Thiophenol-mediated metal-free chemoselective conjugate reduction strategy for 3-alkylidene oxindoles

Abstract

A mild and metal-free thiophenol-mediated chemoselective conjugate reduction of 3-alkylidene oxindoles via a thiol–ene-type Michael addition was effectively carried out. Thiophenol as an efficient reductant is used in DMSO, and the transformation proceeds without the need for metal catalyst, external hydrogen source, or harsh reagents. The reaction displays a broad substrate scope, accommodating both electron-donating and electron-withdrawing substituents, and delivers 3-alkyloxindoles in high yields with excellent β-selectivity. This sustainable and operationally simple method unveils a distinct thiol-mediated reduction mechanism, providing a green and versatile approach for accessing reduced oxindole derivatives and related Michael acceptors.