Polyhydroxyl oligothiophenes. I. Regioselective synthesis of 3,4'- and 3,3'-di(2-hydroxyethyl)-2,2'-bithiophene via palladium catalyzed coupling of thienylstannanes with thienylbromides.

The synthesis of 3,4?- and 3,3?-di(2-hydroxyethyl)-2,2?-bithiophene, building blocks for the preparation of regioregular head-to-tail and head-to-head polyhydroxyl oligothiophenes, is described. The synthesis was achieved through Pd(PPh3)4 catalyzed cross-coupling of 2- and 5-trimethylstannanes of 3-[2-(tetrahydropyranyloxy)ethyl] with the corresponding 2 bromo derivative, followed by deprotection of the hydroxyl groups in acidic medium. The synthesis of 3,4?-[2-(tetrahydropyranyloxy)ethyl]-2,2?-bithiophene afforded a non-negligible amount of the 4,4?-regioisomer, arising from the homocoupling reaction of the 5-trimethylstannane. Conversion of 3,3?-di(2-hydroxyethyl)-2,2?-bithiophene to the corresponding sodium sulfonate salt was shown to occur with 55% yield, indicating that polyhydroxyl oligothiophenes are, in fact, useful precursors in the preparation of water soluble ?self-doping? oligothiophenes.