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Communication | Regular issue | Vol 81, No. 10, 2010, pp.2229-2237
Published online, 18th August, 2010
DOI: 10.3987/COM-10-12023
The Unexpected Formation and Structure of 4,6-Dimethylthieno[3,4-c]thiophene-1(3H)-thione

Nathan C. Tice,* Sarah M. Peak, and Sean Parkin

*Department of Chemistry, Eastern Kentucky University, Richmond, KY, 40475-3102, U.S.A.

Abstract

The reaction of 2,5-dimethylthiophene-3,4-dicarboxaldehye (1) with excess Lawesson’s Reagent afforded the unexpected 5,5-fused ring thienothione derivative, 4,6-dimethylthieno[3,4-c]thiophene-1(3H)-thione (2), in good yield (79%). The desired non-classical thiophene, 1,3-dimethylthieno[3,4-c]thiophene (3), was observed by GC/MS as a minor product (approximately 5%) along with thione 2. The thienothione 2 was characterized spectroscopically and its structure was confirmed by X-ray crystallography. The formation of compound 2 is proposed to occur through a 1,3-hydride shift.