Visible Light Mediated Photocatalyst Free C–S Cross Coupling: Domino Synthesis of Thiochromane Derivatives via Photoinduced Electron Transfer

Abstract

An efficient visible light mediated photocatalyst free C−S cross-coupling reaction has been developed for the synthesis of thiochromane derivatives through photoinduced electron transfer (PET). This methodology was further utilized for the synthesis of thiochroman-4-ol through intermolecular three-component cross-coupling reaction. The reaction proceeds via C−S bond formation through EDA complex/thioester cleavage/inter-or intramolecular sulfa-Michael addition followed by aldol reaction sequence. The EDA complex formation between aryl iodides and xanthate has been substantiated using spectroscopic experiments and DFT calculations.

A photoexcited halogen-bonded EDA complex of the thiophenolate anion with iodobenzene for C(sp3)–H activation and thiolation

“…6 b The halogen bonding EDA complexes have been exploited as efficient protocol for the photochemical transformation. 8 …”

A General Organocatalytic System for Electron Donor–Acceptor Complex Photoactivation and Its Use in Radical Processes

“…The ground-state association between the electron-rich donor catalyst ( A or B ) and the electron-poor substrate 1a would lead to a visible-light-absorbing EDA complex. The formation of the EDA complex is feasible considering the tendency of stoichiometric thiolates and dithiocarbonyl anions to serve as donor partners for EDA complexes . A photoinduced SET would then generate the cyclohexyl radical IV along with the sulfur-centered radical II .…”

Direct Photoexcitation of Xanthate Anions for Deoxygenative Alkenylation of Alcohols

“…Xanthate salts, which can be readily generated from alcohols by treatment with CS 2 under basic conditions, are mainly used as sulfur reagents for the synthesis of sulfur-containing compounds in organic synthesis. Inspired by the potential of photoexcited closed-shell anions to generate strong light-activated reductants for triggering electron-transfer processes, we questioned whether a xanthate anion could independently absorb visible light to afford a strongly reducing excited anion, intrinsically differing from the EDA complexation found in recent reports . To this end, we investigated the photophysical properties of xanthate salts.…”