A transition-metal-free divergent cyclization of ynamides with indolones is presented, enabling the efficient synthesis of spiroindolones and indole-fused seven-membered rings. The site-selective cyclization can be controlled by different reaction conditions. Under base-promoted conditions, the C3-spirocyclization of 2-indolones takes place and affords spiroindolones. In the presence of acid catalyst, the selective O-cyclization of 2-indolones occurs to give indole-fused seven- membered ring products. The notable features of this selective cyclization include readily available catalysts and reagents, simple procedure, mild reaction conditions and broad substrate scope. This research provides a practical pathway for the construction of potentially useful spiroindolones and indole-fused seven-membered rings. Accordingly, K₂CO₃ (2 equiv., 0.4 mmol, 55.3 mg) was added to the solution of ynamide 1 (1 equiv., 0.2 mmol) in MeOH (4 mL) at room temperature. The reaction mixture was then stirred at 60 ℃ and the progress of the reaction was monitored by thin layer chromatography (TLC). Upon completion, the mixture was concentrated and purified by chromatography on silica gel (eluent: petroleum ether/ethyl acetate, V∶V=3∶1), to afford the desired spiroindolone 2. Furthermore, A3 (10 mol%, 0.02 mmol, 9.6 mg) was added to the solution of ynamide 1 (1 equiv., 0.2 mmol) in 1,2-dichloroethane (DCE) (4 mL) at room temperature. The reaction mixture was then stirred at 70 ℃ and the progress of the reaction was monitored by TLC. Upon completion, the mixture was concentrated and purified by chromatography on silica gel (eluent: petroleum ether/ethyl acetate, V∶V=5∶1), to afford the desired indole-fused seven-membered ring product 3. Also, a possible reaction mechanism involving the selective cyclization is proposed based on experimental results.

Key words: ynamide, base-promoted, acid-catalyzed, divergent cyclization, indole derivatives