Experimental and theoretical investigations of regioselective functionalization of 3-hydroxy bisindoles with thiols.

An instant and efficient p-TSA center dot H2O-catalyzed sulfenylation reaction of 3-hydroxy bisindole derivatives is reported. This highly regioselective approach afforded C-3 functionalized products in excellent yield, and this methodology was found to be compatible with both aromatic and aliphatic thiols having electronic and steric divergence as well as diverse functional groups. The sulfenylation reaction was performed at room temperature with a green solvent with minimal catalyst loading and proceeded with the involvement of a quasi-antiaromatic-2H-indol-2-one ring intermediate. Moreover, the experimental results obtained for the sulfenylation reaction of 3-hydroxy bisindoles were supported by theoretical calculations in order to comprehend the regioselectivity and chemical reactivity observed in the thiolation reaction of 3-hydroxy bisindoles. The protocol involved the S(N)1 pathway, as also demonstrated by theoretical calculations.