Ruthenium-catalyzed synthesis of indole derivatives from N-aryl-2-aminopyridines and alpha-carbonyl sulfoxonium ylides

Microwave-Assisted Ru(II)-Catalyzed Regioselective Methyl Acylation of 2-Arylbenzoazoles: Synthesis of Benzofuran Conjugates via C-H Activation/Annulation

An efficient Ru(II)-catalyzed C-H functionalization protocol for 2-arylbenzoazoles as the directing group and sulfoxonium ylide has been developed. Gratifyingly, concomitant annulation was observed when 3-(benzo[d]azol-2-yl) phenol was used, enabling the construction of benzofuran conjugates. Notably, the utilization of water as the solvent and an energy efficient approach makes the reaction greener, contributing to overall sustainability. This protocol exhibits excellent scalability up to the gram scale with a diverse array of substitutions. Furthermore, the mechanism was examined by ESI-MS, and photophysical studies were also performed.

[Cp*IrCl2]2-Catalyzed Amidocarbonation of Olefins with Sulfoxonium Ylides toward Functionalized Isoindolin-1-ones

A [Cp*IrCl2]2-catalyzed amidocarbonation of olefins with sulfoxonium ylides has been developed to generate diverse biologically important isoindolin-1-ones in high efficiency under mild reaction conditions. Mechanism studies indicated that this cascade reaction was triggered by amino-iridation of the olefin unit to generate iridacycle, followed by formal migratory insertion with sulfoxonium ylides. This newly developed method features broad substrate scopes and operational simplicity.

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.

C-H acylation of aniline derivatives with α-oxocarboxylic acids using ruthenium catalyst

An efficient and convenient synthetic strategy for ruthenium(II)-catalyzed ortho-acylation of N-(2-pyridyl)-anilines using α-oxycarboxylic acids as acyl sources is described. The procedure can smoothly proceed under mild conditions, showing good functional group tolerance. Valuable ortho-acylated aniline products have been obtained with moderate to good yields. Furthermore, the reaction could be easily scaled up to the gram scale.

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.

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.

Palladium-catalyzed cross-coupling reaction of sulfoxonium ylides and benzyl bromides by carbene migratory insertion

A palladium-catalyzed cross-coupling reaction of sulfoxonium ylides and benzyl bromides has been developed, which has potential safety advantages over previous carbene coupling reactions using either diazo compounds or their in situ precursors. This reaction affords polysubstituted olefins, and features good substrate tolerance and is suitable for late-stage modification of biologically active molecules. Pd-carbene migratory insertion is supposed to be involved in this coupling reaction.

Iridium(III)-Catalyzed Tandem Annulation of Pyridine-Substituted Anilines and α-Cl Ketones for Obtaining 2-Arylindoles

A facile and expeditious protocol for the synthesis of 2-arylindole compounds from readily available N-(2-pyridyl)anilines and commercially available α-Cl ketones through iridium-catalyzed C-H activation and cyclization is reported here. As a complementary approach to the conventional strategies for indole synthesis, the transformation exhibits powerful reactivity, tolerates a large number of functional groups, and proceeds with good to excellent yields under mild conditions, providing a straightforward method to obtain structurally diverse and valuable indole scaffolds. Furthermore, the reaction could be easily scaled up to gram scale.

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.

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(iii)-catalyzed C–H annulation of 2-acetyl-1-arylhydrazines with sulfoxonium ylides: synthesis of 2-arylindoles

An efficient Rh(iii)-catalyzed synthesis of 2-arylindole derivatives via intermolecular C–H annulation of arylhydrazines with sulfoxonium ylides was accomplished. A variety of 2-acetyl-1-arylhydrazines with sulfoxonium ylides were converted into 2-arylindoles in satisfactory yields. Excellent selectivity and good functional group tolerance of this transformation were also observed.

Rh(iii)-catalyzed intermolecular C–H annulation of arylhydrazines with sulfoxonium ylides for synthesis of 2-arylindole derivatives was well established.

Ruthenium-catalyzed α-carbonyl sulfoxonium ylide annulations with aryl substituted pyrazoles via C–H/N–H bond functionalizations

An efficient method for the construction of various pyrazolo[5,1-a]isoquinolines has been achieved via Ru(ii)-catalyzed α-carbonyl sulfoxonium ylide annulations with aryl substituted pyrazoles.

Theoretical investigation on the Cu(i)-catalyzed N-carboxamidation of indoles with isocyanates to form indole-1-carboxamides: effects of solvents

The solvents act as the hydrogen-bond acceptor to facilitate intermolecular addition, and then play the proton-shuttle to assist H1⁺-shift. The stronger electron-donating property of solvent is favorable for the present Cu(i)-catalyzed reactions.

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.

Synthesis of 2-Arylindoles by Rhodium-Catalyzed/Copper-Mediated Annulative Coupling of N-Aryl-2-aminopyridines and Propargyl Alcohols via Selective C-H/C-C Activation

A versatile rhodium-catalyzed/copper-mediated C-H/C-C activation and cascade annulation reaction was described to form 2-arylindole derivatives. Highly selective C-C bond cleavage of γ-substituted tert-propargyl alcohols occurred, together with pyridine-directed ortho C(sp²)-H bond activation, affording a series of 2-arylindoles with yields up to 90%. Subsequent derivations were smoothly conducted to access polyfunctionalized 2-arylindoles, illustrating the potential applications of this method.

Rhodium(III)-Catalyzed [4+2] Annulation via C-H Activation: Synthesis of Multi-Substituted Naphthalenone Sulfoxonium Ylides

A convenient Rh(III)-catalyzed C-H activation and cascade [4+2] annulation for the synthesis of naphthalenone sulfoxonium ylides has been developed. This method features perfect regioselectivity, mild and redox-neutral reaction conditions, and broad substrate tolerance with good to excellent yields. Preliminary mechanistic experiments were conducted and a plausible reaction mechanism was proposed. The new type naphthalenone sulfoxonium ylides could be further transformed into multi-substituted naphthols, which demonstrates the practical utility of this methodology.

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 1-aminoindole derivatives via Rh(iii)-catalyzed annulation reactions of hydrazines with sulfoxonium ylides

Rhodium(iii)-catalyzed C–H functionalization followed by intramolecular annulation reactions between hydrazines and sulfoxonium ylides is described.

On the nucleophilic derivatization of 4,7-dibromo-[1,2,5]thiadiazolo[3,4-c]pyridine: basis for biologically interesting species and building blocks for organic materials

Eleven new thiadiazolopyridine-derived building blocks were synthesized through a selective S_NAr reaction and the key steps of their reaction mechanism and spectroscopic properties were studied.

Access to 2-naphthols via Ru(ii)-catalyzed C–H annulation of nitrones with α-diazo sulfonyl ketones

Efficient synthesis of 2-naphthols was realized by Ru(ii)-catalyzed C–H activation of aryl nitrones and intermolecular [3+3] annulation with α-diazo sulfonyl ketones under redox-neutral conditions.