Regioselective synthesis of poly-substituted thiophenes from Baylis-Hillman adducts

The reaction of Baylis-Hillman acetates and ethyl mercaptoacetate in the presence of DBU in DMF produced 2,3,4-trisubstituted tetrahydrothiophenes at room temperature as a diastereomeric mixture via the sequential SN2′ and Michael addition. Aromatization of tetrahydrothiophenes by DDQ oxidation produced 2,3,4-trisubstituted thiophenes in good yields.