Tin-Free Radical Carbonylation: Thiol Ester Synthesis Using Alkyl Allyl Sulfone Precursors, Phenyl Benzenethiosulfonate, and CO

Deoxygenation of allyl arylsulfones to allyl arylthioethers via a "cut-sew" strategy: phosphines as bifunctional reagents

Herein, we disclosed a protocol for the deoxygenation of allyl arylsulfones to access the corresponding thioethers under photoredox conditions by a "cut-sew" strategy. The key to the success of the deoxygenation process is using triarylphosphines not only as the terminal reductants, but also as the reaction initiators. Deeper understanding of this deoxygenation process enabled the intermolecular deoxygenative allylation.

Photo-induced decarboxylative C-S bond formation to access sterically hindered unsymmetric S-alkyl thiosulfonates and SS-alkyl thiosulfonates

Due to the high reactivity and versatility of benzenesulfonothioates, significant advancements have been made in constructing C-S bonds. However, there are certain limitations in the synthesis of S-thiosulfonates and SS-thiosulfonates, especially when dealing with substantial steric hindrance, which poses a significant challenge. Herein, we present an innovative approach for assembling unsymmetric S-thiosulfonates and unsymmetric SS-thiosulfonates through the integration of dual copper/photoredox catalysis. Moreover, we also realized the one-pot strategy by directly using carboxylic acids as raw materials by in-situ activation of them to access S-thiosulfonates and SS-thiosulfonates without further purification and presynthesis of NHPI esters. The envisaged synthesis and utilization of these reagents are poised to pioneer an innovative pathway for fabricating a versatile spectrum of mono-, di-, and polysulfide compounds. Furthermore, they introduce a class of potent sulfenylating reagents, empowering the synthesis of intricate unsymmetrical disulfides that were previously challenging to access.

Oxidation of Thiols with IBX or DMP: One-Pot Access to Thiosulfonates or 2-Iodobenzoates and Applications in Functional Group Transformations

o-Iodoxybenzoic acid (IBX) and Dess-Martin periodinane (DMP) are employed for thiol to thiosulfonate conversion at rt. DMP is better than IBX in terms of reaction rate, conversion, and required equivalents. IBX-mediated oxidation of benzyl thiols produced thiosulfonates, whereas DMP afforded O-benzyl esters. The one-pot conversion of a thiol to an ester is unprecedented; this atom-economic transformation has potential for functional group transformations (FGTs), e.g., an alcohol and an aldehyde are accessed from benzyl thiol.

Metal-Free One-Pot Multi-Functionalization of Unsaturated Compounds with Interelement Compounds by Radical Process

In recent years, the importance of "environmentally friendly manufacturing" has been increasing toward the establishment of a resource-recycling society. In organic synthesis, as well, it is becoming increasingly important to develop new synthetic strategies with resource conservation and the recycling of elemental resources in mind, rather than just only synthesis. Many studies on the construction of frameworks of functional molecules using ionic reactions and transition-metal-catalyzed reactions have been reported, but most of them have focused on the formation of carbon-carbon bonds. However, it is essential to introduce appropriate functional groups at appropriate positions in molecules in order for the molecules to express their functions, and furthermore, the highly selective preparation of multiple functional groups is considered important for the creation of new functional molecules. In this review, we focus on radical reactions with high functional group selectivity and overview the recent progress in practical methods for the simultaneous introduction of multiple functional groups and propose future synthetic strategies that emphasize the recycling of elemental resources and environmental friendliness.

Palladium-Catalyzed Desulfonative Carbonylation of Thiosulfonates: Elimination of SO2 and Insertion of CO

A palladium-catalyzed desulfonative carbonylation of thiosulfonates has been explored. Without any additive, a series of S-aryl/alkyl benzenesulfonothioates were successfully transformed to thioesters in moderate to excellent yields by SO₂ extrusion and CO insertion under the pressure of 1 bar of CO. The solvent dimethylacetamide (DMAc) facilitated this desulfonative carbonylation due to its high absorbing ability of SO₂.

Palladium-Catalyzed Reductive Desulfonative Aminocarbonylation of Benzylsulfonyl Chlorides with Nitroarenes to Phenylacetamides

Herein, we demonstrate a new procedure for the direct using benzylsulfonyl chlorides as versatile C(sp3) electrophiles in a palladium-catalyzed reductive desulfonative aminocarbonylation reaction. Using nitroarenes as readily accessible and stable...

