A direct approach to β-keto sulfones via AgNO3/K2S2O8 catalyzed aerobic oxysulfonylation of alkenes in aqueous medium

Arylazo sulfones: multifaceted photochemical reagents and beyond

The photochemical action of arylazo sulfones under visible light irradiation has recently gained considerable attention for the construction of carbon-carbon and carbon-heteroatom bonds in organic synthesis. The inherent dyedauxiliary group (-N2SO2R) embedded in the reagent is responsible for the absorption of visible light even in the absence of a photocatalyst, additive or oxidant, leading to the generation of three different radicals, viz. aryl (carbon-centred), sulfonyl (sulphur-centred) and diazenyl (nitrogen-centred) radicals, under different reaction conditions. Encountering a reagent with such a versatile behaviour is quite rare, which makes arylazo sulfones a highly interesting class of compounds. The mild reaction conditions under which these reagents can operate are an added advantage. Recently, they are also being used as non-ionic photoacid generators (PAGs), electron acceptors, and hydrogen atom transfer (HAT) and imination reagents in a number of synthetic transformations. They have displayed substantial damaging effect on the structure of DNA in the presence of light which can lead to their use as phototoxic pharmaceuticals for cancer treatment. Moreover, their photochemistry is also being exploited in polymerization reactions (as photoinitiators) and in materials chemistry (surface modification).

MOF-Triggered Synthesis of Subnanometer Ag02 Clusters and Fe3+ Single Atoms: Heterogenization Led to Efficient and Synergetic One-Pot Catalytic Reactions

The combination of well-defined Fe³⁺ isolated single-metal atoms and Ag₂ subnanometer metal clusters within the channels of a metal-organic framework (MOF) is reported and characterized by single-crystal X-ray diffraction for the first time. The resulting hybrid material, with the formula [Ag⁰₂(Ag⁰)_1.34Fe^III_0.66]@Na^I₂{Ni^II₄[Cu^II₂(Me₃mpba)₂]₃}·63H₂O (Fe³⁺Ag⁰₂@MOF), is capable of catalyzing the unprecedented direct conversion of styrene to phenylacetylene in one pot. In particular, Fe³⁺Ag⁰₂@MOF─which can easily be obtained in a gram scale─exhibits superior catalytic activity for the TEMPO-free oxidative cross-coupling of styrenes with phenyl sulfone to give vinyl sulfones in yields up to >99%, which are ultimately transformed, in situ, to the corresponding phenylacetylene product. The results presented here constitute a paradigmatic example of how the synthesis of different metal species in well-defined solid catalysts, combined with speciation of the true metal catalyst of an organic reaction in solution, allows the design of a new challenging reaction.

Dioxygen-Triggered Oxosulfonylation/Sulfonylation of Terminal Olefins toward β-Keto Sulfones/Sulfones

A dioxygen-triggered oxosulfonylation/sulfonylation of unactivated olefins to achieve β-keto sulfones/sulfones has been developed. Interestingly, pluralistic mechanisms were found when different types of compounds were applied as substrates, and different products were achieved. The reaction is carried out with a high atomic efficiency in the absence of a metal and a catalyst at room temperature under an air atmosphere. Importantly, as a proof-of-concept, a bioactive molecule was synthesized on a gram-scale level using this method.

Recent advances in the synthesis and applications of β-keto sulfones: new prospects for the synthesis of β-keto thiosulfones

This review mainly focuses on recent developments in the preparation of β-keto sulfones and their extensive synthetic applications. New prospects for the synthesis of β-keto thiosulfones have also been highlighted. Over the last decade, there has been exponential growth in the direct construction of β-keto sulfones using a wide variety of keto and sulfonyl precursors. Of note, the most promising photoredox transformations and electrochemical synthesis methods of β-keto sulfones are also presented. Moreover, β-keto sulfones are versatile building blocks in organic synthesis due to their three essential functional groups: sulfonyl, carbonyl, and active methylene moieties. The convenient preparation of β-keto sulfones allows the synthesis of many valuable carbocyclic and heterocyclic compounds, and the effortless removal of the sulfonyl moiety via transformations is supported. The chemistry of β-keto sulfones (2013 to present) can be divided into several sections based on the sulfonyl surrogates, and ubiquitous synthetic strategies were systematically outlined.

