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Synthesis and reactivity of macrocyclic β-keto lactones Sharadendu, Anurag 1996

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SYNTHESIS AND REACTIVITY OF MACROCYCLIC p-KETO LACTONES by Anurag Sharadendu B.Sc.(Hons.), Delhi University , 1 9 8 7 M.Sc, Indian Institute of Technology Kanpur, 1 9 8 9 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA January 1996 © Anurag Sharadendu, 1996 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Ctfg. Ml sTfiY The University of British Columbia Vancouver, Canada Date J « w ^ ^ DE-6 (2/88) II ABSTRACT As a part of a continuing study of the chemistry and conformational behaviour of macrocyclic p-keto lactones, 3-oxo-13-tetradecanolide (74) and 3-oxo-15-hexadecanolide (84) were synthesized via intra- and intermolecular alcoholysis of hydroxy Meldrum's acid derivatives. A number of 14- and 16-membered lactones, derived from 74 and 84 were used to investigate a series of alkylation and reduction reactions. 74 84 Hydride reduction of 84 gave the diastereomeric alcohols 110 and 111. The relative stereochemistry of these alcohols was determined from an X-ray analysis of a sulfonate derivative of 112. The alkylation of the dianion of hydroxy lactone 110 gave 2-methyl-3-hydroxy lactone 122 in very high Ill stereoselectivity. Alkylations of mono- and dianion of 74 and 84 were carried out. Most of the alkylated lactones were also stereoselectively reduced. The alkylation of the monoanion of 74 gave 90 and that of 84 gave 127. The alkylation of dianion of 74 gave 94 and that of 84 gave 137 and 138. The alkylation of the monoanion of 94 and the dianion of 90 gave 101. The a-dialkylation of the of 94 gave 102 and that of 84 gave 128. Reduction of 127 gave 122 and was identical to the compound synthesized via the alkylation of dianion of 110. The reduction of 128 gave 132 as major and 133 as minor diastereomer, respectively. Compound 132 was identical to the one synthesized by the alkylation of the dianion of 122. The reduction of 102 gave 105 in high diastereoselectivity. 110 111 122 105 132 133 In general, the stereoselectivity exhibited in the reactions of these large rings could be rationalized from the conformational analysis of starting materials or intermediates. Reductions involving p-keto lactones were consistently shown to be controlled by the conformations in which both carbonyl oxygens could chelate a metal ion. The alkylation reactions could be rationalized from the conformational analysis of the enolate. The relative stereochemistry of the chiral centers of majority of the compounds synthesized during this project were successfully assigned by chemical transformation to compounds of known stereochemistry. During this investigation, the use of chiral HPLC to determine relative stereochemistry of distant chiral centers of macrocyclic rings was demonstrated for the first time. TABLE OF CONTENTS ABSTRACT ii LIST OF TABLES x LIST OF FIGURES xi LIST OF SCHEMES xiii ABBREVIATIONS xv ACKNOWLEDGMENTS xvii CHAPTER I INTRODUCTION TO MACROLIDES 1 1.1 Macrolide Antibiotics 2 1.2 Chemical Consequence of the Conformation of Cyclic Compounds 5 1.3 Macrpcyclic p-Keto Lactones 15 1.4 Synthesis of p-Keto Lactones 19 1.5 Conformational Studies of Large Rings 26 1.6 Conformational nomenclature of large rings 27 1.7 Polar maps 29 1.8 Conformational Analysis of Cyclotetradecane 31 1.9 Conformational analysis of cyclohexadecane 36 1.10 The lactone linkage 41 vii CHAPTER II RESULTS AND DISCUSSIONS: SYNTHESIS, CHEMISTRY AND CONFORMATIONAL ANALYSIS OF MACROLIDES 2.1 Chemistry of 14- and 16-Membered Lactones... 44 2.2 Synthesis of 3-Oxo-13-tetradecanolide (74) and 3-Oxo-15-hexadecanolide (84) 45 2.2.1 The Preparation of 3-Oxo-13-tetradecanolide (74) 45 2.2.2 Conformational Analysis of 3-Oxo-13-tetradecanolide (74) 48 2.2.3 The Preparation of 3-Oxo-15-hexadecanolide (84) via Intramolecular Alcoholysis of Acylated Meldrum's Acid Derivative 51 2.2.4 The Preparation of 3-Oxo-15-hexadecanolide (84) via Intramolecular Alkylation of the Dianion of a p-Keto ester 53 2.3 The Conformations and Reactivity of p-Oxygenated 14-Membered Lactones 57 2.3.1 Alkylation of the Monoanion of 3-Oxo-13-tetradecanolide (74) 57 2.3.2 Alkylation of the Dianion of 3-Oxo-13-tetradecanolide (74) 61 viii 2.3.3 Conformational Analysis of {AS* 13S*)-4-Methyl-3-oxo-13-tetradecanolide (94) 68 2.3.4 Alkylation of the Monoanion of (4S*13S> 4-Methyl-3-oxo-13-tetradecanolide (94) and the Dianion of 2-Methyl-3-oxo-13-tetradecanolide (90) 73 2.3.5 Stereoselective Reduction of 2,2,4-Trimethyl-3-oxo-l 3-tetradecanolide (102) 79 2.4 The Conformations and Reactivity of p-Oxygenated 16-Membered Lactones 84 2.4.1 Conformational Analysis of 3-Oxo-15-hexadecanolide (84) 84 2.4.2 Reduction of 3-Oxo-15-hexadecanolide (84) 88 2.4.3 Alkylation of (3S* 15S*)-3-Hydroxy-15-hexadecanolide (110) 99 2.4.4 C-2 Methylation of 3-Oxo-15-hexadecanolide (84) 106 2.4.5 Stereoselective Reduction of 2-Methyl-3-oxo-15-hexadecanolide (127) 108 2.4.6 The C-2 Geminal Alkylation of 3-Oxo-15-hexadecanolide (84) 111 ix 2.4.7 The Reduction of 2,2-Dimethyl-3-oxo-15-hexadecanolide (128) 113 2.4.8 The C-4 Alkylation of 3-Oxo-15-hexadecanolide (84) .....118 C H A P T E R II ICONCLUSION. ..127 C H A P T E R IV EXPERIMENTAL 129 R E F E R E N C E S . . 214 S P E C T R A L APPENDIX. . : . 221 LIST OF TABLES x Table 1. Yields of cyclization vs. elimination product of Q-halo-p-keto esters .....24 Table 2. Five lowest conformations of cyclotetradecane along with their relative energies and polar maps 34 Table 3. Five lowest conformations of cyclohexadecane along with their relative energies and polar maps 39 Table 4. Five lowest conformations of 3-oxo-13-tetradecanolide (74) along with their relative energies and polar maps 50 Table 5. The five lowest energy conformations of (4S* 13S*)-4-methyl-3-oxo-13-tetradecanolide (94) along with their polar maps 70 Table 6. Experimental and Calculated Vicinal Coupling Constants of (4S* 13S*)-4-Methyl-3-0X0-13-tetradecanolide (94) 72 Table 7. Five lowest conformations of 3-oxo-15-hexadecanolide (84) along with their polar maps and relative energies 86 Table 8. Experimental and Calculated Vicinal Coupling Constants of 3-Oxo-15-hexadecanolide (84) 88 Table 9. Yield and selectivity of the reduction of 3-oxo-l 5-hexadecanolide (84) 99 LIST OF FIGURES Figure 1. Conformations and calculated relative energies of the enolates of 2-methylcycloctanone 10 Figure 2. Stereoselective synthesis of 3-deoxyrosaronolide (36) 12 Figure 3. Stereoselective reduction of carbomycin derivatives 14 Figure 4. (a) Corner and (b) pseudo-corner position in large rings 28 Figure 5. Polar maps of (a) 14- and (b) 16-membered rings 31 Figure 6. The [3434] conformation of 14-membered ring superimposed on a diamond lattice 32 Figure 7. The [3434] conformation of cyclotetradecane together with the top view and symmetry elements of this conformation :..35 Figure 8. Transannular hydrogen interactions in the [3434] conformation....36 Figure 9. The [4444] conformation of cyclohexadecane ring superimposed on a diamond lattice 37 Figure 10. Symmetry elements of the [4444] conformation of cyclohexadecane 40 Figure 11. Hydrogen interactions in the [4444] conformation of cyclohexadecane 41 Figure 12. s-Trans and s-cis conformations of an ester ...42 Figure 13. Preferred conformation of ester of a secondary alcohol 42 Figure 14. The preferred conformations of (a) 14- and (b) 16-membered lactones 43 Figure 15. HPLC trace of dibenzoate esters 97 and 98 of 2,11-dodecanediol on Chiralpak OP (+) column 65 xii Figure 16. HPLC trace of the racemic dibenzoate ester of 2,11-dodecanediol derived from 4-methyl-3-oxo-l 3-tetradecanolide on Chiralpak OP (+) column 68 Figure 17. Multiplet of C-13 methine proton of 4-methyl-3-oxo-l 3-tetradecanolide (94) 71 Figure 18. Crystal structure of p-bromobenzenesulfonate derivative of (3S* 15R*)-3-hydroxy-15-hexadecanolide (112) 91 Figure 19. Polar maps of the two conformations observed in the X-ray structure of (3S* 15R*)-sulfonate-112 93 Figure 20. HPLC trace of a mixture of dibenzoate esters 142 and 143 from (d/)- and meso-2,13-tetradecanediol on Chiralpak OP (+) 121 Figure 21. HPLC trace of dibenzoate esters 142 from 4-methyl-3-oxo-15-hexadecanolide (138) 123 Figure 22. HPLC trace of meso-dibenzoate ester 143 derived from 4-methyl-3-oxo-15-hexadecanolide (138) :...125 xiii LIST OF SCHEMES Scheme 1. Stereoselective total synthesis of the marine sesterterpenoid (±)-palauolide (18) 7 Scheme 2. Synthesis of 3-Oxo-13-tetradecanolide (74) 47 Scheme 3. Synthesis of 3-Oxo-15-hexadecanolide (84) via intramolecular alcoholysis of Acylated Meldrum's acid derivative 52 Scheme 4. Synthesis of 3-Oxo-15-hexadecanolide (84) via Intramolecular Alkylation of the Dianion of a p-Keto ester 55 Scheme 5. Synthesis of 2-methyl-13-tetradecanolide from 2-methyl-3-oxo-13-tetradecanolide (90) 59 Scheme 6. Synthesis of 2,11 -dibenzoyloxydodecane (99 and 100) 63 Scheme 7. Synthesis of 2,11 -dibenzoyloxydodecane (99) from 4-methyl-3-oxo-13-tetradecanolide (94) 66 Scheme 8. Synthesis of 2-methyl-15-hexadecanolide from 2-methyl-3-hydroxy-15-hexadecanolide (122) 103 Scheme 9. Synthesis of 2,13-dibenzoyloxytetradecane (142 and 143) 120 Scheme 10. Synthesis of 2,13-dibenzoyloxytetradecane (142 and 143) from 4-methyl-3-oxo-15-hexadecanolide (138) 122 xiv Scheme 11. Synthesis of 2,13-dibenzoyloxytetradecane (143) from 4-methyl-3-oxo-15-hexadecanolide (138) 124 X V ABBREVIATIONS CDCI3 chloroform-d d doublet dd doublets of doublet dq doublets of quartet DMF A/,A/-dimethylformamide Et ethyl eV electron volts FT Fourier transform GC gas chromatography HMPA hexamethylphosphoramide HPLC high-performance liquid chromatography HRMS high resolution mass spectroscopy IR infrared J coupling constant LAH lithium aluminium hydride LDA lithium oV-isopropylamide LRMS low resolution mass spectroscopy m meta m multiplet XVI M MCPBA Me MM mp n 1 3 C NMR 1H NMR P Rf s t TBDMS tert THF TMS UHP molar mete-chloroperoxybenzoic acid methyl molecular mechanics melting point normal nuclear magnetic resonance (carbon) nuclear magnetic resonance (proton) para in thin layer chromatography, ratio of distance traveled by the compound to the distance traveled by the solvent singlet triplet te/f-butyldimethylsilyl tertiary tetrahydrofuran trimethylsilyl urea hydrogen peroxide xvii ACKNOWLEDGMENTS I wish to express my sincere gratitude to Professor Larry Weiler for his guidance and support during the course of this work. His patience and steady manner steered the project and me through some difficult times. I am indebted to the service personnel of the Chemistry Department including the mass spec lab and the microanalytic laboratory. I am especially greatful to the NMR lab for number of routine and non-routine samples and for taking time to solve any problems I faced on the NMR instruments. To people who shared the day-to-day highs and lows, my labmates, I extend my thanks and best wishes for their success in the future. They are too numerous to mention by name, but assuredly each has made a positive contribution to my stay here. Finally, I would like to thank Professor Gordon Bates and Carolyn Joyce for proof reading this thesis on short notice. 1 INTRODUCTION In 1926, Ruzicka's structural elucidation of the musk compounds civetone (1) and muscone (2), which were shown to be large ring ketones,1 marked the beginning of the study of macrocyclic compounds. Shortly after, Kerschbaum showed pentadecanolide (exaltolide 3) and A7-hexadecanolide (ambrettolide 4) to be present in the vegetable musk oils of angelica roots and ambrett seeds, respectively.2 3 4 2 Prompted by the challenge of preparing these novel macrocyclic lactones and also by their commercial importance in the fragrance industry,3"5 synthetic routes to these and related compounds followed. 1.1 Macrolide Antibiotics Interest in the large-ring lactones experienced a second quantum jump in the 1950's after Brockmann and Henkel isolated the first macrolide antibiotic, pikromycin (5), from an actinomyces culture.6 Since then, many macrolides, possessing diverse biological and physiological activity, have been isolated from natural sources. Some have proven to be of considerable importance clinically. They are also used as supplements to animal feeds. The continual discovery of new macrolides and the complexity of their structures and functions has made macrolide chemistry a challenging subject for O HO 5 3 organic chemists. Consequently, the chemical literature abounds with reports of their isolation, structural elucidation, stereochemistry, conformational rigidity, and biosynthesis of macrolide compounds. 7 The term "macrolide" has several connotations. In the earlier sense it referred to a class of antibiotics derived from the species of Streptomyces that possess as characteristic features: (a) a large ring lactone (12 or more carbons) containing few double bonds; (b) the large ring does not contain a nitrogen; and (c) one or more sugars, which may be amino sugars are attached to the large rings. Wider application of the term has come to encompass all natural products with a large lactone ring. In some cases, macrocyclic lactams such as the maytansinoids have also been described as macrolides. Macrolide natural products as a group are diverse in structure and physiological activity. However, a major subgroup of these compounds known as the "polyoxo macrolides," exhibits a remarkable structural similarity among its members. The compounds of this subgroup, which comprise approximately one half of the known macrolides, have structures that meet the criteria originally stated by Woodward. 8 Most of these polyoxo macrolides, produced by streptomyces microorganisms, are clinically important. They are structurally characterized by a 12- (e.g. methymycin 6), 14- (e.g. erythromycin A 7), or 16-membered ring lactone (e.g. tylosin 8) with one or more sugars attached, very often one of them being a nitrogen-containing sugar, and 4 with numerous chiral centers systematically incorporated into the ring, known as the aglycone. 6 7 8 The intricate stereochemical relationship among the substituents that adorn these complex macrocyclic compounds have fascinated organic chemists ever since the structures of these compounds were first elucidated in the 1950's. Approximately thirty years ago, researchers, particularly synthetic chemists, began to seriously consider the preparation of these compounds by total synthesis from readily available starting materials. 9" 1 3 Although great strides have been made in recent years, further advances require improved solutions to many of the problems associated with the synthesis of these compounds. One obvious concern is stereochemical control. Although vicinal chiral centers may be controlled effectively by internal or relative asymmetric induction, the establishment of the correct relationships between widely separated or remote chiral centers still presents problems. 5 1.2 Chemical Consequence of the Conformation of Cyclic Compounds Almost without exception, synthetic approaches to stereochemically complex acylic and macrocyclic natural products rely on some form of absolute stereochemical control to set up remote diastereomeric relationships. This absolute stereochemistry typically originates from some readily available enantiomerically pure starting material, from the resolution of an intermediate, or, more interestingly, from asymmetric induction by an enantiomerically pure reagent. Each of these approaches has its strengths. Each also has inherent problems, for which effective alternatives are clearly needed. In general, the relative stereocontrol methods for the construction of remote stereochemical relationships involves the control of the reaction stereoselectivity by pre-existing substrate chirality, where this chirality may be quite distant from the reaction site. Although such remote asymmetric induction would not be particularly effective if it operated by an interaction between widely separated centers of asymmetry, effective control might originate from a conformational bias that could be provided by remote chirality. This is of course common in cyclohexane-based ring systems, where axial-equatorial preferences are often used for stereocontrol in synthesis. For example, recently, Piers and Wai during stereoselective synthesis of a marine sesterpenoid palaulide (18) illustrated the conformational bias of 6 6-membered rings to control the stereochemical outcome of several steps in the synthesis.14 Intramolecular alkylation of the cyclic ketone 9 was carried out under conditions that would equilibrate the stereogenic centers adjacent to carbonyl group. 1H NMR spectra of the products showed that the trans-fused 10 and cis-fused 12 bicyclic ketones were obtained in a ratio of 94:6 (equation 1). 9 10 12 Out of four possible diastereomeric products, only two were obtained. On the basis of conformational analysis, Piers and Wai suggested that the trans-fused isomer 10 was more stable than 11, and in case of the cis-fused compounds, 12 was of lower energy than 13. Therefore they concluded that the two alkylation products were 10 and 12. 10 11 12 13 7 17 18 Scheme 1: Stereoselective total synthesis of the marine sesterterpenoid (±)-palauolide (18).14 Treatment of the mixture of 10 and 12 with p-toluenesulfonylmethyl isocyanide gave an epimeric mixture of nitriles 14 in an 85:15 ratio. Interestingly, the 1H 8 NMR of 14 showed that under these equilibrating conditions, only trans-fused decalins 14 were obtained. Earlier it had been shown that trans-fused decalins react faster than cis-fused decalins.15 Treatment of mixture of 14 with LDA in THF-HMPA at 0° C produced the anion 15, which upon alkylation with the electrophile gave the alkylated product 17 in 92% diastereoselectivity and 68% yield. The 1,3-diaxial relationship between angular methyl group and the nitrile 17 was determined by 1H NMR. The reaction proceeded preferentially via a lower energy transition state that can be represented by 16. The alternative transition state, involving approach of the electrophile from "bottom" face of the anion, would be destabilized by a steric interaction between the incoming electrophile and the angular methyl group in 15 and is disfavoured resulting in high diastereoselectivity. It has been shown by dynamic NMR measurements,16"22 X-ray crystallography,23"25 and semi-empirical molecular mechanics calculations17,26"30, that the conformations of medium- and large-ring molecules are very different from the floppy "necklace" of atoms suggested by conventional molecular models. Although macrocyclic compounds are usually capable of existing in a number of stable conformations, only a few of these conformations are appreciably populated at room temperature. In 1981, Still and Galynker reported the stereoselective alkylation of a number of simple monosubstituted 8- to 12-membered cyclic ketones and lactones.31 Invariably, these reactions proceeded with high stereoselectivity to yield one of the two possible diastereomeric products. O a. LDATHF, b. Mel -60 °C O O 19 20 21 During the investigation of alkylations of medium ring ketones one of the examples was the alkylation of 2-methylcyclooctanone (19) using LDA followed by the treatment with methyl iodide (equation 2). trans-2,8-Dimethylcyclooctanone (20) was produced in high stereoselectivity (95:5 mixture of trans:cis product).31 10 17.3kcal/mol 22.7kcal/mol 22 20 23 21 17.8kcal/mol 21.2kcal/mol 24 20 25 21 Figure 1: Conformations and calculated relative energies of the enolates of 2-methylcycloctanone.31 Still and Galynker suggested that this kinetic deprotonation-alkylation was best interpreted in terms of an early, reactant-like transition state. Therefore the low energy conformations of the enolates of 2-methylcyclooctanone (19) were compared as shown in Figure 1. Alkylation through either (or both) of the lowest energy enolates 22 or 24 would produce frans-2,8-dimethylcyclooctanone (20). 11 Similar alkylations of 9- and 10-membered lactones were found to be equally selective. The model that evolved from these studies was that of a relatively rigid enolate that was attacked by an electrophile from the more open exo-face. 3 1 Still and Novack illustrated the potential of this approach in designing a total synthesis of 3-deoxyrosaranolide (32) which is outlined in Figure 2 on page 13. 3 2 En route from a relatively simple keto-macrolide 26 to the target molecule, eleven kinetic reactions were employed under conformational stereocontrol in establishing six of eight chiral centers with excellent stereoselectivity on the 16-membered ring. The synthesis of 3-deoxyrosaranolide (32) demonstrated the use of conformational control in the reactions of large-ring lactones using the two adjacent chiral centers at C-14 and C-15 to efficiently control six other chiral centers spanning C-4 to C-13. However, the absence of a simple model to explain the selectivity in these reactions was evident. Indeed, even in this synthesis the stereochemistry of some of the chiral centers appeared unpredictable. The alkylation of 28 gave 29 with the wrong stereochemistry at C-4, although with high stereoselectivity. Hence, supplementary reactions (28 to 30) were needed to invert the required stereochemistry at C-4. 12 o p 31 32 >15:1 stereoselect iv i ty Figure 2: Stereoselective synthesis of 3-deoxyrosaronolide (32).32 13 Although Still and Novack were able to carry out highly regio- and stereoselective reactions on the 15-heptadecanolide system of 26, it was difficult to predict a priori the outcome of all of these reactions. Nakajima et al. have carried out stereoselective reductions and epoxidation on 16-membered lactones related to the carbomycin macrolide antibiotics.33 They were able to rationalize the stereochemical outcome of these reactions using molecular mechanics calculations. 14 O o o OAc MCPBA. -OMPM N a H C 0 3 I ° O' • o ' o OAc -OMPM 33 34 B 1 1 4 N B H 4 , MeOH B U 4 N B H 4 , MeOH OH O O -OMPM O" OAc 1.8:1 stereoselectivity 35 OMPM 22 :1 stereoselectivity 36 Figure 3: Stereoselective reduction of carbomycin derivatives 33 For example, the 16-membered dienone 33 was oxidized with MCPBA, and complete regio- and stereoselectivity was observed during this epoxidation to give the (12S*,13S*)-epoxide 34. Further, reduction of dienone 33 with tetrabutylammonium borohydride gave the C-9 diastereomeric alcohols 35 in a ratio of 1.8 to 1. The reduction of 34 under the same conditions gave two C-9 15 alcohols in a ratio of 22 to 1. The low-energy conformations of 33 and 34 were calculated using molecular mechanics, and selective attack by hydride from the sterically more open face of ketone was used to rationalize the respective products. The relative population distribution of various conformations of 33 and 34 was then used to rationalize the observed ratios of products from 33 and 34, respectively. These relative populations of the conformations were also determined experimentally from NOE and NOESY 1H NMR studies of the substrates and were found to be the similar as obtained from the molecular mechanics calculations. 1.3 Macrocyclic p-Keto Lactones It is generally accepted that macrolides are biochemically synthesized from polyketide chains (p-polyoxoalkanoates).34 Much chemical effort has been devoted to the synthetic studies of these polyketide chains.35 A recent example is the reduction of a cyclic polyketo derivative 37, synthesized from oleandomycin, with the stereochemistry shown. Reduction of 37 with Zn(BH4)2 in the presence of MgBr2, remarkably, gave the single tetraalcohol 38 in 80% yield (equation 3).36 The stereochemistry of 38 was determined by an X-ray crystallographic study. Omission of the MgBr2 in the reduction resulted in lower yield of 38, suggesting that metal-ion chelation may be important in the reduction. The stereochemistry of all the methyl-substituted carbons in 38 was 16 unchanged, which suggested that the (3-dicarbonyls of 37 did not enolize during the reduction. Following up this study, Tatsuta et al. synthesized the simpler tetraketo macrolide 39.37 An X-ray crystallographic investigation of this compound showed that it was a bis-enol in the solid state, and NMR studies confirmed that it retained this bis-enolic form in solution.37 Reduction of 39 with NaBH4 gave a mixture of all eight diastereomers of the corresponding tetrol. Three of the tetrols crystallized and their structures were determined by X-ray crystallography. Thus the chemistry of the unsubstituted macrolide 39 was more complicated and less stereoselective than that of the complex oleandomycin derivative 37. 17 39 40 a: R = OH b: R = H Pikromycin (40a) and narbomycin (40b) are two macrolide antibiotics that contain a p-keto lactone moiety. " Both p-keto macrolides appear to undergo stereoselective reduction. However, the stereochemistry of the product was not determined. Muxfeldt et al. noted that the C-2 proton of pikromycin (40a) does not undergo a facile exchange.43 Attempts to exchange the C-2 proton with deuterium in chloroform, pyridine, and D 20 at room temperature were unsuccessful even after stirring for several days. This was attributed to the rigid conformation of the 14-membered ring. These authors also found that the 1H NMR spectrum of 40a was unchanged on heating to 160 °C. The C-2 hydrogen of pikromycin can be deprotonated by strong base. In contrast to 1H NMR results, the temperature dependence of CD spectra of 40a and 40b suggested that there may be a fast conformational equilibrium for these compounds at room temperature.44 These results combined with the above results from Tatsuta's 18 laboratory indicate that macrocyclic (3-keto lactones have unusual physical and chemical properties that may depend on the conformation of the large ring. It is noteworthy that although a large number of macrolide antibiotics and their analogues with a p-hydroxy lactone moiety have been synthesized, only two of these compounds have been prepared by stereoselective reduction of the corresponding p-keto lactone - one of the examples is the transformation 37 to 19 1.4 Synthesis of p-Keto Lactones For several years our laboratory has studied the applications of p-keto ester chemistry.45 The existence of natural products such as pikromycin (40a), narbomycin (40b) and diplodialide A (41), which all contain the p-keto lactone moiety, raises the question of the preparation of such macrocycles. In addition, P-keto lactones might also function as useful precursors to more complex macrolides. Boeckmann and Pruitt used an ingenious intramolecular cyclization of an ©-hydroxydioxolenone 42 to give the p-keto lactone 43. 