaction mixturewas concentrated to about 10 mL under reducedpressure and a plugof sublimed Cr(CO)6(1.1g) was recovered from the condenser. Theconcentrated reaction mixturewas chromatographed on neutral alumina(Fisher, 80-200mesh) with hexaneas the eluent. A single yellow band was collectedand the solvent wasremoved in vacuo. TLCanalysis, on alumina (eluent: hexane), ofthe yellow residueshowed the presence oftwo components. Column chromatographywas repeated on the121two-component mixture using silica gel with hexane/ether(5:1). The first fraction, aftersolvent removal, afforded 0.42g 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 (0.12g) was collected, which contained a mixture of 1 and 6, with6 being the dominant component as determinedby ThC analysis (silica gel; eluent:hexane/ether, 1:1). This material unfortunatelyunderwent partial decomposition andwas discarded.A final fraction was collected, and afterthe eluate was evaporated to drynessin vacuo,0.11 g of yellow crystals were isolated,mp 97-100°C. TLC analysis (silica gel;eluent:hexane/ether, 1:1) showed this materialto be a mixture of 1 and 6, with 1being themajor component present. Massspectrometric analysis of this mixture gave thefollowingresults; mass spectrum, m/z: compound1, 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 yieldof 6 (obtained from the first fraction)was 12%, based on theamount of Cr(CO)6consumed.122Preparation of(q6-N,N-dimethylaniline)tricarbonylchromium7.Chromium hexacarbonyl (4.00g, 18.2 mmol) and N,N-dimethylaniline (20 mL, 0.16mol) were dissolved ina mixture of (n-Bu)20/THF (60 mL/5 mL)in glassware A. Thestirred reaction mixture was heatedto reflux for 21 h. After coolingto roomtemperature, the volume of thereaction mixture was concentrated underreducedpressure and a large crop of yellowcrystals deposited. The remaining supernatantwasthen canula transferred to anotherflask. The crystals were collectedon a glass frit andwashed repeatedly with cold hexane, thendried in vacuo. Compound 7 was isolatedasyellow crystals, for a yield of 3.30g (70%), mp 137-138°C {lit.6 mp 144°C}.Preparation of ((-benzonitri1e)tricarbony1chromium10.DMSO (2 mL) was addedto compound 1 (44.8 mg, 0.193 mmol)and NaCN (21.4 mg,0.437 minol) contained ina 5-mLReactivia1®under argon. The reaction mixturewasstirred for 23 h at ambient temperature.The reaction mixture was thenadded to water(20 mL) and subsequentlyextracted with diethyl ether (3x 15 mL). The ether extractswere washed with aqueous,saturated sodium chloride solution anddried over anhydrousmagnesium sulfate. The driedether extracts were filtered througha short pad of silicagel and the solventwasjaken to dryness under reduced pressure.Compound 10 wasisolated as yellow crystals, ina yield of 32 mg (69%).123Preparation of(6-N,N,N-trimethy1aniIinium)tricarbony1chromiumtrifluoromethanesulfonate 11.Compound 7 (1.00g, 3.89 rnmol) was added to CH2C1 (25mL) and stirred at roomtemperature until dissolved.Methyltrifluoromethanesulfonate(1.1 mL, 9.7 rnmol) wasadded by syringe and themixture was stirred overnight.Yellow crystals had depositedand the supernatantwas canula transferred to anotherflask. This solution was stirredovernight. The yellowcrystals were dried in vacuo,then dissolved in acetonitrile.Theresulting solution wastransferred by canulafiltration into a Schienk tube. Thevolumeof CH3CN was reducedby a third under reduced pressure,then diethyl ether was addeduntil the solutionbecame slightly cloudy. Thismixture was placed inthe freezerovernight.The previous solution, inwhich the reaction was allowedto continue, afforded anothercrop of yellow crystals.These were isolated and recrystallizedas described for the firstbatch of crystals. Bothbatches of crystals were isolated,and dried under a flowof N2initially, then underhigh vacuum. Compound11 was obtained as yellowcrystals, in atotal yield of 0.97g (59%). An analytical sample was obtainedby performing twosequential recrystallizationsof a portion of 11 from acetonitrile/diethylether, mp 120-121°C(dec.).*Anal. calcd. forC,3H,4CrFNO6S:C 37.06, H 3.35, N 3.32,S 7.61; found:C 37.40, H 353, N3.49, S 7.44. ‘H NMR (270MHz, 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).*Performedin capillaries that werepacked and sealed undernitrogen.124Preparation of N,N,N-trimethylaniliniumtrifluoromethanesulfonate 12.N,N-Dimethylaniline (1.00 mL,7.89 mmol) and methyltrifluoromethanesulfonate(1.1mL, 9.7 mmol) were added sequentiallyby syringe to CH2C1 (25 mL) whileunder anitrogen atmosphere. The reactionmixture was allowed to stirat room temperature.After 30 mm, TLC analysis indicatedthat all the N,N-dimethylaniline presentwasconsumed. The copious quantitiesof white crystals that deposited,were collected anddried in vacuo. These crystals wererecrystallized from dichloromethane/diethylether,which afforded a total yieldof 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-trimethylaniliniumiodide 13.N,N-Dimethylaniline (1.00 mL,7.89 mmol) and iodomethane(0.54 mL, 8.67 mmol)were added to CH2C1(25 mL) under a nitrogen atmosphere.The reaction mixture wasallowed to stir overnightat room temperature. The resulting whitecrystals which haddeposited were collected, washedwith diethyl ether and dried underreduced pressure.Compound 13 was obtained ina yield of 1.16g (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 Reactionsof Organochromium ComplexesSubstitution reactions withstable cyanide.General Procedure: Analiquot (200 L, 10 mg/mL)of aqueous KCN (32 mo1)was125injected into a 5-mL Reacti-vialunder inert atmosphere. The waterwas evaporatedto dryness, using a block heater,under a rapid flow ofnitrogen or argon. The(,-arene)tricarbonylchromium complex(65 mol) was taken up in DMSO(1 mL), thenadded by syringe to theReacti-vial®. The stirred mixturewas heated at the