Iodonium Ylides as Carbene Precursors in Rh(III)-Catalyzed C–H Activation

Sulfenylcarbene-Mediated Carbon Atom Insertion for the Late-Stage Functionalization of N-Heterocycles

Late-stage functionalization (LSF) is a crucial strategy in drug discovery, allowing the modification of complex molecules, including pharmaceuticals, to enhance chemical diversity in drug libraries. We harness the chemoselectivity of sulfenylcarbenes, which selectively react with alkenes even in the presence of more reactive functional groups such as alcohols, carboxylic acids, and amines. This reactivity allows sulfenylcarbenes to insert a single carbon atom bearing diverse functional groups, transforming pyrroles, indoles, and imidazoles into synthetically challenging pyridines, quinolines, and pyrimidines, respectively. Sulfenylcarbene precursors are easily synthesized in two steps from commercially available reagents. Our metal-free LSF approach employs benchtop-stable sulfenylcarbene precursors and enables late-stage modification of natural products, amino acids, pharmaceuticals, and C-glycosides. Mechanistic studies and density functional theory (DFT) calculations were conducted to investigate the regio- and chemoselectivity outcomes.

Rhodium-Catalyzed C(sp2)-H Activation and [3+3] Annulation: Accessing Pyrano[3,2-c]chromene-2,5-diones as TASK-3 Activators

Herein, an efficient Rh-catalyzed C-H activation/annulation between α,β-unsaturated amides and coumarin-derived iodonium ylides has been developed, affording novel pyrano[3,2-c]chromene-2,5-diones and analogues in high yields. Most products could be easily isolated by precipitation in ethanol, followed by simple filtration. Additionally, this protocol demonstrated the benefits of environmentally friendly conditions, air compatibility, good functional group compatibility, scale-up synthesis with low catalyst loading, and a recyclable Rh catalyst. Importantly, compounds 3m and 3w demonstrated moderate agonist activity on the TASK-3 channel, with I/I0 values of 1.7650 ± 0.1058 and 1.400 ± 0.0589, respectively.

Synthesis of 1-Aminoisoquinolines via Rh(III)-Catalyzed C-H Cascade Annulation of Benzamidines with Iodonium Ylides

A Rh(III)-catalyzed C-H cascade annulation reaction of benzamidine hydrochlorides with iodonium ylides has been successfully accomplished, providing an efficient strategy for the synthesis of various 1-aminoisoquinoline derivatives in moderate to good yields. Here, iodonium ylide serves as an accessible and safe carbene precursor. Further derivatizations were implemented to demonstrate the potential utility of this cascade annulation reaction. Furthermore, the photophysical properties of these compounds may have potential applications in photoelectric materials.

Recent advances in carboxyl-directed dimerizations and cascade annulations via C-H activations

C-H functionalization provides an efficient route to construct complex organic molecules. The introduction of directing groups enhances the site-selectivity of the reaction. Carboxyl as a directing group can be easily transformed into other functional groups afterwards. Due to its good reactivity, it can undergo cascade annulation reactions to build valuable heterocycle skeletons in one pot. Moreover, carboxyl can easily be removed via decarboxylation, which allows it to serve as a unique traceless directing group in C-H functionalization. These characteristics make carboxyl a promising directing group, which is superior to nitrogen-containing compounds with strong coordination ability to a certain extent. This feature article reviews the applications of carboxyl as a classical directing group and a unique traceless-directing group in cascade annulation reactions to access diverse carbocycles and heterocycles.

C(sp3)-H Bond Functionalization of 8-Methylquinolines

Quinolines have emerged as essential components in various medicinal agents, playing a key role in treating various ailments. Numerous drugs with a quinoline core have been recognized for their antimalarial, antibacterial, and anticancer activities and have been successfully commercialized, including chloroquine, ciprofloxacin, topotecan, etc. Over the past two decades, a tremendous expansion in the C-H bond functionalization of quinoline scaffolds to widen this chemical space for drug discovery have been witnessed. This review article summarizes the efforts toward C(sp3)-H functionalization of 8-methylquinolines for C(sp3)-C/X bond formation under metal and metal-free strategies. Each section briefly overviews the C(sp3)-H functionalization of 8-methylquinoline, highlighting the metal and metal-free approaches.

