Ligand Redox-Controlled Tandem Synthesis of Azines from Aromatic Alcohols and Hydrazine in Air: One-Pot Synthesis of Phthalazine

A controlled tandem synthetic route to azines from various alcohols and hydrazine hydrate by the use of a Ni(II) complex of 2,6-bis(phenylazo)pyridine as a catalyst is reported. In marked contrast to the previous report, the reaction is operative using an earth-abundant metal catalyst, milder reaction conditions, and aerobic conditions, which though are desirable but unprecedented in the literature. The catalytic reaction has a vast substrate scope including a single-step synthesis of phthalazine from 1,2-benzenedimethanol and hydrazine hydrate via intramolecular coupling. Mechanistic investigation suggests that the coordinated ligand redox controls the reaction by the use of a reversible azo (N=N)/hydrazo (NH-NH) redox couple where the metal center is used primarily as a template.