Visible-light-driven reductive dearomatization of N-arylformyl indoles in EDA complexes with a thiophenol via a HAT pathway

Abstract

The dearomatization of N-(o-haloarylformyl)indoles has been achieved by photochemical methods with a photocatalyst or direct excitation via stepwise reduction/protonation. Herein, we report a visible light-driven dearomatization of an N-(o-haloarylformyl)indole in an electron donor–acceptor (EDA) complex with a thiophenol. Mechanistic studies show that photoinduced electron transfer from the benzenethiolate to the o-haloarylformyl moiety triggers a radical reaction to form 2-arylindoline, and the radical termination proceeds through a concerted hydrogen atom transfer (HAT). The photochemical method is adaptable to a broad range of substrates including three aryl halides (Cl, Br, and I) and various modifications at indole and/or N-arylhalide moieties, and high-yield selective conversion, and provides a new alternative approach to develop the dearomatization of N-arylformylindoles. The obtained indolines can be further modified and transformed into various important blocks of pharmaceuticals and natural alkaloids.