Iodonium(III) Ylide: An Iodoalkylation Reagent with Aryne

A tandem Hexadehydro-Diels-Alder (HDDA)/[2 + 2] cycloaddition/aryl migration reaction of iodonium ylide with tetrayne is described, in which iodonium ylide served as a unique double bond and reacted with aryne to form a four-membered iodonium(III) cycle, then converted to iodoarene after aryl group migration from iodine to adjacent carbon. This strategy allows the efficient construction of fully substituted iodoarene compounds.

Bioinspired Synthesis of Phelligridin Analogues via Ru-Catalyzed C-H Activation/[4 + 2] Annulation of Aryl Imidates with Heteroaromatic Iodonium Ylides

The first Ru(II)-catalyzed C-H activation/[4 + 2] annulation of aryl imidates with heteroaromatic iodonium ylides is reported. Our approach features the utilization of a commercially available ruthenium catalyst, providing a one-step construction of phelligridin analogues from easily available and nonpreactivated starting materials. The developed methodology is successfully employed for the total synthesis of phelligridin A, significantly streamlining previous multistep synthesis. The potential of this approach is further demonstrated through a modular synthesis of the core structure of phelligridin C/D.

Cyclic Iodonium Ylide Unlocked Pd-Catalyzed α-Acyloxylation of Cyclic 1,3-Dicarbonyls with Carboxylic Acids

To date, a general approach for the direct α-acyloxylation of cyclic 1,3-dicarbonyls remains challenging. Herein, we report a Pd-catalyzed α-acyloxylation of cyclic 1,3-dicarbonyl-derived hypervalent iodine compounds with highly abundant carboxylic acids. Our approach utilizes a commercially available Pd(OAc)2 catalyst, which exhibits mild reaction conditions, scalability, operational simplicity, and robustness against moisture and air. Importantly, our approach eliminates the need for excess carboxylic acids (only 1 equiv) and the use of explosive peroxides and is compatible with diverse complex substrates (e.g., glycyrrhetinic acid and celastrol). The power of this method is further demonstrated through significantly simplifying a previous synthesis.

Transition Metal-Catalyzed C-H Activation/Functionalization of 8-Methylquinolines

8-Methylquinoline is regarded as an ideal substrate to participate in diversely C(sp3)-H functionalization reactions. The presence of the chelating nitrogen atom enables 8-methylquinoline to easily form cyclometallated complexes with various transition metals, leading to the selective synthesis of functionalized quinolines. Considering the great importance of quinoline cores in medicinal chemistry, in this review article, we have covered the publications related to the C-H activation and functionalization of 8-methylquinoline under transition metal catalysis during the last decade.

Recent Progress in Synthetic Applications of Hypervalent Iodine(III) Reagents

Hypervalent iodine(III) compounds have found wide application in modern organic chemistry as environmentally friendly reagents and catalysts. Hypervalent iodine reagents are commonly used in synthetically important halogenations, oxidations, aminations, heterocyclizations, and various oxidative functionalizations of organic substrates. Iodonium salts are important arylating reagents, while iodonium ylides and imides are excellent carbene and nitrene precursors. Various derivatives of benziodoxoles, such as azidobenziodoxoles, trifluoromethylbenziodoxoles, alkynylbenziodoxoles, and alkenylbenziodoxoles have found wide application as group transfer reagents in the presence of transition metal catalysts, under metal-free conditions, or using photocatalysts under photoirradiation conditions. Development of hypervalent iodine catalytic systems and discovery of highly enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important recent achievement in the field of hypervalent iodine chemistry. Chemical transformations promoted by hypervalent iodine in many cases are unique and cannot be performed by using any other common, non-iodine-based reagent. This review covers literature published mainly in the last 7-8 years, between 2016 and 2024.

