New and efficient access to 3-substituted 2,5-dibromothiophenes. Consecutive nickel-catalyzed electrochemical conversion to thienylzinc species

We have achieved the stepwise synthesis of 3-substituted thienylzinc reagen ts using both electrochemical methods and an original bromination procedure . For several compounds 3-bromothiophene was the starting substrate, which was functionalized according to recently developed electrochemical procedur es. The nickel-catalyzed electrochemical reduction of the resulting 3-subst ituted 2,5-dibromothiophenes in the presence of zinc salts allowed the form ation of monothienylzinc species in good yields. The selectivity of this re action is discussed within the context of the electrochemical synthesis of regioregular polythiophenes.