Coupling reactions and coupling-alkylations of thiophenecarbaldehydes promoted by samarium diiodide

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