Tunable Rh(III)-Catalyzed C(sp2)-H Bond Functionalization of Aryl Imidates with Cyclic 1,3-Diones: Strategic Use of Directing Groups

A tunable Rh(III)-catalyzed C(sp2)-H bond functionalization of aryl imidates with cyclic 1,3-diones was developed. With suitable and straightforward reaction condition adjustments, the C-H bond functionalization of diverse aryl imidates with cyclic 1,3-diones occurred smoothly and precisely at room temperature. Accompanied by different directing group transformations, a series of corresponding aryl nitriles, hydrophenanthridin-1(2H)-ones, spiro isoindoles, or hydrophenanthridine-1,6(2H,5H)-diones were synthesized in good yields to provide a rational directing group utilization strategy for the Rh(III)-catalyzed C(sp2)-H bond activation. Control experiments and primary mechanistic studies revealed that solvent effects and functional group electronic effects might influence the reaction's selectivity.

Rhodium(III)-Catalyzed C-H Activation/[5 + 2] Cascade Annulation of Aroyl Hydrazides with Iodonium Ylides for the Synthesis of Seven-Membered Dibenzodiazepinediones

A novel Rh(III)-catalyzed C-H activation/[5 + 2] cascade annulation of aroyl hydrazides with iodonium ylides is accomplished, in which diverse seven-membered dibenzodiazepinediones were afforded in moderate to excellent yields. This annulation reaction features an ideal functional group tolerance and a wide substrate scope. Large-scale and derivatization reactions were conducted to demonstrate the potential utility of this transformation.

Rh(III)-catalyzed [4 + 1] annulation of 1-arylindazolones with alkynyl cyclobutanols: access to indazolo[1,2-a]indazolones

A convenient and efficient synthesis of structurally diverse indazolo[1,2-a]indazolones via a Rh(III)-catalyzed [4 + 1] annulation of 1-arylindazolones with alkynyl cyclobutanols has been achieved by combining C-H and C-C bond cleavage. This cascade reaction features readily available starting materials, good functional group tolerance, broad substrate scope, and excellent atom-economy.

Transition-Metal-Catalyzed Directed C-H Bond Functionalization with Iodonium Ylides: A Review of the Last 5 Years

Transition-metal-catalyzed directed C-H functionalization with various carbene precursors has been widely employed for constructing a wide range of complex and diverse active molecules through metal carbene migratory insertion processes. Among various carbene precursors, iodonium ylides serve as a novel and emerging carbene precursor with features including easy accessibility, thermal stability and high activity, which have attracted great attention from organic chemists and have achieved tremendous success in organic transformation. In this review, recent progress on the application of iodonium ylides with multifunctional coupling characteristics in C-H bond activation reactions is summarized, and the potential of iodonium ylides is discussed.

Rhodium(III)-Catalyzed Oxidative Cross-Coupling of N-Pyrimidylindoles with Cyclic β-Keto Esters for Accessing All-Carbon Quaternary Centers

Rh(III)-catalyzed direct oxidative C-H/C-H cross-coupling between N-pyrimidylindoles and β-ketoesters is presented. Easily available β-ketoesters are used as an alkylating agent for the facile construction of all-carbon quaternary centers under mild conditions. The ester group in the product can undergo decarboxylation or decarboxylative amination.

Accessing 7,8-Dihydroquinoline-2,5-diones via Rh-Catalyzed Olefinic C-H Activation/[4+2] Cyclization

Herein, we report a rhodium-catalyzed C-H activation/[4+2] cyclization reaction between α,β-unsaturated amides and iodonium ylides for the synthesis of novel 7,8-dihydroquinoline-2,5-diones and analogues. This protocol provides a series of pyridones fused with saturated cycles with good functional group compatibility, good water and air tolerance, and good to excellent yields under mild and green reaction conditions. Additionally, scale-up synthesis can be smoothly performed with as low as 0.25 mol % catalyst loading. Recycling experiments and different transformation experiments were also carried out to demonstrate the potential synthetic utility of this protocol.