Synthesis and applications of sodium sulfinates (RSO2Na): a powerful building block for the synthesis of organosulfur compounds

This review highlights the preparation of sodium sulfinates (RSO2Na) and their multifaceted synthetic applications. Substantial progress has been made over the last decade in the utilization of sodium sulfinates emerging as sulfonylating, sulfenylating or sulfinylating reagents, depending on reaction conditions. Sodium sulfinates act as versatile building blocks for preparing many valuable organosulfur compounds through S-S, N-S, and C-S bond-forming reactions. Remarkable advancement has been made in synthesizing thiosulfonates, sulfonamides, sulfides, and sulfones, including vinyl sulfones, allyl sulfones, and β-keto sulfones. The significant achievement of developing sulfonyl radical-triggered ring-closing sulfonylation and multicomponent reactions is also thoroughly discussed. Of note, the most promising site-selective C-H sulfonylation, photoredox catalytic transformations and electrochemical synthesis of sodium sulfinates are also demonstrated. Holistically, this review provides a unique and comprehensive overview of sodium sulfinates, which summarizes 355 core references up to March 2020. The chemistry of sodium sulfinate salts is divided into several sections based on the classes of sulfur-containing compounds with some critical mechanistic insights that are also disclosed.

Photosensitizer-free synthesis of β-keto sulfones via visible-light-induced oxysulfonylation of alkenes with sulfonic acids

A practical and environment-friendly methodology for the construction of β-keto sulfones through visible-light induced direct oxysulfonylation of alkenes with sulfonic acids at ambient temperature under open-air conditions was developed. Most importantly, the reaction proceeded smoothly without the addition of any photocatalyst or strong oxidant, ultimately minimizing the production of chemical waste.

Palladium-catalyzed intramolecular aerobic alkenylhydroxylation of allenamides with alkenyl iodides

An efficient palladium-catalyzed aerobic alkenylhydroxylation cyclization of allenamide derivatives was developed. Mechanistic studies indicated that the reaction might undergo a radical process.

Cross coupling of sulfonyl radicals with silver-based carbenes: a simple approach to β-carbonyl arylsulfones

A radical–carbene coupling reaction of sulfonyl radicals and silver-based carbenes has been well established, which provides an efficient approach to various β-carbonyl arylsulfones.

Sulfated tungstate/dioxygen: a new catalytic system for oxysulfonylation of styrenes to form β-keto sulfones

A new green cat./O₂ oxidation system is mild, safe, heterogeneous, simple to make, stable, noncorrosive, produces N₂ as by product, and has an easy to recover–reuse catalyst and wide substrate scope.

Organic photoredox catalysis enabled cross-coupling of arenediazonium and sulfinate salts: synthesis of (un)symmetrical diaryl/alkyl aryl sulfones

Transition-metal- and oxidant/reductant-free visible-light-mediated synthesis of (un)symmetrical diaryl/alkyl aryl sulfones from aryl diazonium and sulfinate salts employing eosin Y as an organo-photoredox catalyst is reported.

Visible-light promoted aerobic difunctionalization of alkenes with sulfonyl hydrazides for the synthesis of β-keto/hydroxyl sulfones

A practical method has been developed for the conversion of alkenes to β-keto/hydroxyl sulfones by their reaction with sulfonyl hydrazides under metal-free conditions. This reaction proceeds through the oxidative addition of alkenes by sulfonyl radicals that are generated by visible-light induced oxidation of sulfonyl hydrazides. Notaly the reaction uses O2 as the terminal oxidant, instead of metal catalysts or oxidants like TBHP, leading to H2O and N2 as the clean by-products. The key features of this reaction include readily available reagents, mild reaction conditions and broad substrate scope.

A one-pot protocol for the synthesis of β-ketosulfones from α,α-dibromoketones

A one-pot debromination/sulfonylation strategy was developed for the direct transformation of α,α-dibromoketones into β-ketosulfones in the presence of sulfinate salts in a methanol solution.

tert-Butyl nitrite-mediated vicinal sulfoximation of alkenes with sulfinic acids: a highly efficient approach toward α-sulfonyl ketoximes

A novel vicinal sulfoximation of alkenes was achieved under mild and metal-free conditions by using readily available sulfinic acids as the sulfonating agent and tert-butyl nitrite (TBN) as the radical initiator and the oxime source.

Synthesis of β-keto sulfones via a multicomponent reaction through sulfonylation and decarboxylation

A copper(i)-catalyzed synthesis of β-keto sulfones through reaction of aryldiazonium tetrafluoroborates, 3-arylpropiolic acids, sulfur dioxide, and water is realized. This reaction proceeds through a tandem radical process involving sulfonylation and decarboxylation.