Cp*Co(III)-Catalyzed C–H Acylmethylation of Arenes by Employing Sulfoxonium Ylides as Carbene Precursors

Catalyst-Free [4+1] Annulation of α-Imidoyl Sulfoxonium Ylides and Diazo Compounds Enabling the Modular Synthesis of 2-Indanones and 3(2H)-Furanones

A novel substrate-regulated [4+1] annulation of α-imidoyl sulfoxonium ylides with diazoketones under catalyst-free conditions is described. The reaction proceeds through a coupling of sulfoxonium ylides and in situ-generated ketenes to form the key reactive zwitterionic intermediates, followed by selective formation of C-C or C-O bonds to achieve five-membered ring systems. The cascade reaction permits the direct synthesis of synthetically useful 2-indanones and 3(2H)-furanones, which expands the reaction pattern of sulfoxonium ylides in annulation transformation.

Annulative coupling of sulfoxonium ylides with 2-amino(thio)phenols: easy access to 2-acyl benzox(thio)azoles

A novel method for synthesizing 2-acyl benzothiazoles and benzoxazole derivatives has been developed via the annulative coupling of sulfoxonium ylides with 2-aminobenzenethiol and 2-aminophenol derivatives, respectively. This metal-free, one-pot protocol employs elemental sulfur as a mediator to efficiently construct C-N, C-S, or C-O bonds and demonstrates a broad range of functional group compatibility. The potential utility of this approach is further demonstrated through large-scale reactions and the synthesis of some bioactive compounds.

Isocyanide-Based Multicomponent Reaction: Cascade α-Acyloxylation/Carboxamidation and [3 + 1+1] Cyclization of I(III)/S(VI)-Ylides

A metal-free cascade of α-acyloxylation/carboxamidation of I(III)/S(VI)-ylides, carboxylic acids, and isonitriles via a Passerini-like multicomponent reaction is reported. Unexpectedly, [3 + 1+1] cyclization involving I(III)/S(VI)-ylides and two molecules of ethyl isocyanoacetate was observed. The strategy allows for the synthesis of unsymmetrical α,α-disubstituted ketones and functionalized pyrroles with up to 99% yield and wide substrate compatibility. Notably, the procedure has been extended to the late-stage modification of drugs and natural products, offering an elegant complement to the classic Passerini reaction.

Copper-Mediated Cyclization of Terminal Alkynes with CF3-Imidoyl Sulfoxonium Ylides To Construct 5-Trifluoromethylpyrroles

A copper-mediated [3 + 2] cyclization of CF3-imidoyl sulfoxonium ylides and terminal alkynes has been demonstrated. This work provides a practical approach for assembling 5-trifluoromethylpyrroles with the merits of a broad substrate scope, good functional tolerance, and mild reaction conditions. Control experiments and DFT studies indicate that this reaction may involve the addition of π-bonds of terminal alkynes by copper-carbene radicals and hydrogen migration.

Rhodium-catalyzed annulation of hydrazines with vinylene carbonate to synthesize unsubstituted 1-aminoindole derivatives

Herein, we describe rhodium-catalysed C-H bond activation for [3 + 2] annulation using hydrazide and vinylene carbonate, providing an efficient method for synthesising unsubstituted 1-aminoindole compounds. Characterised by high yields, mild reaction conditions, and no need for external oxidants, this transformation demonstrates excellent regioselectivity and a wide tolerance for various functional groups.

Pathway to Construct α-Acyloxy Esters by B(C6F5)3-Catalyzed O-H Insertion of Carboxylic Acids with Sulfoxonium Ylides

We report the first example of B(C6F5)3-catalyzed O-H insertion reaction of sulfoxonium ylides and carboxylic acids, achieving efficient construction of diester moieties under metal-free condition. This protocol is characterized by broad substrate tolerance, particularly for various phenylacetic acids, and good compatibility with water/air condition, which is superior to most other methods.

Synthesis of α-Carbonyl-α'-amide Sulfoxonium Ylides from Isocyanates with Complete Atom Economy

An efficient catalyst- and additive-free facile synthesis of α-carbonyl-α'-amide sulfoxonium ylides from isocyanates and β-ketosulfoxonium ylides with complete atom economy has been described. The β-ketosulfoxonium ylides and isocyanates adorned with various functional groups were well-tolerated and afforded moderate to high yields of the α-carbonyl-α'-amide sulfoxonium ylide derivatives. Finally, using large-scale reactions and converting the synthesized ylides into other valuable compounds, we demonstrated the practicality of this synthetic method.

