Redox-neutral access to 3,3′-disubstituted oxindoles via radical coupling reactions

Abstract

One of the most straightforward strategies for organic synthesis is a visible-light-induced direct coupling between donor and acceptor substrates of a productive EDA complex. In this paper, we report the results of using EDA complexes of in situ formed enolates with redox-active esters for radical-coupling reactions under mild conditions (metal-, photocatalyst-, and base-free). The leaving group from the substrate in these experiments was reused as a base in the reaction. This strategy can successfully be applied to a wide variety of primary, secondary, and tertiary alkyl radical precursors and oxindoles in radical-coupling reactions. The success of sunlight-driven transformation and gram-level synthesis via flow chemistry delivered promising results for further application in industrial settings. Mechanistic investigation, including control experiments, and UV-vis spectroscopy provided insight into the mechanism.