Cascade of C(sp 2 )-H Addition to Carbonyl and C(sp 2 )-CN/C(sp 2 )-H Coupling Enabled by Brønsted Acid: Construction of Benzo[ a ]carbazole Frameworks.

Herein, we report an unprecedented cascade reaction of C(sp 2 )-H addition to carbonyl and the C(sp 2 )-CN/C(sp 2 )-H coupling of 2-(2-oxo-2-arylethyl)benzonitriles with indoles enabled by commercially available TsOH·H 2 O. The protocol represents the first metal-free C(sp 2 )-CN/C(sp 2 )-H coupling, affording a new route for the synthesis of various benzo[ a ]carbazole derivatives with a broad substrate scope, high yields, and simple conditions.