Iridium-Catalyzed B–H Bond Insertion Reactions Using Sulfoxonium Ylides as Carbene Precursors toward α-Boryl Carbonyls

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.

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.

Lithium Bromide-Promoted Formal C(sp3)-H Bond Insertion Reactions of β-Carbonyl Esters with Sulfoxonium Ylides to Synthesize 1,4-Dicarbonyl Compounds

A LiBr-promoted formal C(sp3)-H bond insertion reaction between β-carbonyl esters and sulfoxonium ylides is established. This practical reaction has a wide range of substrate scope for both β-carbonyl esters and sulfoxonium ylides to give a variety of 1,4-dicarbonyl compounds with 43-94% yields. The reaction features transition-metal-free reaction conditions and exclusive C-alkylation chemselectivity. The use of bench-stable sulfoxonium ylides overcomes previous methods that require transition metal as catalysts and unstable diazo compounds or toxic haloketones as alkylation reagents.

Ru(II)-Catalyzed Carboamination of Olefins with α-Carbonyl Sulfoxonium Ylides

The first ruthenium-catalyzed carboamination of olefins with α-carbonyl sulfoxonium ylides is reported. The utilization of an inexpensive ruthenium catalyst enables the concise synthesis of pharmaceutically important isoindolin-1-ones, which possess both a stereogenic center and β-carbonyl side chain. This method is mild, efficient, and scalable and allows for the coupling of a wide range of aryl-, heteroaryl-, alkenyl-, and alkyl-substituted sulfoxonium ylides. Moreover, the carbonyl side chain in the resulting product provides a good handle for downstream transformations. For mechanistic studies, a ruthacyle complex is obtained and proven to be the key intermediate in both catalytic and stoichiometric reactions.

High-Throughput Experimentation and Machine Learning-Assisted Optimization of Iridium-Catalyzed Cross-Dimerization of Sulfoxonium Ylides

A novel and convenient approach that combines high-throughput experimentation (HTE) with machine learning (ML) technologies to achieve the first selective cross-dimerization of sulfoxonium ylides via iridium catalysis is presented. A variety of valuable amide-, ketone-, ester-, and N-heterocycle-substituted unsymmetrical E-alkenes are synthesized in good yields with high stereoselectivities. This mild method avoids the use of diazo compounds and is characterized by simple operation, high step-economy, and excellent chemoselectivity and functional group compatibility. The combined experimental and computational studies identify an amide-sulfoxonium ylide as a carbene precursor. Furthermore, a comprehensive exploration of the reaction space is also performed (600 reactions) and a machine learning model for reaction yield prediction has been constructed.

[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.

Iridium-Catalyzed Diastereo- and Enantioselective [4 + 1] Cycloaddition of Hydroxyallyl Anilines with Sulfoxonium Ylides

We present here an iridium-catalyzed diastereo- and enantioselective [4 + 1] cycloaddition reaction of hydroxyallyl anilines with sulfoxonium ylides under mild reaction conditions, leading to 3-vinyl indolines in moderate to good yields with excellent enantioselectivities. Control experiments disclosed a plausible reaction mechanism.

Demethyl oxidative halogenation of diacyl dimethylsulfonium methylides

α-Halo-α-methylthio-β-ketosulfones containing a quaternary halocarbon stereocenter were prepared via selective demethyl oxidative halogenations of diacyl dimethylsulfonium methylides in moderate to excellent yields (39 examples; up to 98%). The current protocols directly and efficiently introduce a halogen atom into organic compounds with high functional group tolerance under metal-free conditions.

Synthesis of α-Boryl Ketones via Hydration or Oxidation of B(MIDA)-Decorated Alkynes

α-Boryl ketones are traditionally challenging targets in organic synthesis. Reported herein is a mild and metal-free synthesis of α-boryl ketones via the hydration or oxidation of N-methyliminodiacetyl boronate (B(MIDA))-decorated alkynes. A new hydration system comprised of AcCl and H₂O in HFIP allows the hydration of arylethynyl B(MIDA)s at room temperature with decent functional group tolerance. An oxidative carbon deletion process of propargylic B(MIDA)s is also developed for the synthesis of aliphatic α-boryl ketones. An intriguing β-boron effect was observed to account for the unique site- and chemoselectivities. The application of the products in the synthesis of borylated heterocycles was demonstrated.

