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.

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.

Ultrasound accelerated synthesis of O-alkylated hydroximides under solvent- and metal-free conditions

A novel, sustainable, environmentally friendly, high substrate scope, efficient, solvent-free and metal catalyst-free method for the cross-dehydrogenative coupling (CDC) reaction between N-hydroxyphthalimide (NHPI) and benzyl/ether compounds is described. This coupling reaction proceeds through ultrasound acceleration. Compared to conventional heating conditions, the use of ultrasound techniques not only improves the reaction efficiency and enhances the reaction rate but also minimizes the side reactions.

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.

Facile Electrochemical Intramolecular Amination of Urea-Tethered Terminal Alkenes for the Synthesis of Cyclic Ureas

Facile intramolecular amination of unactivated alkenes has been achieved by using electricity as a catalyst that helps to generate an intermediate and accelerates formation of cyclic ureas in high yields. Using this method, no metal catalysts were used. During electrolysis, a nitrogen radical was formed at the urea substrate that cyclised with the alkene and generated a terminal carbon radical which further formed a bond with the 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO). This method of electrolysis not only gives cyclic ureas but also functionalises terminal unactivated alkenes. This method can be considered to be environmentally friendly given that it avoids the issues of toxicity or complicated metal ligands and could therefore be potentially employed in green chemistry.

Engineered C-S Bond Construction

Due to the versatile applications of thioethers and thioesters in organic synthesis, medicinal chemistry, the pharmaceutical industry, and materials science, recently the construction of C-S bonds has emerged as the forefront in the field of cross-coupling reactions. Enough progress has been made in this direction by using both metal catalysis and other alternative processes. A brief review of the recent developments in the area of C-S coupling reaction is described.

Transition-metal-free, visible-light-induced oxidative cross-coupling for constructing β-acetylamino acrylosulfones from sodium sulfinates and enamides

A visible-light-induced, Rose Bengal catalyzed photoredox process for synthesizing β-acetylamino acrylosulfones has been discovered.

Thiosulfonylation of alkenes with the insertion of sulfur dioxide under non-metallic conditions

A three-component reaction of 1-(2-allylaryl)thioureas, sulfur dioxide, and aryldiazonium tetrafluoroborates under mild conditions is realized, leading to sulfonated [3,1]-benzothiazepines in good yields. High efficiency is observed for this non-metallic transformation.

An efficient access to β-ketosulfones via β-sulfonylvinylamines: metal–organic framework catalysis for the direct C–S coupling of sodium sulfinates with oxime acetates

A copper-based framework Cu₂(OBA)₂(BPY) was synthesized and used as a recyclable heterogeneous catalyst for the synthesis of β-sulfonylvinylamines from sodium sulfinates and oxime acetates via direct C–S coupling reaction. The transformation was remarkably affected by the solvent, and chlorobenzene emerged as the best option. This Cu-MOF displayed higher activity than numerous conventional homogeneous and MOF-based catalysts. The catalyst was reutilized many times in the synthesis of β-sulfonylvinylamines without considerably deteriorating in catalytic efficiency. These β-sulfonylvinylamines were readily converted to the corresponding β-ketosulfones via a hydrolysis step with aqueous HCl solution. To the best of our knowledge, this direct C–S coupling reaction to achieve β-sulfonylvinylamines was not previously conducted with a heterogeneous catalyst.

Cu₂(OBA)₂(BPY) was used as catalyst for the synthesis of β-sulfonylvinylamines from sodium sulfinates and oxime acetates. These β-sulfonylvinylamines were readily converted to corresponding β-ketosulfones via a hydrolysis step.

Recent advances in the sulfonylation of alkenes with the insertion of sulfur dioxide via radical reactions

Recent advances in the sulfonylation of alkenes via the insertion of sulfur dioxide are summarized. Two strategies for the sulfonylation of alkenes with the insertion of sulfur dioxide have been developed.

Synthesis of trifluoromethyl-containing isoindolinones from tertiary enamides via a cascade radical addition and cyclization process

A radical trifluoromethylation reaction of tertiary enamides was investigated and trifluoromethyl-containing isoindolinones were prepared under mild conditions. Using TMSCF₃ as a radical source, PhI(OAc)₂ as an oxidant and KHF₂ as an additive, tertiary enamides were converted to isoindolinones via a cascade addition and cyclization process in moderate to good yields.

Radical trifluoromethylation and cyclization of tertiary enamides was developed and trifluoromethyl-containing isoindolinones were obtained in moderate to good yields.

Intramolecular oxysulfonylation of alkenes with the insertion of sulfur dioxide under photocatalysis

Intramolecular oxysulfonylation of alkenes with the insertion of sulfur dioxide promoted by visible light is developed, leading to sulfonated tetrahydrofurans and related compounds in moderate to good yields.

MnO2 -Promoted Oxidative Radical Sulfonylation of Haloalkynes with Sulfonyl Hydrazides: C(sp)-S Bond Formation towards Alkynyl Sulfones

A catalyst-free oxidative radical sulfonylation of haloalkynes with sulfonyl hydrazides is reported. It represents an example of C(sp)-S bond formation using sulfonyl hydrazides as sulfonyl radical sources. Various alkynyl sulfones were synthesized in moderate to good yields. Having MnO₂ as the oxidant is very critical for this transformation. Remarkably, the self-coupling reaction of haloalkynes through C(sp)-C(sp) bond formation is significantly inhibited under the standard reaction conditions.

Recent Advances in Radical C-H Activation/Radical Cross-Coupling

Research and industrial interest in radical C-H activation/radical cross-coupling chemistry has continuously grown over the past few decades. These reactions offer fascinating and unconventional approaches toward connecting molecular fragments with high atom- and step-economy that are often complementary to traditional methods. Success in this area of research was made possible through the development of photocatalysis and first-row transition metal catalysis along with the use of peroxides as radical initiators. This Review provides a brief and concise overview of the current status and latest methodologies using radicals or radical cations as key intermediates produced via radical C-H activation. This Review includes radical addition, radical cascade cyclization, radical/radical cross-coupling, coupling of radicals with M-R groups, and coupling of radical cations with nucleophiles (Nu).

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.

In Situ Generated HypoIodite Activator for the C2 Sulfonylation of Heteroaromatic N-oxides

A mild approach for direct C2 sulfonylation of heteroaromatic N-oxides with sulfonyl hydrazides affording 2-sulfonyl quinolines/pyridines has been developed. A variety of heteroaromatic N-oxides and sulfonyl hydrazides participate effectively in this transformation which uses hypoiodites (generated in situ from NaI and TBHP) as a means of substrate activators. In this reaction, the N-oxide plays a dual role, acting as a traceless directing group as well as a source of oxygen atom.

Novel and efficient transformation of enamides into α-acyloxy ketones via an acyl intramolecular migration process

Hydrogen peroxide and anhydride mediated transformation of enamides to afford substituted α-acyloxy ketones is described.