Palladium-catalyzed syntheses of bi- and terthiophenes

Coupling reactions between 2- or 3-thienylmagnesium bromide and dibromothiophenes in the presence of catalytic amts. of PdCl2[1,1'-bis(diphenylphosphino)ferrocene] gave 48-85% of three isomers of terthiophene as well as several bromobithiophenes.  Thiophene esters I (R = H, 2-thienyl, 3-thienyl) were prepd. by Pd-catalyzed ethoxycarbonylation of bromothiophenes II under mild conditions.  A short synthesis of naturally occurring (propynyl)bithienylcarboxylic acid III, from 2-thienylmagnesium bromide using Pd-catalyzed reactions, is reported.