Facile synthesis of 3-nitro-2-substituted thiophenes.

A new approach to 3-nitro-2-substituted thiophenes has been developed. Exposure of commercially available 1,4-dithane-2,5-diol to nitroalkenes in the presence of 20% triethylamine results in a tandem Michael-intramolecular Henry reaction to form the corresponding tetrahydrothiophene. Subsequent microwave irradiation on acidic alumina in the presence of chloranil effects the solvent free dehydration and aromatization to form 3-nitro-2-substituted thiophenes cleanly and rapidly. A simple workup procedure removes the requirement for purification by chromatography in most cases.