Rh(III)-catalyzed C(sp2)-H functionalization/[4+2] annulation of oxadiazolones with iodonium ylides to access diverse fused-isoquinolines and fused-pyridines

In this study, a Rh(III)-catalyzed C-H/N-H [4+2] annulation of oxadiazolones with iodonium ylides has been developed, which afforded a series of diverse fused-isoquinolines and fused-pyridines in moderate to high yields. These divergent synthesis protocols featured mild conditions, broad substrate scope, and functional-group compatibility. In addition, scale-up synthesis, related applications and preliminary mechanistic explorations were also accomplished.

Rh-Catalyzed α-Arylation of Cyclic 1,3-Dicarbonyls with Benzocyclobutenols Enabled by a Cyclic Iodonium Ylide Strategy

To date, the general and catalytic α-arylation of cyclic 1,3-dicarbonyls remains elusive. We now report the first Rh-catalyzed α-arylation of cyclic 1,3-dicarbonyls with benzocyclobutenols through a cyclic iodonium ylide strategy. Our strategy represents a good solution for the previously challenging α-arylation of cyclic 1,3-dicarbonyls with sterically demanding aryl partners, which is especially appropriate for structurally unique heteroaromatic 1,3-dicarbonyls. Our approach features mild conditions, readily available starting materials, high yields, excellent functional group-tolerance, and simple operation, providing expedient access toward medically important 2-aryl (hetero)cyclic 1,3-dicarbonyls. The practicality of this approach is demonstrated by the gram-scale synthesis, one-pot synthesis, and numerous downstream transformations.

Catalytic and Base-free Suzuki-type α-Arylation of Cyclic 1,3-Dicarbonyls via a Cyclic Iodonium Ylide Strategy

To date, it remains challenging to achieve a general and catalytic α-arylation of cyclic 1,3-dicarbonyls, particularly ubiquitous heteroaromatic ones. In most cases, the preparation of their medically significant arylated derivatives requires multistep synthetic sequences. Herein, we introduce a new, convenient strategy involving the conversion of cyclic 1,3-dicarbonyls to cyclic iodonium ylides (CIYs), followed by rhodium-catalyzed α-arylation with arylboronic reagents via carbene coupling. This approach is mild, operationally simple, base-free, biocompatible, and exhibits broad substrate scope (>100 examples), especially with respect to various heteroaromatic 1,3-dicarbonyls and ortho-substituted or base-sensitive arylboronic acids. Importantly, owing to the excellent compatibility with various arylboronic acids or boronate esters (ArBpin, ArBneop, or ArBF3K), this method allows the late-stage installation of heterocyclic 1,3-dicarbonyl motifs in highly complex settings. The utility of this transformation is further demonstrated through significantly simplifying the synthesis of several bioactive molecules and natural products.

Rhodium-Catalyzed Difunctionalization of Alkenes Using Cyclic 1,3-Dicarbonyl-Derived Iodonium Ylides

Herein, we introduce an iodonium ylide strategy to achieve novel α-alkylation of cyclic 1,3-dicarbonyls through harnessing C(sp3)-Rh species generated from 5-exo-trig cyclization to provide rapid access to molecular hybridization of medically important isoindolin-1-ones and cyclic 1,3-dicarbonyls from readily available substrates. This approach features mild conditions, good yield, excellent functional group tolerance, and the simultaneous formation of two new chemical bonds and one stereogenic center. Moreover, the hydroxyl group of resulting product provides a good handle for downstream transformations. Importantly, we also demonstrate this strategy can be achieved in a one-pot manner. A C(sp3)-Rh complex was prepared and proved to be the key intermediate.

Synthesis of spiropyrans via Ru(II)-catalyzed coupling of 3-aryl-2H-benzo[b][1,4]oxazines with benzoquinones

An efficient Ru(II)-catalyzed C-H activation-based spiroannulation of benzoxazines with the easily available benzoquinone and N-sulfonyl quinone monoimine has been realized, providing a straightforward strategy to access NH-containing spiropyrans in moderate to good yields with good functional group compatibility. The procedure features atom- and step-economy, mild conditions, and excellent chemoselectivity. Moreover, a catalytically competent five-membered cycloruthenated complex has been isolated.

