Reductive double electrophilic reactions of methyl thiophenecarboxylate mediated by samarium diiodide and hexamethylphosphoramide

The pentadienyl anion generated by treating methyl thiophenecarboxylate with samarium diiodide/hexamethylphosphoramide in tetrahydrofuran reacts at the C-5 position with a series of benzaldehydes and acetophenones to give the intermediates of samarium dienolates, which are trapped with the second electrophile, such as acetic anhydride, benzyl bromide and carbonyl compounds, in regioselective manners depending on the nature of the electrophile. Thus, the three-component reactions of methyl thiophenecarboxylate with carbonyl compounds are achieved in a one-pot procedure to give 4,5-disubstituted-4,5-dihydrothiophenecarboxylates. (C) 1997 Elsevier Science Ltd.