THIENOTHIOPHENES .2. SYNTHESIS, METALATION 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 [inclu ding a catalytic vapour-phase reaction (at 550 degrees 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 mo l equiv. of butyllithium thieno[3,2-b]thiophene gives its 2,5-dilithia ted derivative and its 3,6-dibromo derivative gives the 3,6-dilithiate d compound, By quenching with suitable electrophilic reagents these di lithiated compounds have been converted into various 2,5- or 3,6-disub stituted thieno[3,2-b]thiophenes, respectively, Likewise 2,3,5,6-tetra bromothieno[3,2-b]thiophene has been converted into 2,5-disubstituted 3,6-dibromothieno[3,2-b]thiophenes.