Synthesis of Tetrahydro-indolones through Rh(III)-Catalyzed [3 + 2] Annulation of Enaminones with Iodonium Ylides

An unprecedented protocol for a Rh(III)-catalyzed [3 + 2] annulation from simple and readily available enaminones and iodonium ylides has been developed. The novel strategy allows for access to a new class of structurally diverse tetrahydro-indolones with high efficiency and a broad substrate scope. In addition, this transformation represents the first example of the selective Rh(III)-catalyzed alkenyl C-H bond functionalization and annulation of enaminones. Finally, the potential applications of this protocol are demonstrated through gram-scale reaction and late-stage modification.

Rhodium(III)-catalyzed intermolecular [3+3] annulation of benzoxazines with quinone compounds: access to spiro-heterocyclic scaffolds

A rhodium(III)-catalyzed redox-neutral spiroannulation approach to access the spiro[benzo[b][1,4]oxazine-benzo[c]chromene skeleton is described in this contribution. A variety of spiro[5.5]-heterocyclic scaffolds were obtained in moderate to excellent yields under mild conditions. Key features of this protocol are good substrate scope, silver-free conditions, low catalyst loadings, easy handling under air and 100% atom economy. Furthermore, scale-up reactions and late-stage derivatizations highlight the potential synthetic utility of this methodology.

Rh(III)-Catalyzed Direct C-H Cyclization of N-Nitrosoanilines with 1,3-Dicarbonyl Compounds: A Route to Tetrahydrocarbazol-4-ones

A novel and efficient Rh(III)-catalyzed direct C-H bond tandem annulation of N-nitrosoanilines with 1,3-dicarbonyl compounds through two C-H bond cleavage was developed. This protocol provides a rapid access to a series of valuable tetrahydrocarbazol-4-ones with the feature of readily available starting materials, broad functional group tolerance, and in situ generation of carbene precursors. Importantly, some reaction products exhibited promising antiproliferative activity in cancer cell lines.

Rh-Catalyzed C-H Activation/Annulation of Enaminones and Cyclic 1,3-Dicarbonyl Compounds: An Access to Isocoumarins

A facile access to isocoumarins has been established via rhodium(III)-catalyzed C-H bond activation and intramolecular C-C cascade annulation of enaminones and cyclic 1,3-dicarbonyl compounds. The synthetic protocol features a wide range of substrates with high functional group tolerance, mild reaction conditions, and the selective cleavage of the enaminone C-C bond. Notably, the cyclic 1,3-dicarbonyl compounds can in situ-generate iodonium ylide as a carbene precursor to prepare polycyclic scaffolds by reacting with PhI(OAc)₂. The application of this method to prepare useful synthetic precursors and bioactive skeletons is also exemplified.

Practical synthesis of isocoumarins via Rh(III)-catalyzed C-H activation/annulation cascade

Herein, we report an unprecedented Rh(III)-catalyzed C-H activation/annulation cascade of readily available enaminones with iodonium ylides towards the convenient synthesis of isocoumarins. This coupling system proceeds in useful chemical yields (up to 93%) via a cascade C-H activation, Rh-carbenoid migratory insertion and acid-promoted intramolecular annulation. The success of gram-scale reaction and diverse functionalization of isocoumarins demonstrated the synthetic utility of this protocol.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Iodonium ylides: an emerging and alternative carbene precursor for C-H functionalizations

The metal-catalyzed successive activation and functionalization of arene/heteroarene is one of the most fundamental transformations in organic synthesis and leads to privileged scaffolds in natural products, pharmaceuticals, agrochemicals, and fine chemicals. Particularly, transition-metal-catalyzed C-H functionalization of arenes with carbene precursors via metal carbene migratory insertion has been well studied. As a result, diverse carbene precursors have been evaluated, such as diazo compounds, sulfoxonium ylides, triazoles, etc. In addition, there have been significant developments with the use of iodonium ylides as carbene precursors in recent years, and these reactions proceed with high efficiencies and selectivities. This review provides a comprehensive overview of iodonium ylides in C-H functionalizations, including the scope, limitations, and their potential synthetic applications.

