Chirality transfer in Brook rearrangement-mediated SE2′ solvolytic protonation and its use in estimation of the propensity for racemization of the α-lithiocarbanions of the substituents

Chirality transfer from an α-silylalcohol to α-carbmoyloxy- and α-siloxyallyl-carbanions was investigated using a Brook rearrangement-mediated SE2′ protonation in γ-carbamoyloxy- and γ-siloxy-α-silylallyl alcohols. We proposed a hypothesis that the reaction proceeds along one of two pathways that involves (1) a concerted protonation of a silicate intermediate and (2) a concerted lithiation of the intermediate followed by protonation with retention or by protonation after racemization. Comparison of the extent of the chirality transfer provides a new method for semi-quantitative evaluation of the propensity for racemization of lithiocarbanions next to a conjugative electron-withdrawing group.