Ligand-Controlled Synthesis of Azoles via Ir-Catalyzed Reactions of Sulfoxonium Ylides with 2-Amino Heterocycles

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.

Photo-Thermo-Mechanochemical Approach to Synthesize Quinolines via Addition/Cyclization of Sulfoxonium Ylides with 2-Vinylanilines Catalyzed by Iron(II) Phthalocyanine

A novel photo-thermo-mechanochemical approach to assembling quinolines catalyzed by iron(II) phthalocyanine has been realized for the first time. This transformation features a cost-efficient catalytic system and operational simplicity, is free of solvent, and shows good substrate tolerance, providing a green alternative to existing thermal approaches. Mechanistic experiments demonstrate that the in-situ-formed secondary amine may be the key intermediate for the further cyclization/aromatization process.

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.

Catalytic asymmetric cyclopropanation of sulfoxonium ylides catalyzed by a chiral-at-metal rhodium complex

An efficient asymmetric cyclopropanation of sulfoxonium ylides with α,β-unsaturated 2-acyl imidazoles catalyzed by a chiral-at-metal rhodium complex has been developed.

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.

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.

Copper-catalyzed P-H insertion reactions of sulfoxonium ylides

A copper-catalyzed P-H insertion reaction between sulfoxonium ylides and H-phosphorus oxides has been demonstrated, furnishing α-phosphonyl carboxylate derivatives in 41-93% yields. This methodology utilizing bench-stable and thermodynamically stable sulfoxonium ylides as carbene precursors in the presence of the inexpensive and readily available copper catalyst shows advantages such as mild reaction conditions, good functional group compatibility, and easy scale-up, which make this protocol attractive for large-scale chemical processing and processing at the industrial scale.

Ruthenium-Catalyzed Chemoselective N-H Bond Insertion Reactions of 2-Pyridones/7-Azaindoles with Sulfoxonium Ylides

A ruthenium-catalyzed highly chemoselective N-alkylation of 2-pyridones has been developed, affording N-alkylated 2-pyridone derivatives in good yields and excellent N-selectivity. The key to achieve this unprecedented N-H rather than O-H insertion reaction is the use of CpRu(PPh₃)₂Cl as the catalyst and sulfoxonium ylides as the alkylation reagents. Moreover, this protocol is also amenable to 7-azaindoles by slightly varying the reaction conditions. Furthermore, sulfonium ylides are also suitable alkylation reagents, providing the N-alkylated 2-pyridones in good selectivity.

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.

Enantioselective S-H Insertion Reactions of α-Carbonyl Sulfoxonium Ylides

The first example of enantioselective S-H insertion reactions of sulfoxonium ylides is reported. Under the influence of thiourea catalysis, excellent levels of enantiocontrol (up to 95 % ee) and yields (up to 97 %) are achieved for 31 examples in S-H insertion reactions of aryl thiols and α-carbonyl sulfoxonium ylides.

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.

Iridium-catalyzed arylation of sulfoxonium ylides and arylboronic acids: a straightforward preparation of α-aryl ketones

A highly efficient iridium(iii)-catalyzed arylation coupling of sulfoxonium ylides with arylboronic acids to generate α-aryl ketones has been established for the first time.

Chemospecific Cyclizations of α-Carbonyl Sulfoxonium Ylides on Aryls and Heteroaryls

The functionalization of aryl and heteroaryls using α-carbonyl sulfoxonium ylides without the help of a directing group has remained so far a neglected area, despite the advantageous safety profile of sulfoxonium ylides. Described herein are the cyclizations of α-carbonyl sulfoxonium ylides onto benzenes, benzofurans and N-p-toluenesulfonyl indoles in the presence of a base in HFIP, whereas pyrroles and N-methyl indoles undergo cyclization in the presence of an iridium catalyst. Significantly, these two sets of conditions are chemospecific for each groups of substrates.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

Organosulfur compounds have long played a vital role in organic chemistry and in the development of novel chemical structures and architectures. Prominent among these organosulfur compounds are those involving a sulfur(IV) center, which have been the subject of countless investigations over more than a hundred years. In addition to a long list of textbook sulfur-based reactions, there has been a sustained interest in the chemistry of organosulfur(IV) compounds in recent years. Of particular interest within organosulfur chemistry is the ease with which the synthetic chemist can effect a wide range of transformations through either bond formation or bond cleavage at sulfur. This review aims to cover the developments of the past decade in the chemistry of organic sulfur(IV) molecules and provide insight into both the wide range of reactions which critically rely on this versatile element and the diverse scaffolds that can thereby be synthesized.

Rh(iii)-Catalyzed dual C-H functionalization of 3-(1H-indol-3-yl)-3-oxopropanenitriles with sulfoxonium ylides or diazo compounds toward polysubstituted carbazoles

A rhodium-catalyzed annulation of 3-(1H-indol-3-yl)-3-oxopropanenitriles with sulfoxonium ylides or diazo compounds has been developed, leading to a series of polysubstituted carbazoles in moderate to good yields. This procedure proceeded with formal Rh(iii)-catalyzed (4 + 2) cycloaddition, with the functionalization of 2-C-H bonds of indole in a step-economical procedure. Additionally, this reaction could also be conducted under acidic conditions when diazo compounds were employed as the reaction partners, which was a complement to the annulation of sulfoxonium ylides under weak basic conditions.

Ruthenium(ii)-catalyzed selective C–H bond activation of imidamides and coupling with sulfoxonium ylides: an efficient approach for the synthesis of highly functional 3-ketoindoles

Ruthenium-catalyzed selective C–H bond activation of imidamides and annulation of sulfoxonium ylides were achieved, which afforded a series of 3-ketoindole derivatives in good yields, with good functional group compatibility.

Synthesis of indoles and quinazolines via additive-controlled selective C–H activation/annulation of N-arylamidines and sulfoxonium ylides

Selective synthesis of indoles and quinazolines was achieved through a precise control of C–H activation/annulation by changing additives.

A Catalytic Cross-Olefination of Diazo Compounds with Sulfoxonium Ylides

A ruthenium‐catalysed cross‐olefination of diazo compounds and sulfoxonium ylides is presented. Our reaction design exploits the intrinsic difference in reactivity of diazo compounds and sulfoxonium ylides as both carbene precursors and nucleophiles, which results in a highly selective reaction.

Sulfur-Based Ylides in Transition-Metal-Catalysed Processes

Traditionally employed in the synthesis of small ring systems and rearrangement chemistry, sulfur-based ylides occupy a unique position in the toolbox of the synthetic organic chemist. In recent years a number of pioneering researchers have looked to expand the application of these unorthodox reagents through the use of transition metal catalysis. The strength and flexibility of such a combination have been shown to be of key importance in developing powerful novel methodologies. This chapter summarises recent developments in transition metal-catalysed sulfonium/sulfoxonium ylide reactions, as well as providing a historical perspective. In overviewing the successes in this area, the authors hope to encourage others into this growing field.