Heating 3,4-di-t-butyl-1,2-dithiete (5) with dimethyl acetylenedicarboxylate (5 equiv) in refluxing o-dichlorobenzene affords dimethyl 2,5-di-t-butyl-3,4-thiophenedicarboxylate (6) (44%), dimethyl 2,3-di-t-butyl-4,5-thiophenedicarboxylate (7) (5%), tetramethyl 1,4-dithiin-2,3,5,6-tetracarboxylate (8) (4%), and tetramethyl 2,3,4,5-thiophenetetracarboxylate (9) (43%). Mechanism of the formation of these products is discussed. Treatment of the hindered ester 7 with lithium 1-propanethiolate affords 2,3-di-t-butyl-4,5-thiophenedicarboxylic acid (13) in 59% yield, which can be decarboxylated by treatment with copper powder to give 2,3-di-t-butylthiophene (4) in 88% yield. The thiophene 4 rearranges to 2,4-di-t-butylthiophene (1) on treatment with aluminum chloride. Oxidation with m-CPBA affords the corresponding sulfone (23). Electrophilic substitutions (bromination and nitration) of 4 occur exclusively at the less hindered and more electronically favored 5-position.

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1994organo-selenium compounds, nonmetal heterocycles organo-selenium compounds, nonmetal heterocycles S 0137 -188A One-Pot Synthesis of Substituted Thieno(3,2-b)thiophenes and Selenolo(3,2-b)selenophenes.-Heating the hexynediols (I) with elemental sulfur or selenium yields directly the fused heterocycles (II) and (III) in low yield. -(CHOI, K. S.; SAWADA, K.; DONG, H.; HOSHINO, M.; NAKAYAMA, J.; Heterocycles 38 (1994)

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