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.