A New and Efficient Method for the Generation of Sulfene (Thioformaldehyde Dioxide)

Chlorosulfonylmethylene(dimethyl)ammonium chloride (1) is a highly reactive dehydrating agent which provides an efficient entry to 3,4-dihydro-3-phenyl-2H-benzothiazine 1,1-dioxides 4, 4,5-dihydro-4-(4-oxo-4H-1-benzopyran-3-yl)-3H-1,2,5-benzoxathiazepine 2,2-dioxides 6 and 2-aryl-5-dimethylamino-5,6-dihydro-2H-1,2,4-thiadiazine 1,1-dioxides 8 via cycloaddition reactions of imines 3, nitrones 5 and 1,3-diazabutadiene derivatives 7 with in situ generated sulfene directly from the corresponding sulfonic acids. The seven-membered azasultone structural assignments are supported by speotroscopic data