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 reagents 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 procedures. The nickel-catalyzed electrochemical reduction of the resulting 3-substituted 2,5-dibromothiophenes in the presence of zinc salts allowed the formation of monothienylzinc species in good yields. The selectivity of this reaction is discussed within the context of the electrochemical synthesis of regioregular polythiophenes.