Coupling Reactions and Coupling−Alkylations of Thiophenecarbaldehydes Promoted by Samarium Diiodide

The coupling reactions of 2-thiophenecarbaldehyde with aromatic or aliphatic aldehydes were promoted by samarium diiodide in the presence of hexamethylphosphoramide to give C-5 hydroxyalkylation products. The coupling reactions of 3-thiophenecarbaldehyde occurred at C-2, and the subsequent alkylations occurred at the sulfur atom, accompanied by a concurrent opening of the thiophene ring to afford γ-lactols. Double hydroxyalkylations of 2- and 3-thiophenecarbaldehydes were also carried out under appropriate reaction conditions. Synthetic applications of these thiophenecarbonyl coupling products were demonstrated, for example, by elaboration to furans, butenolides, and thiophene-fused polycyclic compounds.