Addition of elemental fluorine to 2,5-dihydrothiophene-1,1-dioxide (4) provided a mixture of isomeric 3,4-difluoro-2,3,4,5-tetrahydrothiophene-1,1-dioxides (5) in moderate yield. Photochemical chlorination of each of these isomers gave the same product mixture consisting mainly of trans-3-chloro-3,4-difluoro-2,3,4,5-tetrahydrothiophene-1,1-dioxide (9a) and trans-3,4-dichloro-3,4-difluoro-2,3,4,5-tetrahydrothiophene-1,1-dioxide (11b). Dehydrohalogenation of the former gave 3,4-difluoro-4,5-dihydrothiophene-1,1-dioxide (12) as the main product, whereas dehydrohalogenation of the latter gave 3,4-difluorothiophene-1,1-dioxide (3) as the main product.