Ruthenium(II)‐Catalyzed C‐H/C‐H (4+2) Annulation of 2‐Aryl‐N‐heterocycles with Vinylene Carbonate

A ruthenium(II)‐catalyzed direct C‐H/C‐H (4+2) annulation of 2‐aryl‐N‐heterocycles such as 2‐aryl‐4H‐pyrido[1,2‐a]pyrimidin‐4‐ones, 2‐arylimidazo[1,2‐a]pyridines, 2‐aryl‐2H‐indazoles and 2‐arylquinolin‐4(1H)‐ones with vinylene carbonate has been described. This one‐pot cascade strategy provided the diversely substituted fused‐polyheterocycles such as 7H‐benzo[h]pyrido[2,1‐b]quinazolin‐7‐ones, naphtho[1',2':4,5]imidazo[1,2‐a]pyridines, indazolo[2,3‐a]quinolines and benzo[c]acridin‐7(12H)‐ones in moderate to excellent yields. The developed protocol exhibited a broad substrate scope with good functional group tolerance and acid/base‐free conditions. Based on a preliminary mechanistic investigation, a tentative mechanism of Ru(II)‐catalyzed (4+2) annulation reaction has been proposed.