desiredtemperature in a thermostatedsilicone oil bath for 10 minutes.After cooling (ice/waterbath) to room temperature, thereaction mixture was quantitativelytransferred to avolumetric flask and diluted toa known volume with DMSO. This solutionwas analyzedby HPLC, which was standardizedwith known solutions of expectedaryl nitrile product,to determine the extent of productformation. The chemical yields werecalculated usingKCN as the limiting reagent.A separate set of reactionswere performed to isolatethe organic products and identifythese by GC-MS, therefore,the workup of these reaction mixtures,after cooling, wasconducted as follows.The reaction mixture was dilutedwith water or saturated NaC1solution (3 mL), andextracted with diethyl ether (1 x6 mL, 2 x 3 mL). The combinedether extracts were washedwith water or saturated NaC1solution (2 x 3 mL). Thestirred ether solution wastreated with iodine (146 mo1)at 0°C for 2 hours to ensurecomplete decomplexation.The treatment was quenched withthe addition of aqueoussodium thiosulfate solution(5 mL, 0. 1M) and the ether layerwas washed further withsodium thiosulfatesolution (4 mL, 0.1M), then withsaturated NaC1 solution (2 x 4mL)and was dried over anhydrousmagnesium sulfate. Thedried ether layer was filteredandconcentrated under reducedpressure to 1 mL. Theconcentrated ether solutionwasanalyzed initiallyby GC and HPLC, thenby GC-MS.126Reaction of 1 with cyanide.A typical reaction trial was performedas follows. Compound 1 (15.6 mg,67.21Lmol)was allowed to react withKCN (2.10 mg, 32.2 mol),at 135°C, as described inthegeneral procedure above.The final DMSO mixture wasanalyzed 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 benzonitrile14(RT*= 5.4 mm) was present,for a yield of 40%.Other reaction trials were conductedat 105, 115, 120, and 150°C, whichgave yieldstof 12, 32, 31, and 33%, respectively.Reaction of 4 with cyanide.A typical reaction trial was performedas follows. Compound 4 (16.2 mg,65.8 mol)was allowed to react withKCN (2.10 mg, 32.2 jmol),at 105°C, as described in thegeneral procedure. The finalDMSO mixture was analyzedby HPLC (column B; eluent:solvent C; flow rate, 2.5mL/min; UV detection, 270rim) and it was determinedthat1.62 mg of 2-tolunitrile15(RT=12.1 mm) was present,for a yield of 43%.Other reaction trials wereconducted at 95, 115, 125,and 135°C, which gave yieldstof 26, 41, 29, and36%, respectively.Two reaction trialswere performed using 1.5mg (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 mgof 15‘RT denotes retention time.1These results represent thebest chemical yields obtainedwhere more than onereaction trial was performed.127was obtained, for a yield of58% based on 4 as the limiting reagent.A separate reaction trial was doneto identify the organic productsby GC-MS.Compound 4 (16.2 mg, 65.8 mol)was allowed to react withcyanide, at 120°C, asdescribed in the general procedure.The concentrated ether solutionwas analyzed byGC and only two significantpeaks were observed, whichwere identified as 2-fluorotoluene(RT=3.2mm) and 2-tolunitrile 15(RT=5.7mm). This sample was furtheranalyzed by HPLC (columnA; eluent: solvent C;flow rate, 2.5 mL/min; UV detection,270 nm) and found that15 eluted first(RT=7.3 mm), followed by 2-fluorotoluene(RT16.2 nun). Identificationof the above products wasaccomplished by thecomparison of the GCand HPLC retention timeswith those of authentic samples. Theidentity of the productswas further confirmedby GC-MS, using for comparisonthe massspectra (acquired under verysimilar instrumental conditions)obtained from a premadesolution of authenticsamples. 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 trialwas performed as follows.Compound 5 (16.1 mg, 65.4ILmol)was allowed to react withKCN (2.10 mg, 32.2/Lmol), at 115°C, as describedin thegeneral procedure.The final DMSO mixturewas analyzed by HPLC(column B; eluent:solvent C; flow rate,2.5 mL/min; UV detection,270 nm) and itwas determined that1.11 rng of 4-toluriitrile16(RT=12.2 mm) was present,for a yield of 29%.128Other reaction trials were conductedat 105, 125, 135, and 150°C, which gaveyields*of 11, 21, 26, and 21%, respectively.A separate reaction trialwas done to identify the organic productsby GC-MS.Compound 5 (16.5 mg,67.0 mo1) was allowed to react withcyanide, at 135 °C, asdescribed in the general procedure.The concentrated ether solutionwas analyzed byGC and only two prominentpeaks were observed, whichwere 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; UVdetection,270 mm) and found that 16eluted first(RT=7.mm), followed by 4-fluorotoluene(RT=15.9 mm). Identification of theabove products was performedby the comparisonof the GC and HPLCretention times with those of authenticsamples. The identity ofthe products was further confirmedby GC-MS, using for comparison themass spectra(acquired under very similar instrumentalconditions) obtained from a premadesolutionof 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 trialwas performed as follows. Compound6 (18.2 mg, 68.3 1mol)was allowed to react withKCN (2.10 mg, 32.2Mmol),at 115°C, as described in the‘These results representthe best chemical yields obtainedwhere more than onereaction trial was performed.129general procedure. The final DMSO mixturewas analyzed by HPLC (column B; eluent:solvent C; flow rate, 2.5 mL/min; UVdetection, 270 urn) and it was determined that1.53 mg of 4-chlorobenzonitrile 17(RT=12.5 mm) was present, for a yield of34%.A reaction trial was also conductedat 135°C, which gave a yield of 21%.An additional reaction trial was performedat 115°C that was heated only for 5 mm(instead of 10 mm) and gave a chemicalyield of 17%.A separate reaction trial was doneto identify the organic products byGC-MS.Compound 6 (17.7 mg, 66.3 mo1) wasallowed to react with cyanide, at 115°C,asdescribed in the general procedure.The