Synthesis of 1-(2,3-dihydrobenzofuran-3-yl)-methanesulfonohydrazides through insertion of sulfur dioxide

A three-component reaction of 2-(allyloxy)anilines, sulfur dioxide and hydrazines under mild conditions is developed, which gives rise to 1-(2,3-dihydrobenzofuran-3-yl)-methanesulfonohydrazides in good yields. This radical process involves an intramolecular 5-exo-cyclization and insertion of sulfur dioxide.