[Development and synthetic application of epoxysilane rearrangement].
O-Silyl cyanohydrins of beta-silyl-alpha,beta-epoxyaldehyde can function as a highly functionalized homoenolate equivalent via a tandem sequence involving base-promoted ring opening, Brook rearrangement, and alkylation at the allylic position. We named this rearrangement epoxysilane rearrangement. Based on results of mechanistic studies involving competitive experiments using diastereomeric cyanohydrins, we propose a reaction pathway involving a silicate intermediate formed by a concerted process via an anti-opening of the epoxide followed by the formation of an O-Si bond. Moreover, results of mechanistic studies on the rearrangement led to a conceptually novel approach to the chirality transfer in which epoxide chirality can be transferred into carbanion. We demonstrate the usefulness of the rearrangement through application to the following reactions: (1) reaction of gamma-p-toluenesulfonyl-alpha,beta-epoxysilane with alkyl halides and aldehydes followed by treatment with n-Bu4NF, which affords alpha,beta-unsaturated aldehydes (2) reaction of gamma-phosphonio-alpha,beta-epoxysilane with aldehydes, which affords dienol silyl ether derivatives (3) reaction of an enoate bearing an eposysilane moiety at the alpha-position with lithium enolate of 2-chloroacetamide, which affords highly functionalized cyclopropane derivatives.
Sasaki
Michiko
M
Graduate School of Medical Sciences, Hiroshima University, Hiroshima, Japan. misasaki@hiroshima-u.ac.jp
D000478:Alkylation; D002244:Carbon / Q000737:chemistry; D002625:Chemistry, Organic; D003500:Cyclization; D004852:Epoxy Compounds / Q000737:chemistry*; D006801:Humans; D006844:Hydrocarbons, Cyclic / Q000138:chemical synthesis*; D055601:Organic Chemistry Phenomena; D012821:Silanes / Q000737:chemistry*; D013237:Stereoisomerism
D004852:Epoxy Compounds; D006844:Hydrocarbons, Cyclic; D012821:Silanes; D002244:Carbon