Visible-Light-Promoted Desulfurative Alkylation of Alkyl Thianthrenium Salts with Activated Olefins

Abstract

Reactions involving an alkyl radical generated from a primary alcohol by photochemistry are rare and challenging. Herein, we present a photocatalyst- and metal-free approach that enables the generation of an alkyl radical from the corresponding alcohol and the subsequent C­(sp3)–C­(sp3) bond formation with activated olefin, via an alkyl thianthrenium salt/Hantzsch ester electron donor–acceptor complex. This protocol for the conversion of a C–OH bond to a C–C bond is highly functionality tolerant and can successfully be used in late-stage functionalization of pharmaceuticals.

Organothianthrenium salts: synthesis and utilization

“…In 2022, Zhang and co-workers developed a photocatalyst- and metal-free approach for the conversion of a C–OH bond to a C–C bond via an alkyl thianthrenium salt/Hantzsch ester electron donor–acceptor complex ( Scheme 39 ). 100 Alkyl thianthrenium salt 3 interacted with a Hantzsch ester to form an alkyl thianthrenium salt/Hantzsch ester electron donor–acceptor complex (EDA complex). The EDA complex was converted to an alkyl radical, thianthrene and an oxidized Hantzsch ester via SET by using blue LEDs.…”

Catalyst‐free Hantzsch Ester‐mediated Organic Transformations Driven by Visible light

“…Very recently Xuan Zhang and co‐workers reported desulfurative alkylation of the alkyl thianthrenium salt (easily prepared from primary and secondary alcohols, and the thianthrene reagent) with activated olefin enabled by an EDA complex under visible‐light irradiation (Scheme 40). [57] The reaction exhibits good efficiency and a broad substrate scope and provides a sustainable approach for using abundant alcohol as an alkylating reagent in organic synthesis. In order to show the potential applications of their methodology the authors turned out late‐stage functionalization derived from indomethacin, estrone, methoxone and ospemifene gave the functionlized products in good to moderate yields ( 91 a – d ).…”

Non-classicalC-saccharide linkage of dehydroalanine: synthesis ofC-glycoamino acids andC-glycopeptides

“…14 However, the use of thianthrenium salts in radical glycosylation, particularly as a tool for the glycosylative modification of peptides, has not been disclosed. 15 As a result of our interests in radical glycosylation, 7 we reasoned that the saccharide-derived thianthrenium salts could potentially generate glycosyl radicals at C5 (pentose) or C6 (hexose) positions, which could overcome the restrictions of anomeric carbons in the previously reported radical glycosylations (Scheme 1b).…”