α-Carbonyl sulfoxonium ylides in transition metal-catalyzed C-H activation: a safe carbene precursor and a weak directing group

Transition metal-catalyzed cross-coupling of sp² C-H bonds with diazo compounds via carbene migratory insertion represents an efficient strategy for the construction of C-C and C-heteroatom bonds in organic synthesis. Despite the popularity of diazo compounds as coupling partners in C-H activation, they pose serious safety and stability issues due to potential exothermic reactions linked with the release of N₂ gas. However, compared with diazo compounds, sulfoxonium ylides are generally crystalline solids, more stable, widely used in industrial scales, and easier/safer to prepare. Therefore, recent years have witnessed an upsurge in employing α-carbonyl sulfoxonium ylides as an alternative carbene surrogate in transition metal-catalyzed C-H activation. Unlike diazo compounds, α-carbonyl sulfoxonium ylides contain inherent potential to serve as a coupling partner as well as a weak directing group. This review will summarize the progress made in both categories of reactions.

Rhodium(III)-Catalyzed Redox-Neutral [4 + 1]-Annulation of Unactivated Alkenes with Sulfoxonium Ylides

A novel methodology for redox-neutral [4 + 1] annulation of unactivated alkenes with sulfoxonium ylides leads to the synthesis of a diverse library of indanone compounds. The developed annulation reaction was found to be highly versatile due to its compatibility with various unactivated alkenes functionalized with various sensitive functional groups as well as substituted sulfoxonium ylides. Further, multiple transformations such as ring-expansion, reduction, aldol condensation, and Wittig reaction were carried out with indanones. Using this way, highly useful cyclic heterocycles such as indene, dihydroisocoumarin, and 1-indanilidene were prepared in a single step. A possible reaction mechanism was supported by deuterium labeling studies, competitive studies, and kinetic isotopic studies.

Ru(II)-Catalyzed regioselective carbene insertion into β-carbolines and isoquinolines

A protocol for carbene insertion into the inert C(sp²)-H bond has been established wherein β-carbolines and isoquinolines are explored as intrinsic directing groups. The Ru(II)-catalyzed strategy employing sulfoxonium ylides as the carbene precursor offers an effective and atom-economical functionalization of substrates of biological interest with only DMSO as the sole by-product. The strategy is scalable to gram scale, and it also showcases a wide range of functional group tolerance. ESI-MS studies assisted in the identification of intermediates and consolidation of a probable mechanistic pathway. Furthermore, investigations revealed that the functionalized molecules not only displayed selective inhibition against cancer cell lines, but also demonstrated promising photophysical properties.

Cobalt(III)-Catalyzed Chemo- and Regioselective [4 + 2]-Annulation of Aromatic Sulfoxonium Ylides with 1,3-Diynes

Air-stable, highly abundant, and cost-effective Co(III)-catalyzed redox-neutral [4 + 2]-annulation of aromatic sulfoxonium ylides with 1,3-diynes providing useful substituted 1-naphthol derivatives in a regioselective manner is described. Further, the prepared 1-naphthols having internal alkyne were converted into useful polycarbocyclic molecules and spiro-dienone derivatives in good-to-excellent yields. A possible reaction mechanism involving ortho C-H activation as a key step was proposed and supported by deuterium labeling and kinetic isotope labeling studies.

Asymmetric transformations from sulfoxonium ylides

Sulfoxonium ylides are important surrogates for diazo compounds, and their use in industry as safer alternatives has been evaluated during recent years. Beyond the known classical transformations, these ylides have also been used in a surprising plethora of novel and intrinsic chemical reactions, especially in recent years. Bench stability and handling are also an advantage of this class of organosulfur molecules. Despite this, efficient asymmetric transformations, specifically catalytic enantioselective versions, have only recently been reported, and there are specific reasons for this. This perspective article covers this topic from the first studies up to the latest advances, giving personal perspectives and showing the main challenges in this area in the coming years.

Rh(III)-catalyzed C-H annulation of sulfoxonium ylides with iodonium ylides towards isocoumarins

The direct synthesis of isocoumarin skeletons has been realized through the Rh(III)-catalyzed [3 + 3] annulation of sulfoxonium ylides with iodonium carbenes. The synthetic protocol was constructed efficiently with broad functional group tolerance and mild reaction conditions. This reaction can be formally viewed as the result of C-H activation, carbene insertion and nucleophilic addition processes. Furthermore, the further conversions of the product and gram-scale reactions were also demonstrate to support the effectiveness of the synthesis protocol.