Desulfonylation via Radical Process: Recent Developments in Organic Synthesis

As the "chemical chameleon", sulfonyl-containing compounds and their variants have been merged with various types of reactions for the efficient construction of diverse molecular architectures by taking advantage of their incredible reactive flexibility. Currently, their involvement in radical transformations, in which the sulfonyl group typically acts as a leaving group via selective C-S, N-S, O-S, S-S, and Se-S bond cleavage/functionalization, has facilitated new bond formation strategies which are complementary to classical two-electron cross-couplings via organometallic or ionic intermediates. Considering the great influence and synthetic potential of these novel avenues, we summarize recent advances in this rapidly expanding area by discussing the reaction designs, substrate scopes, mechanistic studies, and their limitations, outlining the state-of-the-art processes involved in radical-mediated desulfonylation and related transformations. With a specific emphasis on their synthetic applications, we believe this review will be useful for medicinal and synthetic organic chemists who are interested in radical chemistry and radical-mediated desulfonylation in particular.

Visible-light-promoted synthesis of secondary and tertiary thiocarbamates from thiosulfonates and N-substituted formamides

A general visible-light-promoted metal-free synthesis of secondary and tertiary thiocarbamates starting from thiosulfonates and N-substituted formamides is developed. By employing rhodamine B as a photocatalyst and tert-butyl hydroperoxide (TBHP) as an oxidant, a wide scope of thiocarbamates can be obtained through direct thiolation of acyl C-H bonds under irradiation of blue light at room temperature for 12 h.

Radical-mediated vicinal addition of alkoxysulfonyl/fluorosulfonyl and trifluoromethyl groups to aryl alkyl alkynes

The addition of sulfonyl radicals to alkenes and alkynes is a valuable method for constructing useful highly functionalized sulfonyl compounds. The underexplored alkoxy- and fluorosulfonyl radicals are easily accessed by CF₃ radical addition to readily available allylsulfonic acid derivatives and then β-fragmentation. These substituted sulfonyl radicals add to aryl alkyl alkynes to give vinyl radicals that are trapped by trifluoromethyl transfer to provide tetra-substituted alkenes bearing the privileged alkoxy- or fluorosulfonyl group on one carbon and a trifluoromethyl group on the other. This process exhibits broad functional group compatibility and allows for the late-stage functionalization of drug molecules, demonstrating its potential in drug discovery and chemical biology.

An unprecedented method for vicinal addition of alkoxysulfonyl/fluorosulfonyl and trifluoromethyl groups to aryl alkyl alkynes has been developed to afford useful alkenylsulfonate esters and alkenylsulfonyl fluorides.

Synthesis of quaternary centres by single electron reduction and alkylation of alkylsulfones

A new method for the generation of tertiary radicals through single electron reduction of alkylsulfones promoted by Zn and 1,10-phenanthroline has been developed. These radicals could be employed in the Giese reaction, affording structurally diverse quaternary products in good yields. With the high modularity and functional group compatibility of sulfones, the utility of this method was demonstrated by intramolecular and iterative reactions to give complex structures. The radical generation process was investigated by control experiments and theoretical calculations.

A new method for the generation of tertiary radicals through single electron reduction of alkylsulfones promoted by Zn and 1,10-phenanthroline has been developed.

The same oxygenation-state introduction of hypervalent sulfur under transition-metal-free conditions

This review discusses the application of the same oxygenation-state introduction of hypervalent sulfur strategy under transition-metal-free conditions.

Metal-free NaI/TBHP-mediated sulfonylation of thiols with sulfonyl hydrazides

A highly efficient sulfonylation of thiols has been achieved through the metal-free NaI/TBHP-mediated cross-coupling of sulfonyl hydrazides and thiols at room temperature. This method provides a convenient and practical route to thiosulfonates in 84-99% yields (39 examples) with wide functional group compatibility.

An unexpected reaction of aryldiazonium tetrafluoroborates, sodium metabisulfite, and thiourea under photoinduced conditions

A photoinduced synthesis of S-aryl thiosulfonates through a three-component reaction of aryldiazonium tetrafluoroborates, sodium metabisulfite, and thiourea is achieved. In this transformation, a radical coupling pathway is proposed.

