Cobalt-Catalyzed 2‑(1-Methylhydrazinyl)pyridine-Assisted C–H Alkylation/Annulation: Mechanistic Insights and Rapid Access to Cyclopenta[c]isoquinolinone Derivatives

We have developed cobalt-catalyzed, bidentate 2-(1-methylhydrazinyl)­pyridine (MHP)-directed C­(sp²)–H alkylation/annulation of benzoic hydrazides with various alkenes. Notably, diverse cyclopenta­[c]­isoquinolinones and dihydroisoquinolinones were obtained via this functional group-tolerant protocol. The reaction can be performed on a gram scale while maintaining an excellent yield, and the directing group can be removed efficiently under mild conditions. Furthermore, density-functional theory (DFT) calculations provide an incisive understanding of the observed regioselectivities for different olefins.