concentrated ether solution wasanalyzed byGC and two major peaks were observed,which were identified as 4-chlorofluorobenzene(RT = 3.5mm) 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(RT4.5mm). This sample was further analyzedby HPLC (column A; eluent: solvent A; flowrate, 2.5 niL/mill; UVdetection, 270 nni) and found that 14 elutedfirst(RT= 4.6 mm),followed by 17(RT = 7.6mm) and an unidentified peak(RT= 10.1 mm), then finally 4-chlorofluorobenzene(RT= 18.3 mm) appeared last. Identificationof the principalproducts was performedby the comparison of the GC and HPLC retentiontimes withthose of authentic samples.The identification of the products was completedby GCMS, using for comparison themass spectra (acquired under verysimilar instrumentalconditions) obtained from a premadesolution of authentic samples in thecase of theprincipal products, andby inspection of the mass spectrumobtained 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 presenceof 18-crown-6 and DMSO.A typical reaction trial was performedas follows. Compound 4 (16.0 mg, 65.01Lmol)was allowed to react with KCN (2.10mg, 32.2 1Lmol), at 105°C, as describedin thegeneral procedure except that about 1.2equivalents of 18-crown-6 (9.8 mg, 371.mol) wasadded to the reaction mixturebefore heating. The final DMSOmixture was analyzedby HPLC (column B; eluent: solventC; flow rate, 2.5 mL/min; UV detection, 270 nm)and it was determined that 1.65 mg of2-tolunitrile 15(RT=14.3 mm) was present, fora yield of 44%.Other reaction trials were conductedat 95, 115, 125, and 135°C, which gave yields of35, 40, 42, and 41%, respectively.An additional reaction trialwas performed using 16.2 mg (65.8 1.mol) of 4 withKCN(2.10 mg, 32.2 mol),at 105°C, which used approximately 3 equivalentsof 18-crown-6(26 mg, 98 1Lmol) and affordeda chemical yield of 46%.Reaction of 4 withcyanide in the presence of 18-crown-6and CH3CN.Two reaction trials wereperformed as follows. In the firsttrial, 4 (16.2 mg, 65.81Lmol) was allowed to reactwith KCN (2.10 mg, 32.2Mmol),at 80°C, as described in the131general procedure except that1 equivalent of 18-crown-6(8.5 mg, 321mol) was addedto the reaction mixture and CH3CNwas used as the reaction solvent.The final CH3CNmixture was analyzedby HPLC (column B; eluent: solventC; flow rate, 2.5 mL/min; UVdetection, 270 nm) and itwas determined that 0.094 mgof 2-tolunitrile 15(RT=13.8mm) was present, fora yield of 3%. This mixturewas stored and reanalyzedapproximately 18 hours laterby HPLC; it was found that 0.81 mg of15 was now present,which represents a yieldof 21%. The mixture was storedagain, then reanalyzed 13.5days after the initial HPLC analysis.At this time, 1.90 mg of 15 was determinedto bepresent, for a final yield of50%.The second reaction trialwas performed in the same wayas the first, except that anoil bath temperature of95°C was used (it was noted thatthe reaction mixture wasrefluxing). A chemical yieldof 4% was obtained, as determinedby HPLC. The mixturewas stored, and upon reanalysisabout 16 hours later, the yield was foundto be increasedto 21%. This mixturewas stored again, then reanalyzed13.5 days after the initial HPLCanalysis. The final yield of 15was found to be 46%.Attempted reaction of 11with cyanide.Two reaction trials were performedas follows. In the first trial, 11 (27mg, 64 mo1)was allowed to react withKCN (2.10 mg, 32.2 mo1),at 100°C, as described in thegeneral procedure.The final DMSO mixture wasanalyzed by HPLC (columnA; eluent:solvent C; flow rate,2.5 mL/min; UV detection,270 nm) and the chromatogramexhibited a large peak(RT=7.9mm) and a much smallerpeak(RT=18.2 mm), but132neither peak could beidentified. Under theseHPLC conditions, benzonitrile14 wasexhibiting a retentiontime of 4.4 mm. Therefore,HPLC analysis confirmed theabsenceof any desired 14 in theproduct mixture.The second reactiontrial was performed inthe same way as the first,except thereaction temperatureused was 120°C. Thesame essential results wereobtained asreported in the first trialabove.Heating of 11 in DMSOwithout cyanide present.Compound 11 (27 mg,64 mol) was heatedin DMSO (1 mL) for 10mm at 100°C,in the same fashion asdescribed in the generalprocedure; the addition ofaqueous KCNand its associateddrying was not done.The resulting DMSOsolution was analyzedbyHPLC (column A; eluent:solvent C; flow rate,2.5 mL/min; UV detection,270 nm) andthe chromatogram exhibiteda single large peak(RT=8.1 mm) which could not beidentified.Attempted reactionof fluorobenzene with cyanide.Fluorobenzene (5.7 1.L,60 mo1) was allowedto react with KCN (2.00 mg,30.7!mo1),at 135°C, as describedin the general procedure.The final DMSO mixturewas analyzedby HPLC (column A;eluent: solvent B; flow rate,2.5 mL/min; UVdetection, 270 urn)and the chromatogramexhibited a single peak(RT= 4.2 mm) whichwas identified asfluorobenzene.Under these HPLCconditions, benzouitrile14 had a retentiontime of2.8 mm, thereby confirmingthe absence of 14 inthe product mixture.133Attempted reaction of 2-fluorotoluenewith cyanide.2-Fluorotoluene (6.6 L, 60 mol) wasallowed to react with KCN (2.00mg, 30.7mol), at 135°C, as described in the generalprocedure. 