Substrate-controlled divergent synthesis of substituted carbazoles through a cascade reaction of 2-alkenylindoles with α,β-unsaturated ketones.

Substituted carbazoles are valuable N-heterocycles for synthesizing biologically relevant compounds. We established the phosphomolybdic acid/ionic liquid-promoted divergent synthesis of substituted carbazoles, leveraging readily available 2-alkenylindoles and unsaturated ketones as starting materials. Switchable product selectivity was achieved using different unsaturated ketones. This protocol features transition-metal-free conditions, broad substrate scope, and excellent scalability. In addition, a plausible reaction mechanism is proposed based on control and real-time NMR experiments.