Photoredox‐Mediated Synthesis of β‐Hydroxydithioacetals from Terminal Alkynes

Photocatalytic Thiol-Yne Reactions of Alkynyl Sulfides

Thiol-yne reactions typically employ thiols and terminal alkynes as the reaction partners. The thiol-yne reaction of alkynyl sulfides and thiols is possible when employing a nonmetal photocatalyst eosin Y, green LED irradiation, under an air atmosphere. Alkynyl sulfides were transformed in good overall yields (58-90% total yields, 11 examples) favoring the cis isomer. No addition to the α-position of the alkynyl sulfide is observed, and regioselectivity is believed to be controlled through the stabilization of radical intermediates by the adjacent sulfur atom. Furthermore, control experiments with "all-carbon" internal alkynes demonstrate that alkynyl sulfides possess improved reactivity and regioselectivity profiles during thiol-yne processes.

Exploring the Divergent Reactivity of Vinyl Radicals Emanating from Alkynes and Thiols via Photoredox Catalysis

Organic chemistry has seen a surge in visible-light-driven transformations, which offer unique reaction pathways and access to new synthetic possibilities. We aim to provide a comprehensive understanding of state-of-the-art photo-mediated alkyne functionalization, with a focus on the reactive behavior of vinyl radicals. This review outlines our contributions to the field, including developing new methods for forming carbon-carbon and carbon-heteroatom bonds.

Synthesis of dithioacetals via gold-catalysed hydrothiolation of vinyl sulfides

The synthesis of unsymmetrical dithioacetals based on gold catalysis is described. Although many approaches to the preparation of symmetrical dithioacetals have been developed, the methods to access unsymmetrical ones remain limited. In this regard, we report a mild synthetic method with a broad substrate scope. Screening of various gold catalysts identified a catalyst, which allows the hydrothiolation of both activated and unactivated vinyl sulfides with high efficiency. Moreover, the reaction displays broad compatibility for both aryl and aliphatic thiols.

t BuOLi-promoted terminal alkyne functionalizations by aliphatic thiols and alcohols

Selective radical addition to terminal alkynes is always a difficult task to achieve because it gives a mixture of stereo- and regioisomers. Herein we describe the selective addition of aliphatic thiols or alcohols to N-phenylpropiolamides (terminal alkynes) using lithium tert-butoxide (^tBuOLi) in ethanol as a promoter. Mechanistically, it has been shown that the reaction proceeded through the generation of a thiyl radical intermediate, and the amide group in N-phenylpropiolamide could help in the activation of the alkyne, which led to thioacetalization via the formation of a (Z)-selective anti-Markovnikov vinyl sulfide. The (Z)-selectivity during the formation of vinyl sulfides was controlled by an intramolecular sulfur⋯oxygen interaction.

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

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.

Direct synthesis of 1,3-dithiolanes from terminal alkynes via visible light photoredox catalysis

AA visible light-mediated, metal-free, regioselective dihydrothionation of terminal aromatic as well as heteroaromatic alkynes has been achieved by using Eosin Y as a photoredox catalyst at room temperature. The protocol...

Visible-Light-Promoted Oxidative Annulation of Naphthols and Alkynes: Synthesis of Functionalized Naphthofurans

A visible-light-mediated site-selective oxidative annulation of naphthols with alkynes for the synthesis of functionalized naphthofurans has been developed. The reaction relies on the in situ formation of an electron donor acceptor pair between phenylacetylene and thiophenol as the light-absorbing system to obviate the requirement of an added photocatalyst. The protocol facilitates the transformation of 1-naphthol and 2-naphthol as well as 1,4-naphthoquinone into a wide variety of highly functionalized naphthofurans.

Photocatalytic functionalizations of alkynes

Visible light mediated functionalizations have significantly expanded the scope of alkynes by unraveling new mechanistic pathways and enabling their transformation to diverse structural entities. The photoredox reactions on alkynes rely on their innate capability to generate myriad carbon-centred radicals via single electron transfer (SET), thereby, allowing the introduction of new radical precursors. Moreover, an array of methods have been developed facilitating transformations such as vicinal or gem-difunctionalization, annulation, cycloaddition and oxidative reactions to construct numerous key building blocks of natural and pharmaceutically important molecules. In addition, the introduction of photoredox chemistry has successfully been used to deal with the challenges associated with alkyne functionalization such as stereoselective and regioselective control. This article accounts for several visible light mediated functionalization reactions of alkynes, wherein they have been transformed into α-oxo compounds, β-keto sulfoxides, substituted olefins, N-heterocycles, internal alkynes and sulfur containing compounds. The article has been primarily categorized into various sections based on the reaction type with particular attention being paid to mechanistic details, advancement and future applications.