Turning on Imine Photoreactivity: Ambiphilic BICAAC-Directed C─N Bond Formation

Abstract

Herein, we report that bicyclic (alkyl)(amino) carbene (BICAAC), by virtue of its superior ambiphilicity, can emulate the role of transition metals for the borrowing hydrogen (BH) reaction. We prove this carbene-driven BH reaction by choosing the N-alkylation reaction of amines using a variety of alcohols as alkylating agents. During the process, alcohol is dehydrogenated by a proton and hydride transfer in a concerted, asynchronous process, where the stripped hydrogen is stored on the carbene carbon in the form of BICAAC-H₂ (1^H,H). The overall process is photo-thermal in nature, where the in situ generated imine needs photoactivation before being reduced by a mild reductant. The photochemically activated α-amino radical conducts hydrogen atom transfer reactions from 1^H,H so that imine hydrogenation can be completed. This process showcases the power of a carbon center, a main group element, in steering the full BH catalytic cycle.