Photocatalytic Hydrazonyl Radical-Mediated Radical Cyclization/Allylation Cascade: Synthesis of Dihydropyrazoles and Tetrahydropyridazines.

A novel photocatalytic hydrazonyl radical-mediated radical cyclization/allylation cascade reaction of β,γ-unsaturated hydrazones is developed using allyl sulfones and Morita-Baylis-Hillman adduct as allyl sources, which provides an efficient and practical access to various diversely functionalized dihydropyrazoles and tetrahydropyridazines. The reaction is enabled by controllable generation of hydrazonyl radicals via an oxidative deprotonation electron transfer strategy and selective trapping of the resultant C-centered radicals under visible light irradiation.