Photocatalytic decarboxylative carbamoylation/cyclization of N-Homoallyl and N-Allyl aldehyde hydrazones: access to carboxamide-functionalized tetrahydropyridazines and dihydropyrazoles

Herein, we disclose a photocatalytic carbamoylation cascade of unsaturated aldehyde hydrazones with oxamic acids for the modular synthesis of carboxamide-functionalized tetrahydropyridazines and dihydropyrazoles. The reaction proceeds via carbamoyl radical generation and subsequent radical addition/cyclization under metal-free conditions with visible-light irradiation at room temperature. This protocol accommodates a range of substrates with good functional-group compatibility, although reduced efficiency is observed for certain sterically hindered substrates and nitrogen-containing heteroaromatic derivatives, allowing access to diverse N–N heterocycles. The method can be further extended to trifluoromethyl-containing carboxylic acids, Minisci-type carbamoylation, and radical cascade cyclization. The successful implementation of a recirculating-flow photochemical system further highlights the scalability and practical utility of the protocol. Mechanistic experiments and DFT calculations support the proposed radical pathway.