4 6 Thermolysis of 42 under mild neutral conditions in the absence of other nucleophiles afforded good yields of the large-ring p-keto lactone. Thus they synthesized 43 in 60% yield by refluxing a 10"4 M solution of 42 in toluene for two hours (equation 4). They extended this reaction to the synthesis of other medium- and large-ring p-keto lactones.46 20 In model studies directed toward the synthesis of simple p-keto lactones, Ireland and Brown provided a direct route to such systems through a modified Claisen condensation, in which the thioamide 44 was converted into the enamino lactone 45, which on hydrolysis gave the p-keto lactone 46 (equation 5). 4 7 They suggested that the macrocycle was initially formed via carbon-sulfur bond formation rather than carbon-carbon bond formation as in the Claisen condensation. This thiirane intermediate 47 was readily converted into an enamino lactone as shown on the next page. 21 Booth et al. demonstrated another useful method to synthesize macrocyclic p-keto lactones 49 from intramolecular transesterification of a co-hydroxy-p-keto thioester such as 48 in presence of copper(l) trifluoroacetate (equation 6). 4 8 This strategy failed for medium rings but gave large-ring p-keto lactones in good yields. 22 0 0 C u ( O O C F 3 ) f-BuS' ( C H 2 ) 1 2 O H 0 0 (6)' 48 48 49 During the early 1970's our laboratory developed a method to substitute a |3-keto ester at the y carbon by alkylation of the 2,4-dianion of the p-keto ester such as 50 at the y position. 4 9" 5 3 The dianion 52 could be generated by successive addition of one equivalent each of sodium hydride and n-butyllithium (equation 7). Generally, THF proved to be the solvent of choice. Later, it was found that a slight excess of two equivalents of LDA also produced the dianion 52. Various reactions of the dianion of the p-keto esters have been studied and it was found that the dianions participated in aldol and Claisen reactions as well as alkylations in very good yields. O NaH, .COOMe THF O n-BuLi O .COOMe .COOMe (7) 49 50 51 52 The synthesis of p-keto lactones via the intramolecular alkylation of the dianion of ©-halo-p-keto esters has been reported from our laboratory. 5 4" 5 5 p-Keto esters 55 substituted on the alcohol fragment are readily obtained from the alcoholysis 23 of the acyl Meldrum's acid derivative 53 and the co-bromoalcohol 54. Generation of the dianion and subsequent intramolecular cyclization was attempted using lithium diisopropylamide as base (equation 8). 56 57 For 55, n > 8, the dianion underwent cyclization via y-alkylation to give the fi-keto lactone 56 in modest yield. However, for 55 with n < 7, only the elimination product, the alkene 57, was obtained. The results are shown in Tab le ! This method is used in this thesis to synthesize the 14- and 16-membered ring p-keto lactones. 24 Table 1: Yields of cyclization vs. elimination product of Q-halo-f3-keto esters (equation 8).55 n R Y i e l d 56 (%) Y i e l d 57 (%) 2 H 0 58 4 H 0 41 5 H 0 45 6 H 0 57 7 H 0 41 8 H 43 3 8 Me 47 0 9 H 45 2 10 H 49 4 An alternate strategy, also developed in our laboratory, for the synthesis of p-keto lactones, uses the intramolecular alcoholysis of an co-hydroxy acyl Meldrum's acid derivative 60 instead of the intramolecular dianion alkylation (equation 9).55 The utility of this methodology has also been explored in our laboratory. The benzyloxy protected carboxylic acid 58 was converted into its acid chloride and condensed with Meldrum's acid to give the derivative 59. The benzyl protecting group was removed to give 60. Cyclizations were carried out by slowly adding a dilute THF solution of 60 to refluxing THF. Application of this method was exemplified in the synthesis of the unsubstituted 6-membered p-keto lactone in 87% yield. Again, however, no cyclic product was obtained corresponding to 7- to 13-membered p-keto lactones from the appropriate precursors. However, 3-oxotridecanolide (61) was obtained in 35% yield. The 25 14- and 16-membered p-keto lactones used in this thesis were also synthesized using this strategy and will be discussed further. OCH 2 Ph OH o 60 61 The chemistry of large rings continues to be an actively studied field. In general, current interest in macrolides can be divided into four areas: (a) the isolation and identification of new biologically-active large-ring compounds; (b) the construction of macrolide aglycones; (c) the total synthesis of naturally occurring macrolides; and (d) the investigation and use of the conformations of macrolides in stereoselective and regioselective reactions. 26 1.5 Conformational Studies of Large Rings In Dale's pioneering work, a series of homologous medium and large rings, (CH2)8 to (CH2)3o, were investigated to determine the strain-free conformation(s) available to each ring.56"58 Dale recognized a tendency for saturated large rings to adopt compact conformations consisting of two parallel methylene chains linked by bridges of minimum length. These rectangular or square-shaped conformations were found to possess less torsional strain (Pitzer-strain) and angular strain (Baeyer strain), and hence are more stable than those formed with a large hole in the interior of the ring.56"58 Dale also realized that the network of carbon-carbon bonds within the diamond lattice represented an infinite extension of the ideal tetrahedral geometry. These considerations suggested that large rings tend to adopt a conformation with an anti arrangement of dihedral angles involving the carbon skeleton, which is the same arrangement as in open-chain hydrocarbons, with a minimum number of gauche arrangements to close the ring.56"58 This meant that only even-membered carbon rings with six or more atoms can adopt a conformation in which the carbon atoms are superimposable on the diamond lattice. But the 8-, 10-, and 12-membered (medium) rings have inherent strain because of severe transannular hydrogen interactions. X-ray structures of many large ring compounds and theoretical (molecular mechanics) calculations have also proven the validity of the arguments given by Dale.59 27 1.6 Conformational nomenclature of large rings Only one conformation is possible for the 14-membered ring that is both superimposable on the diamond lattice, and is free of torsional angle strain, and minimum transannular hydrogen interactions (Figures 6, page 32 and Figure 8, page 36). If this minimum-strain conformation is viewed from the "top"(Figure 7, page 35), it is apparent that some carbons have both hydrogens pointing to the outside of the ring, whereas other carbons have at least one hydrogen pointing to the inside of the ring (Figure 8). The hydrogens pointing outside"the ring do not experience any transannular interactions, and carbons with both protons pointing outside are said to occupy a "corner" position. Dale concluded that these corner"atoms should be the only carbons capable of_ accommodating geminal disubstitution without any transannular interactions. These corner positions are formally defined as a sequence of two contiguous gauche-dihedral angles of the same sign flanked on either side by an anti-dihedral angle (e.g. 180°, -60°, -60°, 180°). A top-view diagram of the [3434] conformation immediately illustrates the corner positions: carbon atoms 3, 6, 10, and 13 (Figure 7).56 Another type of corner was also recognized, and had the two gauche-dihedral angles of opposite sign flanked by anti angles (180°, 60°, -60°, 180°). This is called a pseudo-corner position.63 A pseudo-corner position results in an extra gauche interaction hence, the geminal substitution at pseudo-corner positions is less favorable than a corner position. Molecular mechanics calculations suggest that geminal substitution of methyl groups at a 28 pseudo-corner results in a conformation that is 0.6 kcal/mol less favored than the corner geminal disubstituted [3434] conformation (Figure 4). I Figure 4: (a) Corner and (b) pseudo-corner position in large rings. Using a shorthand notation, Dale formulated large ring conformational nomenclature as the number of bonds between each corner and pseudo-corner atoms.60 These numbers were then placed in square brackets using two rules: (1) The number of bonds between corner atoms were numbered in the order found in the conformation. (2) The smallest numbers were listed first within the square brackets without violating rule (1). Subsequently, Neeland stated that 29 the number of bonds between a corner and pseudo-corner atom or between two pseudo-corner atoms be denoted with a primed number, and proposed that the numbers in the square brackets be reported in priority: (comer-corner) > (corner-pseudo-corner) > (pseudo-corner-pseudo-corner).63 However, it was not possible to name all the conformations obtained for these large rings using Dale's nomenclature or Neeland's extension, thus in some cases alphabetic letters were assigned arbitrarily to these conformations ([C]* and [D]* later in Table 2 on page 34). In addition, during studies of the macrolide antibiotic oleandomycin, Ogura and coworkers assigned conformations-rwith letters as A, B, C, D,-E and F. In this case the [3434] conformation was shown to-be. conformation A . 6 4 " 6 6 1.7 Polar maps It is evident that the full conformational analysis of large rings may be complex, and the identification of different conformations can be quite cumbersome, time consuming, and prone to error. To circumvent this problem, Ogura et al. introduced the use of polar maps of torsional angles vs. bonds in their study of oleandomycin.64"66 A polar map reduces the three dimensional conformation to a two dimensional pattern. We have extensively used polar maps in the conformational analysis of the 14-membered rings.67 In order to construct a polar map, the endocyclic torsional angles (torsional angles involved in the ring forming atoms) of the conformation are plotted on a graph consisting of 30 concentric circles that represent the torsional angles of 0°, ±60°, ±120°, and +180°.68 The magnitude and sign of the torsional angle is determined using a Newman projection along the torsional bond. The endocyclic torsional angles can be obtained from X-ray crystallography or from molecular mechanics calculations. The torsional angle of each endocyclic bond is plotted and numbered in a clockwise manner on a polar coordinate system although, the starting point can be chosen randomly (Figure 5). The torsional angles uniquely describe the conformation of a molecule; as a result, polar maps exhibit a unique pattern for each conformation as shown section 1.8. Fyles and Gandour proposed that the torsional angles be plotted from center at 0° to the outer edge (Figure 5).69 This convention is a modification of the one suggested earlier by our group. This convention reduces the ambiguity about anti torsional angles (+175° vs. -175°) and accentuates the equally small differences between eclipsed torsional angles (+5 vs. -5). However, the frequency of eclipsed torsional angles in these large rings is much less compared to anti torsional angles. 31 (a) (b) Figure 5: Polar maps of (a) 14- and (b) 16-membered rings.68"69 1.8 Conformational Analysis of Cvclotetradecane In his conformational analysis of cyclotetradecane, Dale only considered those ring conformations which were superimposable on a diamond lattice.60 He reported a total of five conformations that were superimposable on a diamond-lattice with the [3434] conformation having the lowest energy. However, researchers were not sure that Dale was able to identify all the possible diamond lattice superimposable conformations. 32 [3434] conformation Figure 6: The [3434] conformation of 14-membered ring superimposed on a diamond lattice.60 Later, Saunders determined that there were thirteen possible diamond-lattice conformations for cyclotetradecane.61 He also found that the [3434] conformation was the lowest energy conformation. However, he did not provide the diagrams of these conformations. E. G. Neeland in our research group conducted a conformational search using molecular mechanics with the MM2* force field parameters62 and found, along with these thirteen diamond-lattice superimposable conformations, two additional low-energy conformations that were non-superimposable on the diamond lattice.63 These are designated as the [3344] and the [3335] conformations. The fifteen conformations found exhibited a relative strain energy in the range of 0-12 kcal/mol.63 Most of the diamond-lattice superimposable conformations have high relative strain energy compared to the lowest [3434] conformation.60 Only the lowest five conformations of cyclotetradecane are shown in Table 2, along with their relative strain energy compared to the lowest energy [3434] conformation and their 33 corresponding polar maps. Conformations [C]* and [D]* shown in Table 2 are not the same as the C and D used by Ogura. At first glance, the conformational analysis of these large rings seems to be overwhelmingly complex. While in fact, macrocyclic compounds may exist in a number of stable conformations, only a few of these conformations are of low enough energy to be appreciably populated at room temperature. 34 Table 2: Five lowest conformations of cyclotetradecane along with their relative energies and polar maps. 35 The strain-free [3434] conformation of the 14-membered ring in cyclotetradecane belongs to the C2h point group (Figure 7). It contains four diastereotopic methylene groups. A single monosubstitution can produce eight possible [3434] conformational isomers. The hydrogens, of the four unique methylenes, experience different transannular interactions (Figure 8). The substitution of the hydrogen with the most severe transannular interactions by a hetero-atom or an sp2 carbon will lead to the most stable conformation of that derivative. For example, in the case of tridecanolide, in the most stable [3434] conformation, the ether oxygen should occupy position 1 in Figure 8, i.e. replacing the hydrogen that occupies the most crowded position inside the ring with a lone pair of electrons. Molecular mechanics calculations using MM3* force field parameters also lead to the same conclusion. 12 11 1 3 0 m 0 " 0 " 0 ' ° O 9 I J C2 axis through the C11-C12 and C4-C5 bonds, 7 ' o o « plane of symmetry bisecting C1 & C8, J | and center of symmetry 20 o 7 I I 3 0 — 0 — " ~ 0 ^ — 0 6 « 5 [3434] Top view Figure 7: The [3434] conformation of cyclotetradecane together with the top view and symmetry elements of this conformation. 36 • Most Severe [3434] O Least Severe Figure 8: Transannular hydrogen interactions in the [3434] conformation. 1.9 Conformational analysis of Cvclohexadecane In principle, 16-, 20-, and 24-membered rings would each have the option of adopting a square or a rectangular conformation. From X-ray studies, it was known that the 24- and 28-membered cyclic diketone unit cells, were long and thin, indicating structures analogous to those of aliphatic hydrocarbons.70 It seemed that sufficiently large rings would be rectangular rather than square in shape, since a large square has a hole in the center, and lacks the stabilizing van der Waals attraction between the opposite sides that can be obtained with a rectangular arrangement. But it was not clear how large the ring had to be before it would adopt the rectangular conformation. 37 Figure 9: The [4444] conformation of cyclohexadecane ring superimposed on a diamond lattice. Subsequent to Dale's initial semiquantitative strain-energy calculations on cyclohexadecane,71 very few molecular mechanics calculations have been carried out on 16-membered rings. In fact, only cyclohexadecane conformations have been studied in any detail. Saunders found 82 conformations within 0-5 kcal/mol of the minimum-energy [4444] conformation using a stochastic method.72 Earlier work in our research group using molecular mechanics with MM2* force field parameters found 64 conformations in the same energy range.73 We found three extra conformations within 3 kcal/mol of the global minimum, one of which was the second lowest in energy (about 2 kcal/mol higher in energy than the [4444] conformation). Also, infrared,74 1 3 C NMR,1 9 as well as X-ray studies75 are consistent with [4444] conformation as the lowest energy conformation for the 16-membered rings in solution and the solid state, respectively. Theoretically cyclohexadecane can also exist in a large number of conformations. However, only a few of them are of low enough energy to be appreciably populated at room temperature. An energy difference of 3 kcal/mol 38 between two conformations at room temperature corresponds to an equilibrium ratio of 99.98:0.02. Thus only the five lowest energy conformations of cyclohexadecane are shown in Table 3 and used in this thesis. As noted earlier, the Dale nomenclature proved inadequate for naming all the conformations of cyclotetradecane, as was the case for cyclohexadecane. However, using a nomenclature similar to that of Ogura et al. 6 4" 6 6 the other conformations can be listed alphabetically. 39 Table 3: Five lowest conformations of cyclohexadecane along with their relative energies and polar maps. 40 The lowest energy [4444] conformation of cyclohexadecane has a higher symmetry than the [3434] of cyclotetradecane and belongs to the D2d point group (Figure 10). The [4444] conformation has three diastereotopic methylene environments. A single monosubstitution produces a total of six possible conformational isomers. The hydrogens of three unique carbons experience different magnitudes of transannular interactions, as shown in Figure 11. 14 13 12 1 5 0 " — O — - " 0 " " — O " O n I I 16° rjio c 2 axis through center of | | the ring, two perpendicular C2 axes 1? V through C3-C11 and C7-C15, I 1 two diagonal planes of symmetry J ° j 6 through C1 & C 9 a n d C 5 & C 1 3 3 0 " 0 aOm 0 " 0 7 4 5 6 Top view elements of the [4444] conformation of cyclohexadecane. Since most of the conformational strain in this [4444] conformation comes from the transannular interactions between the hydrogens, substitution of carbonyl groups at position 1 over position 2 should favour the removal of such transannular interactions (Figure 11). Allinger et al. showed that in the case of [4444] conformation, position 1 was the most favoured of the three possible diastereomeric methylenes to be substituted as a carbonyl group. But molecular mechanics calculations with the MM2* force field parameters suggested that a substitution at position 2 was energetically favoured.76 However, using the [4444] Figure 10: Symmetry 41 MM3* force field parameters, it was found that the original suggestion that substitution of a methylene by a carbonyl group at position 1 to be favored by 0.24 kcal/mol over substitution at C-2. Most Severe [4444] O Least Severe Figure 11: Hydrogen interactions in the [4444] conformation of cyclohexadecane 76 1.10 The lactone linkage To simplify the conformational analysis of large rings, a further reduction in the number of conformations was considered. Huisgen and Ott reported that an ester group can exist in two planar conformations, s-trans or s-cis. Using boiling points, dipole moments, and rate constants of alkaline hydrolysis of the homologous aliphatic ©-lactones they showed that the ring structure constrains small-ring lactones (4-7 atoms) into the energetically less favoured s-cis conformation. On the other hand, lactones with ring sizes of ten and more can assume the more stable s-trans conformation, found in open chain esters.77 Jones and Owen estimated that the energy difference between the conformations of s-trans and s-cis esters to be of the order of 3.0 kcal/mol, thus 42 explaining the predominance of s-trans conformations in open chain esters (Figure 12). 78 o V r T > 0 ^ / \ , / s-cis R ' s-trans Figure 12: s-Trans and s-cis conformations of an ester. The 14- and 16-membered rings are large enough to accommodate the considerably more stable s-trans lactone, so conformations with the s-cis lactone linkage can be ignored in the conformational analysis. Furthermore, Schweizer and Dunitz collected X-ray structural data on a large number of esters of secondary alcohols, which showed that the C-O-C-H dihedral angle in these compounds was in the range of 0-60°, with 85% of the esters in the 0-40° range (Figure 13).79 H R' Figure 13: Preferred conformation of ester of a secondary alcohol.79 Applying this trend to lactones of secondary alcohols and using the s-trans lactone moiety on the [3434] conformation, only three major conformations of 13-tetradecanolide need to be considered, and only two conformations of [4444] need to be considered for 15-hexadecanolide (Figure 14). 43 Figure 14: The preferred conformations of (a) 14- and (b) 16-membered lactones. In this project reactivity and conformations of large ring p-keto lactones were studied to understand the conformational behaviour of these simple large rings and to develop a better model to predict the reactivity and the relative stereochemistry of the reactions of large ring p-keto lactones. 44 RESULTS AND DISCUSSION 2.1 Chemistry of 14- and 16-Membered Lactones Conformational control of reactions on large rings can be used to introduce new chiral centers with high stereoselectivity as described previously in the Introduction. In this project, the reactivity and conformational rigidity of 14- and 16-membered rings were studied. A number of stereo- and regioselective alkylations and reductions were carried out on 14- and 16-membered lactones with 74 and 84 as the starting cyclic compounds for these studies. Subsequently, through X-ray crystallography and chemical correlations, the relative stereochemistry of the chiral centers of most of the compounds prepared from 74 and 84 was determined. Molecular mechanics calculations were then carried out on these compounds, and correlations were drawn between the calculations and the experimental results. This work is a continuation of investigation into the chemistry of large rings carried out in our laboratory. 74 84 45 2.2 Synthesis of 3-Oxo-13-tetradecanolide (74) and 3-Oxo-15-hexadecanolide (84) Two new methods for the preparation of medium- and large-ring p-keto lactones using inter- and intra-molecular reactions of Meldrum's acid derivatives had been developed earlier in our laboratory. At that time the cyclization of mainly primary alcohols to yield 6- to 14-membered p-keto lactones was examined (Introduction, section 1.4). 2.2.1 The Preparation of 3-Oxo-13-tetradecanolide (74) via Intramolecular Alcoholvsis of Acvlated Meldrum's Acid 11-Hydroxydodecanoic acid (67) was synthesized from 11-undecenoic acid (62) in six steps in 59% overall yield. These reactions have been previously used in our laboratory (Scheme 2, page 47).80 The hydroxy acid 67 was reacted with a slight excess of two equivalents of te/f-butyldimethylsilyl chloride and triethylamine as base, followed by basic hydrolysis to give the siloxy acid 69. The protected 11-hydroxydodecanoic acid 69 was activated with 1,1'-carbonyldiimidazole. The activated imidazolide was not isolated, but was immediately added to a solution of the anion 71 to give the acylated Meldrum's acid derivative 72. Meldrum's acid (70) itself was prepared in 50% yield from malonic acid and acetone, in the presence of acetic anhydride and a catalytic 46 amount of sulfuric acid.55 The protecting group of 72 was cleaved with 10% hydrofluoric acid in acetonitrile to give 73. The final step in the formation of 3-oxo-l 3-tetradecanolide (74) was an intramolecular alcoholysis. Thermolysis of 73 by the slow addition of a dilute THF solution of this compound to THF heated at reflux resulted in production of the 14-membered (3-keto lactone 74 as a yellow oil in 19% overall yield from 69 (Scheme 2). Spectral data for 74 was identical to that reported earlier for this compound.55 Meldrum's acid derivatives 72 and 73 could not be purified and the crude materials were used directly in the next step. 47 73 74 Scheme 2: (a) LAH, THF, 0 °C, 3 h; (b) PBr3, Et20, 24 h; (c) KCN, DMF, 40 °C, 24 h; (d) KOH, EtOH, A, 4 h; (e) Hg(OAc)2, THF-H20 (3:1), 2 h; (f) NaBH4, NaOH, 1 h; (g) TBDMS-CI, Et3N, DMAP, CH2Cf2, 72 h; (h) 10% NaOH (aq), A, 1 h; (i) py, CH2CI2, 45 min; (j) (lm)2CO, CH2CI2, 30 min; (k) 71, 14 h; (I) 10% HF, CH3CN, 4 h; (m) THF, A, 4 h. 48 2.2.2 Conformational Analysis of 3-Oxo-13-tetradecanolide (74) Schweizer and Dunitz have found that esters of secondary alcohols usually have small torsional angles for the (0=)C-0-C-H angle (Introduction, section 1.10).79 It has been shown that a similar effect exists for macrocyclic lactones of secondary alcohols.81 This effect is not included in the MM2* force fields. Later, MM3* force field parameters were developed and these parameters do give lower energy conformations to those that have small (0=)C-0-C-H torsional angles. Earlier, molecular mechanics calculations were performed on 3-oxo-13-tetradecanolide (74) using MM2* force field parameters in our laboratory.63 Here the results from the molecular mechanics calculations using MM3* force field parameters are presented. A total of 33 conformations within 3 kcal/mol of the global minimum conformation were found. Although all 33 of these conformations were considered to rationalize the reactivity of 74, for the sake of convenience only five lowest energy conformations along with their polar maps and relative energies are given in Table 4. It is interesting to note that all five conformations were within 1 kcal/mol. These findings are consistent with earlier studies which showed that 3-oxo-13-tetradecanolide (74) exists in a number of conformations in solution.67 The [3434] conformation was found to be the lowest energy conformation, which can be readily identified from its polar map. The [3434] conformation was also 49 found to be the lowest energy conformation in cyclotetradecane (Introduction, section 1.6). The ether oxygen of the lactone occupied position 1, which in case of a methylene group has the most hindered hydrogen, pointing inside in the ring (Introduction, Figure 6). The two carbonyl groups of the lactone and ketone groups occupied position 2 and 4 respectively and the methyl substituent at C-13 occupied a non-corner position 2. Most of the conformations have the two carbonyl groups of the lactone and ketone group respectively, anti periplanar to each other except for the second lowest energy conformation where the two carbonyl groups were syn periplanar to each other. The fifth lowest energy conformation was found to be the [3434] geometry also. The ether oxygen of the lactone group occupied position 4. The two carbonyl groups of lactone and ketone groups occupied position 4 and 2 respectively and the methyl substituent at C-13 occupied a corner, position 3. It is interesting to note that the difference between the two [3434] conformations was that the lowest energy conformation has the transannular hydrogen interaction removed at position 1. Whereas the fifth conformation has a transannular hydrogen interaction removed at position 4. This suggests that the difference in energy is 0.83 kcal/mol between the two conformations equals the difference between a hydrogen pointing inside the ring at position 1 vs. position 4. 