Comparison of conventional and microwave-assisted synthesis of some new sulfenamides under free catalyst and ligand

Abstract

Sulfenamide and its derivatives (S–N bond) have been synthesized with classical method in the literature. However, microwave-assisted synthesis of a series of N-(substituted phenylthio), N-(benzylthio), N-(cyclothio), and N-(2-mercaptobenzimidazolyl)amines has been not in the literature yet. They have been obtained from treating some amines (4 mmol) with thiophthalimides (PhthSR, 1 mmol) using sulfur transfer reagent in the presence of 2-ethoxyethanol (β-ee, neat) under microwave irradiation at 50 °C. The scope of this reaction was shown by the efficient synthesis of sulfenamides in good to excellent yields of 70–98% under free catalyst and ligand. Nine of the synthesized sulfenamide derivatives are novel. All of the thiols react with morpholine to give corresponding sulfenamides in excellent yields of 78–98%. Thiophenol, 4-methylthiophenol, 4-chlorothiophenol, and 4-fluorothiophenol react with cyclohexylamine to give corresponding sulfenamides in high yields 81–92%. Thiophenol, 4-methylthiophenol, 4-chlorothiophenol react with pyrrolidine to give corresponding sulfenamides in good yields of 70–76%. We observed that the reaction of t-butylamine with N-(phenylthio)phthalimide gave desired sulfenamide under microwave irradiation in the presence of DPPH as radical scavenger reagent in high yield of 93%. Aniline, benzylamine, 1-hexylamine, ethanolamine, diethylamine, N-ethyl-n-butylamine, N-ethylaniline, N-benzylmethylamine, t-butylamine react with thiols to give symmetrical disulfides instead of desired products under microwave irradiation, 2-ethoxyethanol as a solvent (neat), and at 50 °C. In this study, microwave-assisted synthesis method was compared with the classical method. All the products obtained were purified with chromatographic method and the analysis of these products was confirmed with IR, 1H NMR, 13C NMR spectroscopy, MS spectrometry, and elemental methods.