Enantioconvergent Deacylative Functionalization toward α-Quaternary Nitriles

Abstract

The use of readily available prochiral or racemic quaternary carbons to access enantioenriched ones offers a promising alternative to conventional synthesis from tertiary or planar substrates. Unlike desymmetrization, which modifies an existing substituent with limited reactivity, a functional group swap can install a new motif, which is structurally distinct and nonderivable from the replaced group. However, achieving enantioconvergence in these quaternary-to-quaternary transformations is challenging, especially for acyclic stereocenters. Here, we report that acyl groups of β-ketonitriles can be stereoselectively replaced by allyl, propargyl, or benzyl moieties using easily accessible alcohols under palladium catalysis. The deacylative functionalization proceeds through a retro-Claisen-type elimination of ketonitrile with alkoxide and the absence of diastereoisomerism in the resulting ketenimine anion assists the subsequent asymmetric addition. Together with the pair of α-substituents, the retained nitrile and the incoming alkyl motif instill significant derivatization potential into the enantioenriched quaternary stereocenters.