One-pot synthesis of 3-trifluoromethylbenzo[b][1,4]oxazines from CF3-imidoyl sulfoxonium ylides with 2-bromophenols

A one-pot two-step fashion for the synthesis of 3-trifluoromethyl-1,4-benzoxazines from CF3-imidoyl sulfoxonium ylides and 2-bromophenols via lithium-bromide-promoted O–H insertion of sulfoxonium ylides and annulation has been demonstrated.

Recent Advances in the High-Valent Cobalt-Catalyzed C-H Functionalization of N-Heterocycles

Direct functionalization of heterocycles using C-H activation widely relies on the precious metal complexes. In past decade, the use of earth abundant and inexpensive transition metal to functionalize heterocycles has become an attractive alternate strategy. This concept is also interesting due to the unique reactivity pattern of these inexpensive metals. In this context we and other research groups have utilized the high-valent cobalt complexes as an inexpensive and readily available catalyst for the functionalization of heterocycles. In this review, we intend to brief recent progress made in the area of high-valent cobalt complexes catalyzed C-H functionalization of N-containing heterocycles.

Pd-Catalyzed Sequential Formation of C-C Bonds: A New Strategy for the Synthesis of (E)-α,β-Unsaturated Carbonyl Compounds from Sulfoxonium Ylides and 1-Iodo-2-((2-methylallyl)oxy)benzene Compounds

α,β-Unsaturated carbonyl compounds are significant moieties in many biological molecules and have attracted considerable attention in organic synthetic chemistry. A Pd-catalyzed cascade cyclization for the synthesis of (E)-α,β-unsaturated carbonyl compounds with the sequential formation of C-C bonds was developed. This method offers high efficiency, good functional group tolerance, and moderate to excellent yields and generally displays high stereoselectivity.

Hydroxyl-Directed Ruthenium-Catalyzed peri-Selective C-H Acylmethylation and Annulation of Naphthols with Sulfoxonium Ylides

Herein, we report a highly efficient ruthenium-catalyzed peri-selective C(sp²)-H acylmethylation of 1-naphthols with α-carbonyl sulfoxonium ylides by utilizing hydroxyl as a weakly coordinating directing group. This new method imparts good reactivity, excellent chemo- and regioselectivity, and broad functional group tolerance and involves mild reaction conditions. The C-H acylmethylated products can be readily cyclized into fluorescent annulated pyrans by a one-pot process.

Rhodium(iii)-catalyzed switchable C-H acylmethylation and annulation of 2,2'-bipyridine derivatives with sulfoxonium ylides

A novel protocol for Rh(iii)-catalyzed switchable C-H acylmethylation and annulation of 2,2'-bipyridine derivatives with sulfoxonium ylides is reported. This protocol provides a facile approach to synthesize structurally diverse acylmethylated 2,2'-bipyridine derivatives and acyl pyrido[2,3-a]indolizines with a broad range of functional group tolerance.

Synthesis of C3-sulfone substituted naphthols via rhodium(III)-catalyzed annulation of sulfoxonium ylides with alkynylsulfones

C-H activation of sulfoxonium ylides catalyzed by rhodium(iii) with subsequent annulation by alkynylsulfones was accomplished. This methodology offers a step-economical approach for assembling C3-sulfone-substituted naphthols with a high level of regioselectivity that is complementary to previous protocols. The approach has an extensive substrate spectrum and broad functional group tolerance.

Directed Cobalt-Catalyzed C-H Activation to Form C-C and C-O Bonds in One Pot via Three-Component Coupling

Herein, we disclose an efficient cobalt-catalyzed three-component coupling of benzamides, diazo compounds, and tert-butyl hydroperoxide, which provides an efficient approach to construct C(sp²)-C(sp³) and C-O bonds in one-pot accompanied with C-H activation. This protocol features low catalyst loading (4 mol %), the avoidance of additives, and excellent functional group compatibility, providing three-component coupling adducts with high yields under mild conditions (up to 88%). Mechanism studies show that the reaction may involve a radical process.

