Carbene-Catalyzed Construction of Carbazoles from Enals and 2-Methyl-3-oxoacetate Indoles.

Direct and rapid construction of carbazoles has been successfully developed via carbene-catalyzed oxidative formal [4 + 2] annulation of enals with 2-methyl-3-oxoacetate indoles. This metal-free reaction features a broad substrate scope, features good functional-group tolerance, proceeds under mild conditions, and can be easily scaled up.