Aerobic Photocatalysis: Oxidation of Sulfides to Sulfoxides

Abstract

Sulfoxides constitute one of the most important functional groups in organic chemistry found in numerous pharmaceuticals and natural products. Sulfoxides are usually obtained from the oxidation of the corresponding sulfides. Among various oxidants, oxygen or air are considered the greenest and most sustainable reagent. Photochemistry and photocatalysis is increasingly applied in new, as well as traditional, yet demanding, reaction, like the aerobic oxidation of sulfides to sulfoxides, since photocatalysis has provided the means to access them in mild and effective ways. In this review, we will summarize the photochemical protocols that have been developed for the oxidation of sulfides to sulfoxides, employing air or oxygen as the oxidant. The aim of this review is to present: i) a historical overview, ii) the key mechanistic studies and proposed mechanisms and iii) categorize the different catalytic systems in literature.Scheme 2. Traditional sulfide oxidation methods. Scheme 3. Sulfide oxidation methods utilizing oxygen as the oxidant.

Photochemical aerobic oxidation of sulfides to sulfoxides: the crucial role of wavelength irradiation

“…In general, two different mechanistic pathways for the photochemical aerobic sulfide oxidation are reported in literature. 24 The first mechanism is promoted by singlet oxygen ( 1 O 2 , I ), which is generated in the presence of a photosensitizer (Scheme 5A). The generated singlet oxygen mediates the oxygenation of the sulfide to afford persulfoxide intermediate II (Scheme 5A).…”

“…34 Then, a variety of known additives, able to quench either mechanistic pathways, have been reported in literature. 24 Initially, to commence our investigations in establishing the exact mechanistic pathway of our protocols, we conducted a series of fluorescence quenching studies. 34 For this purpose, we examined the impact of singlet oxygen quenchers, such as sodium azide, DABCO or Co(acac) 3 on the fluorescence of anthraquinone ( 4a ).…”

“…Also, in their proposed mechanism, although they employ DFT calculations, they proposed a thiadioxirane intermediate as the active intermediate, 32 however, this intermediate has been discarded by researchers as a possible intermediate in the recent past. 24…”

A sustainable photochemical aerobic sulfide oxidation: access to sulforaphane and modafinil

“…In the literature, two different mechanistic pathways for photochemical aerobic sulfide oxidation are reported. 23 In the first mechanism singlet oxygen, 1 O 2 , is generated using a photosensitizer (Scheme 6). Singlet oxygen performs the oxygenation of the sulfide, leading to persulfoxide intermediate I (Scheme 6).…”

Photochemical Ring Editing: Access to Privileged 1,2,5-Thiadiazole Scaffolds via Efficient Carbon Excision from Thiadiazines Under Ambient, Aerobic Conditions

“…[11][12][13][14] This is true for all sulfoxide-bearing scaffolds, as they are prone to overoxidation, and many chemoselective methods for their synthesis from sulfides use harsh reagents and high temperatures. 15 The ring contraction of 1,2,6-thiadiazines to access thiadiazoles has been previously reported, but generally involves high temperatures and the presence of acid to form non-S-oxidised 3,4-substituted-1,2,5-thiadiazole products. [16][17][18][19][20] The most accessible synthetic pathways towards S-oxidised 1,2,5-thiadiazoles involve reacting thionyl chloride with vic-1,2-bisimines or bis(trimethylsilyl) derivatives, 21 but these reactions offer low to moderate yields.…”