A One-Pot synthesis of Substituted Thieno[3,2-b]thiophenens and Selenolo[3,2-b]selenophenes

Abstract

Heating a mixture of 2,5-dimethyl-3-hexyne-2,5-diol (3a) with elemental sulfur in benzene at 190-200 °C in an autoclave affords 3,6-dimethyl- thieno[3,2-b]thiophene (5a) in 26% yield. The reaction provides a practical one-pot synthesis of several gram quantifies of (5a), even if the yield is moderate, since (3a) is commercially available and inexpensive. The reaction proceeds via 2,5-dimethyl-1,5-hexadiene-3-yne (4a) as one of probable intermediates, which is produced by dehydration of (3a). Addition of p-toluenesulfonic acid promotes the dehydration of (3a) and thus can lower the reaction temperature. In addition, the reaction of 4a, prepared from (3a) independently, with sulfur affords (5a) in a somewhat improved yield (33%). The reaction of (3a) with elemental selenium also provides a one-pot synthesis of 3,6-dimethyl- selenolo[3,2-b]selenophene (9a) in 16% yield. Reactions of some other acetylenic diols with elemental sulfur and selenium are also described