50 Table 4: Five lowest conformations of 3-oxo-13-tetradecanolide (74) along with their relative energies and polar maps. 51 2.2.3 The Preparation of 3-Oxo-15-hexadecanolide (84) via Intramolecular Alcoholvsis of Acvlated Meldrum's Acid Derivative 11-Bromoundecanoic acid (75) was esterified to give methyl 11-bromoundecanoate (76). The anion of methyl acetoacetate (77) was generated with NaH, and treatment with the bromo ester 76 followed by hydrolysis and decarboxylation under acidic conditions gave 13-oxotetradecanoic acid (78). The 13-hydroxytetradecanoic acid (79) was obtained by NaBH4 reduction of keto acid 78. The overall yield of 79 obtained in this sequence of reactions was 77%. The hydroxy acid 79 was reacted with a slight excess of two equivalents of terf-butyldimethylsilyl chloride in the presence of triethylamine as base and then followed by hydrolysis to give the protected hydroxy acid 81. Using the same methodology as above (Scheme 2), the protected 13-hydroxytetradecanoic acid 81 was activated with 1,1'-carbonyldiimidazole in situ and then added to the anion of Meldrum's acid in dichloromethane to give the acylated Meldrum's acid derivative 82. Once obtained, 82 was stirred for 4 hours in a solution of hydrofluoric acid in acetonitrile to cleave the protecting group. A THF solution of hydroxy Meldrum's acid derivative 83 was added slowly, over a period of six hours with a syringe pump, into THF heated at reflux to give 3-oxo-15-hexadecanolide (84) as a yellow oil (Scheme 3). Meldrum's acid derivatives, 82 and 83, could not be purified. The overall yield from 81 to 84 was 12%, with yield of the cyclization step being quite low. 52 C O O H C O O M e 75 O O X A b.c OMe 77 OH 79 O T B D M S 70 81 76 C O O H d_ 78 O T B D M S C O O H C O O H 71 O T B D M S h, i 82 80 C O O T B D M S OH o 0 = ^ 0 OH 83 OH o O _ L 0 = ^ o 84 Scheme 3: (a) MeOH, H+, 1 h; (b) NaH, THF-DMF, 76, A, 14 h; (c) HCI (cone), A, 24 h; (d) NaBH4, EtOH, 1 h; (e) TBDMS-CI, Et3N, DMAP, CH2CI2, 72 h; (f) 10% NaOH (aq), 4 h; (g) py, CH 2CI 2 l 45 min; (h) (lm)2C0, CH2CI2, 30 min; (i) 71, CH2CI2, 14 h; fl) 10% HF, CH 3CN, 4 h; (k) THF, A, 6 h. 53 The 1H NMR spectrum of p-keto lactone 84 had a multiplet at 4.95 ppm that corresponded to the C-15 methine proton. An AB quartet was also observed at 3.4 and 3.2 ppm for the C-2 protons of 84 and are characteristic peaks observed in 1H NMR of macrocyclic p-keto lactones of secondary alcohols. The infrared spectrum of 84 showed peaks for two carbonyls at 1735 and 1711 cm"1 due to the lactone and ketone group respectively. This initial evidence, and later the microanalysis and mass spectrum confirmed the structure of the new p-keto lactone as 84. Spectral data is included in the Experimental section, in addition a Spectral Appendix consisting of the 1H NMR and the IR spectra of all the new compounds synthesized in this project has been provided at the end of the thesis. 2.2.4 The Preparation of 3-Oxo-15-hexadecanolide (84) via Intramolecular Alkylation of the Dianion of a p-Keto ester In the early 1970's our laboratory developed a method to induce reactivity at the y-carbon of a p-keto ester.49"54 The dianion of these p-keto esters could be generated by treating the p-keto ester with one equivalent of NaH followed by one equivalent of /7-BuLi, or by the addition of a slightly more than two equivalents of LDA to the p-keto ester. Such dianions of p-keto esters and p-keto lactones were extensively used in the present project. To begin with, p-keto lactones were obtained via intramolecular alkylation of the dianion of Q-bromo-p-keto ester of a substituted secondary alcohol. 54 o-bromo-p-keto ester of a substituted secondary alcohol. 3-Oxo-l 3-tetradecanolide (74) had already been synthesized during earlier studies using this methodology.55 Here the synthesis of 3-oxo-l 5-hexadecanolide (84) is presented. 55 89 84 Scheme 4: (a) LAH, THF, 0 °C, 3 h; (b) PBr3, Et20, 24 h; (c) KCN, DMF, 40 °C, 24 h; (d) DIBAL, THF, -78 °C, 1 h; (e) LAH, THF, 0 °C, 1 h; (f) PBr3, Et20, 24 h; (g) Hg(OAc)2, THF-H20 (3:1), 2 h; (h) NaBH4, NaOH, 1 h; (i) py, CH2CI2, 45 min; (j) CH3COCI, 6 h; (k) 87, THF, A, 4 h; (I) LDA (2.2 eq),-78 °C-> rt, 5 h. 56 In three steps the carbon chain of the commercially available 11-undecenoic acid (62) was extended by one carbon to 11-cyanoundecene (65), which was reduced in two steps to give 11-hydroxydodecene (85), which in turn was converted to 11-bromododecene (86). Oxymercuration of 86 gave 1 -bromo-11 -hydroxydodecane (87), obtained in an overall yield of 51% from 62 (Scheme 4). The acylated Meldrum's acid (88) was synthesized by the addition of acetyl chloride to the anion of Meldrum's acid. Intermolecular alcoholysis of acetyl Meldrum's acid (88) and 12-bromo-2-hydroxydodecane (87) in refluxing THF gave the desired p-keto ester 89 in quantitative yield. Finally, the dianion of 89 was generated at -78 °C by addition of a slight excess of two equivalents of LDA in a dilute solution of 89 in THF (1x10"3 M). The solution was allowed to warm to room temperature over a period of five hours and worked up to give 84 in 32% yield (Scheme 4). Compound 84 prepared in this manner was identical to that prepared earlier (Scheme 3). 57 2.3 The Conformations and Reactivity of f3-Oxvaenated 14-Membered Lactones During the earlier studies of 14-membered p-keto lactones, monoakylation of 3-oxo-l 3-tetradecanolide (74) at the C-2 and C-4 positions was investigated.63 Conformations of the intermediate enolates were calculated from molecular mechanics calculations using the MM2* force field parameters, and the relative stereochemistry in these alkylation products was deduced from these calculations. However, no experimental data was available to confirm the relative stereochemistry of the chiral centers in these compounds. In the present project it was decided to reinvestigate these reactions and to explore various chemical transformations of these compounds which might be used to correlate the stereochemistry of the alkylation products with compounds of known relative stereochemistry. 2.3.1 Alkylation of the Monoanion of 3-Oxo-13-tetradecanolide (74) The anion of 3-oxo-13-tetradecanolide (74) was generated with slightly more than one equivalent of potassium ferf-butoxide in te/f-butanol at reflux. This anion was reacted with methyl iodide to give 2-methyl-3-oxo-13-tetradecanolide (90) as a mixture of diastereomers in a ratio of 2:1 in 68% yield (equation 10). 1H NMR, 1 3 C NMR, and IR spectra were identical to those obtained earlier for compound 90.63'82 58 Earlier work on the 14-membered lactones in our laboratory resulted in the unambiguous assignment of, the relative stereochemistry of the two diastereomers of 2-methyl-13-tetradecanolide. 8 3 Furthermore, it was found that the retention time of (2R*,13S*)-91 was less than that of (2S*,13S*)-92 on a DB-210 gas chromatography column. 8 3 The use of the star superscript indicates the presence of both enantiomers possessing the same relative stereochemistry at the numbered atoms, e.g. 2S*,13S* refers to an equal amount of 2S.13S and 2R.13R stereoisomers. This star notation is used throughout this thesis. 91 92 59 Thus it was decided to convert 2-methyl-3-oxo-13-tetradecanolide (90) into 91 and/or 92. For this purpose, a synthetic procedure for selective carbonyl protection under mild conditions was chosen. 91 92 Scheme 5: (a) TMS-SCH2CH2S-TMS, Znl2, Et20, 14 h; (b) n-Bu3SnH, AIBN, A, toluene, 10 h. 1,2-Bis(trimethylsilylthio)ethane has been used to convert aldehydes and ketones into their thioketals without any epimerization.84 Thus the isomeric mixture of 2-methyl-3-oxo-13-tetradecanolide (90) was reacted with 1,2-bis(trimethylsilylthio)ethane in diethyl ether with zinc iodide as catalyst to 60 give the thioketal 93 in 65% yield as a mixture of diastereomers in a 2:1 ratio by GC. The thioketals were then desulfurized via a radical reduction with tributyltin hydride to give (2R*,13S*)-91 and (2S*13S*)-92 in a ratio of 2:1 (Scheme 5). The relative stereochemistry of these diastereomers was proven by correlation with authentic diastereomers synthesized earlier in our laboratory. Hence, the relative stereochemistry of the chiral centers of the major diastereomer of 2-methyl-3-oxo-13-tetradecanolide (90) was identified as 2R*,13S* and that of the minor isomer was 2S*, 13S*. In a conformational study of the two diastereomers of 2-methyl-3-oxo-13-tetradecanolide (90) using MM3* force field it was found the lowest energy conformation of (2R*,13S*)-90 was 19.66 kcal/mol and that of (2S*,13S*)-90 was 19.77 kcal/mol. This would lead to a predicted equilibrium ratio of 55:45 at 25 °C based on the global minimum energies of the two diastereomers compared to the observed value of 66:33. Earlier work had shown that the 2:1 ratio of diastereomers of 90 was the equilibrium value.67 The theoretical results show that although the predicted relative stereochemistry of the major and minor isomer are the same as experimental, still better set of parameters are needed for theoretical results to be closer to experimental ones. The calculations also suggested that the (2R*13S*)-90 was the major isomer as was found experimentally. 2.3.2 Alkylation of the Dianion of 3-Oxo-13-tetradecanolide (74) 61 0. ,0 0 1. LDA (2.3 equiv), THF, 0 °C. 30 min 2. Mel, THF 74 0 (11) 94 The dianion of 3-oxo-13-tetradecanolide (74) was generated using slightly more than two equivalents of LDA at 0 °C and it was reacted with one equivalent of methyl iodide to give the monoalkylated product 94 in 80% yield (equation 11).63 All spectral properties of this compound were found to be identical to those reported earlier for this compound.63 Chromatographic and the 1H NMR data suggested that alkylation was highly stereoselective with only one of the two possible diastereomers of the product being obtained. Previous conformational analysis using the MM2* force-field parameters suggested that the dianion had the distorted [3434] conformation 95 with chelation of the metal ion possible while, also the positioning of methyl group on C-13 outside the ring. This conformation would expose the 3-re, 4-re face of the 62 enolate 95 to an electrophile and lead to the 4S*,13S* stereochemistry upon alkylation. However, this model had not been verified experimentally. Initially, it was decided to convert 94 to 2,11-dodecanediol in an effort to determine the relative stereochemistry of the dianion alkylation product. To obtain the necessary reference compounds, mixture of the two diastereomers of 2,11-dodecanediol, 97 and 98, were synthesized in 80% yield by a double Grignard reaction of 1,6-dibromohexane (96) with racemic propylene oxide. Similarly, enantiomerically pure (2S,11S)-2,11-dodecanediol (97) was synthesized from 96 and (S)-propylene oxide (Scheme 6). 95 63 OCOPh (-)-99 Scheme 6: (a) Mg, l2, Et20, 30 min; (b) propylene oxide, 18 h; (c) PhCOCI, py, 30 min; (d) (S)-propylene oxide, 3 h. Once these diols were obtained, methods to separate and characterize them were investigated. However, separation of diastereomers 97 and 98 turned out to be quite a formidable task. They were inseparable by TLC, GC, normal-, and reverse-phase HPLC as well they could not be distinguished by 1H NMR, 1 3 C NMR or IR. The diols were subsequently esterified to give the dibenzoate esters 99 and 100. However, they also were inseparable or indistinguishable by 64 any of the above physical techniques. At this stage, the separation of the diastereomers of the diols and the corresponding diesters on chiral GC columns was investigated without success. Next, the attention was shifted to their separation on chiral HPLC columns, in particular, Chiralcel OD and Chiralpak OP(+) columns. Finally, the dibenzoate esters 99 and 100 resolved on the Chiralpak OP(+) column into three peaks in a ratio of 1:2:1 with a retention time of 9.1 minutes, 9.9 minutes, and 10.5 minutes respectively at a flow rate of 0.6 mL/min with methanol as eluant (Figure 15). It was expected to obtain a 1:2:1 ratio of peaks if the two diastereomers were present in equal amounts because one diastereomer 99 was a pair of enantiomers, while the other, 100, was meso. Thus, the peak at 9.9 minutes was assigned to the meso compound 100. When this mixture of diastereomers was co-injected with the enantiomerically pure (2S,11S)-99 dibenzoate it was found that the peak at 9.1 minutes was from the enantiomer (2S,11S)-99. Thus the peak at 10.5 min was assigned to (2R, 11 R)-99. 65 0.6 r E c CM CD 0.4 c o CO - Q < > 0,2 l i l i l 0 2 4 6 8 10 12 14 16 18 20 Time (min) Figure 15: HPLC trace of dibenzoate esters 97 and 98 of 2,11-dodecanediol on Armed with this knowledge, the efforts were directed towards the conversion of 4-methyl-3-oxo-13-tetradecanolide (94) to one of the 2,11-dodecanediols with retention of stereochemistry. One possible way to carry out such a conversion might be a direct Baeyer-Villiger oxidation of 94, followed by hydrolysis to yield the diol. The Baeyer-Villiger oxidation is known to proceed with retention of stereochemistry.85 However, earlier studies on the Baeyer-Villiger oxidation of p-keto esters gave 2-hydroxy-3-keto esters, presumably via epoxidation of the enol.86 Thus it was decided to first hydrolyze the lactone, decarboxylate the resultant p-keto acid, and then subject the ketone to Baeyer-Villiger oxidation. However, during this reaction a mixture of both diastereomers of the dibenzoate Chiralpak OP (+) column. 66 ester of 2,11-dodecanediol was obtained in an equal ratio. At this stage, I was unsure if this was a result of epimerization during these reactions or if there was no selectivity in the initial y-alkylation of 3-oxo-13-tetradecanolide (78). However, when similar experimental results were obtained during conversion of a single diastereomer of 4-methyl-15-hexadecanolide (section 2.4.8), it was clear that the epimerization of methyl group took place during the conversion of the lactone to diol. Since there was no evidence for the enolized form of the P-keto lactone 94 from 1H NMR and IR spectra, it was decided to directly carry out the Baeyer-ViNiger oxidation on 94. OH 6 C O P h 97 99 Scheme 7: (a) (NH2)2CO.H202, Na 2 H P 0 4 , (CF 3CO) 20, CH2CI2, 12 h; (b) PhCOCI, py, 1 h. 67 Peroxytrifluoroacetic acid was generated in situ by the addition of trifluoroacetic anhydride to urea hydrogen peroxide in dichloromethane.87 The p-keto lactone 94 as a solution in dichloromethane was added to the solution of peroxytrifluoroacetic acid in dichloromethane and a buffer, Na 2HP0 4 was added to prevent any transesterification of the product catalyzed by trifluoroacetic acid generated during the reaction.87 We 2,11-dodecanol was obtained in an overall 60% yield from 94. None of the dilactone could be detected; it was believed to be unstable under these conditions, and was hydrolyzed to the diol (Scheme 7). The diol was converted into its dibenzoate ester, and HPLC analysis showed only the peaks due to the racemic (2S* 11 S*)-99 were observed (Figure 16). The stereochemical assignment was also confirmed by co-injection of the racemic dibenzoate with authentic (2S,11S)-99. Hence, the relative stereochemistry of the dianion alkylation product was confirmed to be (4S*,13S*)-4-methyl-3-oxo-13-tetradecanolide (94). This also supported the postulated geometry in 95 of the dianion enolate in a distorted [3434] conformation. This conformation would expose the 3-re, 4-re face of the enolate 95 to an electrophile and produce the observed 4S*,13S* stereochemistry upon alkylation. 68 0 2 4 6 8 10 12 14 16 Time (min) Figure 16: HPLC trace of the racemic dibenzoate ester of 2, 11-dodecanediol derived from 4-methyl-3-oxo-13-tetradecanolide on Chiralpak OP (+) column. 2.3.3 Conformational Analysis of (4S*.13S*)-4-Methvl-3-oxo-13-tetradecanolide 194) A conformational search was carried out on (4S*13S*)-4-methyl-3-oxo-13-tetradecanolide (94) using the MM3* force field parameters and found a total of 58 conformations within 3 kcal/mol of the global minimum. The lowest energy conformation had a conformation that couldn't be defined by Dale's nomenclature. The next two conformations were found to be 0.05 kcal/mol and 69 1.03 kcal/mol higher in energy than the lowest energy conformation, respectively. An equilibrium ratio from these energy values would favour the first two conformations over the rest by a ratio of 6:1 at 25 °C. Table 5 shows the five lowest energy conformations of 94 and their polar maps. 70 Table 5: The five lowest energy conformations of (4S* I S S ^ - m e t h y l - S - o x o -IS-tetradecanolide (94) along with their polar maps. 71 In the macrocyclic p-keto lactones either a six or an eleven line pattern was observed for the C-13 methine proton ca. chemical shift 5 ppm and here only a clean eleven line pattern was observed as shown in Figure 17. Figure 17: Multiplet of C-13 methine proton of 4-methyl-3-oxo-13-tetradecanolide (94). The conformational analysis would suggest that the experimentally observed coupling constants should have values close to the average of first two conformations. In Table 6 the vicinal coupling constants of the two methine protons at C-4 and C-13, calculated by M A C R O M O D E L for the two lowest energy conformations, and the experimentally observed values are shown. Proton decoupling experiments were used to obtain accurate coupling constants for these multiplets. M 72 Table 6: Experimental and Calculated Vicinal Coupling Constants of (4S* 13S*)-4-Methyl-3-oxo-13-tetradecanolide (94). Vicinal Coupling constants Experimental (Hz) Conformation 1 (Hz) Conformation 2 (Hz) J4-15 7 6.5 6.6 J4-5A 5.4 3.1 2.1 J4-5B 7.5 12.3 12.3 J13-12A 2.9 1.9 1.4 J13-12B 8.4 11.6 11.3 J13-14 6.2 5.8 5.8 From the experimental and the calculated values of the coupling constants it appears that (4S* 13S*)-4-methyl-3-oxo-13-tetradecanolide (94) exists as a mixture of conformations that equilibrate faster than the NMR time scale at room temperature resulting in an averaged value for the coupling constants. 73 2.3.4 Alkylation of the Monoanion of (4S*13S*)-4-Methvl-3-oxo-13-tetra-decanolide (94) and the Dianion of 2-Methvl-3-oxo-13-tetradecanolide (90) Having solved the stereochemistry of a- and y-monoalkylated products of 74, the focus was turned, to the a-alkylation of 4-methyl-3-oxo-13-tetradecanolide (94) and the y-alkylation of 2-methyl-3-oxo-13-tetradecanolide (90) to investigate the effect of the additional methyl substituents on these alkylations of the 14-membered ring. The monoanion of 94 was generated at C-2 with potassium fe/t-butoxide and this anion was alkylated with 1.3 equivalents of methyl iodide. Two new spots were observed on the TLC plate. The two compounds were separated via radial chromatography on silica with 1:20 petroleum ether and ethyl acetate as eluant. The less polar material (Rf 0.42) was the major product from the alkylation and the more polar material (Rf 0.35) was the minor product. The 1H NMR showed that higher running fraction was the geminal a-dialkylated product 102 and the material with Rf 0.35 was the a-monoalkylated product 101 (equation 12). The two products 101 and 102 were isolated in 27% and 44% yield, respectively. 94 101 102 74 2,2,4-Trimethyl-3-oxo-13-tetradecanolide (102) was identified from its spectral data. The 1H NMR showed the disappearance of the AB quartet at 3.5 ppm corresponding to C-2 methylene protons of 94 and the appearance of two singlets at 1.30 and 1.42 ppm of relative intensity of three protons corresponding to the two methyl groups at C-2. The infrared spectrum of 102 had peaks at 1703 and 1723 cm"1 for the ketone and lactone groups, respectively. The 1H NMR of 101 showed that both C-2 epimers were present in a ratio of 8:1. C-2 monoalkylation was supported by the disappearance of the AB quartet corresponding to C-2 methylene protons of 94 and the appearance of two quartets in the 1H NMR of 101 integrating to one proton. The two diastereomers of 101 have different chemical shifts for this quartet. In the major diastereomer this quartet appears at 3.74 ppm whereas, in the minor diastereomer it appears at 3.7 ppm. A new doublet of relative intensity three corresponding to the C-2 methyl substituent appeared at 1.28 ppm and presumably the other doublet is embedded in the methylene envelope. The infrared spectrum of 101 showed peaks at 1710 and 1736 cm"1 for the two carbonyl groups of ketone and lactone groups respectively. At this stage, the relative stereochemistry at C-2 of the major and minor diastereomers of 101 could not be determined. The conformation of the enolate 103 from ketone 94 suggested that the 2-re, 3-si face of the enolate would be considerably hindered by the inside hydrogens of 75 the 14-membered ring. Hence, enolate 103 would be attacked by methyl iodide from the ring periphery to produce the 2S*,4S*,13S* diastereomer. However, under the conditions employed, equilibration at C-2 is expected.67 The observed 8:1 ratio suggests that the two diastereomers do not have similar energies. This was confirmed by molecular mechanics calculations. It was found that the lowest energy conformation of 2S*,4S*,13S* was 23.38 kcal/mol and that of 2R*,4S*,13S* was 25.07 kcal/mol. These enthalpic energies would correspond to a calculated ratio of 20:1 at 25 °C. 103 However, when the synthesis of the 2,4-dimethyl-3-oxo-13-tetradecanolide was carried via a different route, the number of diastereomers and their ratios were not the same. The dianion from 90 was generated by the addition of slight excess of two equivalents of LDA at 0 °C and then alkylated with methyl iodide. The reaction mixture showed only one new spot on TLC plate, which ran slightly higher than the starting material 90 and had an identical Rf to 101. This compound was isolated via radial chromatography on silica with 1:20 petroleum 76 ether and ethyl acetate as eluant in 48% yield and 44% of starting material was recovered (equation 13). 90 101 The 1H NMR of the product obtained here was very complicated and it seems that all four possible diastereomers were present. The disappearance of the multiplet due to the two C-4 protons at 2.9-2.2 ppm of 90 and appearance of a new two multiplets at 2.89-2.71 and 2.55-2.48 ppm of relative intensity one indicated that the alkylation at C-4 had occurred. The signal corresponding to the C-13 methine proton in the product was a multiplet of more than 20 peaks, which seemed to be comprised of two sets of multiplets, stretching from 5.1-4.8 ppm. In the synthesis of 101 via alkylation of monoanion of 94 (equation 12) a multiplet in the region from 4.99-4.87 was observed for the C-13 proton of 101, and it was already known that this multiplet was due to the two C-2 epimers of (4S*,13S*)-101. Hence, it was concluded that the multiplets in the product from the alkylation of the dianion of 90 could only be due to the two diastereomers at C-4 with respect to the methyl group at C-13 namely the (4R*,13S*)- and 77 (4S*,13S*)-compounds. Further, the single proton at C-2 was two separate quartets at 3.7 and 3.78 ppm in a ratio of 1:2. These peaks were broad suggesting the presence of additional quartets. The peak for the single C-4 proton also appeared as two separate sets of multiplets at 2.89-2.71 and 2.55-2.48 ppm in a ratio of 1:1. Also, the six doublets corresponding to the three different methyl groups were visible. However, the 1H NMR spectrum was very complicated and it was difficult to determine the ratios of these signals. The 1 3 C NMR was more helpful in identifying the number of diastereomers. A total of 39 signals were observed from 0-72 ppm in the 1 3 C NMR spectrum and they could be grouped into three sets in an approximate ratio of 1:1:2. If the four possible diastereomers from the alkylation of the dianion of 90 were produced in equal amounts and the 1 3 C signals of two of these diastereomers were identical, then the expected number of peaks from 0-72 ppm would be 42. Some of the peaks due to methylene carbons in the 1 3 C NMR spectrum were overlapping resulting in 39 observable peaks. The 1 3 C NMR of 101 from the alkylation of the monoanion of 94, had only 14 peaks in the region of 0-72 ppm and these were identical to chemical shifts of the peaks with higher intensity in the 1 3 C NMR spectrum from the mixture of diastereomers from the alkylation of the dianion of 90. This showed that no selectivity had been achieved in the alkylation of the dianion of 90 and the data suggested that all four diastereomers were obtained in a ratio of approximately 1:1:1:1. In the infrared spectrum, peaks 78 corresponding to the ketone and lactone were observed at 1706 and 1727 cm"1, respectively, and they were broad suggesting a mixture of diastereomers. Molecular mechanics calculations suggested that the dianion of 90 has a conformation 104a where the two carbonyl oxygens were anti. Attack of an electrophile from the peripheral face would lead to the 4S*,13S* product. However, if the reaction goes through the chelated transition state 104b then attack from the peripheral face would result in the 4R*,13S* product. 