Cobalt(II)-Catalyzed C(sp2)-H Alkynylation/Annulation with Terminal Alkynes: Selective Access to 3-Methyleneisoindolin-1-one.

A highly efficient cobalt(II)-catalyzed alkynylation/annulation of terminal alkynes assisted by an N,O-bidentate directing group is described. This protocol is characterized by wide substrate scope utilizing cheap cobalt catalysts, and offers a new approach to 3-methyleneisoindolin-1-one, which can be converted into an oxadiazine salt in one step. Moreover, the directing group could be removed in three steps.