Synthesis of isoxazolidines via catalyst-free one-pot three-component cycloaddition of sulfoxonium ylides, nitrosoarenes and alkenes

A general and practical strategy for the construction of various keto-substituted isoxazolidines via one-pot three-component reaction of easily accessible, safer and more stable sulfoxonium ylides, nitrosoarenes and olefins is described.

Ruthenium-catalyzed coupling of α-carbonyl phosphoniums with sulfoxonium ylides via C–H activation/Wittig reaction sequences

A Ru(ii)-catalyzed coupling of various α-carbonyl phosphoniums with sulfoxonium ylides has been realized for the facile synthesis of 1-naphthols in good to excellent yields.

Ruthenium(II)-Catalyzed Homocoupling of α-Carbonyl Sulfoxonium Ylides Under Mild Conditions: Methodology Development and Mechanistic DFT Study

A mild ruthenium(II)-catalyzed homocoupling of α-carbonyl sulfoxonium ylides was developed and the detailed mechanism was understood based on DFT calculations in the current report. The catalytic system utilizes the α-carbonyl sulfoxonium ylide as both the directing group for ortho-sp2 C-H activation and the acylmethylating reagent for C-C coupling. Various substituents are compatible in the transformation and a variety of isocoumarin derivatives were synthesized at room temperature without any protection. The theoretical results disclosed that the full catalytic cycle contains eight elementary steps, and in all the cationic Ru(II) monomer is involved as the catalytic active species. The acid additive is responsible for protonation of the ylide carbon prior to the intramolecular nucleophilic addition and C-C bond cleavage. Interestingly, the intermediacy of free acylmethylation intermediate or its enol isomer is not necessary for the transformation.

Metal-Free Chemoselective Reaction of Sulfoxonium Ylides and Thiosulfonates: Diverse Synthesis of 1,4-Diketones, Aryl Sulfursulfoxonium Ylides, and β-Keto Thiosulfones Derivatives

A diverse chemoselective insertion reaction of sulfoxonium ylides and thiosulfonates under transition-metal-free conditions is developed, which successfully affords 1,4-diketone compounds, arylthiosulfoxide-ylides, and β-keto thiosulfones, respectively. The nucleophilic addition of two molecular sulfoxonium ylides to construct sulfone-substituted 1,4-dione compounds is the highlight of this work.

Copper-Catalyzed Annulation or Homocoupling of Sulfoxonium Ylides: Synthesis of 2,3-Diaroylquinolines or α,α,β-Tricarbonyl Sulfoxonium Ylides

An unprecedented copper-catalyzed reaction of sulfoxonium ylides and anthranils is reported that enables an easy access to 2,3-diaroylquinolines through a [4+1+1] annulation. Copper-catalyzed homocoupling of sulfoxonium ylides provided α,α,β-tricarbonyl sulfoxonium ylides, which provides a strategy to extend the carbon chain through C-C bond formation. The utility of the products as well as the mechanistic details of the process are presented.

Palladium-Catalyzed Synthesis of α-Carbonyl-α'-(hetero)aryl Sulfoxonium Ylides: Scope and Insight into the Mechanism

Despite recent advances, a general method for the synthesis of α-carbonyl-α'-(hetero)aryl sulfoxonium ylides is needed to benefit more greatly from the potential safety advantages offered by these compounds over the parent diazo compounds. Herein, we report the palladium-catalyzed cross-coupling of aryl bromides and triflates with α-carbonyl sulfoxonium ylides. We also report the use of this method for the modification of an active pharmaceutical ingredient and for the synthesis of a key precursor of antagonists of the neurokinin-1 receptor. In addition, the mechanism of the reaction was inferred from several observations. Thus, the oxidative addition complex [(XPhos)PhPdBr] and its dimer were observed by ³¹P{¹H} NMR, and these complexes were shown to be catalytically and kinetically competent. Moreover, a complex resulting from the transmetalation of [(XPhos)ArPdBr] (Ar = p-CF₃-C₆H₄) with a model sulfoxonium ylide was observed by mass spectrometry. Finally, the partial rate law suggests that the transmetalation and the subsequent deprotonation are rate-determining in the catalytic cycle.

Rhodium-catalyzed tandem acylmethylation/annulation of N-nitrosoanilines with sulfoxonium ylides for the synthesis of substituted indazole N-oxides

An atom-economical protocol for synthesizing indazole N-oxides from readily available N-nitrosoanilines and sulfoxonium ylides through the rhodium(iii)-catalyzed C–H activation and cyclization reaction is described here.