104a 104b Through these alkylations, a way to stereo- and regioselectively synthesize one of the diastereomers of 2,4-dimethyl-3-oxo-13-tetradecanolide (101) was developed. The y-alkylation of 90 gave a complex mixture of diastereomers of 101. However, a-alkylation of 94 proceeded with high stereoselectivity due to equilibrium at C-2. 79 2.3.5 Stereoselective Reduction of 2.2.4-Trimethvl-3-oxo-13-tetradecanolide 1102) Sodium borohydride reaction of (4S* 13S*)-2,2,4-trimethyl-3-oxo-13-tetradecanolide (102) in ethanol gave a reduced product. A single new spot was observed on TLC. The product 105 was isolated in a yield of 91% (equation 14). The Rf value of 105 was 0.46 with 9:1 petroleum ether and ethyl acetate as eluant. The Rf values of macrocyclic p-hydroxy lactones were usually found between 0.25-0.35 in 9:1 petroleum ether and ethyl acetate.63 Hence, it was proposed that there might be hydrogen bonding between the hydroxy group and the carbonyl group of the lactone in 105 resulting in a less polar compound with higher Rf value observed for this product. 102 105 The 1H NMR of the product 105 had a sharp doublet at 4.45 ppm with a coupling constant of 10.3 Hz of relative intensity of one proton corresponding to the hydroxy proton. The single proton at C-3 was a doublet of doublets at 3.21 ppm 80 with vicinal coupling constants, J3.0H = 10.3 and J3-4 = 2.1. The infrared spectrum of the compound had a peak at 3462 cm"1 and a sharp peak at 1687 cm'1. No other peaks were observed in the region of 1750 to 1650 cm"1. Hence, the peak due to the carbonyl of the lactone of 105 was at 1687 cm"1. This is unusually low for the carbonyl peak of a lactone which normally appears at 1735-1725 cm"1. Carbonyl peaks are shifted to lower wave numbers in the case of hydrogen bonding and it was suspect that to be the case here. At this point infrared spectra of 105 at various concentrations in deuterochloroform were obtained. The peaks due to the hydroxyl group and the carbonyl group of 105 remained the same. Hence, it was concluded that 105 has an intramolecular hydrogen bond between the hydroxyl group and the carbonyl group of the lactone. This reduction was very stereoselective and only a single diastereomer in the product was detected by chromatographic and spectroscopic analysis. It is suggested that the reduction proceeds through an intermediate, such as 106, in which the counter cation chelates with the two carbonyl oxygen atoms to expose the si face of the keto group to hydride attack, resulting in the (3S*,4S*,13S*) product. 81 106 107 This same mechanism has been proposed in the reduction of other large-ring p-keto lactones.82 In the intermediate 106 the C-2 methyl groups are pointing outside the 14-membered ring. A conformational analysis of the hydroxy lactone (3S*,4S*,13S*)-105 and the other C-3 epimer, (3R*,4S*,13S>2,2,4-trimethyl-3-hydroxy-13-tetradecanolide was also conducted. The global minimum energy conformation 107 was found to be a non-diamond lattice conformation where the C-2 carbon occupies a corner position with both of the geminal methyl groups pointing outside the ring . A total of 38 conformations were found within the 3 kcal/mol of global minimum energy conformation and all of them had the oxygens of hydroxy group and the carbonyl of the lactone group syn with an intramolecular hydrogen bond. On the other hand, the conformational analysis of the epimeric (3f?*4S*13S*)-2,2,4-trimethyl-3-hydroxy-13-tetradecanolide gave a total of 29 conformations within the 3 kcal/mol of the global minimum energy conformation 82 108. This global minimum energy conformation 108 had the geminal dimethyl groups pointing outside the ring. However, the two oxygens of the hydroxyl group and the carbonyl oxygens of the lactone were not aligned in the same direction and hence cannot form an intramolecular hydrogen bond. Thus the intramolecular hydrogen bond observed in the experimental data and found in molecular mechanics calculations is consistent with the proposed 3S*,4S*,13S* stereochemistry of the product in equation 14. An intramolecular hydrogen bond in (2R*3/=?*,13S*)-2-methyl-3-hydroxy-13-tetradecanolide (109) was also observed. However, the carbonyl peak here was observed at 1715 cm"1.82 Note that in carrying out this sequence of reactions starting from 74 which has single chiral center 105, which has three chiral centers was constructed, with good stereoselectivity. 108 84 2.4 The Conformations and Reactivity of B-Oxvaenated 16-Membered Lactones 2.4.1 Conformational Analysis of 3-Oxo-15-hexadecanolide (84) The conformational analysis of the B-keto lactone 84 is quite complex; molecular mechanics calculations using the MM3* force field parameters suggest that there are 95 conformations within 3 kcal/mol of the global minimum energy conformation. This is a much larger number than found in the case of 3-oxo-l 3-tetradecanolide (74), where only 29 conformations were calculated within 3 kcal/mol of the global minimum energy conformation.63 The five lowest energy conformations of 84 are shown in Table 7 (page 86) along with their relative energies and polar maps. These five lowest energy conformations are within 0.9 kcal/mol of the global minimum energy conformation. The global minimum energy conformation was found to be a [4444] conformation. 84 85 Considering the [4444] conformation from the top view as explained earlier in section 1.9 (Figure 10, page 40), ether oxygen of the lactone moiety is in the middle of a side. This leads to removal of the greatest number of transannular interactions between hydrogens pointing inside the ring. The local conformation of the two carbonyl groups is anti periplanar in the three lowest conformations, and these conformations are within 0.75 kcal/mol of each other. The next higher energy conformation is 0.85 kcal/mol above the [4444] conformation and has the two carbonyl groups aligned in same direction. The C-O-C-H dihedral angle in these lowest five conformations is between 0-60°. 87 During earlier studies on 3-oxo-13-tetradecanolide (74) in our laboratory, it was shown, that an eleven-line pattern of the C-13 methine proton does not prove that the molecule exists in a single conformation in solution, but rather it could be present as a number of conformations in solution.63 3-Oxo-l 5-hexadecanolide (84) showed an eleven-line pattern with vicinal coupling constants of J 1 5 . 1 4 A = 8.4, J 1 5 - 1 4 B = 3.5, and J 1 5 . 1 6 = 6.4 Hz respectively for C-15 methine proton. These coupling constant were determined via proton-proton decoupling experiments. Earlier, Egan et al. had shown that in macrocyclic compounds, if vicinal proton coupling constants within the ring are either 10-12 or 0-2 Hz, then the molecule is very likely conformationally rigid.88"89 However, if these values fall in the range of 6-8 Hz, then the molecule probably consists of several conformations in solution, and the coupling constants are the average of the two or more conformations in solution. The above data suggests that 3-oxo-15-hexadecanolide (84) exists in a number of conformations in solution. In Table 8 the experimental and calculated vicinal coupling constants of the C-15 methine proton and the C-4 methylene protons, are shown. Proton decoupling experiments were used to obtain accurate coupling constants for these multiplets at 5.02 (C-15) and 2.57 (C-4) ppm, respectively. These experimental data are consistent with 84 being a mixture of conformations at room temperature. 88 Table 8: Experimental and Calculated3 Vicinal Coupling Constants of 3-Oxo-15-hexadecanolide (84). Vicinal Coupling constants Expt (Hz) Conformer 1 (Hz) Conformer 2 (Hz) Conformer 3 (Hz) Conformer 4 (Hz) Conformer 5 (Hz) J4A-5 7.0 8.7 8.2 3.3 7.6 7.7 J4B-5 7.0 7.7 8.2 7.8 8.7 8.7 Jl5-14A 8.4 11.6 11.6 11.6 11.5 11.5 J-I5-14B 3.5 2.1 2.2 2.2 2.0 2.0 Jl5-16 6.4 5.8 5.8 5.8 5.8 5.8 a Calculated using MACROMODEL Interestingly, there was little spectroscopic evidence for any enol form of the p-keto lactone in 84. For example no peak was observed in 10-12 ppm region of the 1H NMR spectrum and the AB quartet of C-2 protons displayed a very sharp doublet of doublets with no extra peaks in 4-5 ppm. The infrared spectrum of 84 in solution showed very weak bands in 1650-1600 cm"1 region which could be due to the enol form of the p-keto lactone. Two sharp peaks due to two carbonyl groups were found at 1735 and 1711 cm"1. Unfortunately, compound 84 was an oil which could not be crystallized for an X-ray study. 2.4.2 Reduction of 3-Oxo-15-hexadecanolide (84) The first reaction of 3-oxo-15-hexadecanolide (84) studied was hydride reduction, which proceeded with moderate stereoselectivity (equation 15). 89 Reduction of 84 using sodium borohydride in ethanol gave 2.5:1 ratio of the diastereomers in 88% yield. 84 110 111 The two diastereomers were inseparable on TLC, GC, or HPLC. However, they had different chemical shifts in the 1H NMR. The multiplet corresponding to C-3 proton had chemical shifts at 3.88 and 4.05 ppm, respectively in the two diastereomers and ratio of the two diastereomers was determined to be 2.5:1 by integrating these signals. The infrared spectrum had peaks at 3613 and 3527 cm'1 which confirmed that the p-keto lactone was reduced to the p-hydroxy lactones. It was difficult to directly determine the relative stereochemistry in the two diastereomers. However, the two alcohols were derivatized with 4-bromobenzenesulfonyl chloride to give the corresponding 4-bromobenzenesulfonates (equation 16). Fortunately, these two diastereomers separated on silica and were purified by radial chromatography. Furthermore, the minor isomer crystallized from hexane. These colourless crystals were suitable for an X-ray crystallographic study (Figure 18). This derivative was found to be 3S*,15R* and thus 111 is the minor reduction product. The major 90 isomer in the reduction of 84 must accordingly have the 3S*,15S* configuration as in 110. This was a very important result for us it turned out to be the starting point for the determination of the relative stereochemistry of the chiral centers in a number of the 16-membered lactones synthesized during this project. O 113 Figure 18: Crystal structure of p-bromobenzenesulfonate derivative (3S* 15R*)-3-hydroxy-15-hexadecanolide (112). 92 In addition to proving the relative stereochemistry of the minor reduction product from 84, the lactone geometry in the solid state was s-trans and the lactone C-O-C-H torsional angle was found to be 38° in the major conformer and 24.5° in the minor conformer of 112. This X-ray analysis directly supported our earlier proposal on the conformations of lactones of secondary alcohols (Introduction, section 1.10). Furthermore, this was the first opportunity to study the conformation of a simple 16-membered lactone in the solid state in our laboratory. Compound 112 was found to have the [4444'] conformation in the solid, with disorder along one side. Three carbons, C-12, C-13 and C-14, occupy different positions in space in the two conformers observed in the solid state structure. This results in four torsional angles that are different in the two conformers and the two conformations can be easily distinguished from their polar maps as shown in Figure 19. Close examination of the polar maps showed that the major conformer had a [4444'] geometry. Whereas, the minor conformer could not be designated using the Dale nomenclature. 93 Figure 19: Polar maps of the two conformations observed in the X-ray structure of (3S* 15R>sulfonate-112 Molecular mechanics calculations of the (3S*,15R*)-sulfonate-112 showed 20 conformations within 3 kcal/mol of the global minimum energy conformation. The global minimum energy conformation 114 was found to be a [4444] conformation with the phenyl group folded on top of the 16-membered ring. 0 0 114 94 None of these conformations were identical to either of the two conformations present in the X-ray structure. Most of the conformations had the phenyl ring folded on top of the 16-membered ring. Whereas, in the X-ray structure, the two conformations have the phenyl ring rotated away from the 16-membered ring. The solid state conformation as obtained from the X-ray analysis is different from the global minimum energy conformation obtained from the conformational search. It is not unusual to observe the solid state conformation to be different from the global minimum energy conformation; crystal packing energies could play a significant role in the conformation of 112 in solid state The energies of the two conformations that were observed in the X-ray were also carried out using the MACROMODEL program and it was found that the two X-ray conformations were 13.9 and 15.5 kcal/mol higher than the global minimum energy conformation, respectively. However, the two conformations had the same calculated relative order as observed in the X-ray analysis. Once the relative stereochemistry of the reduced products 110 and 111 was established, the reduction of 84 was investigated. It was reasonable to assume from earlier results that varying the counter cation in the hydride reagent might affect the diastereomeric ratio of the products. When L-Selectride [Li(s-Bu)3BH] in THF was used as reducing agent only 110 was observed. However, only 50% of the product was obtained and 50% of the starting material was recovered 95 (equation 17). This ratio of product to starting material, as well as the stereoselectivity, was unaffected by changing temperature, or the number of equivalents of L-Selectride used. These results led us to believe that addition of L-Selectride resulted in two competing reactions: reduction as well as deprotonation of the C-2 methylene proton to give the enolate that did not undergo reduction. Other reducing agents, K-Selectride, LS-Selectride and lithium (diisobutyl)-(/7-butyl)aluminium hydride 9 0 were also tried to improve the yields of reduction. However, they all gave results similar to those obtained with L-Selectride. 84 110 Earlier it has been found that a combination of reducing reagents was more successful in reducing functional groups when a single reducing agent was often ineffective.9 1 Hence, it was decided to add one equivalent of sodium borohydride subsequent to the initial addition of L-Selectride to B-keto lactone 84 in THF. Ethanol was added to improve the solubility of sodium borohydride in the reaction mixture. A ratio of THF to ethanol of 5:1 was arbitrarily chosen for 96 the reduction of 84. This combination of hydrides led to isolation of 110 in 92% yield and none of the other diastereomer 111 could be detected. As already mentioned, the three lowest energy conformations of 84 obtained from molecular mechanics calculations have the two carbonyl groups anti periplanar (Table 7, page 86). Hydride attack from more accessible re face of the keto group in these conformations, such as 115, should result in the formation of (3R*,15S*)-3-hydroxy-15-hexadecanolide (111), which was indeed not the major product observed. 116 110 97 If the reducing agent counter cation chelates the two carbonyl oxygen atoms to expose the re face of the keto group, as in 116, to attack by the hydride reagent will result in formation of (3S* 15S*)-3-hydroxy-15-hexadecanolide (110). To test the hypothesis of chelation, a hydride reagent with a non-chelating counter cation, n-tetrabutylammonium borohydride, was used in THF as solvent. No stereoselectivity was observed and both diastereomers 110 and 111 were obtained in equal amounts. These results were consistent with the proposed chelation hypothesis since the lithium and potassium counter cations are better chelating cations than sodium cation92 hence, produced higher selectivity, whereas the tetrabutylammonium cation does not chelate. Earlier studies had demonstrated a similar failure of a simple conformational analysis to account for the reduction products of substituted and unsubstituted 3-oxo-13-tetradecanolide, and the need to invoke a chelated intermediate to rationalize the experimental outcome.67 Solvent effects on the. reduction were also probed. It was found that stereoselectivity increased from 2.5:1 to 3.5:1 when sodium borohydride was used in 5:1 mixture of THF and ethanol versus ethanol alone as solvent. The selectivity remained the same when a trace amount of ethanol was added to THF, although the reaction time increased considerably. The increased 98 r selectivity in the case of THF versus ethanol seems to confirm that ethanol, being a more polar solvent, will solvate a metal cation better than THF hence reducing the effective chelation with p-keto lactone in ethanol solution, which in turn lowers the diastereoselectivity. These results are summarized in Table 9. 99 Table 9: Yield and selectivity of the reduction of 3-oxo-15-hexadecanolide (84). Reducing reagent Solvent % Yield (110 & 111J Ratio 110:111:84 Time (hours) NaBH4 Ethanol 88 71:29:0 0.5 L-Selectride THF 45 1:0:1 3.0 K-Selectride THF 38 1:0:1 3.0 LS-Selectride THF 43 1:0:1 3.0 Li(n-Bu)-(/Pr)2AIH THF 39 1:0:1 3.0 L-Selectride and NaBH4 THF-Ethanol (5:1) 92 1:0:0 4.0 NaBH4 THF-Ethanol (5:1) 62 78:22:0 2.0 NaBH4 THF with a trace of Ethanol 73 78:22:0 12 n-Bu4NBH4 THF 75 1:1:0 48 2.4.3 Alkylation of (3S*15S*) 3-Hvdroxv-15-hexadecanolide (110) Frater has reported the highly stereoselective alkylations at C-2 in 0-hydroxy esters 117 via their corresponding dianions.93-95 The major product 118 has the hydroxyl and methyl groups anti to each other and the reaction is thought to proceed through a six-membered intermediate 119 where the nucleophile approaches from the si-si face (equation 18).93"95 100 R OH O OR' 2 equiv LDA OR' R OH O OR' (18) si-si 117 119 118 Our research group extended this reaction to macrocyclic lactones. Previously, (3S*,13S*)-3-hydroxy-13-tetradecanolide (120) on treatment with two equivalents of LDA and subsequent alkylation with methyl iodide was found to give 121 with high diastereoselectivity (equation 19).63 Alkylation of the dianion of hydroxy lactone of (3S*,15S*)-3-hydroxy-15-hexadecanolide (110) was examined. The dianion was generated with slightly more than two equivalents of LDA at -78 °C over a period of 12 hours. HMPA and methyl iodide were added in quick succession and the reaction mixture was warmed after 1 hour and quenched (equation 20). A single spot was observed for a new product on the TLC plate. In addition, the 1H NMR HO, O (19) 120 1.21 101 spectrum of the product suggested that only a single diastereomer was produced. In the 1H NMR spectrum the two-proton doublet of doublets of doublets at 2.53 ppm corresponding to the C-2 protons of 110 disappeared and a doublet of quartets was observed at 2.56 ppm with relative intensity of one proton as well as another doublet at 1.27 ppm corresponding to a methyl group at C-2. 110 122 The relative stereochemistry of C-3 and C-15 in 122 were already known and the third chiral center could be deduced on the rationale provided by Frater. However, it was decided to unambiguously determine the relative stereochemistry at C-2. During earlier studies on the alkylation of 15-hexadecanolide lactones in our laboratory, the two diastereomers of 2-methyl-15-hexadecanolide were synthesized and characterized by 1H NMR. It was found that the chemical shifts of two methyl groups in (2S*,15S*)-2-methyl-15-hexadecanolide (123) appeared 102 as doublets at 1.19 and 1.10, with a difference of 0.09 ppm. Whereas in (2R*,15S*)-2-methyl-15-hexadecanolide (124) the chemical shifts of two methyl doublets were at 1.21 and 1.15, with the difference between the chemical shifts being 0.06.96 To establish the stereochemistry of the alkylation product from 110 (equation 20), all that needed to be done was to chemically transform this product 122 into 123 or 124. 123 124 It was decided to use a modified Barton's deoxygenation reaction, to convert the secondary hydroxy group to its thiocarbonate derivative, which could be further reduced to a methylene group.97 Compound 122 was converted into the 3-(2',4',6'-trichlorobenzenethiocarbonate)-2-methyl-15-hexadecanolide (125), which was reduced via a radical reduction to 2,15-dimethylhexadecanolide using tris(trimethylsilyl)silane as a reducing agent (Scheme 8). The 1H NMR spectrum of the compound from 122 was identical to that of (2S*,15S*)-2-methyl-15-hexadecanolide (123) and • none of the other diastereomer of (2R*15S*)-2-methyl-15-hexadecanolide (124) could be detected 103 by the 1H NMR or gas chromatography. Hence, the stereochemistry of 122 was assigned unambiguously as (2S*,3S*,15S*)-2-methyl-3-hydroxy-15-hexadecanolide where the 3-hydroxy and 2-methyl groups had the stereochemistry suggested by the Frater mechanism for alkylation of open-chain p-hydroxy esters.93 The above chemical transformation and GC analysis further confirmed that only one diastereomer was formed during alkylation of the dianion of 110 123 Scheme 8: (a) ArCSCI, py, 2 h; (b) (Me3Si)3SiH, AIBN, A, toluene, 2 h. 104 Although a very high diastereoselectivity was observed in the alkylation of 110, the reaction never went to completion and up to 50% starting material was often recovered, irrespective of the reaction conditions. Seebach has shown that subsequent deprotonation of diisopropylamine generated from LDA during the enolate formation using n-BuLi enhances the yields of the alkylated products in many cases.98 However, addition of an additional two equivalents of n-BuLi after the initial addition of LDA did not produce any change in the yield of 122. Frater did not encounter such problems in his work on the alkylation of acyclic p-hydroxy esters.93"95 However, in earlier work in our laboratory on the alkylation of 3-hydroxy-13-tetradecanolide, starting material was always recovered.63 To explore the reasons why this reaction did not go to completion, the dianion of P-hydroxy lactone 110 was quenched with 99.9% isotopically pure deuterium oxide. The 1H NMR showed that 100% of the product 126 had deuterium at C-2 carbon. Two diastereomers were produced in 2:1 ratio. The peak corresponding to the C-2 proton was two distinct multiplets in a ratio of 2:1. A deuterium decoupled proton NMR spectrum of the product 126 showed two separate doublets for C-2 proton. Hence, it was concluded that the deuterium was fully incorporated into the molecule at the C-2 position (Equation 21) and that dianion generation was quantitative. The vicinal coupling constant, J 2 . 3 was found to be 5.3 Hz in the minor diastereomer and 4.1 Hz in the major diastereomer, respectively. The J2-3 coupling constant was found to be 2.6 Hz in 105 122. This small value for the vicinal coupling constant suggests that the relative stereochemistry in the major diastereomer of 126 is the same as found in 122. Having demonstrated that the anion is formed, we are still unable to offer an explanation as to why the dianion alkylation of 110 does not go to completion. 110 126 106 2.4.4 C-2 Methvlation of 3-Oxo-15-hexadecanolide (84) Alkylation of the p-keto lactone 84 with potasium terf-butoxide followed by treatment with methyl iodide in te/f-butanol gave two components on the TLC plate. The spot with lower Rf was identified as the desired 2-methyl-3-oxo-hexadecanolide (127). Compound 127 was obtained as a 2:1 epimeric ratio in a yield of 65% (Equation 22). The two diastereomers were inseparable by normal physical techniques. The ratio of the two diastereomers of 127 was determined by the 1H NMR. The 1H NMR of the mixture of diastereomers of 127 showed the disappearance of the AB quartet at 3.5-3.4 ppm corresponding to C-2 protons of 84 and an appearance of two quartets at 3.50-3.41 ppm with a relative intensity of one proton. These quartets had chemical shifts of 3.47 and 3.43 ppm and a 1:2 ratio. The spot with higher Rf was identified as the C-2 dialkylated compound 128 and was obtained as side product in 8% yield. 84 127 128 107 Another reported method to monoalkylate at the a-position of B-dicarbonyl compounds involves the use of methyl iodide and tetraethylammonium fluoride in chloroform." Unfortunately, the yields of 127 obtained with this method were very poor. A conformational analysis of the two C-2 epimers of 127 showed that C-2 was a corner or a pseudo-corner position in all conformations within 3 kcal/mol of the lowest energy conformations in the two epimers, respectively. This would suggest that under equilibrating conditions the ratio of the diastereomers would be proportional to the difference of the global minimum energy conformation. The lowest energy conformation of (2R*,15S*)-127 was 21.99 kcal/mol and that of (2S*,15S*)-127 was 22.04 kcal/mol. This would lead to a predicted equilibrium ratio of 52:48 at 25 °C based on the global minimum energies of the two diastereomers compared to the observed equilibrium value of 2:1 (Although exchange studies were not carried out on compound 127 to prove that this was the equilibrium ratio, the precedent with 90 makes this assumption reasonable, see reference 67). Once again it shows that better parameters are needed for the molecular mechanics calculations. 108 2.4.5 Stereoselective Reduction of 2-Methvl-3-oxo-15-hexadecanolide (127) The mixture of a-methylated p-keto lactones 127 was reduced with sodium borohydride and yielded only one of the four possible diastereomers of 2-methyl-3-hydroxy-15-hexadecanolide (122) in 85% yield (equation 23). All the spectral data and chromatographic properties of the product obtained from 127 were identical to that for compound 122 obtained in the alkylation of p-hydroxy lactone 110 (section 2.4.3). The C-15 methyl and C-3 hydroxy groups had the same relative stereochemical arrangement, as in compound 110 from the reduction of simple p-keto lactone 84 (section 2.4.2). 