Metal‐Free Visible‐light Mediated C−S Bond Formation

Abstract

The upsurge in interest in the development of methodologies for the synthesis of sulfur‐containing compounds via the use of visible‐light has been established as a sustainable tool in organic chemistry. Particularly, visible‐light mediated C−S bond formation has gained popularity due to its operational simplicity, minimized by‐products, easy handling, mild reaction conditions, etc. Photochemistry not only provides a sustainable way to synthesize complex molecules but also has the ability to overcome many challenges which are difficult to attain by conventional thermal pathways. Owing to the biological importance of sulfur‐containing compounds, the present review focused on the C−S bond formation under metal‐free conditions mediated by visible‐light. The objective of the current review is to bring out the unearthing collection regarding C−S bond formation via photoredox catalysis. For better understanding, the review is categorized according to the mode of reactions viz, C−S bond formation via difunctionalization of alkenes and alkynes, C−S bond formation via C−H functionalization, and C−S bond formation via radical cyclization. All the reactions in each of the sections are described with selected examples with a proper explanation of the proposed mechanism.

Recent advances in selective mono-/dichalcogenation and exclusive dichalcogenation of C(sp2)–H and C(sp3)–H bonds

“…1). The carbon-chalcogen bond formation represents one of the most powerful methods for synthesizing organochalcogen compounds and it has been achieved mainly through cross-coupling, addition reactions and C-H chalcogenation, utilizing diverse chalcogen sources [14][15][16][17][18][19] under transition metal-catalyzed/mediated, [20][21][22][23][24][25][26] metal-free, [27][28][29][30][31] photocatalyzed, [32][33][34][35][36] electrochemical, 37 organocatalyzed 38,39 or enzymatic conditions. 40 As one of the most commonly employed protocols, transition-metal-catalyzed/mediated crosscouplings generally employ organic (pseudo)halides as reaction partners, 19,[41][42][43][44] however, recent years have also witnessed the increasing use of other sources such as organic boronic acids, carboxylic acids, amines, phenols/alcohols, aldehydes, or esters as the coupling partners.…”

Purple‐Light Promoted Thiol‐ene Reaction of Alkenes

“…Achieving high molecular complexity via photoassisted organic transformations in the absence of a photocatalyst may be challenging. [22] Organic reactions driven by visible-light without external photocatalysts are trending at the moment, thus we questioned us on the feasibility of a light-mediated thiol-ene reaction without a catalyst. As part of our ongoing research on the photocatalyzed functionalization of unsaturated compounds, [23] we have developed an operationally simple anti-Markovnikov hydrothiolation of alkenes.…”

“…Achieving high molecular complexity via photo‐assisted organic transformations in the absence of a photocatalyst may be challenging [22] . Organic reactions driven by visible‐light without external photocatalysts are trending at the moment, thus we questioned us on the feasibility of a light‐mediated thiol‐ene reaction without a catalyst.…”

PIDA/I2-mediated photo-induced aerobic N-acylation of sulfoximines with methylarenes

“…Here, visible light serves as the energy source to facilitate single-electron transfer (SET) for the construction of functionalized molecules and offers an alternative to traditional approaches that otherwise require transition-metal catalysts and high reaction temperatures. 7 With the advancement of visible-light-mediated reactions, researchers have disclosed methodologies to access N -acylsulfoximines under photocatalytic conditions. 8 In 2022, the Song group reported a strategy to access N -acylated sulfoximines utilizing thioacids and organic photoredox catalysts (Me-Acr-MeBF 4 ) (Scheme 1b).…”