Microwave-Assisted Rhodium (III)-Catalyzed [3+3] Annulation of 2-Benzyl-2H-Indazole-6-carboxylic Acids with Iodonium Ylides: A Regioselective Synthesis of Indazole-Fused Chromenes

A Rh(III)-catalyzed redox-neutral C−H activation/[3+3] cyclization of 2-benzyl-2H-indazole-6-carboxylic acids with iodonium ylides under microwave irradiation for the synthesis of indazole-fused chromenes has been reported. The critical feature of this method is that the C−H activation of the C7−H bond of 2-benzyl-2H-indazole-6-carboxylic acid proceeds regioselectively in the presence of the proximate C5−H bond without the need of external oxidant. Microwave irradiation reduced the reaction time as compared to conventional heating. The detailed mechanistic study disclosed the mechanistic pathway of the reaction.