Traceless Bidentate Directing Group Assisted Cobalt-Catalyzed sp2-C-H Activation and [4 + 2]-Annulation Reaction with 1,3-Diynes.

An efficient cobalt-catalyzed [4 + 2] annulation of hydrazones and 1,3-diynes has been developed for the synthesis of 3-alkynylated isoquinolines engaging 2-aminopyridine as a traceless bidentate directing group. The strategy has been successfully extended for the synthesis of 3,3'-biisoquinoline moieties via both one-pot as well as sequential approaches. The utilization of a traceless bidentate directing group with an inexpensive and earth-abundant cobalt-catalyst under operationally simple reaction conditions makes the present transformation more valuable and appealing.