Rapid synthesis of 5-substituted-l-acetyl-2-thiohydantoin derivatives under microwave irradiation

Nine 5-substituted-l-acetyl-2-thiohydantoin derivatives were rapidly synthesized by the reaction of ammonium thiocyanate and α-amino acids using acetic anhydride and acetic acid as mixed solvent under microwave irradiation. The effects of microwave reaction time, microwave reaction temperature, ammonium thiocyanate dosage and acetic anhydride dosage on their yields were examined. The optimum reaction conditions were obtained as follows: 10 mmol α-amino acid, 16 mmol ammonium thiocyanate, 9 mL acetic anhydride (1 mL acetic acid), 100°C, 2 min. Compared with conventional heating method, the reaction time was shortened from 30 to 2 min, and the yield was raised from 55.2%-79.5% to 85.0%-93.0%. The structures of all products were characterized by IH-NMR, IR spectra and elemental analysis.