Discovery of a Thioxanthone–TfOH Complex as a Photoredox Catalyst for Hydrogenation of Alkenes Using p‐Xylene as both Electron and Hydrogen Sources

Abstract

Hydrogenation of alkenes is one of the most fundamental transformations in organic synthesis, and widely used in the petrochemical, pharmaceutical, and food industries. Although numerous hydrogenation methods have been developed, novel types of catalysis with new mechanisms and new hydrogen sources are still desirable. Thioxanthone (TX) is widely used in energy-transfer photoreactions, but rarely in photoredox processes. Herein we show that a catalytic amount of TfOH as a co-catalyst can tune the properties of TX to make it a photoredox catalyst with highly enhanced oxidative capability in the hydrogenation of carbonylated alkenes with the cheap petroleum industrial product p-xylene serving as the hydrogen source. Deuterium can also be introduced by this method by using D 2 O as the D source. To the best of our knowledge, this is the first example of using p-xylene as a hydrogen source.

Oxidative cross-coupling of quinoxalinones with indoles enabled by acidochromism

“…However, the intensity of absorbance in the visible region was weaker than that of B(C 6 F 5 ) 3 ·H 2 O. The acidochromism 12 property further illustrated that the band gap of 3 is changed by protonation; 13 thereby the combination of 3 with B(C 6 F 5 ) 3 ·H 2 O was likely to act as the photocatalyst in the reaction.…”

A Benzophenothiazine/Boronic Acid Hybrid Photocatalyst Enables the Single Electron Transfer (SET) to Carboxy Groups: SET-Initiated Cyclization of α,β-Unsaturated Carboxylic Acids

“…Recently, the Gansäuer group reported the first [2 + 2] cycloaddition of alkyl-substituted bisenones via a titanocene­(III)-mediated inner-sphere electron transfer process . Despite these advances, the [2 + 2] cycloaddition of α,β-unsaturated carboxylic acid derivatives has so far only been reported under harsh reaction conditions due to the low electrophilicity of α,β-unsaturated esters and amides. , To circumvent this substrate limitation, Yoon et al have proposed a “redox auxiliary” strategy in which a cleavable auxiliary group, such as 2-imidazole, is installed on the enone to facilitate the SET and allow subsequent conversion to the desired carboxylic acid (CA) derivative…”

Generation of Thioxanthone Hydrogen Anion by Double Photoreduction and Uses for Catalytic Photoreductions

“…In our previous work, 17 2 was identified as a potent and long-lived photooxidant, albeit with limited reduction potential because of the poor electron-donating ability of p-xylene. With continued interest in this field, we conducted a comprehensive study of the reduced species of 1, which held the potential to function as a robust reductant (Figure 2a).…”