Dimerization reactions with oxidized brominated thiophenes

Abstract

2-Bromo, 3-bromothiophene, 2,5-dibromothiophene, 3,4-dibromothiophene and perbrominated thiophene have been oxidized under different conditions to target thiophene S,S-dioxide. Depending on the substitution, sulfone is obtained when the thiophene is hindered. On the other hand, monosubstituted thiophenes can’t be transformed into sulfone, and the sulfoxide intermediate is too reactive and dimerizes. The obtaining of crystals allowed us to confirm the structures. The 3,4-dibromothiophene is the in-between compound since by modulating the oxidation, either the cycloadduct can be obtained or the sulfone can be isolated. The latter can even evolve to the formation of benzothiophene sulfone.