Catalyst-free system for sulfenylation of free (N–H) indoles with 2,2′-dithiosalicylic acid under alkaline conditions†

      A catalyst-free system for the sulfenylation of free (N–H) indoles using 2,2′-dithiosalicylic acid under alkaline conditions was developed in this study. This system provides a green, convenient and efficient method for sulfenylindole synthesis, with good yields and high selectivity. This simple synthesis was performed in a green solvent (isopropanol/H₂O) under atmospheric and catalyst-free conditions. The procedure was suitable for use with N-unprotected indoles. An electrophilic coupling mechanism was proposed.