Generation of (2-oxoindolin-3-yl) methanesulfonohydrazides via a photo-induced reaction of N-(2-iodoaryl) acrylamide, DABSO, and hydrazine

A photo-induced catalyst-free three-component reaction of N-(2-iodoaryl) acrylamide, sulfur dioxide, and hydrazine is reported. Under ultraviolet irradiation, diverse (2-oxoindolin-3-yl) methanesulfonohydrazides are generated in moderate to good yields. During the process, the sulfonyl group can be easily incorporated via insertion of sulfur dioxide in the absence of any metals or photo-redox catalysts under mild conditions. A plausible mechanism is proposed, which involves 5-exo radical cyclization and subsequent insertion of sulfur dioxide.