エポキシシラン転位の発見とその合成反応への展開

抄録

  O-Silyl cyanohydrins of β-silyl-α,β-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 γ-p-toluenesulfonyl-α,β-epoxysilane with alkyl halides and aldehydes followed by treatment with n-Bu₄NF, which affords α,β-unsaturated aldehydes (2) reaction of γ-phosphonio-α,β-epoxysilane with aldehydes, which affords dienol silyl ether derivatives (3) reaction of an enoate bearing an eposysilane moiety at the α-position with lithium enolate of 2-chloroacetamide, which affords highly functionalized cyclopropane derivatives.