Recent advances in transition-metal-catalyzed carbene insertion to C–H bonds

Abstract

C–H functionalization has been emerging as a powerful method to establish carbon–carbon and carbon–heteroatom bonds. Many efforts have been devoted to transition-metal-catalyzed direct transformations of C–H bonds. Metal carbenes generated in situ from transition-metal compounds and diazo or its equivalents are usually applied as the transient reactive intermediates to furnish a catalytic cycle for new C–C and C–X bond formation. Using this strategy compounds from unactivated simple alkanes to complex molecules can be further functionalized or transformed to multi-functionalized compounds. In this area, transition-metal-catalyzed carbene insertion to C–H bonds has been paid continuous attention. Diverse catalyst design strategies, synthetic methods, and potential applications have been developed. This critical review will summarize the advance in transition-metal-catalyzed carbene insertion to C–H bonds dated up to July 2021, by the categories of C–H bonds from aliphatic C(sp³)–H, aryl (aromatic) C(sp²)–H, heteroaryl (heteroaromatic) C(sp²)–H bonds, alkenyl C(sp²)–H, and alkynyl C(sp)–H, as well as asymmetric carbene insertion to C–H bonds, and more coverage will be given to the recent work. Due to the rapid development of the C–H functionalization area, future directions in this topic are also discussed. This review will give the authors an overview of carbene insertion chemistry in C–H functionalization with focus on the catalytic systems and synthetic applications in C–C bond formation.