Metal-Free Double Csp2-H Bond Functionalization: Strategy for Synthesizing Benzo[ a]carbazoles from 2-Arylindoles and Acetophenones/Alkynes.

A metal-free strategy for the synthesis of benzocarbazoles from 2-arylindoles and aryl ketones is developed. Various 2-aryl-3-vinyl-indoles were generated in situ through dehydrative condensation of aryl ketones and indoles. These key intermediates could be selectively converted into the corresponding benzo[ a]carbazoles via a direct cyclization process between two Csp2-H bonds. Furthermore, terminal alkynes also could be used as the versatile C2 source to afford the corresponding products in good yields.