1,4-Benzo[b]dithiine Derivatives Accessed via Ring Expansion of 1,3-Dithioles

Herein, we disclose an efficient route to the synthesis of 2-bromobenzo[b][1,4]dithiines from benzo[d][1,3]dithioles via ring expansion by introducing a carbon fragment of methyl or methylene groups into the heterocyclic rings promoted by bromine (51–94%). The use of a methyl substituent on an aromatic ring leads to the formation of an inseparable, equimolar mixture of regioisomers. Additionally, a 4-methoxyacetophenone derivative yielded unprecedented dimeric products, whose structure was confirmed by single-crystal X-ray crystallography. We propose a reaction mechanism, rationalizing the formation of the observed regioisomers.