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 exhibiteda single peak(RT= 7.2 mm) which wasidentified as 2-fluorotoluene. Underthese HPLC conditions, 2-tolunitrile 15had aretention time of 3.9 miii, therebyconfirming the absence of 15 inthe product mixture.Attempted reaction of 4-fluorotoluenewith cyanide.4-Fluorotoluene (6.6 L, 60 mo1) wasallowed 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 (columnA; eluent: solvent B; flow rate, 2.5 mL/min; UVdetection,270 mn) and the chromatogramexhibited a single peak(RT= 7.3 mm) which wasidentified as 4-fluorotoluene. Underthese HPLC conditions, 4-tolunitrile16 had aretention time of 4.1 mm, therebyconfirming the absence of 16 in the product mixture.Attempted reaction of 4-chiorofluorobeuzenewith cyanide.4-Chlorofluorobenzene (6.4L, 60 mol) was allowed to react with KCN(2.00 mg,30.7 mol), at 135°C,as described in the general procedure. Thefinal DMSO mixturewas analyzed by HPLC (columnA; eluent: solvent B; flow rate, 2.5 mL/min;UVdetection, 270 mm) and the chromatogramexhibited a single peak(RT=7.6miii) whichwas identified as4-chlorofluorobenzene. Under theseHPLC conditions, 4-134chlorobenzonitrile 17 had aretention time of 4.6 mm,thereby confirming the absenceof 17 in the product mixture.Attempted reactionof 12 with cyanide.Compound 12 (18 mg,63 .4mol) was allowed to react withKCN (2.10 mg, 32.2 pmol),at 100°C, as described in the generalprocedure. The finalDMSO mixture was analyzedby HPLC (colunm A; eluent:solvent C; flow rate, 2.5 mL/min;UV detection, 270 am)and no product peaks wereobserved in the chromatogram(12 is not observableby UVdetection at 270mu). Under these HPLC conditions,benzonitrile 14 had a retentiontime of 4.1 mm, thereby confirmingthe absence of 14 in the product mixture.5.3.5 Labelling Work with[“C] CyanideSubstitution reactions with[“C] cyanide.General Procedure: Afterthe H11CN was generatedand trapped in aqueous NaOHsolution (1 mL,0.1 M), 0.5-1.0 mL ofthis radioactive stock solutionwas taken (thesolution was countedat this stage and the timewasnotedDand a known amount ofnon-radioactive KCN (carrier)was added, then this mixturewas added to a 5-mL Reactivial® (which contained aninert atmosphere). The [“C]cyanidesolution was rapidlyevaporated to dryness (usinga block heater) under a fast flowof nitrogen or argon. Asolution of(,6-arene)tricarbonylchromium(40-65 mol) in DMSO (1mL) was added bysyringe to the Reacti-vial®.The stirred mixture was heatedat the desired temperatureThis point intime was designatedas the start of synthesis (SOS).135in a thermostated siliconeoil bath for 10 minutes.Upon cooling (ice/waterbath) toambient temperature,a small portion of the reaction mixturewas subjected to radioHPLC purification and thepeak correspondingto the[11C]nitrile product wascollectedand counted to determinethe decay corrected radiochemicalyield.Reaction of 1 with [“C]cyanide.A representative reaction trialwas performed as follows.Compound 1 (9.5 mg, 41mol) was treated witha mixture of 27.8 mCi (SOS) of[11C]cyanideand 0.37 equivalentsof carrier KCN (0.98mg, 15 mol), then heatedat 150°C, as described in the generalprocedure. HPLC analysis(column C; eluent: solventA; flow rate, 5.0 mL/min;UVdetection, 254 mn) ofthe reaction mixture determinedthat 9.93 mCi (decay correctedto SOS) of[11C-CN]benzonitrile 18(RT= 6.5 mm) was produced fora radiochemical yieldof 36%.Other reaction trials wereconducted at 150°C whichused varying amounts of carrierKCN (0.11, 0.35,0.49 equiv) and gave21%, 41%, and 34% radiochemicalyields,respectively.An additional reaction trialwas performed at 135 °C, whichused 0.51 equivalents ofcarrier KCN, andafforded a radiochemicalyield of 35%.Reaction of 1with no carrier-added[11Cjcyanide.Compound 1 (15 mg,65 mol) was treatedwith 22.8 mCi (SOS) of [“Cjcyariide(withno carrier KCN added),then heated at 150°C,as described in the generalprocedure.136HPLC analysis (columnC; eluent: solvent A; flowrate, 5.0 mL/min;UV detection, 254nm) of the reaction mixturedetermined that onlya trace of [“C-CN]benzonitrile18(RT = 6.5 mm) was present—the activity of the collectedproduct fraction wastoo low tobe counted with the Capintecwell counter.Reaction of 4 with[“C] cyanide.Compound 4 (14.8 mg,60.1 mol) was treatedwith a mixture of 8.50 mCi(SOS) of[“Cjcyanide and0.51 equivalents of carrierKCN (2.00 mg, 30.7 mol),then heated at135 °C, as described inthe general procedure.HPLC analysis (columnA; eluent: solventB; flow rate, 2.5 mL/min;UV detection, 270 urn)of the reaction mixture determinedthat 2.93 mCi (decay correctedto SOS) of[11C-CN]-2-tolunitrile19(RT= 4.0 mm) wasproduced for a radiochemicalyield of 34%.Reaction of 5 with [“C]cyanide.Compound 5 (14.8 mg,60.1 mol) was treatedwith a mixture of 7.84 mCi(SOS) of[‘1C]cyanide and 0.51 equivalentsof carrier KCN (2.00 mg,30.7 mol), then heatedat135 °C, as described inthe general procedure. HPLCanalysis (column A; eluent:solventB; flow rate, 2.5mE/mm; UV detection,270 mu) of the reactionmixture determinedthat 2.39 mCi (decaycorrected to SOS) of[‘1C-CN]-4-tolunitrile 20(RT=4.lmm) wasproduced for aradiochemical yieldof 31%.137Reaction of 6 with [“C]cyanide.Compound 6 (12.3 mg, 46.1 mol) wastreated with a mixture of 16.73 mCi (SOS) of[‘1C]cyariide (in this case the H11CN wastrapped 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, 254mn) of the reaction mixture determined that 3.54 mCi(decay corrected to SOS) of[11C-CN]-4-chlorobenzonitrile21(RT= 12.0 mm) wasproduced for a radiochemical yield of21%.Another reaction trial was performedat 135°C, which used 0.51 equivalents of carrierKCN, and afforded a radiochemical yieldof 19%.Reaction of 6 with [‘1C]cyanide in theabsence of base.An experiment was done to eliminatethe presence of base (both ammonia andhydroxide) from the labelling[11C]cyauidereagent. TheH11CN/NH3gas stream waspassed through a glass loop, whichwas emersed in a CC14/C02(-23°C) cooling bath, andtrapped out the H11CN, while sweepingaway the NH3 with helium gas flow. The glassioop was removed from the coolingbath and H’1CN was slowly purged intoa Reactivial® which contained a mixtureof 6 (10.0 mg, 37.5 mo1), carrier KCN (1-2 mg,15-31mol*),and DMSO (1 mL) underN2 atmosphere. When the H11CNtransfer wascomplete, the radioactive mixturewas counted (3.87 mCi, SOS). This mixturewasTwo small crystalsof KCN were used, which were not weighed,thus the quantityindicated was estimated.138heated for 10 minutesat 125-130°C. After cooling,HPLC analysis (columnC; eluent:solvent