Chem. Rev. 1997, 97, 2341−2372 2341 Asymmetric Ylide Reactions: Epoxidation, Cyclopropanation, Aziridination, Olefination, and Rearrangement† An-Hu Li and Li-Xin Dai* Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, China Varinder K. Aggarwal Department of Chemistry, Dainton Building, The University of Sheffield, Sheffield S3 7HF, The United Kingdom Received March 10, 1997 (Revised Manuscript Received May 28, 1997) Contents Scheme 1 I. Introduction 2341 II. Asymmetric Epoxidations 2342 A. Reagent-Controlled Asymmetric Epoxidations 2342 1. Chiral Aminosulfoxonium Ylides 2343 2. Chiral Sulfonium Ylides 2343 3. Chiral Arsonium Ylides 2346 4. Other Related Reagents 2347 B. Substrate-Controlled Asymmetric Epoxidations 2347 C. Related Reactions 2349 III. Asymmetric Cyclopropanations 2350 A. Reagent-Controlled Asymmetric 2351 Cyclopropanations 1. Chiral Aminosulfoxonium Ylides 2351 2. Other Ylides and Related Reagents 2351 B. Substrate-Controlled Asymmetric 2352 Cyclopropanations 1. Chiral R,â-Unsaturated Bicyclic 2352 γ-Lactams 2. L-Tartaric Acid- and 2354 D-Glyceraldehyde-Derived R,â-Unsaturated Esters 3. Other Chiral R,â-Unsaturated Compounds 2355 IV. Asymmetric Aziridinations 2356 A. Reagent-Controlled Asymmetric Aziridinations 2356 only realized after the birth of Wittig reaction in B. Substrate-Controlled Asymmetric 2357 1953.1 Since then, the chemistry of ylides grew Aziridinations rapidly and they have now become powerful and V. Asymmetric Rearrangements 2358 versatile synthetic tools in the arsenal of organic A. [2,3]-σ-Rearrangements 2358 chemists. In addition to the synthetically important 1. Allylic and Propargylic Sulfonium and 2358 phosphonium2 and sulfonium3 ylides, ylides of Oxonium Ylides other heteroatoms,4 namely ammonium,5 azo- 2. Allylic Ammonium Ylides 2362 methine,6 pyridinium,7 nitrile,8 aminosulfoxonium,9 B. Other Rearrangements 2363 thiophenium,10 thiocarbonyl,6c,6f carbonyl,8,11 As,12 VI. Asymmetric Olefinations 2367 Sb,12a,b,13 Bi,12a,b Se,14 Te,14a,15 Ge,16 Sn,16 and I17 have A. Desymmetrization 2367 been developed and reviewed in recent years. B. Kinetic and Dynamic Kinetic Resolutions of 2368 An ylide can be viewed as a special carbanion, Racemic Carbonyl Compounds which bears a neighboring positively charged het- C. Preparation of Chiral Allenes 2369 eroatom. Ylides undergo three types of reactions: VII. Concluding Remarks 2369 olefination, cyclization to a three-membered ring VIII. Acknowledgments 2369 (epoxidation, cyclopropanation or aziridination), and IX. References 2370 rearrangement reactions ([2,3]-σ-rearrangement or Stevens rearrangement) as shown in Scheme 1. The reaction of an ylide with an electrophilic carbon atom I. Introduction of a CdX(X)O, C, N) bond (carbonyl compounds, Although the first ylide appeared as early as the † Dedicated to Professor Yao-Zeng Huang on the occasion of his 1900s, the recognition of these structurally interest- 85th birthday and for his significant contributions to the ylide ing compounds as synthetically useful reagents was chemistry. S0009-2665(96)00411-6 CCC: $28.00 © 1997 American Chemical Society 2342 Chemical Reviews, 1997, Vol. 97, No. 6 Li et al. An-Hu Li was born in Sichuan Province, China, in 1968. He received his Varinder Kumar Aggarwal was born in Kalianpur (a small village in the B.A. (1990) from Sichuan Normal University, M.S. (1993) from Lanzhou state of Punjab) in North India in 1961 and emigrated to the United Institute of Chemical Physics, Chinese Academy of Sciences, and Ph.D. Kingdom in 1963. He received his B.A. (1983) and Ph.D. (1986) from (1996) from SIOC, the last under the guidance of Professor Li-Xin Dai. Cambridge University, the latter under the guidance of Dr. Stuart Warren. He has been a research assistant in Professor Dai’s group at SIOC for He was subsequently awarded a Harkness Fellowship and carried out one year since receiving his Ph.D. degree and is now in Dr. Kenneth A. postdoctoral work with Professor Gilbert Stork at Columbia University, Jacobson’s group at NIDDK/NIH, Bethesda, MD, for his postdoctoral NY (1986−1988). He returned to a lectureship at Bath University and in research. His research interests are in synthetic methodology, asymmetric 1991 moved to Sheffield University where he is currently Reader in synthesis, and ylide chemistry. Chemistry. His research interests are in synthetic organic chemistry and asymmetric synthesis. II. Asymmetric Epoxidations The notable biological significance20 and various chemical transformations21 of nonracemic epoxides make them one of the most useful synthetic inter- mediates.22 They can be prepared by either enanti- oselective oxidation of a prochiral CdC bond (route a) or by enantioselective alkylidenation of a