Halide-promoted pyridinylation of α-acylmethylides with 2-halo-1-methylpyridinium iodides as reagents

Halide-promoted pyridinylation between α-acyl sulfonylmethylides and 2-halo-1-methylpyridinium iodides in a transition-metal-free protocol is described. A broad range of α-acyl sulfonylmethylides were transformed to bifunctionalized vinylsulfones in moderate to good yields, thereby providing a facile and practical approach for constructing methylthio- and pyridinoxyl-substituted vinylsulfones. The substrates can be extended to other acyl methylides. The reaction was shown to entail the formation of a C-O bond and consecutive breaking of C-S, C-Cl and C-N bonds.

The thiol-sulfoxonium ylide photo-click reaction for bioconjugation

Visible-light-mediated methods were heavily studied as a useful tool for cysteine-selective bio-conjugation; however, many current methods suffer from bio-incompatible reaction conditions and slow kinetics. To address these challenges, herein, we report a transition metal-free thiol-sulfoxonium ylide photo-click reaction that enables bioconjugation under bio-compatible conditions. The reaction is highly cysteine-selective and generally finished within minutes with naturally occurring riboflavin derivatives as organic photocatalysts. The catalysts and substrates are readily accessible and bench stable and have satisfactory water solubility. As a proof-of-concept study, the reaction was smoothly applied in chemo-proteomic analysis, which provides efficient tools to explore the druggable content of the human proteome.

Gold-Catalyzed Cyclization/Hydroboration of 1,6-Enynes: Synthesis of Bicyclo[3.1.0]hexane Boranes

The gold-catalyzed cyclization/hydroboration of 1,6-enynes offers facile, versatile, and atom-economical one-step access to bicyclo[3.1.0]hexane boranes. This new protocol proceeds in moderate to good yields under mild conditions. Different from bicyclo[3.1.0]hexane borates, these products are stable in air and during chromatography. Moreover, the borane moiety of the products can readily undergo a diverse array of transformations. The kinetic isotope effect experiment indicates that the hydrogen-transfer step is a fast process, which is not involved in the rate-limiting step.

Synthesis of I(III)/S(VI) reagents and their reactivity in photochemical cycloaddition reactions with unsaturated bonds

The development of novel methodologies for the introduction of the sulfoxonium group under mild conditions is appealing but remains underexplored. Herein we report the synthesis of a class of hypervalent iodine reagents with a transferrable sulfoxonium group. These compounds enable mixed iodonium-sulfoxonium ylide reactivity. These well-defined reagents are examined in visible-light-promoted cyclization reactions with a wide range of unsaturated bonds including alkenes, alkynes, nitriles, and allenes. Two distinct cyclization pathways are identified, which are controlled by the substituent of the unsaturated bond. The cycloaddition protocol features simple operation, mild reaction conditions, and excellent functional group tolerance, affording a broad range of sulfoxonium-containing cyclic structures in moderate to excellent yields. Furthermore, the sufoxonium group in the product can be transformed into diverse functional groups and structural motifs via single electron transfer and transition-metal catalysis.

Visible-light-driven PhSSPh-catalysed regioselective hydroborylation of α,β-unsaturated carbonyl compounds with NHC-boranes

A photo-induced transition-metal-free regioselective hydroborylation of α,β-unsaturated carbonyl compounds is developed. The PhSSPh reagent was employed as the photocatalyst, and NHC-BH₃ was used as the boron source. This transformation shows a broad substrate scope and provides a wide range of α-borylcarbonyl molecules in good to excellent yields.

Copper-catalyzed B−H bond insertion reaction of azide-ynamide with borane adducts via α-imino copper carbenes

A new copper-catalyzed B−H bond insertion reaction between azide-ynamides and borane adducts has been developed, which represents the first B−H bond insertion into α-imino metal carbenes. This protocol enables the...

Enantioselective Indole Insertion Reactions of α-Carbonyl Sulfoxonium Ylides

The first example of organocatalytic enantioselective C-H insertion reactions of indoles and sulfoxonium ylides is reported. Under the influence of phosphoric acid catalysis, levels of enantiocontrol in the range of 20-93% ee and moderate yields (up to 50%) were achieved for 29 examples in formal C-H insertion reactions of free indoles and α-carbonyl sulfoxonium ylides. No nitrogen protection on the indole is necessary.

Uncommon carbene insertion reactions

Transition-metal-catalysed carbene insertion reaction is a straightforward and efficient protocol for the construction of carbon–carbon or carbon–heteroatom bonds. Compared to the intensively studied and well-established “common” carbene insertion reactions, including carbene insertion into C–H, Si–H, N–H, O–H, and S–H bonds, several “uncommon” carbene insertion reactions, including carbene insertion into B–H, Sn–H, Ge–H, P–H, F–H, C–C, and M–M bonds, have been neglected for a long time. However, more and more studies on uncommon carbene insertion reactions have been disclosed recently, and clearly demonstrate the great synthetic potential of these reactions. The current perspective reviews the history and the newest advances of uncommon carbene insertion reactions, discusses their potential applications and challenges, and also presents an outlook of this promising field.