127 122 The ratio of C-2 epimers in the starting ketone was 2:1, the yield of the alcohol 122 was greater than 80%. Thus, there must be an equilibration of the C-2 isomers during the reduction, with the minor (2S*15S*)-isomer undergoing reduction preferentially, while the major diastereomer with the (2R*15S*) configuration is epimerized under the reaction conditions and then reduced. A 109 conformational search revealed that the global minimum energy conformation 127 had both carbonyls pointing in the same direction, and the C-2 methyl group occupied a corner position as shown in 129. In this conformation, the two carbonyls are aligned for a facile coordination to a metal cation. Reduction of 129 from the more open, outside face would give the observed 3S*,15S* relative stereochemistry. Also, a conformational analysis of the (3-hydroxy lactone 122, gave the global minimum energy conformation 130 with the [3544] conformation with the lactone and the hydroxy group on the "side" with five atoms. The carbonyl group of the lactone and the C-3 hydroxy group were close to coplanar with the possibility of intramolecular hydrogen bonding. The hydroxyl proton in the 1H NMR of 122 was a broad singlet at 2.78 ppm. The infrared spectrum showed OH stretches at 3691, 3607 and 3554 cm"1 which suggests that both inter- as well as intramolecular hydrogen bonding may be present. The peak due to the carbonyl of lactone group was shifted to 1705 cm"1 again suggesting hydrogen bonding. M 129 110 130 Earlier it was found that reduction of 2-methyl-3-oxo-13-tetradecanolide (90), which was a 2:1 mixture of C-2 epimers, gave a mixture of all four diastereomers in a ratio of 13:3:2:1.82 In this case epimerization at C-2 must also occur faster than reduction but the reduction is not as stereoselective. 111 2.4.6 The C-2 Geminal Alkylation of 3-Oxo-15-hexadecanolide (84) During an earlier study of the alkylation 3-oxo-13-tetradecanolide (74), the C-2 geminal dialkylated product crystallized and was the first simple 14-membered ring that crystallized without derivatization.63 Here, in hopes of similar results for the 16-membered ring, 2,2-dimethyl-15-hexadecanolide (128) was synthesized. The starting 3-oxo-15-hexadecanolide (84) was deprotonated with an excess of potassium ferf-butoxide and reacted with an excess of methyl iodide to produce the geminal substituted p-keto lactone 128 in 77% yield (equation 24). 84 128 Product 128 was identified from its 1H NMR. The spectrum showed the disappearance of the C-2 AB quartet of the starting material 84 and the appearance of two new three-proton singlets at 1.33 and 1.32 ppm corresponding to the C-2 methyl groups of 128. The infrared spectrum showed peaks at 1732 and 1707 cm'1 for the lactone and the ketone group, respectively. Unfortunately, the compound did not crystallize. However, the stereochemical effects of the geminal dimethyl group on the reduction of this hexadecanolide 112 were investigated. It was anticipated that the ground state conformation of 128 would be one in which the geminal dimethyl groups would occupy a corner position. A conformational analysis of 128 gave a total of 112 conformations within 3 kcal/mol of the global minimum energy conformation 131 which has [4444] conformation with the C-2 at a corner position and the two carbonyl groups of the ketone and the lactone anti-periplanar to each other. Indeed, as expected all the conformations found within 3 kcal/mol of the global minimum energy conformation 131 had the geminal substituted C-2 carbon at a corner position. The carbonyl groups of the ketone and lactone were also found to be anti-periplanar in all 112 conformations. O O 131 113 2.4.7 The Reduction of 2.2-Dimethvl-3-oxo-15-hexadecanolide (128) Sodium borohydride reduction of the p-keto lactone 128 gave two components on TLC. The alcohols 132 and 133 were subsequently obtained in 94% yield and a ratio of 2:1 (equation 25). 128 132 133 These alcohols were identified from their spectral properties. Alcohol 132 had a multiplet at 3.47 ppm corresponding to the C-3 proton. The infrared spectrum also showed peaks at 3691, 3613, and 3510 cm"1 for the hydroxyl group. There were two peaks at 1716 and 1691 cm'1 in the infrared spectrum of 132 and it seems that both inter- and intramolecular hydrogen bonding between the hydroxyl group and the carbonyl oxygen of the lactone resulted in two different carbonyl stretches and a number of hydroxyl peaks. Similar results were observed in the 2,2,4-trimethyl-3-hydroxy-13-tetradecanolide (105) synthesized during the current project (section 2.3.4). Although, in the earlier case only intramolecular hydrogen bonding was observed. Alcohol 133 had multiplet at 3.59 ppm corresponding to the C-3 proton. The infrared spectrum also showed 114 peaks at 3691, 3623 and 3500 cm'1 for the hydroxyl group. The peak for the carbonyl of the lactone group was a broad peak at 1710 cm"1 and again it was believed that the infrared spectrum of 133 shows hydrogen bonding between the hydroxyl group and the carbonyl oxygen of the lactone resulting in lower value for the carbonyl stretch at 1710 cm"1 compared to that usually observed (ca. 1735 cm'1). Reduction of the p-keto lactone 128 with L-Selectride produced essentially a single diastereomer 132 in 89% yield. The spectral data for this product was identical to that obtained from the major isomer in the reduction with NaBH4. However, the L-Selectride reaction was very sluggish. This problem was circumvented by addition of one equivalent of NaBH4 and a trace of ethanol to the solution of 128 in THF 30 minutes after addition of L-Selectride. The stereochemistry of the alcohols 132 and 133 was proven from the following chemical correlation. Compound 122 was subjected to a second Frater alkylation (equation 26). Again the alkylation did not go to completion. However the C-2 dialkylated product was obtained was in 48% yield with some starting material recovered. This product must have the stereochemistry shown in 132. Compound 132 from equation 26 was identical to the major NaBH4 reduction product from 128 (equation 25) 115 122 132 The reduction of macrolide 128 was considered to be influenced by two factors: the geminal methyl groups and the chelation effect of the counter metal ion of the reducing agent. The geminal methyl groups are expected to occupy a corner position, which was reinforced by corresponding molecular mechanics calculations. Placing the geminal methyl groups on a corner position essentially locked the remainder of the ring in a rigid arrangement, and every conformation within 3 kcal/mol of the global minimum energy conformation exposed the re face of the ketone for attack as shown in 131. However, chelation plays an important role in these reductions and again strongly influences the stereochemical outcome, which in this case results in the attack of the hydride from the si face of the ketone as shown in 134. 116 134 132 Conformational analyses of the p-hydroxy lactones 132 and 133 were conducted using MM3* force field parameters. The global minimum energy conformations of the lactones 132 and 133 had the oxygens of the hydroxyl group and the carbonyl of the lactone group syn to each other with the possibility of forming an intramolecular hydrogen bond as shown below in 135 and 136, respectively. However, a large number of conformations were found within 3 kcal/mol of the global minimum energy conformation. A total of 66 conformations for 132 and 60 conformations for 133 were found. 118 2.4.8 The C-4 Alkylation of 3-Oxo-15-hexadecanolide (84) To this point, mono- and dialkylation had been investigated only at the C-2 position of the p-keto lactone 84. However, the corresponding alkylation at C-4 position was considered to offer new challenges in probing the conformational behaviour of the 16-membered rings. The dianion of p-keto lactone 84 was formed by the addition of a slightly more than two equivalents of LDA to 84 at -78 °C. The resulting dianion was alkylated with one equivalent of methyl iodide at -78 °C to produce two new products. However, in a number of attempts at this reaction the yields were not very good and some starting material was always recovered. At that time it was decided to generate the dianion of p-keto lactone 84 using a procedure, first introduced by Seebach.98 An hour after of adding the two equivalents of LDA to the p-keto lactone 84, another two equivalents of n-BuLi were added to deprotonate the diisopropylamine regenerated from the LDA during the initial enolate formation. Fortunately, this modification resulted in a dramatic improvement in yield of product which now was obtained in 91% yield (equation 28). The TLC analysis of the reaction mixture showed two components in a 1:1 ratio very close to each other. They were separated on silica chromatography. However, unlike the 14-membered lactone, no stereoselectivity was observed in this dianion alkylation. These new compounds were identified as the two y-alkylated p-keto 119 lactones. The chemical shifts of the C-4 protons in 84 were found to be 2.57 and 2.50. In the products from the dianion alkylation, one-proton multiplets were observed at 2.61 and 2.70 ppm respectively for the separate products, corresponding to a single proton at C-4. Also, appearance of a new doublet at 1.07 and 1.09 ppm in 137 and 138, respectively, corresponding to a methyl group, proved that alkylation of the p-keto lactone 84 had occurred at the y-position. Again, as with most of the 14- and 16-membered p-keto lactones, evidence for very little enolization was found. No peaks were observed in the region of 10-12 ppm in the 1H NMR spectrum. A very weak peak was observed around 1640 cm"1 in both of the diastereomers from the infrared spectrum, which could be due to the enol form. 84 137 138 Initially, it was decided to convert 137 and 138 to 2,13-tetradecanediol. Earlier, a procedure to separate the diastereomers of such diols in the case of the 14-membered p-keto lactone had been devised (section 2.3.2). A mixture of dl-and /77eso-2,13-tetradecanediol (140 and 141) was synthesized by a double Grignard reaction of 1,8-dibromooctane (139) with racemic propylene oxide in 120 80% yield. Similarly, pure (2S,13S)-2,13-tetradecanediol (140) was synthesized from 1,8-dibromooctane (139) and (S)-propylene oxide. These diols were converted into their dibenzoate esters 142 and 143 (Scheme 9). OH Br a, b OH 139 (±)-140 OH 141 OCOPh OCOPh OCOPh (±)-142 143 OCOPh OH .Br a, d 139 OCOPh (-)-142 OCOPh OH (-)-140 Scheme 9: (a) Mg, l2, Et20, 30 min; (b) propylene oxide, 18 h; (c) PhCOCI, py, 30 min; (d) (S)-propylene oxide, 18 h. The dibenzoate esters 142 and 143 were resolved on a Chiralpak OP(+) HPLC column to give three peaks in a ratio of 1:2:1, with a retention time of 9.3, 10.1, and 12.3 minutes, respectively (Figure 20). This is exactly the pattern expected for a 1:1 mixture of dl- and meso-dibenzoate esters with the meso-dibenzoate 121 ester corresponding to the 10.1-minute peak. The pure (2S,13S)-dibenzoate had a retention time of 9.3 minutes. Therefore the peak at 12.3 minutes is due to the (2f?,13R)-dibenzoate. 1.2 E c in 1 CM "co 8 0.8 c CO . Q o 0.6 co . Q CO § 0.4 0.2 0 2 4 6 8 10 12 14 16 Time (min) Figure 20: HPLC trace of a mixture of dibenzoate esters 142 and 143 from (o7)-and meso-2,13-tetradecanediol on Chiralpak OP (+). Efforts then turned to the conversion of the slower moving of the two diastereomers of 4-methyl-3-oxo-15-hexadecanolide (138) to 2,13-tetradecanediol with conservation of stereochemistry. Following the earlier literature that Baeyer-Villiger oxidation of B-keto esters gave 2-hydroxy-3-keto esters, it was decided not to oxidize the lactone directly.86 Instead, the slower moving diastereomer of 138 was first converted to a benzyl ester 144 via transesterification using benzyl alcohol and DMAP as catalyst.100 The benzyl 122 group was hydrogenolyzed with 5% Pd-C as catalyst, and the resultant p-keto acid also decarboxylated in the same step to give the hydroxy ketone 145. The hydroxy ketone 145 was then subjected to Baeyer-Villiger oxidation and subsequent base hydrolysis to give the desired 2,13-tetradecanediol. The diol was esterified with benzoyl chloride in pyridine to its dibenzoate ester (Scheme 10). 140 1 « Scheme 10: (a) PhCH2OH, DMAP, A, toluene, 4 days; (b) H2, Pd-C (5%), EtOH, 2h; (c) (NH2)2CO.H202, Na 2HP0 4, (CF3CO)20, CH2CI2, 12 h; (d) NaOH (aq), A, 2 h; (e) PhCOCI, py, 1 h. Unfortunately, chromatography of the dibenzoate 142 from 138 (Scheme 10) using chiral-HPLC showed that it was a mixture of the (oV) and 123 meso-dibenzoates (Figure 21). It was believed that epimerization at C-4 occurred during the hydrogenolysis reaction (step b in Scheme 10). Commercially available Pd-C on charcoal often has a trace of acid present which could have epimerized the methyl group next to the ketone. Figure E c CN "co CD o c CD .Q o CO jQ CO > 8 10 Time (min) 21: HPLC trace of dibenzoate 4-methyl-3-oxo-15-hexadecanolide (138). 12 14 esters 142 from Since no enol tautomer could be detected in the 1H NMR of the B-keto lactone 138, it was decided to disregard the earlier literature on Baeyer-Villiger oxidation of B-keto esters, and to directly carry out the Baeyer-Villiger oxidation on 4-methyl-3-oxo-15-hexadecanolide (138). 2,13-Tetradecanediol was obtained in overall 58 % yield. The intermediary dilactone could not be isolated or characterized. It appears that the dilactone was unstable and that it hydrolyzed 124 under the reaction conditions. The diol was converted into its dibenzoate (Scheme 11). This time only one peak due to the meso-(2R*, 13S*)-2,13-dibenzoyloxytetradecane (143) was observed on HPLC (Figure 22). OH OCOPh 141 143 Scheme 11: (a) (NH2)2CO.H202, Na 2HP0 4, (CF3CO)20, CH2CI2, 12 h; (b) PhCOCI, py, 1 h. Only one peak was observed in the region of interest. The single peak had a retention time of 10.1 minute and there were no peaks at 9.4 and 12.3 minutes. This confirmed that the relative stereochemistry of chiral centers in the (3-keto lactone 138 were (4R*15S*)-4-methyl-3-oxo-15-hexadecanolide. 125 E c m CM CO CD o c CO .Q o CO _Q CO > 3 1.6 h 1.4 1.2 h 1 0.8 -0.6 -0.4 0.2 0 i I i i I 6 8 10 Time (min) j I i 12 14 Figure 22: HPLC trace of meso-dibenzoate ester 143 derived from 4-methyl-3-oxo-15-hexadecanolide (138). A molecular mechanics calculation was carried out on the dienolate from the p-keto lactone 84. Unlike the 14-membered ring where the dienolate adopted a distorted [3434] geometry and had only one face of the enolate exposed, here the dienolate is in a twisted [643'3'] conformation 147. 147 126 An interesting feature of this conformation was that the six-carbons arm that also accommodated the dienolate was in a plane perpendicular to the rest of the ring, resulting in exposure of the ketone enolate from both faces. 127 CONCLUSION In general, the stereoselectivity exhibited in the reactions of large rings was predictable from the conformational analysis of starting materials or intermediates. However, reductions involving B-keto lactones were consistently shown to be controlled by the conformations in which both carbonyl oxygens could chelate a metal ion. The use of chiral HPLC to determine relative stereochemistry of distant chiral centers of macrocyclic rings was demonstrated for the first time. Conformational rigidity and reactivity of 14- and 16-membered rings were investigated and it is found that they are not completely conformationally mobile. In fact, only a few conformations are appreciably populated at room temperatures. Out of the two ring sizes studied, 16-membered rings have significantly higher conformational freedom than 14-membered rings. This observation was also verified by the molecular mechanics calculations. Substituents on the macrolide were generally located outside the ring and geminal substitution preferentially occurred at the corner position. Lactones containing 14- and 16-membered rings are large enough to have the ester functionality in an s-trans geometry and its C-O-C-H torsional angel is restricted 128 to a 0°-40° range. These restrictions were also verified by an X-ray crystallographic analysis. The relative stereochemistry of the chiral centers of most of the compounds synthesized during this project were successfully assigned by chemical transformation to compounds of known stereochemistry. These results also gave us more confidence in the conformational analysis of these large ring compounds and in our ability to predict the stereochemical outcome of these compounds. This understanding of the nature of large rings and the importance of conformational bias might result in a novel method to synthesize macrolide antibiotics by first forming the lactone and subsequently introducing the chiral centers in the ring. 129 EXPERIMENTAL General Unless otherwise stated, all reactions were performed under nitrogen atmosphere in flame-dried glassware. The cold temperature baths used were: dry ice-acetone (-78 °C) and ice-water (0 °C). Anhydrous reagents and solvents were prepared according to procedure given in the literature.104 Alkyllithium reagents (Aldrich Chemical Co.) were standardized against diphenylacetic acid in THF, a faint yellow colour being indicative of the end-point. Analytical gas-liquid chromatography (GC) was performed on a Hewlett-Packard model 5880A, equipped with a split mode capillary injector and a flame-ionization detector, using a 0.22 mm DB210 column of 12 meter in length with helium as a carrier gas. Silica gel 60, 230-400 mesh, supplied by E. Merck Co., was used for preparative flash column chromatography. Silica gel 60 PF254 containing gypsum was used for radial chromatography. Precoated TLC aluminium sheets of silica gel 60 F254 were used in TLC analysis. 130 Melting points were performed on a Fisher-Johns hot stage melting point apparatus and were uncorrected. Infrared (IR) spectra were recorded on a Bomem FT-IR Michaelson-100 connected to an IBM compatible computer. IR spectra were taken in CDCI3 solution using NaCI cells of 0.2 mm thickness. The data was processed on Bomem spectra Calc program. Nuclear magnetic resonance (proton and carbon) spectra were recorded in CDCI3 solution on a Bruker AC-200 (200 MHz), Bruker WH-400 (400 MHz), or a Bruker AMX-500 (500 MHz) instrument. Chemical shifts were recorded in parts per million (ppm) on a 8 scale calibrated to CDCI3 (7.24) as an internal standard. Signal multiplicity, coupling constants, and integration ratios are given in parenthesis. The data was processed using the WINNMR program on an IBM compatible 486 computer. An Spectral Appendix consisting of 1H NMR and IR spectra of all the new compounds synthesized during this project has been provided at the end of the thesis. Low resolution mass spectra (LRMS) were recorded in the mass spectrum laboratory of the Department of Chemistry at UBC on a Kratos-AEI model MS-50 or model MS-9 spectrometer. Only peaks with greater than 20% relative 131 intensity or those that were analytically useful are reported. High resolution mass spectra (HRMS) were obtained on a Kratos-AEI model MS-50 spectrometer. An ionization energy of 70 eV was used in all measurements. DCI low resolution mass spectra (LRMS) were recorded on a Delsi Nermag RIO-IOC mass spectrometer with ammonia as the chemical ionization gas. DCI HRMS were recorded on a Kratos Concept II HQ mass spectrometer with ammonia or methane as the chemical ionization gas. High performance liquid chromatography (HPLC) was performed on a Waters 600E instrument. The columns used were analytical normal phase silica, analytical reverse phase, Chiralcel OD, and Chiralpak OP(+) columns. The peaks were detected by a Waters 410 Differential Refractometer and Waters 486 Tunable Absorbance Detector. All data were processed by Waters Maxima HPLC processing software on an IBM compatible 386 computer. Microanalyses were carried out at the Microanalytical Laboratory at UBC on a Carlo Erba Elemental Analyzer 1106 and 1108. 132 Conformational Analysis of 14- and 16-Membered Macrolides BATCHMIN, a part of the MACROMODEL molecular modeling program developed by Still et al. 1 0 1" 1 0 3 was used to determine the global minimum conformations of the macrolides studied in this work. A starting structure was chosen, random variations to internal coordinates were applied (torsional angles), the new structure was minimized using the MM3* force-field parameters, and the result was compared with minima found during previous conformational search steps. After this resulting structure had been either stored as a new, unique conformer or rejected as a duplicate, the cycle was repeated. There are many types of programs available to carry out such cycles. The one provided with BATCHMIN is the Monte Carlo method. The entire procedure is known as Monte Carlo Multiple Minimum Search (MCMM). In case of simple hydrocarbons, the standard deviation between the calculated heats of formation and the measured values have approximately reached the experimental errors. Standard deviation of the calculated values obtained with MM3 force field parameters and experimental values for heat of formation of a wide range of cycloalkanes studied by Allinger et al. was found to be 0.12 kcal/mol.105 The average probable error in the experimental values of heats of formation has been estimated to be 0.40 kcal/mol for this same group of hydrocarbons.106 133 The parameters in the MM3 program for esters and lactones are only preliminary parameters. Standard deviation of the theoretical values obtained with MM3 force field parameters and experimental values for the heat of formation of 4- to 8-membered lactones was found to be 0.33 kcal/mol.107 The inaccuracy of the calculated values could be attributed to limitations in the parameters for the MM3* calculations for large ring lactones. The calculated energies are reported to two decimal places* In a number of reactions the experimental equilibrium ratio of products was compared with the difference in enthalpy of formation of the minimum energy conformations of the two diastereomers of the products.108 The effect of the change in entropy between the two diastereomers is assumed to be negligible. * [ For a recent example of the use of such calculations see reference 108] 134 10-Undecen-1-ol (63) 63 To a suspension of LAH (1.1 g, 29.3 mmol) in THF (100 mL) at 0 °C a solution of 10-undecenoic acid (62 4.5 g, 24.5 mmol) in THF (20 mL) was added dropwise and the resulting mixture was allowed to warm to room temperature and stirred overnight. After cooling to 0 °C, the reaction was quenched with aqueous 1 M NaOH to give a clear solution containing a white precipitate. The precipitate was removed by suction filtration and washed with ether. The layers of the filtrate were separated, and the organic layer was washed with brine and dried. Concentration of solvent followed by distillation under reduced pressure (132-133 °C , 17 mm of Hg) gave 63 (3.89 g, 22.4 mmol) as a clear, colourless liquid in 94% yield. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory.80 IR (CDCI3): 3622, 2934, 2861, 1639, 1426 cm"1; 1H NMR (200 MHz, CDCI3) ppm: 5.82 (m, J= 17, 10 Hz, 1H), 4.98 (m, J= 17, 2 Hz, 1H), 4.94 (m, J = 10, 2 Hz, 1H), 3.64 (t, J = 6 Hz, 2H), 2.05 (m, 2H), 1.57 (m, 2H), 1.42-1.22 (m, 12H). 135 10-Undecen-1 -bromide (64) 64 Compound 63 (3.8 g, 22.4 mmol) dissolved in ether (100 mL) was cooled to 0 °C and to this solution phosphorus tribromide was added dropwise. The reaction mixture was warmed to room temperature and further stirred for 24 hours. Water (30 mL) was added to quench the reaction. The organic layer was separated and washed with aqueous saturated solution of NaHC0 3 l brine and dried over anhydrous MgS04. Concentration of the solvent followed by column chromatography using ethyl acetate and petroleum ether (1:10) as eluant yielded 64 (4.6 g, 19.9 mmol) as clear, colourless oil in 89% yield. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory.80 IR (CDCI3): 3077, 2930, 2857, 1639, 1443, 1249, 1001 cm"1; 1H NMR (200 MHz, CDCI3) ppm: 5.81 (m, J = 17, 10 Hz, 1H), 4.96 (m, J = 17, 2 Hz, 1H), 4.92 (m, J = 10, 2 Hz, 1H), 3.38 (t, J = 6 Hz, 2H), 2.21-1.22 (m, 16H). 136 A mixture of 64 (11.0 g, 47.2 mmol) and potassium cyanide (4.4 g, 67.6 mmol) in DMF (150 mL) was heated to 45 °C for 4 hours. The reaction mixture was cooled and diluted with ether, washed with aqueous saturated FeS0 4, water, brine, and dried over anhydrous MgS04. Concentration of solvent followed by column chromatography using ethyl acetate and petroleum ether (1:10) as eluant gave 65 (7.76 g, 43.4 mmol) in 92% yield. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory.80 IR (CDCI3): 3076, 2931, 2857, 2244, 1639, 1438, 1309, 998 cm'1; 1H NMR (200 MHz, CDCI3) ppm: 5.82 (m, J = 17, 10 Hz, 1H), 4.98 (m, J = 17, 2 Hz, 1H), 4.93 (m, J = 10, 2 Hz, 1H), 2.34 (t, J = 7.3 Hz, 2H), 2.05 (m, 2H), 1.64 (m, 2H), 1.48-1.20 (m, 12H). 137 11-Dodecenoic acid (66) COOH 66 A suspension of 65 (7.5 g, 41.8 mmol) in aqueous 10% NaOH (100 mL) was refluxed for 4 hours. The reaction mixture was cooled to room temperature and diluted with ether and acidified. The organic layer was separated and the aqueous layer was further extracted with ether (3x100 mL). The combined organic layer was washed with water, brine and dried over anhydrous MgS04. Concentration of solvent, followed by column chromatography using ethyl acetate and petroleum ether (1:5) as eluant gave 66 (7.9 g, 39.8 mmol) in 95% yield. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory.80 IR (CDCI3): 3500, 3190, 3058, 2934, 2861, 1707, 1639, 1426, 1275, 1018, 843 cm*1; 1H NMR (200 MHz, CDCI3) ppm: 11.4 (br s, 1H), 5.9-5.7 (m, 1H), 5.00-4.8 (m, 2H), 2.32 (t, J = 7.3 Hz, 2H), 2.0 (m, 2H), 1.6 (m, 2H), 1.45-1.15 (m, 12H). 