Rh(III)-catalyzed C-H/C-C bond annulation of enaminones with iodonium ylides to form isocoumarins

A straightforward approach to synthesise isocoumarins via Rh(III)-catalyzed C-H/C-C bond activation/annulation cascade of enaminones and iodonium ylides has been explored. The established protocol is characterized by an exceedingly simple reaction system, high regioselectivity and good functional group tolerance. Moreover, this strategy may provide a new route to cleavage of the C(sp²)-C(O) bond of unstrained ketones.

Lewis Acid-Catalyzed [3 + 2]-Cyclization of Iodonium Ylides with Azadienes: Access to Spiro[benzofuran-2,2'-furan]-3-ones

A highly regioselective synthesis of spiro[benzofuran-2,2'-furan]-3-ones has been explored via Lewis acid-catalyzed [3 + 2] cyclization of iodonium ylides with azadienes. The acidity of the Lewis acid was significantly strengthened with strong hydrogen bond donors, thereby promoting the enolization isomerization of iodonium ylides for the subsequent cycloaddition. This reaction was compatible with a broad range of substrates under the mild reaction conditions, and efficiently delivered spiro-heterocycles with excellent stereoselectivity.

HFIP in Organic Synthesis

1,1,1,3,3,3-Hexafluoroisopropanol (HFIP) is a polar, strongly hydrogen bond-donating solvent that has found numerous uses in organic synthesis due to its ability to stabilize ionic species, transfer protons, and engage in a range of other intermolecular interactions. The use of this solvent has exponentially increased in the past decade and has become a solvent of choice in some areas, such as C-H functionalization chemistry. In this review, following a brief history of HFIP in organic synthesis and an overview of its physical properties, literature examples of organic reactions using HFIP as a solvent or an additive are presented, emphasizing the effect of solvent of each reaction.

Ru(II)-Catalyzed Decarbonylative Alkylation and Annulations of Benzaldehydes with Iodonium Ylides under Chelation Assistance

A Ru(II)-catalyzed decarbonylative alkylation and annulation of salicylaldehydes and 2-aminobenzaldehydes with iodonium ylides has been developed for the synthesis of dibenzo[b,d]furans and NH-free carbazolones. The reaction proceeds smoothly under mild conditions with a low catalyst loading and a broad substrate compatibility. Notably, hydroxy and free amino groups were demonstrated to be the effective directing groups, enabling the successful aldehyde C-H bond activation and subsequent decarbonylation and annulation under the inexpensive Ru(II) catalyst.

Insights into the Activation Mode of α-Carbonyl Sulfoxonium Ylides in Rhodium-Catalyzed C-H Activation: A Theoretical Study

A computational study has been performed to investigate the mechanism of RhIII -catalyzed C-H bond activation using sulfoxonium ylides as a carbene precursor. The stepwise and concerted activation modes for sulfoxonium ylides were investigated. Detailed theoretical results showed that the favored stepwise pathway involves C-H bond activation, carbonization, carbene insertion, and protonation. The free energy profiles for dialkylation of 2-phenylpyridine were also calculated to account for the low yield of this reaction. Furthermore, the substituent effect was elucidated by comparing the energy barriers for the protonation of meta- and para-substituted sulfoxonium ylides calculated by density functional theory.

Rhodium(III)-catalyzed regioselective C(sp2)-H activation of indoles at the C4-position with iodonium ylides

Herein, we report a Rh(III)-catalyzed C4-selective activation of indoles by using iodonium ylides as carbene precursors. This protocol proceeded under redox neutral reaction conditions and provided important coupling products with good tolerance of functional groups and high yields. In addition, one-pot synthesis and scale-up and mechanistic studies were also conducted.

Synthesis of Tetrahydrocarbazol-4-ones via Rh(III)-Catalyzed C-H Activation/Annulation of Arylhydrazines with Iodonium Ylides

The rhodium(III)-catalyzed C-H activation followed by intramolecular annulation reactions between arylhydrazines and iodonium ylides under suitable conditions has been described. Tetrahydrocarbazol-4-ones are readily achieved with moderate to excellent yields. The synthetic protocol features a wide range of substrates with high functional group tolerance. The gram-scale reaction and derivatization of the product demonstrate the synthetic practicality and utilization of this method.

