Synthesis of (Z)-Allylsilanes by Cu-Catalyzed Regioselective Protosilylation of Allenes via a Single-Electron Process

Abstract

Hydrosilylation of allenes has gained prominence as an economically viable method for preparing vinylsilanes or allylsilanes. However, development of transition metal (TM)-catalyzed hydrosilylation remains challenging owing to the difficulty in controlling the regioselectivity and stereoselectivity. Specifically, access to (Z)-allylsilanes via first-row TM-catalyzed hydrosilylation is limited by the lack of mechanistic diversity, indicating the need for unprecedented approaches to achieve this valuable yet underexplored chemical space. We herein present the Cu-catalyzed protosilylation of allenes in either organic solvent or water, which affords (Z)-allylsilanes in high yields, with up to >98:2 regioselectivity and (Z)-selectivity. In contrast to conventional TM-catalyzed hydrosilylation or Cu-catalyzed protosilylation, our process involves a single-electron pathway for inserting Cu-SiMe2Ph into the allene. Radical trap experiments and systematic computational studies support the proposed mechanism. Our method is gram-scalable, and the synthetic utility is demonstrated by the preparation of deuterium-incorporated (Z)-allylsilanes through reactions in D2O.