138 11-Hvdroxvdodecanoic acid (67) OH COOH 67 To a solution of mercury (II) acetate (4.82 g, 15.1 mmol) in 7 mL of water was added 21 mL of THF. The colour of reaction mixture turned bright yellow and then 66 (2.0 g, 10 mol) was added and the reaction mixture was further stirred for 3 hours, until all the colour disappeared. To this solution 10 mL of aqueous 3 M NaOH was added followed by 10 mL of a solution of 0.5 M NaBH4 in aqueous 3 M NaOH. The reduction of the organomercury compound was instantaneous. The reaction mixture was diluted with 100 mL of ether and saturated with sodium chloride and filtered. The organic layer was washed with aqueous 1 M HCI (100 mL), brine (100 mL) and dried over anhydrous MgS04. Evaporation of solvent followed by column chromatography using 1:4 ethyl acetate-petroleum ether as eluant to give 67 (1.7 g, 8.1 mmol) in 80% yield as a yellow oil. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory.80 IR (CDCI3): 3622, 2933, 2858, 1712, 1420, 1327, 1046 cm'1; 139 1H NMR (200 MHz, CDCI3) ppm: 6.35 (br s, 2H), 3.76 (m, Jn. 1 2 = 6.1 Hz, 1H), 2.34 (t, J 2 . 3 = 6.9 Hz, 2H), 1.75-1.15 (m, 16H), 1.16 (d, Jn. 1 2 = 6.1 Hz, 3H). 11-ferf-Butvldimethvlsiloxvdodecanoic acid (69) OTB DMS COOH 69 A 250-mL single-neck round bottom flask equipped with a nitrogen inlet was charged with 11-hydroxydodecanoic acid (67) (3.41 g, 16.1 mmol), tert-butyldimethylchlorosilane (5.94 g, 39.3 mmol), triethylamine (11.0 mL, 79.5 mmol), a trace of DMAP, and dichloromethane (200 mL). The resulting solution was stirred for 72 hours, then water (100 mL) was added to quench the reaction. The organic layer was separated , and the aqueous layer was further extracted with ether (3x100 mL). The combined organic extracts were washed with water (150 mL), brine (150 mL), then dried over anhydrous magnesium sulfate. Then a 100-mL single-neck round bottom flask was charged with crude 68 and aqueous 10% NaOH solution (50 mL). The resulting solution was stirred at room temperature for 4 hours and then was acidified with aqueous 1 M HCI. The aqueous layer was extracted with ether and (3x100 mL) and the organic extracts 140 were washed with water (150 mL), brine (150 mL), then dried over anhydrous MgS04. Removal of the solvent followed by vacuum distillation at 115 °C, 0.05 mm of Hg gave 69 (4.7 g, 14.2 mmol) in 89% yield for the two steps as a thick, colourless oil. IR (CDCIs): 2933, 2856, 1714, 1432, 1254, 1191, 1134, 1051, 834 cm"1; 1H NMR (200 MHz, CDCI3) ppm: 11.0 (brs, 1H), 3.77 (m, J 1 3 - i 4 = 6.4 Hz, 1H), 2.35 (t, J2-3 = 7.1 Hz, 2H), 1.58 (m, 2H), 1.4-1.15 (m, 13H), 1.12 (d, j=13.14 = 6.4 Hz, 3H), 0.9 (s, 9H), 0.0 (s, 6H). 2.2-Dimethvl-1,3-dioxan-4.6-dione (70V 70 To a suspension of malonic acid (52 g, 0.50 mol) and acetic acid (60 mL, 0.60 mol) was added 1.5 mL of concentrated H 2 S0 4 with constant stirring. The temperature of the mixture was maintained at 20-23 °C by means of an ice-water bath while acetone (40 mL, 0.55 mol) was added slowly. The mixture was then allowed to stand in a refrigerator (4 °C) overnight. The resultant crystals were 141 filtered by suction and allowed to air dry. The resulting white solid was dissolved in 110 mL of acetone, filtered to remove any undissolved material, then diluted with 220 mL of water. Filtration gave a flocculent white solid which was dried in a vacuum dessicator over phosphorus pentoxide to give 70 (37.8 g, 0.26 mol) in 53% yield. The spectral properties of 70 were identical to the Meldrum's acid synthesized earlier in our laboratory.109 IR(CDCI3): 1785, 1755 cm"1; 1H NMR (200 MHz, CDCI3) ppm: 3.58 (s, 2H), 1.77 (s, 6H). 5-(11 '-ferf-Butvldimethvlsiloxv-l '-hvdroxvdodecvlidene^^-dimethvl-l ,3-dioxan-4.6-dione (72) A 50-mL single-necked round bottom flask was charged with 69 (4.7 g, 14.2 mmol) and CH2CI2 (30 mL). 1,1'-Carbonyldiimidazole (3.46 g, 21.1 mmol) was added in portions and the reaction mixture was stirred until gas evolution 72 142 ceased. A 100-mL single-neck round-bottom flask was charged with Meldrum's acid (70 3.07 g, 21.1 mmol) and CH2CI2 (40 mL). Pyridine (3.45 mL, 42.0 mmol) was introduced in a single portion and the reaction mixture was stirred for one hour while the colour of the solution turned pink. The contents of the first flask were then syringed into the second flask and the combined reaction mixture was stirred for an additional 14 hours. The colour of the reaction mixture turned to dark red from pink. A solution of aqueous 1 M HCI (50 mL) was added to quench the reaction. The organic layer was separated and the aqueous layer was extracted with CH2CI2 (3x50 mL). The combined organic layers were washed with water (75 mL), brine (75 mL) and then dried over anhydrous MgS04. Removal of the solvent gave 72 (6.25 g, 14.1 mmol) in 98% crude yield as a orange-red thick oil. IR (CDCI3): 3159, 2930, 1720, 1632, 1418, 1271, 1039, 828 cm"1; 1H NMR (200 MHz, CDCI3) ppm: 3.75 (m, 1H), 2.95 (t, J 6 . 7 = 7.1 Hz, 2H), 1.7 (s, 6H), 1.4-1.15 m, 16H), 1.12 (d, J13.14 '= 6.4 Hz, 3H), 0.9 (s, 9H), 0.0 (s, 6H). 143 5-( 11 '-Hvdroxv-1 '-hvdroxvdodecvlidene)-2.2-dimethvl-1.3-dioxane-4.6-dione (73) 73 A 100-mL single-neck round bottom flask equipped with a nitrogen inlet was charged with 72 (6.25 g, 14.1 mmol), and 10% hydrofluoric acid in acetonitrile (100 mL). The resulting solution was stirred for 4 hours. The colour of reaction mixture turned to yellow from red. Water (30 mL) and ether (50 mL) were added to quench the reaction. The organic layer was separated, washed with water (75 mL) brine (75 mL), then dried over anhydrous MgSCV Removal of the solvent gave 73 (4.7 g, 13.7 mmol) in 97% crude yield as a yellow oil. IR (CDCI3): 3615, 2933, 2858, 1725, 1650, 1574, 1419, 1258, 1152, 1035, 822 cm"1; 1H NMR (200 MHz, CDCI3) ppm: 3.75 (m, 1H), 2.95 (t, = 7.1 Hz, 2H), 1.7 (s, 6H), 1.4-1.15 m, 16H), 1.12 (d, J 1 3 . . 1 4 . = 6.4 Hz, 3H). 144 3-Oxo-l 3-tetradecanolide (74) 0 74 To a 250-mL two-necked, round-bottom flask equipped with a pressure-equalizing dropping funnel and a nitrogen inlet was added THF (100 mL). The solvent was heated to reflux and a solution of 73 (4.45 g, 13.3 mmol) in THF (50 mL) was added dropwise over 6 hours via a syringe pump. The reaction mixture was allowed to cool and ether (100 mL) was added. The organic phase was washed with aqueous saturated solution of NaHC0 3 (2x50 mL), water (2x50 mL), brine (50 mL) and then dried over anhydrous MgS04. Removal of the solvent, followed by purification via radial chromatography using petroleum ether-ethyl acetate (20:1) gave 74 (0.65 g, 2.7 mmol) in 19% yield as a pale yellow oil in three steps from 69. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory63 Rf: 0.31 (petroleum ether-ethyl acetate 20:1); 145 IR (CDCb): 2934, 2859, 1733, 1710, 1451, 1409, 1354, 1273, 1130, 1063, 1007, 907 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 4.99 (m, 1H), 3.46 (d, J 2 A - B = 14 Hz, 1H), 3.35 (d, J 2 A . B = 14 Hz, 1H), 2.70 (dt, J 4 A - B = 18 Hz, J 4 A - 5 = 7.0 Hz, 1H), 2.51 (dt, J 4 A . B =18 Hz, J 4 B - 5 = 7.0 Hz, 1H), 1.79-1.15 (m, 16H), 1.26 (d, Jia-14 = 7 Hz, 3H). Methyl 11-bromoundecanoate (76) To a solution of 11-bromoundecanoic acid (75 20 g, 75.0 mmol) in methanol (200 mL) 1.5 mL of concentrated H 2 S0 4 was added and the resultant reaction mixture was refluxed for an hour. Approximately, half of the solvent was evaporated and the residue was diluted with ether (100 mL) and water (50 mL). The organic phase was washed with aqueous saturated solution of NaHC03, brine and dried over anhydrous MgS04. The solvent was removed followed by column chromatography with ethyl acetate and petroleum ether (1:19) as eluant to give 76 (22.2 g, 74 mmol) in 95% yield. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory.109 COOMe Br 76 146 IR (CDCU): 2930, 2856, 1730, 1669, 1574, 1419, 1258, 1152, 1035, 822 cm'1; 1H NMR (200 MHz, CDCI3) ppm: 3.59 (s, 3H), 3.38 (t, Jn. 1 0 = 7.3 Hz, 2H), 2.3 (t, J2.3=6.9Hz, 2H), 1.85-1.15 (m, 16H). LRMS (El) m/z (relative intensity): 280 (M+, 0.2), 278 (M+, 0.2) 87 (42), 74 (100), 55 (28); HRMS (El): Calculated for C12H2302Br (M+): 280.0859, 278.0881; found: 280.0869,278.0891; Analysis calculated for C 1 2H 2 30 2Br: C, 51.62; H, 8.30; found: C, 51.89; H, 8.45. 13-Oxotetradecanoic acid (78) Methyl acetoacetate (10.1 mL, 94.3 mmol) was slowly added to a suspension of NaH (3.8 g, of a 60% suspension in mineral oil, 94.3 mmol) in THF (150 mL) and DMF (50 mL). After the effervescence had subsided, 76 (21.0 g, 75.2 mmol) in THF (50 mL) was added dropwise over 15 minutes and the resulting solution was refluxed for 44 hours. The mixture was then quenched with aqueous saturated NH4CI, diluted with ether and washed with water and brine. The solvent was removed and the golden oil obtained was refluxed in concentrated O COOMe 78 147 HCI (100 mL) and methanol (35 mL) for 1.5 hours. The mixture was then extracted with CH2CI2. The organic phase was washed successively with aqueous saturated solution of NaHC03, brine, then dried over anhydrous MgS0 4 and filtered. Evaporation of the solvent and column chromatography with ethyl acetate and petroleum ether (1:5) gave 78 (16.3 g, 67.7 mmol) in 90% yield as a white solid. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory.110 Melting pt.: 73 °C; IR (CDCI3): 2933, 2858, 1708, 1417, 1254 cm'1; 1H NMR (200 MHz, CDCI3) ppm: 2.35 (t, J n . 1 0 = 6.9 Hz, 2H), 2.25 (t, J 2 . 3 = 7.1 Hz, 2H), 2.1 (s, 3H), 1.65-1.02 (m, 18H). LRMS (El) m/z (relative intensity): 242 (M+, 0.1), 166 (23), 149 (25), 98 (47), 97 (21), 84 (21), 83 (28), 71 (36), 69 (28), 67 (21), 59 (29), 58 (100), 55 (60); HRMS (El): Calculated for C i 4 H 2 6 0 3 (M+): 242.1882; found: 242.1885; Analysis calculated for Ci 4 H 2 6 0 3 : C, 69.38; H, 10.81; found: C, 69.46; H, 10.84. 148 13-Hvdroxvtetradecanoic acid (79) COOH 79 To a solution of 78 (20.0 g, 18.1 mmol) in 200 mL of ethanol at room temperature was added NaBH4 (6.57 g, 0.17 mol). After stirring at room temperature for 2 hours, the reaction was quenched with aqueous 1 M HCI and diluted with 200 mL of ethyl acetate. The organic layer was separated and the aqueous layer was further extracted with ethyl acetate (3x200 mL). The combined organic phase was washed twice with 200 mL of brine, dried over anhydrous MgS04, and concentrated under reduced pressure to give the crude product as a yellow oil. Hydroxy acid 79 was crystallized from ethyl acetate and petroleum ether (1:1) to give 79 (18.2 g, 74.7 mmol) in 90% yield. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory.110 Melting pt.: 64-66 °C; IR (CDCI3): 3621, 2932, 2857, 1709, 1420, 1260, 1048 cm"1; 149 1H NMR (200 MHz, CDCI3) ppm: 3.74 (m, J 1 3 - i 4 = 6.1 Hz, 1H), 2.31 (t, J 2 . 3 = 7.2 Hz, 2H), 1.75-1.15 (m, 20H), 1.16 (d, Jn. 1 2 = 6.1 Hz, 3H). 13-fe/t-Butvldimethvlsiloxvtetradecanoic acid (81) A 250-mL single-neck round-bottom flask equipped with a nitrogen inlet was charged with 13-hydroxytetradecanoic acid (79) (5.24 g, 20.1 mmol), fe/f-butyldimethylchlorosilane (7.76 g, 51.3 mmol), triethylamine (15.0 mL, 107 mmol), a trace of DMAP and dichloromethane (200 mL). The resulting solution was stirred for 72 hours, then water (100 mL) was added to quench the reaction. The organic layer was separated, and the aqueous layer was further extracted with ether (3x100 mL). The combined organic extracts were washed with water (150 mL), brine (150 mL), then dried over anhydrous magnesium sulfate. Removal of the solvents gave crude 80 which was used directly in the next step. A 100-mL single-neck round-bottom flask was charged with crude 80 and aqueous 10% NaOH solution (50 mL). The resulting solution was stirred at room temperature for 4 hours, then was acidified to pH 4 with aqueous 1 M HCI. The OTB DMS COOH 81 150 aqueous layer was extracted with ether (3x100 mL) and the organic extracts were washed with water (150 mL), brine (150 mL), then dried over anhydrous MgS04. Removal of the solvent followed by vacuum distillation at 176 °C, 0.5 mm Hg, gave 81 (7.29 g, 19.1 mmol) in 95% yield for the two steps as a thick, colourless oil. IR(CDCI3): 2933, 2856, 1714, 1432, 1254, 1191, 1134, 1051,834 cm'1; 1H NMR (400 MHz, CDCI3) ppm: 3.77 (m, J 1 3 . 1 4 = 6.4 Hz, 1H), 2.35 (t, J 2 . 3 = 7.1 Hz, 2H), 1.61 (m, 2H), 1.45-1.18 (m, 18H), 1.12 (d, J 1 3 . 1 4 = 6.4 Hz, 3H), 0.9 (s, 9H), 0.0 (s, 6H). 1 3 C NMR (50 MHz, CDCI3) ppm: 180.6, 68.7, 39.7, 36.1, 34.1, 29.6, 29.2, 29.1, 25.9, 25.8; 25.6, 25.5, 24.7, 23.8, 23.7, 18.1, 17.6; LRMS (El) m/z (relative intensity): 329 (66), 283 (100), 159 (38), 138 (28), 121 (30), 97 (57), 83 (53), 75 (79), 55 (22); HRMS (El): calculated for C 2 0H 4 3O 3Si (M++1): 359.2981; found: 359.2982; Analysis calculated for C 2 0H 4 2O 3Si: C, 66.98; H, 11.81; found: C, 67.3; H, 11.80. 151 5-( 1 S'-terf-Butvldimethvlsiloxv-l '-hvdroxvtetradecvlidene)-2.2-dimethvl-1,3-dioxan-4,6-dione (82) OTBDMS OH o 82 A 50-mL single-neck round-bottom flask was charged with 81 (5.0 g, 14.1 mmol) and CH2CI2 (30 mL). 1,1'-Carbonyldiimidazole (3.39 g, 21.2 mmol) was added in portions and the reaction mixture was stirred until gas evolution ceased. A 100-mL single-neck round-bottom flask was charged with Meldrum's acid (3.01 g, 21.2 mmol) and CH2CI2 (40 mL). Pyridine (3.38 mL, 41.8 mmol) was introduced in a single portion and the reaction mixture was stirred for one hour while the colour of the solution turned to pink. The contents of the flask containing activated 81 were then syringed into the second flask containing the anion of Meldrum's acid, and the combined reaction mixture was stirred for an additional 14 hours. The colour of the reaction mixture turned from pink to dark red. Aqueous 1 M HCI (50 mL) was added to quench the reaction. The organic layer was separated and washed successively with water (75 mL), brine (75 mL) and then dried over anhydrous MgS04. Removal of the solvent gave 82 (6.7 g, 0.014 mol) in 97% yield as a thick orange-red oil. 152 IR (CDCb): 3159, 2908, 1722, 1630, 1417, 1271, 1039, 828 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 3.75 (m, 1H), 2.95 (t, J2-.3< = 7.1 Hz, 2H), 1.7 (s, 6H), 1.4-1.15 (m, 21H), 1.12 (d, J 1 3 . . 1 4 . = 6.4 Hz, 3H), 0.9 (s, 9H), 0.0 (s, 6H); 1 3 C NMR (50 MHz, CDCI3) ppm: 198.3, 104.7, 91.2, 68.6, 39.7, 35.7, 29.6 (2), 29.4 (2), 26.8, 26.7, 25.9, 25.8, 23.8, 18.1, -4.4, -4.7; LRMS (DCI): 485 (M+1); HRMS (DCI): calculated for C26H 4906Si (M++1): 485.3298; found: 485.3277. 153 5-(1\13'-Dihydroxytetrad^^ (83) 83 A 100-mL single-neck round-bottom flask equipped with a nitrogen inlet was charged with 82 (4.59 g, 9.47 mmol) and 10% hydrofluoric acid in acetonitrile (100 mL). The resulting solution was stirred for 4 hours and the colour of reaction mixture turned from red to yellow. Water (30 mL) and ether (50 mL) were added to quench the reaction. The organic layer was separated, washed with water (75 mL), brine (75 mL), then dried over anhydrous MgS0 4. Removal of the solvent gave 83 (3.3 g, 9.0 mmol) in 95% yield as a yellow oil. IR (CDCI3): 3612, 2930, 2856, 2244, 1730, 1669, 1574, 1419, 1258, 1152, 1035, 822 cm'1; 1H NMR (400 MHz, CDCI3) ppm: 3.75 (m, 1H), 2.95 (t, J 2 , 3 - = 7.1 Hz, 2H), 1.7 (s, 6H), 1.4-1.15 (m,21H), 1.12 (d,Ji3..i4' = 6.4 Hz,-3H); 1 3 C (50 MHz, CDCI3) ppm: 198.3, 170.6, 160.2, 104.7, 91.2, 68.1, 39.7, 39.3, 35.7, 29.6, 29.4, 26.9, 26.7, 26.1, 25.9, 25.8, 23.4, 18.2; LRMS (DCI): 371 (M++1), 388 (M++18); HRMS (DCI): calculated for CzoHasOe (M++1): 371.2434; found: 371.2423. 154 3-Oxo-l 5-hexadecanolide (84) 84 (a) By intramolecular alcoholvsis of 83 To a 250-mL two-necked, round-bottom flask equipped with a pressure-equalizing dropping funnel and a nitrogen inlet was added THF (100 mL). The solvent was heated to reflux and a solution of 5-(1',13'-dihydroxytetradecylidene)-2,2-dimethyl-1,3-dioxane-4.6-dione (83, 705 mg, 1.89 mmol) in THF (20 mL) was added dropwise over 6 hours via a syringe pump. The reaction mixture was allowed to cool and ether (100 mL) was added. The organic phase was washed with aqueous saturated solution of NaHC0 3 (2x50 mL), water (2x50 mL), brine (50 mL), then dried over anhydrous MgS04. Removal of the solvent, followed by purification via radial chromatography using petroleum ether-ethyl acetate (20:1) gave 84 (60 mg, 0.23 mmol) in 12% yield as a pale yellow oil in three steps from 81. 155 Rf: 0.30 (petroleum ether-ethyl acetate 20:1); IR (CDCI3): 3606, 2932, 2859, 1735, 1711, 1411, 1279, 1131, 1066 cm"\ 1H NMR (400 MHz, CDCI3) ppm: 4.96 (m, J 1 5.I 4A= 8.4 Hz, J 1 5-I 4B = 3.5 Hz, J 1 5 . 1 6 = 6.4 Hz, 1H), 3.46 (d, J 2 A . B = 14.8 Hz, 1H), 3.32 (d, J 2 A-B = 14.8 Hz, 1H), 2.57 (m, J4A-B = 16.8 Hz, J 4A- 5 = 7.0 Hz, 1H), 2.50 (m, J 4 A . B = 16.8 Hz, J 4 B - 5 = 7.0 Hz, 1H) 1.62 (m, 2H), 1.53-1.37 (m, 18H), 1.23 (d, J 1 5 . 1 6 = 6.4 Hz, 3H); PROTON DECOUPLED 1H NMR (400 MHz, CDCI3): Irradiation at 6 (ppm) 1.23 Simplification of signals at 5 (ppm) 4.96 (dd) Coupling constants (Hz) Jl5-14A = 8.4 J-I5-14B = 3.5 1 3 C NMR (50 MHz, CDCI3) ppm: 202.8, 166.9, 72.5, 50.2, 42.0, 35.7, 29.7, 27.1, 27.0, 26.9, 26.2, 25.9, 25.4, 23.7, 22.5, 20.2; LRMS (El) m/z (relative intensity): 268 (M+, 11), 97 (40), 83 (47), 75 (32), 69 (74), 55 (99), 43(100); HRMS (El): Calculated for C 1 6 H 2 8 0 3 (M+): 268.2039; found: 268.2042 Analysis calculated for C i 6 H 2 8 0 3 : C, 71.59; H, 10.52; found: C, 71.76; H, 10.48. (b) Bv intramolecular alkylation of the dianion from 89 To a solution of diisopropyl amine (1.1 mL, 7.6 mmol) in 150 mL of dry THF, stirred at 0 °C under a nitrogen atmosphere, was added n-BuLi (5.1 mL, 7.6 156 mmol). The solution was stirred for 30 minutes at 0 °C, then cooled to -78 °C. A solution of 89 (1.21 g, 3.5 mmol) in 10 mL of THF was added in one portion and the mixture was allowed to warm to room temperature during 5 hours. The reaction mixture was quenched with aqueous 1 M HCI and diluted with ether. The organic layer was washed with aqueous 1 M HCI (2x50 mL), brine (50 mL), dried over anhydrous MgS04. The solvent was removed under reduced pressure, followed by radial chromatography using 1:20 ethyl acetate-petroleum ether as eluant to give 84 (0.3 g, 1.1 mmol) in 32% yield. 11-Dodecen-1-ol (85) DIBAL (20.0 mL, 1 M in hexanes, 20.0 mmol) was added dropwise to a solution the reaction mixture was stirred for 1 hour. The reaction was quenched with aqueous 1 M HCI, and then diluted with CH2CI2. The layers were separated and the aqueous layer was extracted with CH2CI2. The combined organic extracts were washed with aqueous 1 M HCI, brine and dried over anhydrous MgS04. OH 85 of 10-undecen-1-nitrile (65, 2 .4 g, 13.2 mmol) in CH2CI2 (50 mL) at -78 °C and 157 Concentration of the solvent yielded a yellow oil (2.0 g, 11 mmol) which was used without further purification. Lithium aluminium hydride (0.84 g, 22 mmol) was suspended in THF (100 mL) and the solution was cooled to 0 °C. A solution of 11-dodecenal (2.0 g, 11 mmol) in THF (10 mL) was added to the LAH suspension and the reaction mixture was allowed to warm to room temperature and stirred for 1 hour. After cooling to 0 °C, the reaction was quenched with 1 M NaOH and resulting precipitate was removed by filtration and washed with ether. The layers of the filtrate were separated and the organic layer was washed with brine, dried over anhydrous MgS04. Concentration of the solvent followed by column chromatography using ethyl acetate and Petroleum ether (1:5) as eluant yielded 85 (1.94 g, 10.6 mmol) as clear, colourless oil in 80% yield from 65. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory.80 158 Compound 85 (1.94 g, 10.6 mmol) was dissolved in ether (100 mL) and the resulting solution was cooled to 0 °C. To this solution phosphorus tribromide (2.0 mL, 21 mmol) was added dropwise. The reaction mixture was warmed to room temperature and further stirred for 24 hours. Water (30 mL) was added to quench the reaction. The organic layer was separated and washed with aqueous saturated solution of N a H C 0 3 , brine and dried over anhydrous M g S 0 4 . Concentration of the solvent followed by column chromatography using ethyl acetate and petroleum ether (1:10) as eluant yielded 86 (2.1 g, 8.7 mmol) as clear, colourless oil in 82% yield. All spectral data of this compound were identical to those of material synthesized earlier in our laboratory. 8 0 159 12-Bromo-2-dodecanol (87) 87 To a solution of mercury (II) acetate (3.8 g, 0.01 mol) in 7 mL of water was added 21 mL of THF. The colour of reaction mixture turned bright yellow and then 12-bromo-dodecene (86) (2.7 g, 10 mol) was added and reaction mixture was further stirred for 3 hours, until all the colour disappeared. To this solution 10 mL of aqueous 3 M NaOH was added followed by a 10 mL of solution of 0.5 M NaBH4 in aqueous 3 M NaOH. The reduction of the organomercury compound was instantaneous. The reaction mixture was diluted with 100 mL of ether and saturated with sodium chloride and filtered. The organic layer was washed with aqueous 1 M HCI (100 mL), brine (100 mL) and dried over anhydrous MgS04. Evaporation of solvent followed by column chromatography using 1:4 ethyl acetate-petroleum ether as eluant to give 87 (2.6 g, 9.8 mmol) in 90% yield as a yellow oil. IR (CDCI3): 3614, 2931, 2857, 2385, 1443, 1250, 829 cm"1; 160 1H NMR (400 MHz, CDCI3) ppm: 3.76 (m, J 1 3 . i 4 = 6.1 Hz, 1H), 3.39 (t, J 2 . 3 = 6.9 Hz, 2H), 1.83 (m, 2H), 1.51-1.18 (m, 16H), 1.16 (d, J 2 . 3 = 6.1 Hz, 3H); 1 3 C (50 MHz, CDCI3) ppm: 112.5, 68.2, 39.3, 34.0, 32.8, 29.6, 29.5, 29.4, 28.7, 28.1,25.7,23.5; LRMS (El) m/z (relative intensity): 267 (M++1, 4), 265 (M++1, 4), 164 (25), 162 (20), 150 (45), 148 (40), 137 (20), 135 (25), 125 (21), 111 (55), 109 (28), 104 (31), 103 (95), 102 (38), 97 (78), 95 (26), 87 (34), 85 (100); HRMS (El): Calculated for C1 2H2 507 9Br(M+): 264.1089; Ci2H2 508 1Br(M+): 266.1069; found: 264.1099; 266.1087; Analysis calculated for Ci2H25OBr: C, 54.34; H, 9.50; found: C, 53.97; H, 9.53. 5-(1 '-Hvdroxvethvlidene)-2.2-dimethvl-1.3-dioxane-4.6-dinone (88) V OH 88 To a solution of 70 (5.0 g, 35 mmol) at 0 °C and under a nitrogen atmosphere was added dry pyridine (5.7 mL, 71 mmol) in one portion and the resulting solution was stirred at 0 °C for 30 minutes. Acetyl chloride (2.7 mL, 39 mmol) 161 was added dropwise over a period of 20 minutes and the temperature was maintained at 0 °C during the addition. The reaction mixture was stirred at 0 °C for 30 minutes and then at room temperature for another 1 hour. The reaction mixture was diluted with CH2CI2 and then washed with 1 M HCI (3x100), brine (100), and dried over anhydrous MgS04. The solvent was removed under reduced pressure to give an orange solid. Recrystallization from ether afforded 88 (5.4 g, 29 mmol) in 83% yield as a yellow solid. All spectral properties of this compound were identical to those of material synthesized earlier in our laboratory.109 (12'-Bromo-2'-dodecvl)-3-oxobutanoate O O 89 A solution of alcohol 87 (i.O g, 3.8 mmol) and acetyl Meldrum's acid (88, 0.77 g, 0.15 mmol) in 100 mL of dry THF was heated at reflux under a nitrogen atmosphere for 4 hours. The cooled reaction mixture was diluted with 100 mL of ether, washed with aqueous saturated solution of NaHC0 3 (2x100 mL), with brine (100 mL), dried over anhydrous MgS04, and the organic phase 162 concentrated under reduced pressure followed by radial chromatography using 1:20 ethyl acetate-petroleum ether to give product 89 (1.21 g, 3.5 mmol) in 92% yield as a colourless oil. IR (CDCI3): 3692, 3607, 3213, 2932, 2857, 2361, 2257, 1735, 1713, 1602, 1452, 1315, 1249, 1196 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 4.94 (m, J v . 2 . = 6.3 Hz, 1H), 3.40 (m, 4H), 2.25 (s, 3H), 1.83 (m, 2H), 1.61-1.26 (m, 18H), 1.21 (d, J r . 2 . = 6.3 Hz, 3H); 1 3 C (50 MHz, CDCI3) ppm: 200.7, 166.8, 112.6, 72.4, 50.5, 35.7, 34.0, 32.8, 30.1, 29.4, 29.3, 28.7, 28.1, 27.1, 25.3, 19.8; LRMS (El) m/z (relative intensity): 351 (M++1, 5), 349 (M++1, 5), 164 (26), 162 (28), 150(45), 148 (46), 137 (21), 135(23), 125 (21), 111 (54), 109 (20), 104 (31), 103 (94), 102 (39), 97 (77), 95 (27), 87 (36), 85 (100); HRMS (El): Calculated for Ci 6H 2 903 7 9Br(M+): 348.1300; Ci 6H 290 3 8 1Br(M +): 350.1280; found: 348.1308; 350.1299; Analysis calculated for C 1 6 H 2 9 0 3 Br: C, 55.02; H, 8.37; found: C, 55.24; H, 8.54. 163 2-Methvl-3-oxo-13-tetradecanolide (90) Freshly sublimed potassium terf-butoxide (61.1 mg, 0.55 mmol) was weighed into a dry flask equipped with a nitrogen inlet and septum. Freshly distilled terf-butanol (5.0 mL) was injected and the macrolide 74 (90.4 mg, 0.38 mmol) dissolved in 2.0 mL of terf-butanol was added dropwise. After 30 minutes of refluxing, the reaction mixture was cooled to room temperature and Mel (0.030 mL, 0.45 mmol) was injected and the reaction was further refluxed for 10 minutes. The reaction mixture was then poured into aqueous NH 4CI and the aqueous layer was extracted with ether (3x20 mL). The organic layer was washed with water, brine and dried over anhydrous M g S 0 4 . Then it was reduced under reduced pressure. The crude oil was purified via radial chromatography using petroleum ether-ethyl acetate (19:1) to give 127 (65.1 mg, 0.26 mmol) in 68% yield and 9% of 2,2-dimethyl-3-oxo-13-tetradecanolide. Diastereomers 90 were obtained as a single spot in the ratio of 2:1 as 164 determined by 1H NMR. All spectral properties of this compound were identical to those of material synthesized earlier in our laboratory.63 3-M .-Dithiolan-2-vl)-2-methvl-13-tetradecanolide (93) To a dry, nitrogen-purged, 25-mL round-bottom flask was charged with 2-methyl-3-oxo-13-tetradecanolide (90, 44 mg, 0.17 mmol), Znl 2 (catalytic amount) and 5 mL of ether. To this mixture, 1,2-bis(trimethysilylthio)ethane (401 mg, 1.7 mmol) was added dropwise. After 14 hours the reaction was quenched with 5 mL of water. The aqueous layer was extracted with ether (3x10 mL). The organic layer was washed with water (15 mL), brine (15 mL) and dried over anhydrous MgS0 4 The solvent was evaporated and the crude product was purified by radial chromatography using petroleum ether-ethyl acetate (20:1) as eluant to yield 93 (37 mg, 0.1 mmol) in 65% yield as a clear oil. 93 165 Rf: 0.35 (petroleum ether-ethyl acetate 20:1); GLC (OV101): 11.39 min (65%) 12.72 min (34.2%), GLC Conditions: 100-200 °C, initial time: 2 min, prg. rate: 20 °C/min, final time: 5 min, flow rate: 25 mL/min; IR(CDCI3): 3691,3156, 2931, 1806, 1715, 1602, 1460, 1261, 965, 828 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 5.08 (m, 0.33H), 4.94 (m, 0.67H), 3.24 (m, 4H), 3.05-2.95 (two q, 2H), 1.87-1.07 (m, 17H), 1.45 (d, J 2 - i 7 = 6.1 Hz, 3H), 1.06 (d, J 1 3 . 