Regiospecific silylation of 2,5-dibromothiophene: a reinvestigation

Lithiation of 2,5-dibromothiophene by LDA with ensuing silylation proceeds regiospecifically in accordance with the halogen dance mechanism to yield 3,5-dibromo-2-trimethylsilylthiophene or 3,4-dibromo-2,5-bis(trimethylsilyl)thiophene depending on the ratio of reagents. The outcome of the reaction was confirmed by further chemical transformations of the latter compound to 2,5-bis(trimethylsilyl)thiophene and 2,5-bis(trimethylsilyl)thiophene-1,1-dioxide. The structures of the compounds obtained were determined by 1H, 13C and 29Si NMR, and X-ray analysis in the case of a sulfone.