A cobalt-catalyzed annulation of the C(sp²)—H/N—H bond of 3-indolecarboxamides with alkynes assisted by 8-aminoquinoline is reported for the preparation of γ-carbolinones. The research results indicated that under the optimal reaction conditions, the isolated yield was up to 90% with Co(acac)₂ (10 mol%) as catalyst, Mn(acac)₃ (1.0 equiv.) as oxidant, NaOPiv (2.0 equiv.) as base, trifluoroethanol (2.0 mL) as solvent at 120 ℃ for 24 h. The protocol has a broad scope for alkynes. Both 1,4-diarylbuta-1,3-diynes and dialkyl diynes could react with N-(quinolin-8-yl)-1H-indole-3-carboxamide, giving the desired products in moderate to good yield. It was noteworthy that terminal and internal alkynes were found to be applicable to this transformation, affording the γ-carbolinones in good yield and high selectivity. This method has the advantages of applying cheap and commercially available cobalt and manganese salts as the catalytic system, requiring no additional ligands and indole nitrogen protecting groups, providing a new method for the synthesis of γ-carbolinone compounds with wide application value.

Key words: cobalt-catalysis, indole carboxamide, alkynes, [4+2] annulation, γ-carbolinones