Copper-catalyzed direct regioselective C5-H alkylation reactions of functionalized indoles with α-diazomalonates.

Functionalization of the pyrrole nucleus in indoles has been extensively investigated, whereas benzenoid ring functionalization studies remain scarce. Advances in direct C-H functionalization have been hindered by the inherent low reactivity and need for precise control of regioselectivity. Herein, we developed regioselective C5-H alkylation reactions of indoles bearing carbonyl functionalities at the C3 position using copper-carbene species. This methodology regioselectively affords functionalized heteroarenes bearing synthetically useful structural motifs characteristic of bioactive molecules and natural products. Experimental and computational mechanistic findings underscored the pivotal importance of the copper catalyst system and rationalized the origin of regioselectivity.