Transition-metal-catalysed carbene insertion reaction is a straightforward and efficient protocol for the construction of carbon–carbon or carbon–heteroatom bonds.

Dirhodium-Catalyzed Enantioselective B-H Bond Insertion of gem-Diaryl Carbenes: Efficient Access to gem-Diarylmethine Boranes

The scarcity of reliable methods for synthesizing chiral gem-diarylmethine borons limits their applications. Herein, we report a method for highly enantioselective dirhodium-catalyzed B-H bond insertion reactions with diaryl diazomethanes as carbene precursors. These reactions afforded chiral gem-diarylmethine borane compounds in high yield (up to 99 % yield), high activity (turnover numbers up to 14 300), high enantioselectivity (up to 99 % ee) and showed unprecedented broad functional group tolerance. The borane compounds synthesized by this method could be efficiently transformed into diaryl methanol, diaryl methyl amine, and triaryl methane derivatives with good stereospecificity. Mechanistic studies suggested that the borane adduct coordinated to the rhodium catalyst and thus interfered with decomposition of the diazomethane, and that insertion of a rhodium carbene (generated from the diaryl diazomethane) into the B-H bond was most likely the rate-determining step.

Copper-Catalyzed Cyclization of N-Propargyl Ynamides with Borane Adducts through B-H Bond Insertion

An efficient copper-catalyzed cyclization of N-propargyl ynamides with borane adducts through B-H bond insertion has been developed. A series of valuable organoboron compounds are constructed in generally good yields with a wide substrate scope and good functional group tolerance under mild reaction conditions. Importantly, this protocol via vinyl cation intermediates constitutes a novel way of B-H bond insertion.

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.

Synthetic Routes Towards the Synthesis of Geminal α-Difunctionalized Ketones

The importance of gem-difunctionalized ketones is represented by their broad applications across chemical boundaries over recent years. The interesting reactivities that this class of compounds possess have made them ideal building blocks to access high-value organic molecules. Furthermore, the gem-difunctionalized ketone moiety has featured in numerous bioactive molecules. For these reasons, a plethora of routes to access such significant molecules have been developed by research groups worldwide - this account looks at delineating the synthesis of gem-difunctionalized ketones from carbonyl substrates, diazo compounds, sulfur ylides and alkynyl reactants.

Synthesis of disubstituted γ-butyrolactones and spirocyclopropanes via a multicomponent reaction of aldehydes, Meldrum's acid and sulfoxonium ylides

An efficient synthesis of disubstituted γ-butyrolactones and spirocyclopropanes via multicomponent reaction of aldehydes, Meldrum's acid and sulfoxonium ylides has been developed.

Insertion of Alkylidene Carbenes into B-H Bonds

We have developed a protocol for insertion of alkylidene carbenes into the B-H bonds of amine-borane adducts, enabling, for the first time, the construction of C(sp²)-B bonds by means of carbene-insertion reactions. Various acyclic and cyclic alkenyl borane-amine adducts were prepared from readily accessible starting materials in good to high yields and were subsequently subjected to a diverse array of functional group transformations. The unprecedented spiro B-N heterocycles prepared in this study have potential utility as building blocks for the synthesis of pharmaceuticals. Preliminary mechanistic studies suggest that insertion of the alkylidene carbenes into the B-H bonds of the amine-borane adducts proceeds via a concerted process involving a three-membered-ring transition state.

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-catalyzed B-H insertion of sulfoxonium ylides and borane adducts: a versatile platform to α-boryl carbonyls

Iridium-catalyzed boron-hydrogen bond insertion reactions of trimethylamine-borane and sulfoxonium ylides have been demonstrated, furnishing α-boryl ketones in moderate to excellent yields in most cases (51 examples; up to 84%). This practical and scalable insertion reaction showed broad substrate scope, high functional-group compatibility and could be applied in late-stage modification of structurally complex drug compounds. Further synthetic applications were also demonstrated.

Sulfoxonium ylides: simple compounds with chameleonic reactivity

Sulfoxonium ylides, manageable compounds with an appealing safety profile, adapt to reaction partners like chameleons to their environment, resulting in a variety of useful, and sometimes surprising and unique, reactions.