Site-Selective Remote Radical C-H Functionalization of Unactivated C-H Bonds in Amides Using Sulfone Reagents

A general and practical strategy for remote site-selective functionalization of unactivated aliphatic C-H bonds in various amides by radical chemistry is introduced. C-H bond functionalization is achieved by using the readily installed N-allylsulfonyl moiety as an N-radical precursor. The in situ generated N-radical engages in intramolecular 1,5-hydrogen atom transfer to generate a translocated C radical which is subsequently trapped with various sulfone reagents to afford the corresponding C-H functionalized amides. The generality of the approach is documented by the successful remote C-N₃ , C-Cl, C-Br, C-SCF₃ , C-SPh, and C-C bond formation. Unactivated tertiary and secondary C-H bonds, as well as activated primary C-H bonds, can be readily functionalized by this method.

Polycyclic heteroaromatic ring construction driven by silver/cobalt co-catalyzed desulfonylative and defluorinative fragment-recombination of enol nonaflates with amidines

A novel Ag(i)/Co(ii) co-catalyzed tandem fragmentation and recombination reaction commencing from detachable nonaflates and amidines has been developed.

Metal-free radical oxidative alkoxycarbonylation and imidation of alkanes

The metal-free radical oxidative carbonylation of alkanes proceeded to give the corresponding esters and imides in good to high yields.

Iron-catalyzed cross-coupling of unactivated secondary alkyl thio ethers and sulfones with aryl Grignard reagents

The first systematic investigation of unactivated aliphatic sulfur compounds as electrophiles in transition-metal-catalyzed cross-coupling are described. Initial studies focused on discerning the structural and electronic features of the organosulfur substrate that enable the challenging oxidative addition to the C(sp(3))-S bond. Through extensive optimization efforts, an Fe(acac)3-catalyzed cross-coupling of unactivated alkyl aryl thio ethers with aryl Grignard reagents was realized in which a nitrogen "directing group" on the S-aryl moiety of the thio ether served a critical role in facilitating the oxidative addition step. In addition, alkyl phenyl sulfones were found to be effective electrophiles in the Fe(acac)3-catalyzed cross-coupling with aryl Grignard reagents. For the latter class of electrophile, a thorough assessment of the various reaction parameters revealed a dramatic enhancement in reaction efficiency with an excess of TMEDA (8.0 equiv). The optimized reaction protocol was used to evaluate the scope of the method with respect to both the organomagnesium nucleophile and sulfone electrophile.

Efficient carboazidation of alkenes using a radical desulfonylative azide transfer process

The radical-mediated carboazidation of terminal alkenes using electrophilic alkanesulfonyl azides is reported. A single reagent delivers the necessary electrophilic alkyl radical as well as the azido group, and good yields are obtained by using a moderate excess of the carboazidating reagent (1.5-2 equiv). Interestingly, in addition to the starting sulfonyl azide, this method requires only the use of a radical initiator, di-tert-butyldiazene. In terms of atom economy, this azide transfer reaction is close to ideal, as SO2 (1 equiv) is the only side product. The synthetic potential of this process has been demonstrated by a formal synthesis of the alkaloid lepadiformine C.

Radical and radical-ionic multicomponent processes

All in one pot! Radical, radical-ionic, and radical-organometallic MCR are highly convergent processes, representing a useful pathway to molecular and structural diversity (see scheme). This concept article highlights recent developments in the field and shows the potential of the strategy for the economical elaboration of various kinds of organic substrates.Progress in multicomponent reactions (MCRs) based on ionic and organometallic processes has recently allowed the synthesis, with high efficiency, of large collections of drug-like molecules. In contrast, MCRs based on cascade radical reactions appear to have attracted, so far, much less interest. This concept article highlights the latest progress in the field and underlines the potential of such an approach. The collected examples demonstrate that radical and radical-ionic MCRs are highly convergent processes leading to useful structural diversity.

Tin-free radical carbonylation of alkylsulfonyl derivatives into alkylcarbonyl derivatives

A simple radical approach based on tin-free radical carbonylation is devised for the direct conversion of alkylthiosulfonates, alkylsulfonyl cyanides, and alkylsulfonyl oxime ethers into the corresponding alkyl thiol esters, acyl cyanides, and acylated oxime ethers in a single step. The present approach is very simple, highly efficient, and minimizes the formation of byproducts.