Recent Advances in Visible-Light Photoredox Catalysis for the Thiol-Ene/Yne Reactions

Abstract

Visible-light photoredox catalysis has been established as a popular and powerful tool for organic transformations owing to its inherent characterization of environmental friendliness and sustainability in the past decades. The thiol-ene/yne reactions, the direct hydrothiolation of alkenes/alkynes with thiols, represents one of the most efficient and atom-economic approaches for the carbon-sulfur bonds construction. In traditional methodologies, harsh conditions such as stoichiometric reagents or a specialized UV photo-apparatus were necessary suffering from various disadvantages. In particular, visible-light photoredox catalysis has also been demonstrated to be a greener and milder protocol for the thiol-ene/yne reactions in recent years. Additionally, unprecedented advancements have been achieved in this area during the past decade. In this review, we will summarize the recent advances in visible-light photoredox catalyzed thiol-ene/yne reactions from 2015 to 2021. Synthetic strategies, substrate scope, and proposed reaction pathways are mainly discussed.

Porphyrins as Promising Photocatalysts for Red-Light-Induced Functionalizations of Biomolecules

“…With this proof, we turned our attention to reactions suitable for the functionalization of biomolecules. In this context, the cysteine moiety is often regarded as the first choice due to its low natural abundance in peptides and proteins and the high nucleophilicity of the thiol group, and several conjugation methods based on photoredox-based technologies have recently been developed. − Such transformations under red-light irradiation have the potential to become practical tools in bio-orthogonal chemistry for even in vivo experiments. With this in mind, we evaluated the activity of porphyrins in photocatalytic additions of thiols to alkenes and alkynes that involved the thiyl radical as the key reactive intermediate. − The thiol–yne model reaction of cyclohexanethiol ( 16c ) with phenylacetylene ( 15a ) in the presence of 1 mol % H 2 TPP ( 1 ) under red LED irradiation gave the desired product 17c in a 45% yield (Scheme B).…”

Thiol–yne chemistry of diferrocenylacetylene: from synthesis and electrochemistry to theoretical studies

“…The radical addition of a thiol to a double CC bond for the formation of new carbon–sulfur bonds, denoted as thiol–ene reactions, 1,2 or to a triple CC bond, as part of the thiol–yne chemistry, 1,3 is currently attracting increasing interest. Despite thiol–yne chemistry being discovered at the beginning of the 20th century, 4 it was over the past few years that this alkyne hydrothiolation procedure has been developed more extensively.…”

“…Because of their facile nature and efficient and robust characteristics, hydrothiolation reactions have been included in the category of “click” chemistry. 1,2,13 Both thiol–ene and –yne reactions can proceed via a free-radical-based mechanism. 1,2,14 The thiyl radicals are normally formed using either thermally activated radical initiators, such as 2,2′-azobis(isobutyronitrile) (AIBN), 15 or photoinitiators, 16 such as dimethoxy-2-phenylacetophenone (DMPA).…”

“…1,2,13 Both thiol–ene and –yne reactions can proceed via a free-radical-based mechanism. 1,2,14 The thiyl radicals are normally formed using either thermally activated radical initiators, such as 2,2′-azobis(isobutyronitrile) (AIBN), 15 or photoinitiators, 16 such as dimethoxy-2-phenylacetophenone (DMPA). 17 Some metal-based catalysts have also been employed.…”

Electrochemical Sulfoxidation of Thiols and Alkyl Halides

“…Overoxidation of sulfoxides to sulfones is also inevitably observed . The recent development of green, sustainable, and highly controllable oxidation processes, such as photoredox catalysis and electrosynthesis, provides ideal solutions to address above-mentioned shortcomings. In contrast with traditional redox reactions, electrosynthesis relies on the passage of charge (current) rather than using traditional oxidants or reductants .…”