Chirality Transfer In Brook Rearrangement-Mediated S(E)2 ' Solvolytic Protonation And Its Use In Estimation Of The Propensity For Racemization Of The Alpha-Lithiocarbanions Of The Substituents

Chirality transfer from an alpha-silylalcohol to alpha-carbmoyloxy- and alpha-siloxyallyl-carbanions was investigated using a Brook rearrangement-mediated S(E)2' protonation in gamma-carbamoyloxy- and gamma-siloxy-alpha-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. (C) 2013 Elsevier Ltd. All rights reserved.