Highly Efficient Access to Both Geometric Isomers of Silyl Enol Ethers: Sequential 1,2-Brook/Wittig Reactions

Novel sequential 1,2-Brook/Wittig reactions were developed for the preparation of silyl enol ethers. This method enables highly selective preparation of both geometric isomers of glyoxylate silyl enol ethers, using aldehydes (E-selective) and tosylimines (Z-selective) as a Wittig electrophile. The salt-free conditions of this reaction system are likely to be advantageous for switching the selectivity. The optimal reaction conditions and generality of the reaction were investigated, and plausible explanations for the observed selectivity were also discussed.