1 4 = 6.8 Hz, 3H); LRMS (DCI): 331 (M++1); HRMS (DCI): Calculated for C i 7 H 3 1 0 2 S 2 (M++1): 331.1765; found: 331.1775. 166 (4S* 13S*)-3-Oxo-4-methvl-13-tetradecanolide (94) 94 To a 25-mL single-necked round-bottom flask diisopropylamine (0.53 mL, 3.8 mmol) and n-BuLi (2.6 mL, 3.8 mmol) were injected into 10.0 mL of THF under a nitrogen atmosphere at 0 °C and stirred for 30 minutes. Macrolide 74 (0.4 g, 1.7 mmol) dissolved in 2.0 mL of THF, was added and the reaction was stirred at 0 °C for 30 minutes. Mel (0.11 mL, 1.8 mmol) was injected into the reaction which was stirred for a further 15 minutes. The anion was quenched by pouring the reaction mixture into 30 mL of cold (0 °C) aqueous 1 M HCI. The solution was saturated with sodium chloride and extracted with ether (3x30 mL). The combined ether layers were concentrated under reduced pressure to give a red oil, followed by radial chromatography using 1:19 petroleum ether-ethyl acetate gave 94 (0.38 g, 1.5 mmol) 90% yield as a light yellow oil. All spectral properties of this compound were identical to those of material synthesized earlier in our laboratory.63 167 2. 11-Dodecandiol (97 and 98) OH OH OH OH ( ± ) - 9 7 98 A solution of 1,6-dibromohexane (96, 4.88 g, 20.1 mmol) in THF (10 mL) was added dropwise to a suspension of magnesium turnings (1.04 g, 52.1 mmol) in THF (100 mL) in a two-necked round-bottom flask equipped with a reflux condenser. The Grignard reagent was initiated by the addition of a small amount of iodine. The resulting complex was stirred under reflux conditions for 20 minutes and then cooled to room temperature. Copper(l) iodide (120 mg) was added to the reaction mixture and stirred for 5 minutes and then cooled to 0 °C and propylene oxide (2.0 mL, 0.03 mol) was added dropwise. The solution was further stirred for 2 hours at 0 °C and then at room temperature for another 16 hours. Aqueous saturated NH4CI was added to quench the reaction. The solution was extracted with ether (3x100 mL). The combined ether layers were concentrated under reduced pressure to give a yellow solid. Purification by radial chromatography using 1:1 petroleum ether-ethyl acetate gave 97 and 98 (3.8 g, 0.02 mol) in 94% yield as a white solid. The two diastereomers were a single spot on TLC plate. 168 Rf: 0.35 (petroleum ether-ethyl acetate 1:1); IR (CDCI3): 3614, 3441, 2930, 2856, 1454, 1251, 1057 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 3.7 (m, U2 = 6.1 Hz, 2H), 1.6 (bs, 2H), 1.6-1.2 (m, 16H), 1.17 (d, J L 2 = 6.1 Hz, 6H); 1 3 C NMR (50 MHz, CDCI3) ppm: 68.1, 39.3, 29.6, 29.5, 25.7, 23.4; LRMS (DCI): 203 (M++1); HRMS (DCI): Calculated for Ci 2 H 2 60 2 (M+): 202.1933; found: 202.1938; (2S.11S1-2. 11-Dodecandiol (97) A solution of 1,6-dibromohexane (96, 2.1 g, 8.6 mmol) in THF (10 mL) was added dropwise to a suspension of magnesium turnings (0.42 g, 17 mmol) in THF (50 mL) in a two-necked round-bottom flask equipped with a reflux condenser. The Grignard reagent was initiated by the addition of a small amount of iodine. The resulting complex was stirred under reflux conditions for 20 minutes and then cooled to room temperature. Copper (I) iodide (20 mg) was added to the reaction mixture and stirred for 5 minutes and then cooled to 0 °C and (S)-propylene oxide (1.2 mL, 17.2 mmol) was added dropwise. The solution was further stirred for 2 hours at 0 °C and then at room temperature for another 16 hours. Aqueous saturated NH4CI was added to quench the reaction. The solution was extracted with ether (3x50 mL). The combined ether layers were concentrated under reduced pressure to give a yellow solid. Purification by 169 radial chromatography using 1:1 petroleum ether-ethyl acetate gave (2S,11S)-97 (1.7 g, 8.4 mmol) in 98% yield as a white solid. The spectral properties of this compound were identical to those of the racemic material. Baever-ViNiger oxidation of 94 Trifluoro acetic anhydride (0.09 mL, 1.3 mmol) was added dropwise to a stirred mixture of urea hydrogen peroxide (0.12 g, 1.3 mmol), Na 2HP0 4 (0.21 g, 1.5 mmol), 94 (52.5 mg, 0.21 mmol) in CH2CI2 (3 mL) at 0 °C in a 25-mL single-necked round-bottom flask. The mixture was allowed to warm to room temperature and stirred overnight. An aqueous saturated solution of NaHC0 3 (2 mL) was added to neutralize the acids and the aqueous layer was extracted with CH2CI2 (3x10 mL). The combined organic layers were washed with water (20 mL), brine (20 mL) and dried over anhydrous MgS04. The solvent was removed and followed by radial chromatography using 1:1 petroleum ether-ethyl acetate to give 97 (25.5 mg, 0.13 mmol) in 60% yield. The spectral properties for this compound were identical to the mixture of 97 and 98 obtained above. 170 2.11-Dibenzoyloxydodecane (99 and 100) OCOPh OCOPh OCOPh OCOPh (±)-99 100 A 100-mL single -necked round bottom flask equipped with a nitrogen inlet was charged with a mixture of (±)-97 and 98 (1.2 g, 5.9 mmol), benzoyl chloride (2.8 mL, 24 mmol), and pyridine (30 mL). The resulting solution was stirred for 30 minutes at room temperature, then 1M HCI (30 mL) was added to quench the reaction. The aqueous layer was extracted with ether (3x50 mL). The combined organic extracts were washed with water (150 mL), brine (150 mL), then dried over anhydrous magnesium sulfate. The combined ether layer was concentrated under reduced pressure to give a red oil, followed by radial chromatography using 1:19 petroleum ether-ethyl acetate to give (±)-99 and 100 (2.29 g, 5.6 mmol) in 95% yield as a light yellow oil. Rf: 0.43 (petroleum ether-ethyl acetate 20:1); IR (CDCI3): 2933, 2858, 1707, 1585, 1451, 1355, 1315, 1280, 1177, 1118, 1070, 1026 cm"1; 1:H NMR (400 MHz, CDCI3) ppm: 8.2-7.35 (m, 10H), 5.12 (m, 2H), 1.8-1.18 (m, 16H), 1.38 (d, J L 2 = 6.2 Hz, 6H); 171 1 3 C NMR (50 MHz, CDCI3) ppm: 166.0, 132.2, 130.1, 129.0, 128.4, 71.7, 36.0, 29.5 (2), 25.4, 20.1; LRMS (El) m/z (relative intensity): 411 (M++1, 0.1), 410 (M+, 0.1), 166(28), 123 (49), 105 (100), 82 (36), 77 (28); HRMS (El): Calculated for C 2 6 H 3 4 0 4 (M+): 410.2457; found: 410.2454; HPLC: Flow rate: 0.6 mL/minute with methanol as eluant; peaks at 9.1, 9.9 and 10.5 minutes in a 1:2:1 ratio. (2S. 11SV2.11 -Dibenzovloxvdodecane (99) A 50-mL single -necked round-bottom flask equipped with a nitrogen inlet was charged with (2S,11S)-97 (0.82 g, 4.1 mmol), benzoyl chloride (1.9 mL, 16 mmol), and pyridine (10 mL). The resulting solution was stirred for 30 minutes at room temperature, then 1M HCI (10 mL) was added to quench the reaction. The aqueous layer was extracted with ether (3x25 mL). The combined organic extracts were washed with water (75 mL), brine (75 mL), then dried over anhydrous magnesium sulfate. The combined ether layer was concentrated under reduced pressure to give a red oil, followed by radial chromatography using 1:19 petroleum ether-ethyl acetate to give (2S,11S)-99 (2.29 g, 5.6 mmol) in 95% yield as a light yellow oil. HPLC: Flow rate: 0.6 mL/minute with methanol as eluant; peak at 9.1 minutes. 172 Alkylation of the monoanion from 4-methvl-3-oxo-13-tetradecanolide (94) 101 102 Freshly sublimed potassium terf-butoxide (0.10 g, 0.87 mmol) was weighed into a dry 2-necked, round-bottom flask equipped with a nitrogen inlet and septum and reflux condenser. Freshly .distilled terf-butanol (3.0 mL) was injected and (4S*,13S*)-4-methyl-3-oxo-13-tetradecanolide (94) (99.7 mg, 0.39 mmol) in 2 mL of ferf-butanol, was added dropwise. After 1 hour of refluxing, the reaction mixture was cooled to room temperature and Mel (0.050 mL, 0.49 mmol) was injected and further refluxed for 1 hour. The reaction mixture was poured into aqueous saturated NH4CI (20 mL) and the aqueous layer was extracted with ether (3x20 mL). The organic layer was washed with 30 mL of water, 30 mL of brine, and dried over anhydrous MgS04. Removal of the solvent followed by radial chromatography using 1:19 ethyl acetate-petroleum ether gave 101 (27.9 mg, 0.11 mmol) and 102 (48.6 mg, 0.17 mmol) in 27% and 44% yield, respectively. 173 101 Rf: 0.33 (petroleum ether-ethyl acetate 20:1); IR (CDCI3):2935, 2862, 1736, 1710, 1455, 1196, cm"1; 1H NMR (400 MHz, CDCI3) ppm: 4.95 (m, J 1 3 . 1 2 A = 7.5 Hz, J 1 3-I 2B = 4.2 Hz, J 1 3 . 1 4 = 6.1 Hz, 1H), 3.74 (q, J 2 . 1 5 = 7.0, 1H), 2.83 (m, J 4 - i 6 = 7.1 Hz, J 4 - 5 = 6.4 Hz, 1H), 1.62 (m, 2H), 1.59-1.02 (m, 14H), 1.28 (d, J 2 . i 5 = 7.0 Hz, 3H) 1.21 (d, J 1 3 . 1 4 = 6.1 Hz, 3H), 1.09 (d, J 4 . 1 6 = 7.1 Hz, 3H); PROTON DECOUPLED 1H NMR (400 MHz, CDCI3): Irradiation at 5 (ppm) 1.21 1.09 Simplification of signals at 6 (ppm) 4.95 (dd) 2.83 (t) Coupling constants (Hz) J-I3-12A = 7.5 Jl3-12B = 4.2 J 4 - s = 6.4 1 3 C NMR (50 MHz, CDCI3) ppm: 209.2, 169.9, 72.0, 51.6, 44.2, 35.2, 29.9, 26.3, 25.5, 25.1, 25.06, 24.2, 22.8, 20.4, 16.8, 13.4; LRMS (El) m/z (relative intensity): 268 (M+, 17), 111 (43), 98 (27), 88 (34), 86 (25), 74 (50), 69 (79), 58 (35), 56 (25), 41 (58); HRMS (El): Calculated for C 1 6H 2 80 3(M +): 268.2039; found: 268.2035. 102 Rf: 0.42 (petroleum ether-ethyl acetate 20:1); IR (CDCI3): 2934, 2862, 1723, 1703, 1457, 1272, 1156, 1025, 807 cm"1; 174 1H NMR (400 MHz, CDCI3) ppm: 5.02 (m, J 1 3-I 2A = 8.1 Hz, J 1 3 - i 2 B = 3.1 Hz, J 1 3 - i 4 = 6.4 Hz, 1H), 2.83 (m, J 4 . 1 6 = 6.4 Hz, J 4 . 5 = 6.7 Hz, 1H), 1.74-1.17 (m, 16H), 1.42 (s, 3H), 1.30 (s, 3H), 1.23 (d, J 1 3 - i 4 = 6.4 Hz, 3H), 1.05 (d, J 4 . 1 6 = 6.4 Hz, 3H); PROTON DECOUPLED 1H NMR (400 MHz, CDCI3): Irradiation at 5 (ppm) 1.23 1.05 Simplification of signals at 6 (ppm) 5.02 (dd) 2.83 (t) Coupling constants (Hz) J-I3-12A = 8.1 J-I3-12B = 3.1 J 4-s = 6.7 1 3 C NMR (50 MHz, CDCI3) ppm: 215.1, 173.2, 71.4, 55.7, 40.4, 35.3, 31.9, 26.2, 26.1 (2), 24.3, 22.9, 22.7, 21.7, 20.4, 20.1, 17.6; LRMS (El) m/z (relative intensity): m/z (relative intensity): 282 (M+, 5), 111 (24), 88 (72), 85 (31), 84 (49), 83 (32),; HRMS (El): Calculated for C 1 7 H 3 0 O 3 (M+):282.2195, (M++1): 283.2273; found: (M+) 282.2192, (M++1): 283.2230; Alkylation of the dianion from 2-methvl-3-oxo-13-tetradecanolide (90) Diisopropylamine(0.015 mL, 0.10 mmol) and n-BuLi (0.08 mL, 0.1 mmol) were injected into 2.0 mL of THF under nitrogen atmosphere at 0 °C in a 10-mL single-necked round-bottom flask. After 30 minutes, 2-methyl-3-oxo-13-tetradecanolide (90, 12 mg, 0.05 mmol) as a solution in 2.0 mL of THF, was added and stirred at 175 0 °C for 45 minutes. Mel (3 uL, 0.052 mmol) was injected and stirred a further 1 hour. The anion was quenched by pouring the reaction mixture into 20 mL of cold 0 °C aqueous 1 M HCI. The solution was saturated with sodium chloride and extracted with ether (3x15 mL). The combined ether layer was washed with 20 mL of brine, and dried over anhydrous MgS04. The solvent was removed under reduced pressure and followed by radial chromatography to give 101 (6.1 mg, 0.02 mmol) in 48% yield and 44% of 90 (5.3 mg, 0.02 mmol) was recovered. Rf: 0.33 (petroleum ether-ethyl acetate 20:1); IR (CDCI3):2934, 2861, 1727, 1706, 1508, 1455, 1315, 1266, 1181, 1130, 1068, 791 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 5.05-4.95 (m's, 1H), 3.75-3.55 (two q, 1H), 2.92-2.38 (m's, 1H), 1.84-1.02 (m, 25H); 1 3 C NMR (50 MHz, CDCI3) ppm: 209.2, 169.9, 72.2, 72.17, 72.0 (2), 53.2, 51.6 (2), 44.5, 44.2 (2), 36.4, 35.8, 35.3, 35.2 (2), 34.6, 33.9, 31.0, 30.2, 29.9 (2), 26.8, 26.3 (2), 25.9, 25.7, 25.5 (2), 24.4, 25.3, 25.2, 25.1 (2), 25.06 (2), 24.9 (3), 24.6, 24.3, 24.2 (2), 23.6, 22.8 (2), 21.7, 20.4 (2), 20.0, 17.7, 16.8(2), 13.4 (2), 12.4; LRMS (El) m/z (relative intensity): 268 (M+, 7), 195 (30), 97 (22), 69 (30), 47 (21); HRMS (El): Calculated for C 1 6H 2 80 3(M +): 268.2039; found: 268.2044. 176 (3S*4S*13S*)-2.4-Dimethvl-3-hvdroxv-13-tetradecanolide (105) 105 To a solution of 102 (47.9 mg, 0.17 mmol) in 2.0 mL of ethanol at room temperature was added NaBH4 (10.1 mg, 0.27 mmol). After stirring at room temperature for 2 hours, the reaction was quenched with 2 mL of aqueous 1 M HCI and diluted with 15 mL of ether. The organic phase was washed twice with 15 mL brine, dried over anhydrous MgS04, and concentrated under reduced pressure followed by radial chromatography using petroleum ether-ethyl acetate (9:1) as eluant to give 105 (44.1 mg, 0.16 mmol) in 91% yield. Rf: 0.46 (petroleum ether-ethyl acetate 9:1); IR (CDCI3): 3462, 2933, 2862, 1687, 1445, 1298, 1263, 1163, 1128 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 5.02 (m, J 1 3-I 2A = 3.4 Hz, J13-12B =11.4 Hz, J13-14 = 6.1 Hz, 1H), 4.45 (d, J3-0H = 10.3 Hz, 1H), 3.21 (dd, J3-0H = 10.3 Hz, 177 J 3 . 4 = 2.1 Hz, 1H), 1.71-0.9 (m, 17H), 1.38 (s, 3H), 1.19 (d, J 1 3 . 1 4 = 6.1 Hz, 3H), 1.1 (s, 3H), 0.96 (d4-i6 = 7.2 Hz, 3H); PROTON DECOUPLED 1H NMR (400 MHz, CDCI3): Irradiation at 5 (ppm) 1.19 Simplification of signals at 6 (ppm) 5.02 (dd) Coupling constants (Hz) Jl3-12A=114 Jl3-12B = 3.4 1 3 C (50 MHz, CDCI3) ppm: 179.6, 84.3, 69.8, 43.8, 35.0, 34.2, 28.0, 27.2, 26.2, 25.8, 25.3, 24.7, 24.6, 22.0, 21.7, 19.8, 17.3; LRMS (El) m/z (relative intensity): 284 (M+, 9), 117 (100), 99 (30), 98 (60), 54 (30), 43 (28), 40(31); HRMS (El): Calculated for C i 7 H 3 2 0 3 (M+): 284.2351; found: 284.2352. (3S*.15S*)-3-Hvdroxv-15-hexadecanolide (110) and (3R*15S*)-3-Hvdroxv-15-hexadecanolide (111) 110 111 178 (a) NaBH4 in ethanol To a solution of 84 (12.5 mg, 0.046 mmol) in 10 mL of ethanol at room temperature was added NaBH4 (1.8 mg, 0.05 mmol). After stirring at room temperature for 30 minutes, the reaction was quenched with aqueous 1 M HCI and diluted with 15 mL of ether. The organic phase was washed twice with 15 mL of brine, dried over anhydrous MgS04, and concentrated under reduced pressure to give crude product as a yellow oil. Purification by radial chromatography using petroleum ether-ethyl acetate (5:1) as eluant gave 110 and 111 ( 11.0 mg, 0.041 mmol) as a single spot in 88% yield as a pale yellow oil. Diastereomeric ratio was determined by 1H NMR and the spectral data for the mixture is given below. Rf: 0.36 (petroleum ether-ethyl acetate 5:1); IR (CDCI3): 3613, 3527, 2931, 2859, 1713, 1446, 1414, 1363, 1336, 1264, 1188, 1150, 1128, 1046, 835 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 5.01 (m, J 1 5 . i 6 = 6.4 Hz, 1H), 4.05 ( m, 0.3H), 3.88 (m, 0.7H), 2.86 (d, J 3 . 0 H = 10.0 Hz, 1H), 2.62-2.36 (m, 2H), 1.59-1.27 (m, 22H), 1.19 (d, J 1 5 . 1 6 = 6.4 Hz, 3H); 1 3 C NMR (50 MHz, CDCI3) ppm: 172.3, 172.2, 71.2, 68.6, 68.1, 42.1, 40.9, 35.8, 35.7, 35.6, 35.0, 27.5, 27.4, 27.3, 27.2, 26.9, '26.5, 26.1, 26.01, 26.0, 25.8, 25 71, 25.68, 24.5, 24.3, 24.1, 23.6, 20.2; 179 LRMS (El) m/z (relative intensity): 270 (M+, 1), 111 (33), 110 (27), 109 (36) 102 (23), 98 (36), 96 (50), 95 (62), 89 (100); HRMS (El): Calculated for C 1 6H 3o0 3 (M+): 270.2195; found: 270.2191; Analysis calculated for Ci 6H 3o0 3: C, 71.05; H, 11.19; found: C, 71.20; H, 11.19. (b) L-Selectride-NaBH4 To a solution of 84 (0.26 g, 0.97 mmol) in 10 mL of dry THF at 0 °C and under a nitrogen atmosphere, was added 0.97 mL (0.97 mmol) of a 1.0 M solution of L-Selectride in THF and the resulting mixture was stirred at 0 °C for 3 hours. Then NaBH4 (0.2 g, 5.3 mmol) and ethanol (2 mL) were added and the reaction mixture was further stirred for 1 hour. The reaction was quenched with 3 mL of aqueous 30% hydrogen peroxide and 5 mL of aqueous 1 M HCI. The mixture was stirred for additional 10 minutes at room temperature. The aqueous layer was extracted with ether (3x30 mL). The organic layer was washed with water (50 mL), brine (50 mL), dried over anhydrous MgS0 4 and concentrated under reduced pressure, followed by radial chromatography using petroleum ether-ethyl acetate (9:1) to give 110 (0.24 g, 0.89 mmol) in 92% yield as a pale yellow oil. IR(CDCI3): 3534, 2932, 2859, 1713, 1429, 1265, 1187, 1128, 1047, 907, 829, 733 cm"1; 180 1H NMR (400 MHz, CDCI3) ppm: 4.99 (m, J 1 5 - I 4 A = 7.9 Hz, J 1 5 - I 4 B = 4.0 Hz, J 1 5 - i 6 = 6.4 Hz, 1H), 3.86 (m, J 3 - 2 A = 15.5 Hz, J 3 2 B = 4.0 Hz J ^ O H = 7.0 Hz, 1H), 2.91 (d, J 3 . O H = 7.0 Hz, 1H), 2.57 (m, J 2 A . B = 15.4 Hz, J 2 A - 3 = 4.0 Hz, 1H), 2.49 (m, J 2 A - B = 15.4 Hz, J 2 B . 3 = 15.5 Hz, 1H), 1.59-1.27 (m, 22H), 1.19 (d, J 1 5 . 1 6 6 .4Hz , 3H); PROTON DECOUPLED 1H NMR (400 MHz, CDCI3): Irradiation at 5 (ppm) 1.19 2.91 Simplification of signals at 6 (ppm) 4.99 (dd) 3.86 (dd) Coupling constants (Hz) J-I5-14A = 7.9 J 1 5 - 1 4 B = 4.0 J 3 - 2 A =15.5 J 3 . 2 B = 4.0 1 3 C NMR (50 MHz, CDCI3) ppm: 172.2, 71.2, 68.6, 40.9, 35.8, 27.3, 27.1, 26.9, 26.1, 25.9, 25.7, 25.69, 24.5, 24.2, 23.2, 20.2. LRMS (El) m/z (relative intensity): 270 (M+, 0.3), 97 (22), 96 (20), 95 (23), 89 (23); HRMS (El): Calculated for C i 6 H 3 0 O 3 (M+): 270.2195; found: 270.2198. (c) L-Selectride in THF To a solution of 84 (44.6 mg, 0.17 mmol) in 10 mL of dry THF at 0 °C and under a nitrogen atmosphere, was added 0.2 mL (0.20 mmol) of a 1.0 M solution of L-Selectride in THF and the resulting mixture was stirred at 0 °C for 3 hours. The reaction was quenched with 3 mL of 30% hydrogen peroxide and 5 mL of aqueous 1 M HCI. The mixture was stirred for additional 10 minutes at room 181 temperature. The aqueous layer was extracted with ether (3x15 mL). The organic layer was washed with water (25 mL), brine (25 mL), dried over anhydrous MgS0 4 and concentrated under reduced pressure, followed by radial chromatography using petroleum ether-ethyl acetate (9:1) to give 110 (20.7 mg, 0.08 mmol) in 45% yield as a clear oil and 48% unreacted p-keto lactone 84 (21.9 mg, 0.08 mmol) was recovered. (d) K-Selectride in THF To a solution of 84 (20.1 mg, 0.075 mmol) in 10 mL of dry THF at 0 °C and under a nitrogen atmosphere, was added 0.10 mL (0.10 mmol) of a 1.0 M solution of K-Selectride in THF and the resulting mixture was stirred at 0 °C for 3 hours. The reaction was quenched with 3 mL of 30% aqueous hydrogen peroxide and 5 mL of aqueous 1 M HCI. The mixture was stirred for additional 10 minutes at room temperature. The aqueous layer was extracted with ether (3x15 mL). The organic layer was washed with water (25 mL), brine (25 mL), dried over anhydrous MgS0 4 and concentrated under reduced pressure, followed by radial chromatography using petroleum ether-ethyl acetate (9:1) to give 110 (8.1 mg, 0.03 mmol) in 38% yield as a clear oil and 38% unreacted p-keto lactone 84 (7.6 mg, 0.03 mmol) was recovered. 182 (e) LS-Selectride in THF To a solution of 84 (10.0 mg, 0.037 mmol) in 10 mL of dry THF at 0 °C and under a nitrogen atmosphere, was added 0.05 mL (0.05 mmol) of a 1.0 M solution of LS-Selectride in THF and the resulting mixture was stirred at 0 °C for 3 hours. The reaction was quenched with 3 mL of 30% aqueous hydrogen peroxide and 5 mL of aqueous 1 M HCI. The mixture was stirred for additional 10 minutes at room temperature. The aqueous layer was extracted with ether (3x15 mL). The organic layer was washed with water (25 mL), brine (25 mL), dried over anhydrous MgS0 4 and concentrated under reduced pressure, followed by radial chromatography using petroleum ether-ethyl acetate (9:1) to give 110 (4.3 mg, 0.02 mmol) in 43% yield as a clear oil and 38% unreacted p-keto lactone 84 (3.8 mg, 0.01 mmol) was recovered. (f) Lithium (diisobutvOfn-butvOaluminium hydride in THF To a cold (-78 °C) solution of 84 (10.0 mg, 0.037 mmol) in 10 mL of dry THF and under a nitrogen atmosphere, was added a 0.4 M solution of lithium (diisobutyl)(n-butyl)aluminium hydride in ether (0.13 mL, 0.05 mmol) and the resulting mixture was stirred at this temperature for 2 hours and at 0 °C for 1 hour. Finely ground, solid Na 2S0 4.H 20 (0.50 g) was added to the solution and the mixture was stirred for 15 minutes. Aqueous NaOH (1 M, 10 mL) was slowly added to the reaction mixture and the stirring was continued for another 15 183 minutes. The mixture was diluted with ether (30 mL) and'the organic layer was separated. The organic layer was washed with aqueous saturated NH4CI (25 mL), brine (25 mL), dried over anhydrous MgS0 4 and concentrated under reduced pressure, followed by radial chromatography using petroleum ether-ethyl acetate (9:1) to give 110 (3.9 mg, 0.01 mmol) in 39% yield as a clear oil and 45% unreacted B-keto lactone 84 (4.5 mg, 0.02 mmol) was recovered. (i) NaBhtin THF-ethanol To a solution of 84 (4.0 mg, 0.015 mmol) in 2 mL of THF at 0 °C was added NaBH4 (0.7 mg, 0.02 mmol). After stirring at 0 °C for 1 hour, 0.4 mL of ethanol was added and the reaction mixture was further stirred for 1 hour. The reaction was quenched with aqueous 1 M HCI and diluted with 5 mL of ether. The organic phase was washed with brine (2x5 mL), dried over anhydrous MgS04, and concentrated under reduced pressure, followed by purification via radial chromatography using petroleum ether-ethyl acetate (9:1) as eluant to give 110 and 111 (2.5 mg, 0.009 mmol) in 62% yield as a pale yellow oil in 1:3.2 diastereomeric ratio, as determined by 1H NMR. (j) NaBH4 in THF and a trace of ethanol To a solution of 84 (7 mg, 0.03 mmol) in 2 mL of THF at 0 °C was added NaBH4 (1 mg, 0.03 mmol). After stirring at 0 °C for 1 hour, 2 \iL of ethanol was added and the reaction mixture was further stirred overnight at room temperature. The 184 reaction was quenched with aqueous 1 M HCI and diluted with 10 mL of ether. The organic phase was washed with brine (2x15 mL), dried, and concentrated under reduced pressure, followed by radial chromatography using petroleum ether-ethyl acetate (9:1) as eluant to give 110 and 111 (5.1 mg, 0.02 mmol) in 72.3% yield as a pale yellow oil in a ratio of 1:3.2 as determined by 1H NMR. (IO n-BuaNBH* in THF To a solution of 84 (10 mg, 0.04 mmol) in 1 mL of dry THF at 0 °C and under a nitrogen atmosphere, was added n-tetrabutylammonium borohydride (0.010 g, 0.04 mmol) and the resulting mixture was stirred at 0 °C for 48 hours. The reaction was quenched with 2 mL of aqueous 1 M HCI and the mixture was stirred for 5 minutes at room temperature. The mixture was then diluted with 10 mL of ether and the organic layer was washed with 10 mL of brine, dried over anhydrous MgS04. Concentrated under reduced pressure, followed by radial chromatography to give 110 and 111 (7.5 mg, 0.03 mmol) in 75% yield. The products were obtained in 1:1 diastereomeric ratio, as determined by 1H NMR. 185 (3S* 15/"?*)-3-(4'-Bromo)-benzenesulfonate-15-hexadecanolide and (3S*. 15S*)-3-(4,-Bromo)-benzenesulfonate-15-hexadecanolide (112 and 113) O O 112 113 To a solution of 110 and 111 (0.06 g, 0.2 mmol) in pyridine (10 mL) an excess of 4-bromobenzenesulfonyl chloride (0.27 g, 1.1 mmoL) was added and the resultant reaction mixture was stirred overnight, then poured into aqueous 1 M HCI. The aqueous layer was extracted with CH2CI2 (3x15 mL). The organic layer was washed with aqueous saturated solution of NaHC0 3 (20 mL), water (20 mL) and dried over anhydrous MgS0 4 which was followed by radial chromatography using petroleum-ether and ethyl acetate (20:1) to give 112 (31 mg, 0.06 mmol) and 113 (70 mg, 0.14 mmol) in 92% yield as white solids. 112 Rf: 0.27 (petroleum ether-ethyl acetate 20:1); 186 IR ( C D C I 3 ) : 2933, 2859, 1724, 1578, 1187, 1070 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 7.78 (d, J 0 . m = 8.8 Hz, 2H), 7.67 (d, Jo-m = 8.8 Hz, 2H), 4.96 (m, J 1 5 . i 4 A = 8.6 Hz, J 1 5 . 1 4 B = 3.7 Hz, J 1 5 - i 6 = 6.1 Hz, 1H), 4.89 (m, 1H), 2.73 (dd, J 2 A . 3 = 4.6 Hz, J 2 A - 2 B = 15.6 Hz, 1H), 2.63 (dd, J 2 B - 3 = 9.3 Hz, J 2 A . 2 B = 15.6 Hz, 1H), 1.71-1.16 (m, 22H), 1.19 (d, J 1 5 - i 6 = 6.1 Hz, 3H); PROTON DECOUPLED 1H NMR (400 MHz, CDCI3): Irradiation at 5 (ppm) 1.19 Simplification of signals at 6 (ppm) 4.96 (dd) Coupling constants (Hz) Jl5-14A = 8.6 J-I5-14B = 3.7 1 3 C NMR (50 MHz, CDCI3) ppm: 167.7, 133.1, 132.6, 129.4, 128.4, 79.9, 71.3, 39.7, 35.7, 33.2, 27.1, 26.4, 26.0, 25.8, 25.7, 25.6, 24.2, 22.5, 20.5; LRMS (DCI): 506 (M++18), 489 (M++1); HRMS (DCI): Calculated for C 2 2 H 3 4 0 5 S 7 9 Br (M++1): 489.1310; C^H^OsS^Br 491.1268; found: 489.1254; 491.1324. X-ray Structure: Results and Discussion, section 2.4.2, Page 90. 113 Rf: 0.22 (petroleum ether-ethyl acetate 20:1); IR (CDCI3):2933, 2859, 1726, 1578, 1269, 11.86, 1070, 1013, 824 cm"1; 187 1H NMR (400 MHz, CDCI3) ppm: 7.78 (d, J 0-m = 8.6 Hz, 2H), 7.68 (d, J 0 . M = 8.6 Hz, 2H),4.90 (m, 2H), 2.79 (dd, J 2 A . 3 = 4.4 Hz, J2 A-2B = 14.7 Hz, 1H), 2.58 (dd, J 2 B . 3 = 8.2Hz, J 2 A . 2 B = 14.7 Hz, 1H), 1.72-1.18 (m, 22H), 1.20 (d, Jis-16 = 6.1 Hz, 3H); 1 3 C (50 MHz, CDCI3) ppm: 203.2, 168.4, 136.1, 132.5, 129.3, 129.0, 79.6, 72.2, 41.1, 35.6, 33.5, 26.7, 26.4, 26.1, 25.8, 25.7, 25.6, 24.1, 23.8, 20.1; HRMS (DCI): Calculated for C 2 2H 340 5S 7 9Br (M++1): 489.1310; C 2 2 H 3 4 0 5 S 8 1 Br 491.1268; found: 489.1312; 491.1271. (2S*3S*15S*)-2-Methvl-3-hvdroxv-15-hexadecanolide (122) via alkylation of (3S*15S*)-3-hvdroxv-15-hexadecanolide (120) 0 122 Equimolar amounts of diisopropylamine (0.10 mL, 0.69 mmol) and n-BuLi (0.49 •mL, 0.69 mmol) were stirred in 1.5 mL of THF at 0 °C for 30 minutes in a 10-mL single-necked round-bottom flask. The macrolide 110 (21 mg, 0.08 mmol) 188 dissolved in 1 mL of THF was added dropwise to the LDA solution. After 12 hours of stirring at -78 °C, HMPA (0.11 mL, 0.69 mmol) and Mel (13.4 [il, 0.23 mmol) were injected in quick succession with further stirring for 1 hour at -78 °C. The dry ice-acetone bath was removed and the mixture was poured into aqueous saturated NH4CI and extracted with ether (3x10 mL). The organic layer was washed with aqueous saturated CuS04(2x15 mL), brine (15 mL) and dried over anhydrous MgS04. Concentration of the extracts under reduced pressure, followed by radial chromatography gave unreacted 110 (10.0 mg, 0.037 mmol), 48% and 122 (9.0 mg, 0.03 mmol), 41%. Rf: 0.34 (petroleum ether-ethyl acetate 10:1); IR(CDCI3): 3691, 3607, 3554, 2932, 2858, 1705, 1602, 1456, 1339, 1188, 1126, 1049,827 cm'1; 1H NMR (400 MHz, CDCI3) ppm: 5.00 (m, J 1 5 - i 4 A = 6.7 Hz, J 1 5 - i 4 B = 4.0 Hz, J 1 5 -ie = 6.1 Hz, 1H), 3.51 (m, J 2 . 3 = 2.6 Hz, J S - O H = 10.0 Hz, 1H), 2.78 (bs, 1H), 2.56 (dq, J 2 . 3 = 2.6 Hz J 2 . 1 7 = 7.9 Hz, 1H), 1.27 (d, J 2 . 1 7 = 7.9 Hz, 3H), 1.59-1.27 (m, 22H), 1.19 (d, J 1 5 . 