Thieno[3,4-b]thiophene has been obtained in greater than 50% yield starting from 3,4-dibromothiophene by a sequence of PdII-CuI-catalysed cross-coupling with trimethylsilylacetylene, bromine-lithium exchange, thiolation with elemental sulfur and ring-closure in aqueous medium.
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Brandsma et al. (1990) studied this question.
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