A; flow rate,3.0 mL/min; UV detection,254 nm) of the reactionmixturedetermined that 1.11mCi (decay correctedto SOS) of [“C-CN]-4-chlorobenzonitrile21(RT=14.9 mm) was producedfor a radiochemical yieldof 29%.5.4 Experimental forChapter 35.4.1 Sources of Materialsl7cr-Ethynylestradiol 23 wasobtained from SigmaChemical Co. Tri-n-butyltinhydridewas purchased from the AldrichChemical Co. and AlfaProducts, and 2,2 ‘-azobis- (2-methylpropionitrile), commonlyreferred to as AIBN,was supplied by Aldrich ChemicalCo.The O-methylatedestradiols, 3-methoxy-l7cr-ethynyl- 1,3,5( 10)-estratriene-17f3-ol 24and 3, 17fl-dimethoxy-17a-ethynyl- 1,3,5( 10)-estratriene25, were prepared byadapting themethod of Johnstoneand Rose.9 Compound23 was treated withpowdered potassiumhydroxide in DMSO,followed by the additionof iodomethane. Flashchromatographyof the crude productmixture on silica gelwith hexanes/diethyl ether(2:1) afforded 24and 25 in 67% and31% yields, respectively.3-Methoxy-l7cr-vinyl-1,3,5(10)-estratriene-17fl-ol 41 wasalso prepared by an adaptationof the procedure ofJohnstone and Rose.9A mixture of 23 and17a-vinyl-1,3,5(10)-estratriene-3,17f3-diol35, obtained from thehydrostarinylation of 23(see Subsection 5.4.3),was treated with potassiumhydroxide inDMSO, and thenwith iodomethane.Flash chromatographyon silica gel with hexanes/diethyl ether(1:1) gave pure 41 in52% yield (based on theamount 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 itsL-glycero-a-D-galacto epimer 29,were prepared accordingtopublished procedures intwo steps. First,1,2:3,4-di-O-isopropylidene-a-D-galacto-hexodialdo- 1,5-pyranose 27was prepared by oxidationof 1,2:3,4-di-O-isopropylidene-a-D-galactopyranose 26 (Koch-LightLaboratories Ltd.) using eitherchromium trioxidedipyridine complex (in52% yield) as describedby Arrick and co-workers,’° orthechromium trioxide-pyridinecomplex in the presenceof acetic anhydride (in 68% yield)according to Garegg andSamuelsson.” Then 27was treated with ethynylmagnesiumbromide according to the procedureof Hems et al.12 anda mixture of 28 and 29 wasobtained (85% yield) ina ratio of 62:38 (determinedby ‘H NMR), respectively. Thismixture was separated usingcolumn chromatographyon silica gel with dichloromethane/hexanes/diethyl ether (6:2:1).Research grade Neand 1% F2 in Ne gas mixture werespecially prepared in ultra-highpurity (suitable for 18Fproduction) by either MathesonGas Products (Edmonton, AB)or Canadian Liquid AirLtd. (Vancouver, BC).Freon-li (CFC13)was purchasedfrom Matheson Gas Products.5.4.2 GeneralFluorine gas is toxic, highlycorrosive, and generallydangerous, and therefore requireshandling with greatcare.’3”4 Hence, a specializedfluorine gas handlingsystem wasused to perform allstudies involving elementalfluorine and acetyl hypofluorite,and isshown in Figure 5.1. Thisgas handling system was constructedfrom components,such140CYCLOTRONSHIELDINGventmetering(valvepressure pressuretransducer transducerreactionFigure 5.1: Schematicof the fluorinegas handling system usedto perform thefluorination reactions.as stainless steel and Teflon,that are compatible withreactive fluorinegas. The fluorinetank and gas handlingsystem are stationedin a fume hood specificallydesigned for usewith radionucides.The gas handling systemis connected via 1/8in. o.d. stainless steeltubes to the gastargets used on the TRIUMF/NordionCP-42 cyclotron andthe largerTRIUMF 500MeV cyclotron.The cyclotron gas targetsare essentially gas-tightcylinders, fabricatedfrom nickel (forthe CP-42 cyclotron)’5or Inconel 600, a nickel-based alloy (for the500 MeV cyclotron).’6The gas handling systemwas connected tothe reaction vesselwith Teflon tubing(1/16 or 1/8 in.o.d.) using Swagelokfittings141(Crawford Fitting Co., Salon, OH) and Teflon ferrules.Gaseous CH3COOF was produced by passinga dilute mixture of F2 (—0.1%) in Nethrough a column containing a solid mixture ofpotassium acetate/acetic acid in a molarratio of 2:3. TheCH3COOK/CHCOOH mixturewas prepared according to the methodof Jewett et al.17The quantification of the amount of F2or CH3COOF used for fluorinationexperiments was accomplished by iodometric titration.18”9Prior to performing actualfluorination reactions with vinyl-tin substrates, oneor two “dummy” trials would be donein which the fluorinating agentwas added to an aqueous solution of excess KI, and theliberated12was then titrated with standardized 0.1 Msodium thiosulfate solution.[‘8F1F2was produced by the20Ne(p,Spall)’8Freaction with a target gas mixture of 0.1%F2 in natural neon that was irradiatedwith 500 MeV protons from the TRIUMFcyclotron.16Gaseous CH3COO’8Fwas prepared by ventingthe [‘8F]F2 produced after targetirradiation through the solidCH3COOK/CHCOOHcolumn17that was described earlier.5.4.3 Preparation of Vinyl-Tin SubstratesGeneral procedures for hydrostannylation of acetyleniccompounds.Procedure A: Under an N2atmosphere, a solution of acetylenic compound in 1,4-dioxane was prepared. Tothis stirred solution, five equivalents of tri-n-butyltinhydridewas added by syringe, then themixture was refluxed overnight. Thesolvent wasremoved and the crude mixture waschromatographed on a silica gel column to obtain142the stannylated product.Procedure B: Underan N2 atmosphere,a mixture of acetylenic compound,a catalyticamount of AIBN, andtwo equivalents of tri-n-butyltinhydride were combined,and thestirred mixture was heatedovernight (thermostatedsilicone oil bath,95°C). Aftercooling, the entire reactionmixture was chromatographedon a silica gel columntoisolate the stannylatedproduct.General: In all cases,the vinyl-tin productsafter chromatographicisolation werethoroughly driedunder high vacuum, thenstored in vacuo over sodiumhydroxide pellets.Vinyl-tin compoundsare sufficiently air-stableso that they can be easilyhandled in theopen under normalconditions, however,prolonged