FACILE SYNTHESIS OF 4,6-DIHYDROTHIENO[3,4-B]THIOPHENE 5,5-DIOXIDE - A SYNTHETIC EQUIVALENT OF 2,3-DIHYDRO-2,3-DIMETHYLENETHIOPHENE

4,6-Dihydrothieno[3,4-b]thiophene 5,5-dioxide 4, a stable precursor of 2,3-dihydro-2,3-dimethylenethiophene 3, conveniently prepared from 4-bromo-3-chloro-2,3-dihydrothiophene S,S-dioxide, can easily be alkylated and losses SO2 upon heating so that 4 serves as a useful synthetic equivalent of 3.