2-(1-Methylhydrazinyl)pyridine as a reductively removable directing group in a cobalt-catalyzed C(sp2)–H bond alkenylation/annulation cascade

We describe a new application of 2-(1-methylhydrazinyl)pyridine as a bidentate directing group to directing cobalt-catalyzed C(sp2)–H alkenylation/annulation of the corresponding benzoic hydrazides to form an isoquinoline backbone, via reacting with a terminal or internal alkyne followed by annulation. The reaction shows a broad substrate scope with the products obtained in good to excellent yields and high regioselectivity. Moreover, the directing group can be reductively removed in one step under mild conditions.