exposureto the atmosphere willresult in gradual decomposition.Proper storage, therefore,is very important.Preparation ofl7cr-(E)-tributylstannylvinyl-1,3,5(10)-estratriene-3,1713-diol 30 andl7a-vinyl-1,3,5(10)-estratriene-3,17j3-diol35.Method A: Compound23 (1986 mg, 6.70mmol) in 1,4-dioxane (10mL) was hydrostannylated as describedin procedure A.Flash chromatography ofthe crude mixturewas performed on silicagel (3.5 cm x 15 cm)with dichloromethane/hexanes/diethylether (6:2:1).The first fraction contained30 as the dominant productplus twounidentified byproducts,while further elutionisolated a mixtureof 23 and 35 (1090 mg)in a ratio of 29:71as determined by ‘H NMR.Therefore, 774 mgof 35 was estimatedto be present inthe second fraction fora yield of 38%. The first fractionwas furtherpurified by columnchromatography on silicagel (150 mg) withdichloromethane/143hexanes /ether (6:4:1) whichafforded 780 mg of30 (20% overall isolatedyield) as a veryviscous syrup, and upondrying overnight in vacuo,crystallized as an off-whitesolid. Ananalytical sample wasobtained by flash chromatographyon 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. forC32H52O2Sn: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(CH2CH3)),1.20-2.37 (severalm, 26H, 17-OH, Sn(CH2CH3),CH and CH2 of steroidnucleus), 2.80 (m, 2H,CH2 of steroid nucleus),5.30 (s, 1H, 3-011), 6.07(d,J2021 = 19.4 Hz,2JSn,H70 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 separate35 from 23 for characterization,column chromatographyofa portion of the mixture of 23and 35 was performed on silicagel with dichloromethane/hexanes/ether (6:4:1).Unfortunately, completeseparation was not achievedas 23 coeluted with all fractionscontaining 35, with thelargest percentage of 23being presentin the early fractions. Therefore,a sample was obtained by combiningseveral of the latefractions that containedthe lowest percentage of23. This sample was recrystallizedfrombenzene/hexanes, then analyzedby HPLC (column C; eluent:methanol/water, 3:1; flowrate, 6.0 mL/min; UVdetection, 280 nm) and foundthat a ratio of 23(RT=3.6mm) to35 (R.=5.0 mm) of 19:81was present. As a result,to effectively isolate 35 an HPLCseparation was carriedout by injecting this sample(dissolved in THF) in severalportionsonto column C and eluting35 using the same conditions(flow rate was changedto 3.0mL/min) employedfor HPLC analysis.The peaks correspondingto 35 were collected,144but due to a minute amount of 23 stillpresent, the isolated material was subjectedtoadditional HPLC purification. Thematerial obtained from the second HPLCpurification was recrystallized frombenzene/hexanes, which afforded35 as whitecrystals, mp 169.5-170°C,[a15+ 58.5° (c 1, 1,4-dioxane). Anal. calcd.forC20H2602: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 (hrs, 1H, 3-OH), 5.15 (dd,J2021a10.8 Hz,‘21a,21b1.2Hz, 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. forC20H2602:298.1934;found:298.1934.Method B: Compound 23 (1.00g, 3.37 mmol) was hydrostannylated as described inprocedure B. Columnchromatography on silica gel (100g) with dichloromethane/hexanes/diethyl ether (6:4:1)afforded in one portion 1.17g (59%) of 30. Physical andspectral (‘H NMR) propertiesof this material were identical with those reportedearlier.TLC analysis of the reaction mixture confirmedthe presence of 35, but the compoundwas not eluted off the column.Preparation of 3-methoxy-17o&(E)-tributyIstanny1vinyI-1,3,5(10)-estratriene-173-o131.Compound 24 (492 mg,1.59 mmol) was bydrostannylatedas described in procedureB. Column chromatographyon silica gel (100g) with hexanes/diethyl ether (5:1) yieldedin the first fraction 114 mgof crude 3-methoxy-17a-(Z)-tributylstannylvinyl-1,3,5(10)-145estratriene-17fl-ol 36, and in the followingtwo fractions, 860 mg of 31.Compound 31was isolated as a colourless oil in90% 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, H9.00, 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)-estratriene32.Compound 25 (1.00g, 3.08 minol) was hydrostannylated as described in procedureB.Column chromatography onsilica gel (200g) with hexanes/diethyl ether (20:1) yieldedin the first fraction 0.23g of 32 plus a minute amount of unidentified byproduct, andinthe second fraction 1.56g of pure 32. Compound 32 was isolated in an overall yieldof94% as an oil, and after drying in vacuofor 15-30 minutes, crystallized as a whitesolid.The material from the secondfraction 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(CH2CH3)),1.01 (m, 6H, Sn(CH2CH3)),1.12 (s, 3H, 18-CH3), 1.21-2.29(several m, 25H,Sn(CH2CH3),CH andCH2 of steroid nucleus), 2.63-2.86 (m,2H, CH2 of steroidnucleus), 3.23 (s, 3H, 17-OCH3),3.39 (s, 3H, 3-OCH3),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-enopyranose33.Compound 28 (884 mg, 3.11mmol) was hydrostannylatedas described in procedureB. Column chromatographyon silica gel (200g) with dichioromethane/hexanes/diethylether (6:6:1) afforded in onefraction 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 (2m, 24H, 2 x C(CH3)2andSn(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, 3.16mmol) was hydrostannylatedas described in procedureB except that after 19hours of heating, 0.50 mL oftri-n-butyltin hydride(0.54 g, 1.86nimol) was added and heatingwas continued for anotherthree hours. Columnchromatography on silica gel(200 g) with hexanes/diethylether (4:1) yielded in the firstfraction 444 mg ofa mixture of (Z)-7,8-dideoxy-1,2:3,4-di-O-isopropylidene-8-C-tributylstanny1-L-glycero-c-D-galacto-oct-7-enopyranose37 and 7,8-dideoxy- 1,2:3,4-di-O-147isopropylidene-7-C-tributylstannyl-L-glycero-cr-D-galacto-oct-7-enopyranose38 in a ratioof 3:2 as determinedby 1H NMR. As a result, 266 mg of37 and 178 mg of 38 wasestimated to be present in the mixture,for chemical yields of15% and 10%, respectively.Further elution afforded 1076mg of 34 in a second fraction,for a 59% yield.Compound 34 was isolated asa colourless syrup, [a]4 -37.0° (c 1.3, CHC13).