Thienothiophenes. Part 2.1 Synthesis, metallation and bromine→lithium exchange reactions of thieno[3,2-b]thiophene and its polybromo derivatives

Methods for the large-scale synthesis of thieno[3,2-b]thiophene [including a catalytic vapour-phase reaction (at 550 °C) between 2-(2-thienyl)ethanol and carbon disulfide], its 2-carboxylic acid and its 3,6-dibromo and 2,3,5,6-tetrabromo derivatives are reported. With 2 mol equiv. of butyllithium thieno[3,2-b]thiophene gives its 2,5-dilithiated derivative and its 3,6-dibromo derivative gives the 3,6-dilithiated compound. By quenching with suitable electrophilic reagents these dilithiated compounds have been converted into various 2,5- or 3,6-disubstituted thieno[3,2-b]thiophenes, respectively. Likewise 2,3,5,6-tetrabromothieno[3,2-b]thiophene has been converted into 2,5-disubstituted 3,6-dibromothieno[3,2-b]thiophenes.