Tandem Base-Promoted Ring-Opening/Brook Rearrangement/Allylic Alkylation of O-Silyl Cyanohydrins of β-Silyl-α,β-epoxyaldehyde: Scope and Mechanism

Metalated O-silyl cyanohydrins of β-silyl-α,β -epoxyaldehyde have been found to serve as functionalized homoenolate equivalents by a tandem sequence involving base-promoted ring opening of the epoxide, Brook rearrangement, and alkylation of the resulting allylic anion. On the basis of mechanistic studies involving competitive experiments using the diastereomeric cyanohydrins, we propose a reaction pathway involving a silicate intermediate 36 formed by a concerted process via an anti-opening of the epoxide followed by the formation of an O-Si bond.