Modular and Regioselective Synthesis of Benzo-Fused Five-Membered Rings Enabled by Co/Ti Synergism.

The regiocontrol in constructing benzo-fused five-membered rings by C-H cyclization remains an important challenge. We report a highly general and regioselective methodology to access such heterocycles and indenones, where under the catalysis of CoBr2/bipyridine, aryl titanates, alkynes and EX2 (E = NR, S(O), RP(O), R2Si, CO, etc.) were assembled to various heterocycles and indenones in a modular manner. Unprecedented 1,2-Co/Ti heterobimetallic arylene and benzotitanole intermediates have played crucial roles in these syntheses.