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 Reactionsof Vinyl-Tin CompoundsFluorination of vinyl-tinsubstrates with elementalF2 or gaseous CH3COOF.General Procedure:A solution of vinyl-tin compound(60-200 1mol) was prepared(different solvents were employed)and placed in a glass reactionvessel (oven dried)under inert atmosphere.A stream of inert gas was passed throughthe vinyl-tin solutionvia a 1/16 in. o.d.Teflon tube, positioned atthe bottom of the solution, whichwascontrolled by the fluorinegas handling system (see Figure 5.1).To conduct fluorinationsat 0 or -78°C, the vinyl-tinsolution was cooled with eitheran ice/water (0°C) bath oraC02/2-propanol (-78°C)cooling bath.The desired quantityof 1% F2/Ne gas mixture(60-230 mol F2) was loadedintoeither the CP-42 or 500MeV gas target using thefluorine gas handling system,and thenpure Ne was addedto dilute the F2 concentrationto approximately 0.1% in Ne. Toperform fluorinationswith F2, the dilutedF2/Negas mixture was then added directlytothe vinyl-tin solutionafter the inert gas flowwas turned off. However,to perform148fluorinations with gaseous CH3COOF,the dilutedF2/Ne gasmixture was instead passedthrough a solidCH3COOK/CHCOOHcolumn and the effluent addedto the vinyl-tinsolution. Both fluorinatingagents (F2 or CH3COOF) wereadded at a flow rate of - 50mL/min to the vinyl-tinsolution. After the additionof fluorinating agent was completed,the reaction mixture wastransferred to a round-bottomflask and the solvent wasremoved in vacuo. The residuewas analyzed by TLC, thenworked 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-ol40.Compound 31 (92.7 mg, 154mol) was dissolved in CFC13(20 mL) and added toaglass reaction vessel (2.0cm o.d. x 10 cm length). Thissolution was treated withapproximately 1.3 equivalentsof CH3COOF, at room temperature,as described in thegeneral procedure. Fiveadditional fluorinations ofcompound 31 were conductedin thesame manner, employinga total of 554.6 mg of31 (922 mol).The reaction mixturesobtained were combined, thensubjected to column chromatography on silica gel(100 g) with hexanes/diethyl ether(4:1) as the eluent. Thefirstfraction (55 mg)collected contained 39 in96% purity as indicated by HPLCanalysis(column D; eluent: solventD; flow rate, 3.5 mL/min;UV detection, 280 nm).Withcontinued elution,a second fraction (66 mg) wasobtained which containeda mixture of39(RT=17.8 mm) and 40(RT=26.2 mm) in a ratio of 79:21 by HPLC analysis.Both ofthe isolated chromatographyfractions were subjectedto further purification via HPLC.149Each fraction wasdissolved in a minimumof ether, and then wasinjected in severalportions onto the HPLCsilica gel column andeluted using the sameconditionsemployed for HPLC analysis.The peaks correspondingto 39 and 40 were collected,whereby all of 39 wasisolated in one batch (90.0mg) and all of 40 was isolatedinanother batch (11.5mg). The isolated yields of39 and 40 were 29.5% and3.8%,respectively.Quantification of yieldsfor the reaction of 31 withgaseous CH3COOF.Compound 31 (76.4 mg,127 mol) was dissolvedin CFC13 (20 mL) and addedto aglass reaction vessel(2.0 cm o.d. x 10 cm length).This solution was treated withapproximately 1.3 equivalentsof CH3COOF, at room temperature,as described in thegeneral procedure. Aftersolvent removal, the residuewas dissolved in a knownvolumeof CHC13.The product mixturewas analyzed by HPLC(column C; solvent programA;flow rate, 6.0 mL/min;UV detection, 280 urn)using a standard solutionof 39 as anexternal standard.It was determined that 17.0mg of 39 and 40 (both co-elute,RT=S.Omm) was present, fora yield of 41% based on theamount of 31 used.Additional fluorinationtrials were conductedusing alternative reactionsolvents.Compound 31(74.1 mg, 123 mo1) wasdissolved in dried CH3OH(20 mL) and treatedwith approximately1.3 equivalents ofCH3COOFas described above. It wasdeterminedby HPLC analysis that5.59 mg of 39 and 40 wasobtained, for a yieldof 14%.Compound 31 (80.7mg, 134 mol) was dissolvedin dried CH3CN (20mL), whichrequired about0.5 mL of CHC13 to helpsolubilize 31, and wastreated with150approximately 1.2 equivalentsof CH3COOF as described above. Itwas determined byHPLC analysis that 10.4 mg of39 and 40 was obtained, fora yield of 24%.Compound 31 (71 mg, 118 mo1)was dissolved in dried THF (20 mL) andtreatedwith approximately 1.4 equivalents ofCH3COOF as described above. Itwas determinedby HPLC analysis that 3.62 mg of 39 and40 was obtained, for a yieldof 9.3%.Quantification of yields for the reactionof 31 with elemental F2.Compound 31 (103.2 mg, 172 mol)was dissolved in CFC13 (20 mL) andadded to aglass reaction vessel (2.0 cmo.d. x 10 cm length). This solution wastreated withapproximately 1.25 equivalents of F2,at room temperature, as described in the generalprocedure. After solvent removal,the residue was dissolved in a knownvolume ofCHC13. The product mixturewas analyzed by HPLC (column C;solvent program A;flow rate, 6.0 mL/min; UV detection,280 nm) using a standard solution of39 as anexternal standard. It was determinedthat 5.10 mg of 39 and 40 (both co-elute,RT=4.97mm) was present, for a yieldof 9.0% based on the amountof 31 used. In addition, twoside-products that were presentin significant amounts were identifiedas 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 of24 and 41 were prepared foruse as external standards.HPLC analysis indicated that2.89 mg of 24 and 3.85 mg of41 were present, foryields of 5.4% and7.2%, respectively.An additional fluorinationexperiment was done using95.9 mg (159ILmol)of 31 inCFC13 (20 mL), whichwas treated with approximately 1.35equivalents of F2 at -78°C,151as described above. It was determined by HPLC analysis that 2.23mg of 39 