prochiral CdO bond, such as via an ylide, carbene, or a Darzens reaction (route b) (Scheme 2). Although the Scheme 2 Li-Xin Dai was born in Beijing, China, in 1924. He received his B.A. from Zhejiang University in 1947. He has been assistant professor, associate professor, and full professor of Shanghai Institute of Organic Chemistry (SIOC) since 1953 and was elected as a Member of Chinese Academy of Sciences in 1993. He is now the Vice President of the Academic Committee of SIOC and the President of the Academic Committee of Laboratory of Organometallic Chemistry, Chinese Academy of Sciences. His research interests are focusing on synthetic methodology and asymmetric synthesis. Michael acceptors or imines) gives a betaine or oxidation method has proved overwhelmingly suc- oxetane intermediate. From this intermediate, elimi- cessful,23 the structural requirements of the sub- nation of the heteroatom-containing group can occur strates are a limiting prerequisite: the Sharpless in either one of two different modes resulting in asymmetric epoxidation23a requires allylic alcohols; cyclization or olefination. the Jacobsen method23b only works well with cis The exploration of asymmetric ylide reactions using double bonds; and the dioxirane method good for 23c-e a chiral ylide or a chiral CdX compound began in some trans olefins. The ylide route provides an the early 1960s, and many results have been reported alternative nonoxidative approach to prepare opti- in the field of asymmetric reactions via an ylide route cally active epoxides and many results have appeared over the last 30 years. Although several related in recent years. These will be discussed in two summaries were documented in specialized areas, parts: reagent-controlled and substrate-controlled like cyclopropanation,9,18 epoxidation,9 and [2,3]-σ- ylide asymmetric epoxidations. rearrangement,19 a comprehensive review on asym- metric ylide reaction has not appeared yet. The A. Reagent-Controlled Asymmetric Epoxidations present review aims to summarize the recent work The reaction of a chiral ylide reagent with an in the field of asymmetric ylide reactions, with achiral aldehyde or ketone will give a chiral epoxide respect to epoxidations, cyclopropanations, aziridi- with the recovery of chiral ylide precursor, which can nations, [2,3]-σ-rearrangements, and olefinations. usually be reconverted into the ylide reagent (Scheme Asymmetric Ylide Reactions Chemical Reviews, 1997, Vol. 97, No. 6 2343 Scheme 3 Scheme 6 3). The intermediates used in asymmetric epoxida- tion include sulfonium, aminosulfoxonium, and ar- sonium ylides. Most work has centered around the use of sulfonium ylides and excellent results have been obtained when these intermediates were used. 1. Chiral Aminosulfoxonium Ylides A. W. Johnson24 first showed that the sulfonium Scheme 7 ylides could be used to prepare oxiranes. While it is questionable whether tetrahedral sulfonium ylides can racemize,25,26 there is no dispute about the configurational stability of aminosulfoxonium ylides. Carl Johnson first prepared enantiomerically pure ylide (R)-(-)-3 starting from sulfoxide (R)-(+)-1 and when reacted with benzaldehyde gave (R)-styrene oxide in 20% ee (Scheme 4).9,27-30 Reaction of ylide Scheme 4 cyclopropane was formed. In contrast, treatment of sulfide 11 with MeI followed by base gave styrene oxide in 90% ee. As alkylation of sulfide 11 gave a mixture of diastereomers; reverse betaine formation would have produced a mixture of enantiomeric ylides which could not have produced such high levels of enantiomeric excess. It was therefore concluded that the intermediate betaine from sulfonium ylides was formed irreversibly. Although asymmetric epoxidations using amino- sulfoxonium ylides have not been extensively ex- plored, the work shown above demonstrated for the 4 with heptaldehyde gave the corresponding epoxide first time that nonracemic epoxides could be obtained with opposite enantioselectivity as expected.27,28 The via chiral ylides. mechanism of epoxidation was investigated. Assum- ing a two-step mechanism for epoxidation, ylides can 2. Chiral Sulfonium Ylides react reversibly or irreversibly with carbonyl com- pounds (step 1) prior to irreversible ring closure (step The relative ease of preparation and versatility in 2) (Scheme 5). To probe whether ylide additions to epoxidation reactions of chiral sulfonium ylides make them the more useful ones than aminosulfoxonium Scheme 5 ylides in the preparation of nonracemic epoxides. Sulfonium salts and their corresponding ylides are tetrahedral and are thus capable of exhibiting optical activity.25,26 Sulfonium salts can racemize by inver- sion (and other mechanisms), but the barrier is relatively high and