1 6 = 6.7 Hz, 3H); PROTON DECOUPLED 1H NMR (400 MHz, CDCI3): Irradiation at 6 (ppm) 1.19 2.56 2.78 Simplification of signals at 6 (ppm) 5.00 (dd) 3.51 (d) 3.51 (t) Coupling constants (Hz) J l 5 - 1 4 A = 6.7 J 1 5 - 1 4 B = 4.0 J 3 - 0 H = 10.0 J 2 . 3 = 2.6 189 1 3 C NMR (50 MHz, CDCI3) ppm: 176.3, 74.1, 71.1, 43.7, 36.2, 35.9, 29.7, 27.5, 27.4, 27.1, 26.0, 25.6, 25.4, 25.0, 24.5, 20.2, 14.6; LRMS(DCI):285(M++1); HRMS (DCI): Calculated for C17H33O3 (M++1): 285.2430; found: 285.2436; Analysis calculated for C 1 7H320 3: C, 71.79; H, 11.34; found: C, 71.98; H, 11.33. 3-(2'.4,.6,-trichlorobenzene-thiocarbonate)-2-methvl-15-hexadecanolide (125) 125 To a solution of 122 (10.5 mg, 0.038 mmol) in pyridine (3 mL) 2,4,6-trichlorophenyl thiocarbonyl chloride (0.02 g, 0.04 mmol) was added and the resultant reaction mixture was stirred for 2 hours, then poured into 50 mL of aqueous 1 M HCI to quench the reaction. The aqueous layer was extracted with ether (3x40 mL). The combined organic layer was washed with aqueous saturated solution of NaHC0 3 (30 mL), water (30 mL), brine (30 mL) and dried 190 over anhydrous MgS04, followed by radial chromatography using petroleum-ether and ethyl acetate (20:1) to give 125 (12.2 mg, 0.02 mmol) in 62% yield as a colourless oil. Rf: 0.33 (petroleum ether-ethyl acetate 20:1); IR (CDCI3): 2933, 2859, 2300, 2241, 1770, 1727, 1568, 1453, 1235, 1135, 962, 828 cm'1; 1H NMR (400 MHz, CDCI3) ppm: 7.37 (s, 2H), 5.12 (m, 1H), 4.95 (m, 1H), 3.0 (m, 1H)-, 1.71-1.19 (m, 22H), 1.27 (d, J 2 . 1 7 = 7.5 Hz, 3H), 1.19 (d, J15.16= 7.3 Hz, 3H); 1 3 C NMR (50 MHz, CDCI3) ppm: 172.0, 151.1, 142.9, 132.3, 129.7, 128.6, 80.9, 71.9, 42.9, 35.7, 35.6, 29.7, 29.3, 27.3, 27.0, 26.5, 26.0, 25.8, 24.3, 24.0, 20.1, 20.0; 191 2-Deutero-3-hvdroxv-15-hexadecanolide (126) D 126 Equimolar amounts of diisopropylamine(0.10 mL, 0.68 mmol) and /?-BuLi (0.48 mL, 0.68 mmol) were stirred in 1.5 mL of THF at 0 °C for 30 minutes in a 10-mL single-necked round-bottom flask. The macrolide 110 (20 mg, 0.08 mmol) dissolved in 1 mL of THF was added dropwise to the LDA solution. After 12 hours of stirring at -78 °C, D 20 was added. The dry ice-acetone bath was removed and the mixture was poured into aqueous saturated NH4CI and extracted with ether (3x10 mL). The organic layer was washed with aqueous saturated CuS0 4 (2x15 mL), brine (15 mL) and dried over anhydrous MgS04. Concentration of the crude product under reduced pressure, followed by radial chromatography gave 126 (18.0 mg, 0.03 mmol), in 90% yield as a yellow oil. Rf: 0.34 (petroleum ether-ethyl acetate 10:1); 192 IR (CDCI3): 3155, 2931, 2858, 2255, 1801, 1710, 1643, 1469, 1382, 1174, 1097,910 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 5.05 (m, J15-ie = 6.4 Hz, 1H), 3.85 (m, 1H), 2.5-2.6 (m, J 2 . 3 = 5.3 Hz (minor), J 2 . 3 = 4.1 Hz (major), 1H), 1.59-1.17 (m, 22H), 1.19 (d, J 1 5 . 1 6 = 6.4 Hz, 3H); LRMS (El) m/z (relative intensity): 271 (M+, 2), 192 (27), 182 (28), 125 (20), 111 (35), 110 (38), 109 (32); HRMS (El): Calculated for Ci 6H 2 9D03 (M++1): 272.2336, (M+): 271.2257; found: 272.2306, 271.2250. (2S*15S*)-2-Methvl-15-hexadecanolide (123) O 123 To a 10-mL round-bottom flask containing macrolide 125 (12.2 mg, 0.02 mmol) was added freshly distilled toluene (3.0 mL), tris(trimethylsilyl)silane (11.5 |j,L, 0.04 mmol) and a trace of AIBN. The reaction mixture was refluxed for 3 hours 193 and then was cooled to room temperature. The solvent was removed under reduced pressure. The crude oil was purified via radial chromatography using petroleum ether-ethyl acetate (19:1) to give 123 (5.3 mg, 0.014 mmol) in 60% yield. All spectral properties of 123 were identical to those for authentic 123 synthesized earlier in our laboratory.73 2-Methvl-3-oxo-15-hexadecanolide (127) (a) Alkylation of 84 using potassium fe/f-butoxide as base Freshly sublimed potassium te/t-butoxide (30.5 mg, 0.27 mmol) was weighed into a dry flask equipped with a nitrogen inlet and a septum. Freshly distilled fe/t-butanol (3.0 mL) was injected and the macrolide 84 (66.3 mg, 0.25 mmol) O O 127 194 dissolved in 2.0 mL of fe/f-butanol was added dropwise. After 3 hours of refluxing, the reaction mixture was cooled to room temperature and Mel (16.9 |i.L, 0.27 mmol) was injected and further refluxed for 12 hours. The reaction mixture was then poured into aqueous saturated NH4CI and the aqueous layer was extracted with ether (3x20 mL). The organic layer was washed with water, brine and dried over anhydrous MgS04, and then concentrated under reduced pressure. The crude oil was purified via radial chromatography using petroleum ether-ethyl acetate (19:1) to give 127 (45.8 mg, 0.16 mmol) in 65% yield and 8% of dimethylated product 128. The ratio of diastereomers 127 was found to be 2:1 as determined by 1H NMR. Rf: 0.34 (petroleum ether-ethyl acetate 20:1); IR (CDCI3): 3692, 2930, 2858, 1734, 1709, 1602, 1467, 1381, 1200, 1096, 908 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 4.94 (m, J 1 5 . 1 6 = 7.1 Hz, 1H), 3.50-3.41 (two q, 1H), 2.60-2.40 (m, 2H), 1.59-1.43 (m, 2H), 1.32-1.29 (d, J 1 5 - i 6 = 7.1 Hz, 3H), 1.40-1.17 (m, 18H). 1.21-1.18 (d, J 2 . 1 7 = 7.9 Hz, 3H); 1 3 C NMR (50 MHz, CDCI3) ppm: 207, 171, 72.5, 72.4, 53.8, 53.1, 40.9, 40.4, 35.9, 35.5, 27.3, 27.2, 27.1, 26.9, 26.8, 26.2, 26.0, 25.6, 25.2, 24.0, 22.2,22.0,20.3,19.8,13.0,12.5; LRMS (DCI): 283 (M++1); 195 HRMS (DCI): Calculated for C17H30O3 (M+):282.2273, (M++1): 283.2273; found: (Ivf) 282.2140, (M++1): 283.2281; Analysis calculated for C17H30O3: C, 72.3; H, 10.71; found: C, 72.52; H, 10.82. (b) Alkylation of 3-oxo-15-hexadecanolide (84V using ..tetraethvlammonium fluoride To a solution of 84 (7.4 mg, 0.028 mmol) in CH3CI (2 mL), tetraethylammonium fluoride (4.5 mg, 0.03 mmol) was added. The reaction mixture was warmed to 30 °C and methyl iodide (1.9 JIL, 0.03 mmol) was added and the reaction mixture was stirred for 48 hours. The reaction was quenched with addition of water (1 mL). The organic layer was separated. The aqueous layer was extracted with CH3CI (3x 3 mL). The organic layer was washed with water, brine and dried over anhydrous MgSCM, and was then concentrated under reduced pressure. The crude oil was purified via radial chromatography using petroleum ether-ethyl acetate (19:1) to give 127 (4.0 mg, 0.014 mmol) in 50% yield and 34% of 84 (2.5 mg, 0.009 mmol) was recovered. All the spectral properties of this product were identical to 127 obtained via the above alkylation of the monoanion of 84 generated by potassium fe/f-butoxide. 196 Reduction of 2-methvl-3-oxo-15-hexadecanolide (127) to (2S*3S*15S*)-2-methvl-3-hvdroxv-15-hexadecanolide (122) The epimeric mixture of 127 (86.0 mg, 0.31 mmol) were dissolved in ethanol (5.0 mL) and NaBH4 (12 mg, 0.4 mmol) was added and stirred for 1.0 hour at room temperature. Two mL of aqueous 1 M HCI was added to quench the reaction. The reaction mixture was saturated with NaCI and extracted with ether (3x10 mL). The organic layer was washed with water (2x20 mL), brine (20 mL) and dried over anhydrous MgS04. Removal of the solvent, followed by purification via radial chromatography using petroleum ether-ethyl acetate (9:1) gave 122 (75 mg, 0.26 mmol) in 85% yield as a pale yellow oil which had identical spectral properties to 122 synthesized above (page 184). HO O 122 197 2.2-Dimethvl-3-oxo-15-hexadecanolide (128) 128 The macrolide 84 (29.5 mg, 0.11 mmol) was dissolved in 3 mL of dry fe/f-butanol and added dropwise to a solution of freshly sublimed potassium te/f-butoxide (0.037 g, 0.33 mmol). The reaction mixture was refluxed for 3 hours and then cooled to room temperature. Mel (34 \iL, 0.55 mmol) was injected and further refluxed for 1 hour. The reaction was quenched with aqueous 1 M HCI, saturated with sodium chloride and extracted with ether (3x10 mL). The organic layer was washed with brine (2x15 mL), dried over anhydrous MgS0 4 and concentrated under reduced pressure followed by purification via radial chromatography using 1:9 ethyl acetate-petroleum ether solvent mixture to give 128 (25 mg, 0.08 mmol) in 77% yield as a pale yellow oil. Rf: 0.46 (petroleum ether-ethyl acetate 20:1); IR (CDCI3): 2933, 2859, 1732, 1707, 1463, 1382, 1268, 1161, 908 cm"1; 198 1H NMR (400 MHz, CDCI3) ppm: 4.94 (m, J 1 5 . i 4 = 1.7 Hz, J 1 5 . i 6 = 6.1 Hz, 1H), 2.54-2.39 (m, 2H), 1.52-1.18 (m, 20H) 1.33 (s, 3H), 1.32 (s, 3H), 1.19 (d, J,5-16 = 6.1 Hz, 3H); 1 3 C NMR (50 MHz, CDCI3) ppm: 198.0, 173.5, 72.4, 55.8, 37.4, 35.7, 27.3, 27.0, 26.6, 26.1 (2), 25.8, 25.6, 25.3, 22.5, 22.1, 21.8, 19.9, LRMS (DCI): 314 (M++18), 297 (M++1), 296 (M+); HRMS (DCI): Calculated for Ci 8H 3 2 03 (M+): 296.2352; found: 296.2359; Analysis calculated for Ci 8H 320 3: C, 72.93; H, 10.88; found: C, 73.13; H, 10.68. 199 (3S*.15S*)-2.2-Dimethvl-3-hvdroxv-15-hexadecanolide (132) and (3R*15S*)-2.2-Dimethvl-3-hvdroxv-15-hexadecanolide (133) 132 133 (a) Reduction of 128 using NaBH4 To a solution of 128 (16 mg, 0.05 mmol) in 1.0 mL of ethanol at room temperature was added NaBH4 (2.4 mg, 0.06 mmol). After stirring at room temperature for 3 hours, the reaction was quenched with aqueous 1 M HCI and diluted with 15 mL of ether. The organic phase was washed twice with 15 mL brine, dried over anhydrous MgS04, and concentrated under reduced pressure, followed by purification via radial chromatography using 9:1 petroleum ether-ethyl acetate to give 132 (10 mg, 0.03 mmol) and 133 (5 mg, 0.015 mmol) in 94% yield as a pale yellow oils in a ratio of 2:1. 200 132 Rf: 0.29 (petroleum ether-ethyl acetate 20:1); IR (CDCI3): 3691, 3613, 3510, 2932, 2858, 1716, 1691, 1455, 1251, 1126, 1072 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 4.95 (m, J 1 5 - I 4 A = 7.6 Hz, J 1 5 . 1 4 B = 3.7 Hz, J 1 5 - i 6 = 6.4 Hz, 1H), 3.47 (m, J ^ A = 10.1 Hz, J M B = 1.9 Hz, 1H), 2.32 (bs, 1H), 1.56-1.16 (m, 22H), 1.21 (s, 3H), 1.20 (s, 3H), 1.19 (d, J i 5 . 1 6 = 6.4 Hz, 3H); PROTON DECOUPLED 1H NMR (400 MHz, CDCI3): Irradiation at 6 (ppm) 1.19 2.32 Simplification of signals at 6 (ppm) 4.95 (dd) 3.47 (dd) Coupling constants (Hz) Jl5-14A = 7.6 J-I5-14B = 3.7 J 3 - 4 A = 10.1 J3-4B = 1.9 1 3 C NMR (50 MHz, CDCI3) ppm: 177.3, 76.4, 71.2, 47.2, 35.8, 32.6, 29.7, 27.7, 27.0, 25.9 (2), 25.6, 25.5, 25.0, 24.6, 22.7, 21.5, 20.1; LRMS (DCI): 299 (M++1); HRMS (DCI): Calculated for C^H^Os (M+): 298.2508; found 298.2464; Analysis calculated for C 1 8H 340 3: C, 72.44; H, 11.48; found: C, 72.06; H, 11.17. 133 Rf: 0.23 (petroleum ether-ethyl acetate 20:1); 201 IR (CDCI3): 3691, 3623, 356b, 2933, 2860, 2248, 1710, 1453, 1262, 1137, 1072 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 4.95 (m, J15-16 = 6.4 Hz, 1H), 3.59 (m, 1H), 1.67-1.18 (m, 22H), 1.24 (s, 3H), 1.20 (d, J 1 5 - i 6 = 6.4 Hz, 3H), 1.15 (s, 3H); 1 3 C (50 MHz, CDCI3) ppm: 177.2, 76.2, 70.9, 47.1, 36.1, 33.6, 26.7, 26.6, 26.5, 26.3, 26.1, 25.1, 24.5, 24.3, 24.1, 23.5, 20.4, 19.6. (b) Reduction of 128 using L-Selectride and NaBH4 To a solution of 128 (10 mg, 0.03 mmol) in 1.0 mL of dry THF at 0 °C and under a nitrogen atmosphere, was added 0.04 mL (0.04 mmol) of a 1.0 M solution of L-Selectride in THF and the resulting mixture was stirred at 0 °C for 30 minutes. Then NaBH4 (1.5 mg, 0.04 mmol) and ethanol (0.2 mL) were added and the reaction mixture was further stirred for 2 hours at room temperature. The reaction was quenched with 1 mL of 30% hydrogen peroxide and 2 mL of aqueous 1 M HCI. The mixture was stirred for 10 minutes at room temperature and was then diluted with 15 mL of ether and the organic layer was washed with brine (2x15 mL), dried over anhydrous MgS0 4 l and concentrated under reduced pressure followed by radial chromatography using 9:1 petroleum ether-ethyl acetate to give 132 (9 mg, 0.03 mmol) in 89% yield. None of the other diastereomer was detected. 202 (c) (3S*15S^-2.2-Dimethvl-3-hvdroxv-15-hexadecanolide (132) via a methvlation of (2S*.3S*15S*)-2-methvl-3-hvdroxv-15-hexadecanolide (122) LDA was generated from diisopropylamine (0.014 mL, 0.097 mmol) and n-BuLi (0.069 mL, 0.097 mmol) in 1 mL of THF and stirred at 0 °C for 30 minutes in a 10-mL single-necked round-bottom flask. The macrolide 122 (11 mg, 0.04 mmol) was injected into this mixture as a solution in 1 mL of THF and the reaction mixture was stirred for 14 hours at 0 °C. HMPA (0.01 mL, 0.08 mmol) and Mel (4.8 [it, 0.08 mmol) were injected in quick succession and further stirred for 30 minutes at 0 °C and 4 hours at room temperature. The reaction mixture was poured into aqueous saturated NH4CI and extracted with ether (3x20 mL). The combined ether layer was further washed with aqueous saturated CuS0 4, and dried over anhydrous MgS04. Removal of the solvent followed by radial chromatography using 9:1 petroleum ether-ethyl acetate gave 132 (5.1 mg, 0.02 mmol) in 48% yield as a pale yellow oil. 203 (AS* 15S*)-3-Oxo-4-methvl-15-hexadecanolide and (AR*. 15S*)-3-Oxo-4-methvl-15-hexadecanolide (137 and 138) 137 138 Diisopropylamine (0.13 mL, 0.89 mmol) and /7-BuLi (0.56 mL, 0.89 mmol) were injected into 3.0 mL of THF under a nitrogen atmosphere at °0 C and stirred for 30 minutes in a 25-mL single-necked round-bottom flask. The solution was then cooled to -78 °C. Macrolide 84 (95.6 mg, 0.36 mmol) dissolved in 2.0 mL of THF, was added and stirred for 1 hour. Another two equivalents of n-BuLi (0.56 mL, 0.89 mmol) were added and the reaction mixture was stirred for an additional 11 hours. Mel (28.8 \xL, 0.46 mmol) was injected and stirred a further 5 hours. The anion was quenched by pouring the reaction mixture into 50 mL of cold (0 °C) aqueous 1 M HCI. The solution was saturated with sodium chloride and extracted with ether (3x30 mL). The combined ether layer was concentrated under reduced pressure to give a red oil, followed by radial 204 chromatography using 1:19 petroleum ether-ethyl acetate to give 137 (47 mg, 0.17 mmol) and 138 (44 mg, 0.16 mmol) in 91% yield as light yellow oils. 137 Rf: 0.33 (petroleum ether-ethyl acetate 20:1); IR (CDCI3): 2932, 2858, 1738, 1712, 1620, 1455, 1408, 1307, 1255, 1049 cm"1; NMR (400 MHz, CDCI3) ppm: 4.91 (m, J 15-14A _ 9.9 Hz, J 15-14B _ 4.1 Hz, J 15-16 ~ 6.3 Hz, 1H), 3.54 (d, J 2 A . B = 16.0 Hz, 1H), 3.38 (d, J 2 A - B = 16.0 Hz, 1H), 2.61 (m, J4-i7 = 7.0Hz, J 4 . 5 A = 11.7 Hz, J 4 . 5 B = 4.3HZ, 1H), 1.77-1.18 (m, 20 H), 1.22 (d, J15-16 = 6.3 Hz, 3H), 1.07 (d, J 4 . 1 7 = 7 Hz, 3H); PROTON DECOUPLED 1H NMR (400 MHz, CDCI3): Irradiation at 6 (ppm) 1.07 1.22 Simplification of signals at 5 (ppm) 2.61 (dd) 4.91 (dd) Coupling constants (Hz) J4-5A=11.7 J4-5B = 4.3 Jl5-14A = 9.9 Jl5-14B = 4.1 1 3 C NMR (50 MHz, CDCI3) ppm: 208.5, 167.5, 72.4, 48.8, 46.6, 35.6, 32.8, 27.1, 27.06, 26.9 (2), 26.8, 25.6, 25.3, 22.8, 20.1, 16.9; LRMS (El) m/z (relative intensity): 282 (M\ 2), 116 (100); HRMS (El): Calculated for Ci 7 H 3 0 O 3 (M+): 282.2195; found: 282.2189; Analysis calculated for Ci 7H 3 0O 3 : C, 72.28; H, 10.71; found: C, 72.52; H, 10.66. 138 205 Rf: 0.31 (petroleum ether-ethyl acetate 20:1); IR (CDCI3): 3692, 2932, 2858, 1733, 1707, 1603, 1456, 1290 cm-1; 1H NMR (400 MHz, CDCI3) ppm: 4.94 (m, J 1 5 . 1 4 A = 16.9 Hz, J 1 5 - i 4 B = 8.8 Hz, J 1 5 . i 6 = 6.3 Hz, 1H), 3.45 (d, J 2 A - B = 15.6 Hz, 1H), 3.41 (d, J 2 A - B = 15.6 Hz, 1H), 2.70 (m, J 4 - 5 A = 11.2, Hz, 6.8 Hz, 7.0 Hz, 1H), 1.71-1.21 (m, 20 H), 1.22 (d, J 1 5 . 1 6 = 6.3 Hz, 3H), 1.09 (d, J4.17 = 7.0 Hz, 3H); PROTON DECOUPLED 1H NMR (400 MHz, CDCI3): Irradiation at 5 (ppm) 1.09 1.22 Simplification of signals at 6 (ppm) 2.70 (dd) 4.94 (dd) Coupling constants (Hz) J 4-5A=11.2 J 4 -5B = 6.8 Jl5-1 4 A =16.9 J l 5 - 1 4 B = 8.8 1 3 C NMR (50 MHz, CDCI3) ppm: 208.1, 167.3, 72.3, 47.2, 46.1, 35.3, 33.1, 27.2, 26.9, 26.8, 26.7, 25.8, 25.6, 25.4, 23.0, 20.0, 16.6; 2.13-Tetradecandiol (140 and 141) (±)-140 141 206 A solution of 1,8-dibromooctane (139, 3.0 g, 11.1 mmol) in THF (10 mL) was added dropwise to a suspension of magnesium turnings (0.59 g, 24 mmol) in THF (100 mL) in a 250-mL two-necked round-bottom flask equipped with a reflux condenser. The Grignard reagent was initiated by the addition of a small amount of iodine. The resulting complex was stirred under reflux conditions for 20 minutes and then cooled to room temperature. Copper(l) iodide (120 mg) was added to the reaction mixture and stirred for 5 minutes. The reaction mixture was cooled to 0 °C and propylene oxide (1.7 mL, 24.6 mmol) was added dropwise. The solution was further stirred for 2 hours at 0 °C and then room temperature for another 16 hours. Aqueous saturated NH4CI was added to quench the reaction. The mixture was extracted with ether (3x100 mL). The combined ether layer was concentrated under reduced pressure to give a yellow solid, followed by radial chromatography using 1:1 petroleum ether-ethyl acetate to give 140 and 141 (2.26 g, 10.0 mmol) in 90% yield as a white solid. Melting pt.: 41-44 °C; Rf: 0.36 (petroleum ether-ethyl acetate 1:1); IR (CDCI3): 3691, 3613, 2929, 2856, 1807, 1602, 1459, 1381, 1251, 1031, 829 cm"1; 1H NMR (400 MHz, CDCI3) ppm: 3.75 (m, J L 2 = 6.1 Hz, 2H), 1.5-1.1 (m, 16H), 1.14(d, J i . 2 = 6.1 Hz,6H); 1 3 C NMR (50 MHz, CDCI3) ppm: 68.1, 39.3, 29.6, 29.56, 29.5, 25.7, 23.5; 207 LRMS(DCI):248(M++18); HRMS (DCI): Calculated for C14H27O2 (M++1): 231.2324; found: 231.2319; (2S.13SV2. 13-Tetradecandiol (140) A solution of 1,8-dibromooctane (139, 2.3 g, 8.5 mmol) in THF (10 mL) was added dropwise to a suspension of magnesium turnings (0.42 g, 17 mmol) in THF (50 mL) in a two-necked round-bottom flask equipped with a reflux condenser. The Grignard reagent was initiated by the addition of a small amount of iodine. The resulting complex was stirred under reflux for 20 minutes and then cooled to room temperature. Copper(l) iodide (60 mg) was added to the reaction mixture and stirred for 5 minutes. The reaction mixture was cooled to 0 °C and (S)-propylene oxide (1.2 mL, 17.2 mmol) was added dropwise. The solution was further stirred for 2 hours at 0 °C and then at room temperature for another 16 hours. Aqueous saturated NH4CI was added to quench the reaction. The solution was extracted with ether (3x50 mL). The combined ether layer was concentrated under reduced pressure to give a yellow solid, followed by radial chromatography using 1:1 petroleum ether-ethyl acetate to give (2S,11S)-140 (1.76 g, 7.8 mmol) in 92% yield as a white solid. The spectral properties for this compound were identical to the mixture of 140 and 141 obtained above. 208 Baever-Villiqer oxidation of 138 Trifluoroacetic anhydride (0.010 mL, 0.15 mmol) was added dropwise to a stirred mixture of urea hydrogen peroxide (10.1 mg, 0.15 mmol), Na 2HP0 4 (24.2 mg, 0.17 mmol), 138 (6.9 mg, 0.024 mmol) in CH2CI2 (3 mL) at 0 °C. The mixture was allowed to warm to room temperature and stirred overnight. An aqueous saturated solution of NaHC0 3 (2 mL) was added to neutralize the acids present and the aqueous layer was extracted with CH2CI2 (3x 10 mL). The combined organic layers were washed with water (20 mL), brine (20 mL) and dried over anhydrous MgS0 4. The solvent was removed and followed by radial chromatography using 1:1 petroleum ether-ethyl acetate to give 141 (3.3 mg, 0.014 mmol) in 58% yield. The spectral properties for this compound were identical to the mixture of 140 and 141 obtained above. 2,13-Dibenzovloxvtetradecane (142 and 143) OCOPh OCOPh OCOPh OHCOPh (±)-142 143 A 25-mL single-necked round-bottom flask equipped with a nitrogen inlet was charged with 140 and 141 (0.1 g, 0.4 mmol), benzoyl chloride (0.21 mL, 1.8 209 mmol), and pyridine (10 mL). The resulting solution was stirred for 30 minutes at room temperature, then aqueous 1 M HCI (10 mL) was added to quench the reaction. The aqueous layer was extracted with ether (3x25 mL). The combined organic extracts were washed with water (50 mL), brine (50 mL), then dried over anhydrous magnesium sulfate. The combined ether layer was concentrated under reduced pressure to give a red oil, followed by radial chromatography using 1:19 petroleum ether-ethyl acetate to give 142 and 143 (0.2 g, 0.4 mmol) in 90% yield as a light yellow oil. Rf: 0.44 (petroleum ether-ethyl acetate 20:1); IR(CDCI 3 ) : 2931,2855, 1707, 1585, 1451, 1355, 1315, 1280, 1118, 1070, 1026 cm"1; 1 H NMR (400 MHz, CDCI 3) ppm: 8.1-7.4 (m, 10H), 5.12 (m, 2H), 1,7-1.15 (m, 16H), 1.38 (d, J 1 . 2 = 6 .3Hz, 6H); 1 3 C NMR (50 MHz, CDCI 3) ppm: 166.2, 132.6, 131.0, 129.5, 128.2, 71.7, 36.1, 29.5, 29.2, 25.4, 20.1; LRMS (El) m/z (relative intensity): 438 (M+, 0.3), 410 (M + , 0.1), 194 (38), 123 (97), 105 (100); HRMS (El): Calculated for C28H38O4 (M+): 438.2770; found: 438.2778; HPLC: Flow rate: 0.6 mL/minute with methanol as eluant; peaks at 9.3, 10.1 and 12.3 minutes in a 1:2:1 ratio. 210 (2S. 13S)-2.13-Dibenzovloxvtetradecane (142) A 10 mL single -necked round bottom flask equipped with a nitrogen inlet was charged with 140 (0.050 g, 0.21 mmol), benzoyl chloride (0.10 mL, 0.88 mmol), and pyridine (3 mL). The resulting solution was stirred for 30 minutes at room temperature, then aqueous 1 M HCI (5 mL) was added to quench the reaction. The aqueous layer was extracted with ether (3x15 mL). The combined organic extracts were washed with water (20 mL), brine (20 mL), then dried over anhydrous magnesium sulfate. The combined ether layer was concentrated under reduced pressure to give a red oil, followed by radial chromatography using 1:19 petroleum ether-ethyl acetate to give (2S,13S)-142 (0.08 g, 0.02 mmol) in 93% yield as a light yellow oil. All spectral properties were identical to those of the mixture 142 and 143 shown above. The HPLC trace on the Chiralpak OP (+) column was different from that of 142 and 143. HPLC: Flow rate: 0.6 mL/minute with methanol as eluant; peak at 9.3 minutes. 211 Phenyl 15-hvdroxv-4-methvl-3-oxo-hexadecanoate (145) 144 A 2-necked 10-mL round-bottom flask equipped with a reflux condenser was charged with 138 (3.2 mg, 0.011 mmol), benzyl alcohol (3.1 p.L, 0.033 mmol), a trace of DMAP and 5 mL of toluene. The resultant reaction mixture was refluxed for 6 days. Aqueous saturated NH4CI (3 mL) was added to quench the reaction. The organic layer was separated and the aqueous layer was extracted with ether (3x5 mL). The combined ether layer was washed with 20 mL of brine, and dried over anhydrous MgS04. The solvent was removed under reduced pressure and the crude product 144 (3.5 mg, 0.009 mmol) was used in next reaction. 212 3-Methvl-2-oxo-pentadecan-14-ol (146) OH O 145 Benzyl ester 144 (3.5 mg, 0.009 mmol) and a trace of Pd/C (10%) in ethanol (2 mL) was stirred under a H 2 atmosphere at room temperature overnight. Celite was added, the mixture was filtered and concentrated under reduced pressure to give 145 (2.1 mg, 0.008 mmol). Compound 145 was used in the next step without purification. 13-Hvdroxv-2-methvl ethanoate (146) OH O 146 Trifluoroacetic anhydride (7.2 \xL, 0.09 mmol) was added dropwise to a stirred mixture of urea hydrogen peroxide (8.8 mg, 0.09 mmol), Na 2HP0 4 (20.1 mg, 0.11 mmol) and 145 (2.1 mg, 0.008 mmol) in CH2CI2 (3 mL) at 0 °C. The mixture was 213 allowed to warm to room temperature and stirred overnight. An aqueous saturated solution of NaHC0 3 (2 mL) was added to neutralize the acids present and the aqueous layer was extracted with CH2CI2 (3x 10 mL). The combined organic layers were washed with water (20 mL), brine (20 mL) and dried over anhydrous MgS04. The solvent was removed to give 146 (2.2 mg, 0.008 mmol). Ester 146 was hydrolyzed by stirring in an aqueous 10% NaOH solution for 1 hour to give 2,13-tetradecandiol which was converted into the dibenzoates and analyzed as above. 214 REFERENCES AND FOOTNOTES 1. Ruzicka, L. Helv. Chim. Acta 1926, 9, 1008. 2. Kerschbaum, M. Ber. Dtsc. 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Tetrahedron Lett. 1989, 30, 2619. 98. (a) Seebach, D. Modern Synthetic Methods 1986, Scheffold, R (Ed.); Springer-Verlag; Berlin, Heidelberg, New York, Tokyo, (b) Downham, R.; Kim, K. S.; Ley, S. V.; Woods, M. Tetrahedron Lett. 1994, 35, 769. 99. Clark, J. H.; Miller, J. M. J. Chem. Soc. Chem. Comm. 1977, 64. 100. Taber, D. F.; Amedio, J. C. Jr.; Patel, V. K. J. Org. Chem. 1985, 50, 3618. 101. Still, W. C ; Mohammadi, F.; Richards, N. G. J.; Guida, W. C ; Liskamp, R.; Lipton, M.; Caufield, C ; Chang, G.; Hendricksen, T. Macromodel V 3.5 & 4.5, Department of Chemistry, Columbia University, New York. 102. Chang, J.; Wayne, G. C ; Still, W. C. J. Am. Chem. Soc. 1989, 111, 4379. 103. Still, W. C. Curr. Trends. Org. Synth. Proc. Int. Conf. 4th 1983, 233. 104. Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals; Third Edition; Permagon Press: Toronto, 1988. 105. This value was calculated from the data on cycloalkanes in Table IV of Lii, J.; Allinger, N. L. J. Am. Chem. Soc. 1989, 111, 8566. 106. Allinger, N. L. J. Am. Chem. Soc. 1977, 99, 8127. 107. Allinger, N. L; Zhu, Z. S.; Chen, K. J. Am. Chem. Soc. 1992, 774, 6121. 108. Brown, J. H.; Bushweller, H. C. J. Am. Chem. Soc. 1995, 117, 12567. 109. Ounsworth, J. Ph.D. Thesis, University of British Columbia, January 1985. 110. These compounds were synthesized by Gomez, O. F. in Department of Chemistry, University of British Columbia. SPECTRAL APPENDIX 63 64 T 1 ! 1 I 1 - 1 1 1 ' I 1 1 I 1 1 3 2 0 0 2 4 - 0 0 1 6 0 0 8 0 0 W a v e n u m b e r ( c m — 1 ) 65 225 226 1 O - ' o -1 1 I 1 1 I 1 1 I I I I 1 1 I I 4 0 0 0 3 2 0 0 2 4 0 0 1 6 0 0 B O O W a v e n u m b e r ( c m — 1 ) 227 229 230 9 5 4 W o v e n u m b e r ( c m — 1 ) 231 1 5 - I A O O O 3 2 0 0 2 4 0 0 1 6 0 0 B O O Wave n u m b e r ( c m — 1 ) 232 233 234 235 OTB DMS I i i i | i i i | i i i | i i i | i i i | i . 4000. MOO aOO. BOO. 1600. 1000. CM-i 236 238 7 6 i 4 J i I (pent} > 1 1 1 1 1 1 1 r — i 1 | i I I l i i i I i . 4000- MOO. MOO. BOO. ON. 1000. OH 239 E p 9 0 -f B O T O -6 0 -5 0 -A O 3 0 2 0 1 O H o A : i f " !QO 3 2 0 0 2 A O O 1 6 0 0 W o v e n u m b e r ( c m — 1 ) B O O 240 12.1B (ppm) r n ir 241 243 OCOPh OCOPh 99 & 100 244 245 A - O O O -32*00 2 A O D 1 . 6 0 0 B O O W o v e n u m b e r ( c m — 1 ) 246 247 250 4 0 0 0 - 3 2 0 0 2 4 0 0 1 6 0 0 B O O W a v e n u m b e r ( c m — 1 ) 252 253 254 255 258 •fi-000 3 2 0 0 2 4 0 0 1 6 0 0 B O O W o v e n u m b e r ( c m — 1 ) 259 261 262 

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