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

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. Graphical abstract: .