Gallium(iii)-mediated dimerization routes for (5-phenyl-2-thienyl)cyclopropane-1,1-dicarboxylate

A selectivity-switched dimerization process for (5-phenyl-2-thienyl)cyclopropane-1,1-dicarboxylate under activation conditions with anhydrous Gaiii salts was developed. Using GaCl3 or Ga(NTf2)3 as catalysts, 3a,4,5a,6,7,8-hexahydro-5H-pentaleno[6a,1-b]thiophene and 5,6-dihydro-4H-cyclo-penta[b]thiophene derivatives can be selectively obtained as a result of ipso-type and [3+2]-annulation type dimerization. The crucial role of a phenyl substituent at position 5 of the thiophene ring and some regularities are discussed.