POLYHYDROXYL OLIGOTHIOPHENES .1. 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(PPh(3))(4) catalyzed cross-coupling of 2- and 5-trimethylstannanes of 3-[2-(tetrahydropyranyloxy)ethyl]thiophene 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.