Oxidative C-H/C-H Annulation of Imidazopyridines and Indazoles through Rhodium-Catalyzed Vinylene Transfer.

Transition-metal-catalyzed C-H activation followed by oxidative annulation with alkynes has been an efficient synthetic tool for the assembly of various polyaromatic scaffolds. Despite the substantial progress in this field, it is still a significant challenge to achieve the synthesis of nonsubstituted vinylene-fused compounds. In this contribution, we report a Rh-catalyzed C-H/C-H vinylene cyclization adopting vinylene carbonate as a "vinylene transfer" agent. This protocol achieves the direct annulative pi-extension of imidazole- and pyrazole-fused aromatics.