and 40 wasobtained, for a yield of 4.2%. Furthermore, the side-products 24and 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 dissolvedin CFC13 (20 mL) and added to aglass reaction vessel (2.0 cm o.d. x 10 cm length). Thissolution was treated withapproximately 1.3 equivalents of CH3COOF, 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 mixturesobtained were combined, thensubjected to column chromatography on silicagel (60 g) with dichloromethane/hexanes/diethyl ether (6:2:1) as the eluent.The first fraction (29.5 mg) collected contained 47in —98% purity as indicated by ‘HNMR. The second fraction (4.0 mg) containeda mixture of 47, 48, and 7,8-dideoxy-1,2:3,4-di-O-isopropylidene-L-glycero-a-D-galacto-oct-7-enopyranose 49 ina ratio of43:36:21 as determined by ‘H NMR. Thethird fraction (9.0 mg) containeda mixtureof 47, 48, and 49 in a ratio of 6:83:11. The finalfraction (5.4 mg) contained a singlecompound that was identifiedas (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 thefirst three chromatography fractions, was152determined to be 36% (32 mg). The yieldof 48, as contained in the second andthirdfractions, was determined to be10% (9 mg).A larger scale synthesis of 47and 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 solutionwas treated with approximately 1.35 equivalentsof CH3COOF, at room temperature,as described in the general procedure.Threeadditional fluorinations of compound34 were performed in the same manner, employinga total of 326.5 mg of 34 (567 mol).The reaction mixtures were combined,thensubjected to column chromatographyon silica gel (140g) with dichioromethane/hexanes/diethyl ether (6:2:1) as the eluent.5.4.5 Radiofluorinations with Acetyl[18F]HypofluoriteGeneral procedure for radiofluorinationwith gaseous CH3COO’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 12.5cm length) under inert atmosphere. The500MeV gas target was filledwith 4 or 6 psi (0.27 or 0.41 atm)of 1% F2/Ne gas mixture,then pure Ne was addeduntil 100 psi (6.8 atm) wasreached. For a typical ‘8Fproduction run, thetarget gas mixture was irradiated for 10minutes at 69 1A. Whenthe irradiation of the targetgas was stopped, this time was noted anddesignated as theend of bombardment (EOB).After irradiation, the radioactivegas mixture was passedthrough a solidCH3COOK/CHCOOHcolumn and into the reactionvessel at a flowrate of —50 mL/min. With theaddition ofCH3COO18Fcompleted,the reaction mixture153was transferred to a round-bottom flask, then assayedfor radioactivity. TheCH3COOK/CH3COOH column was also assayed for activity.The reaction mixture was evaporatedto dryness in vacuo and reassayed for activity, then dissolvedin a small amount ofCHC13. An aliquot of this mixture wassubjected to radio-HPLC purification and thepeak corresponding to the18F-labelled productwas collected, then counted to determinethe percentage of product present inthe reaction mixture. The decay correctedradiochemical yield was calculatedby dividing the total activity due to product (in thereaction mixture) with the total activity of 18F produced inthe cyclotron target at EOB.Reaction of 31 with CH3COO18Fat room temperature.Compound 31 (72.1 mg, 120 mol) was radiofluorinatedusing approximately 0.74equivalents ofCH3COO’8F(produced with6 psi of 1%F2/Ne), at room temperature, asdescribed in the general procedure. HPLCanalysis (column C; solvent program A; flowrate, 6.0 mL/min; UV detection, 254 mn) of thereaction 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-ol52(both co-elute,RT=5.5mm) was produced for a radiochemical yield of19%.An additional radiofluorinationtrial was conducted using a greater excess of vinyl-tin31. Compound 31 (71.0mg, 118 1Lmol) was radiofluorinated using approximately0.5equivalents of CH3COO’8F(producedwith 4 psi of 1%F2/Ne), atroom temperature,as described in the general procedure.HPLC analysis (column C; solvent programB;flow rate, 6.0 mL/min; UVdetection, 254 mu) of the reaction mixture determinedthat1543.79 mCi (decay corrected to EOB)of 51 and 52 (both co-elute,RT11.0 mm) wasproduced for a radiochemical yield of19%.Reaction of 31 with CH3COO18Fat -78°C.Compound 31 (69.0 mg, 115 1mol) was radiofluorinatedusing approximately 0.77equivalents of CH3COO’8F(produced with6 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, 254am) of the reaction mixture determined that 1.72 mCi(decay corrected to EOB) of 51 and 52(both co-elute,RT=S.4mm) was produced fora radiochemical yield of9.7%.An additional radiofluorination trial wasconducted using a greater excess of vinyl-tin31. Compound 31 (71.7 mg, 119 mo1)was radiofluorinated using approximately 0.5equivalents of CH3COO18F(produced with 4psi of 1%F2/Ne), at -78°C, as describedin the general procedure. HPLCanalysis (column C; solvent program B; flow rate,6.0mL/min; UV detection, 254 nm) ofthe reaction mixture determined that 1.65 mCi(decay corrected to EOB) of 51and 52 (both co-elute,RT= 10.7 mm) was produced fora radiochemical yield of5.0%.155References1. Gordon, A. 3.; Ford, R. A. TheChemist’s Companion: A HandbookofPractical Data,Techniques and References; WileyInterscience: New York, 1972;p439.2. Still, W. C.; Kahn, M.;Mitra, A. J. Org. Chem. 1978, 43, 2923-2925.3. Shriver, D. F.; Drezdzon, M.A. The Manipulation ofAir-sensitiveCompounds, 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. Chemistiyof Organic Fluorine Compounds:A Laboratoiy Manual withComprehensive Literature Coverage, 2nded.; John Wiley and Sons: New York,1976;pp 13-14.14. MathesonGas Data Book, 5thed.; Matheson Gas Prducts: East Rutherford,NJ,1971;pp261-265.15. 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. Fundamentalsof Analytical Chemistiy; Holt, Rhinehartand Winston: New York,1965;pp462 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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