Rh(III)-Catalyzed C-H Annulation of Alkenyl- or Arylimidazoles and (Hetero)cyclic 1,3-Dicarbonyl Compounds: A Rapid Access to Imidazo-Fused Polycyclic Compounds

A novel strategy for the synthesis of imidazo-fused polycyclic compounds under mild, base-free, and silver-free conditions by a rhodium(III)-catalyzed C-H annulation of alkenyl or arylimidazoles and (hetero)cyclic 1,3-dicarbonyl compounds is reported here. Such a step-economic protocol features the selective cleavage of two different C-H bonds in one step, featuring easy operation, readily available starting materials, gram-scale synthesis, broad functional group tolerance, and no requirement to presynthesize carbene precursors. Notably, the synthetic potential is showcased by the structural modification of drug and the highly step-economic synthesis of Janus kinase inhibitor in only three steps with a satisfactory 26% total yield (previous method: in nine steps with 0.6% yield).

The solvent-controlled Rh(III)-catalyzed switchable [4+2] annulation of 2-arylIndoles with iodonium ylides

Highly selective and switchable [4+2] annulations of 2-arylindoles with iodonium ylides were achieved by performing solvent-controlled Rh(III)-catalyzed C-H activations. When using DCM as a solvent, the C-H functionalization of 2-arylindoles with iodonium ylides selectively delivered indolo[2,1-a]isoquinoline derivatives. In contrast, the same catalytic system with a polar HFIP solvent predominately provided benzo[a]carbazole moieties.

Phase-transfer catalyzed Michael/ammonolysis cascade reactions of enaminones and olefinic azlactones: a new approach to structurally diverse quinoline-2,5-diones

Michael/ammonolysis cascade reactions between cyclohexane-1,3-dione-derived enaminones and olefinic azlactones via phase-transfer catalysis have been developed. This method provides rapid access to a suite of architecturally complex and diverse quinoline-2,5-diones bearing a secondary amide group at the C-3 position in moderate to excellent yields (53-94%) and with excellent diastereoselectivities (>99 : 1 dr in most cases). The achievement of a preparative-scale reaction and the diverse product derivatization that can be obtained highlight the application potential of this protocol both in academic and industrial settings. An investigation of the reaction mechanism implies that tetrabutylammonium hydroxide may be the actual catalyst during this cascade reaction.

Recent advances in transition-metal-catalyzed carbene insertion to C-H bonds

C-H functionalization has been emerging as a powerful method to establish carbon-carbon and carbon-heteroatom bonds. Many efforts have been devoted to transition-metal-catalyzed direct transformations of C-H bonds. Metal carbenes generated in situ from transition-metal compounds and diazo or its equivalents are usually applied as the transient reactive intermediates to furnish a catalytic cycle for new C-C and C-X bond formation. Using this strategy compounds from unactivated simple alkanes to complex molecules can be further functionalized or transformed to multi-functionalized compounds. In this area, transition-metal-catalyzed carbene insertion to C-H bonds has been paid continuous attention. Diverse catalyst design strategies, synthetic methods, and potential applications have been developed. This critical review will summarize the advance in transition-metal-catalyzed carbene insertion to C-H bonds dated up to July 2021, by the categories of C-H bonds from aliphatic C(sp³)-H, aryl (aromatic) C(sp²)-H, heteroaryl (heteroaromatic) C(sp²)-H bonds, alkenyl C(sp²)-H, and alkynyl C(sp)-H, as well as asymmetric carbene insertion to C-H bonds, and more coverage will be given to the recent work. Due to the rapid development of the C-H functionalization area, future directions in this topic are also discussed. This review will give the authors an overview of carbene insertion chemistry in C-H functionalization with focus on the catalytic systems and synthetic applications in C-C bond formation.

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.

Rhodium(III)-catalyzed cascade C-H functionalization/annulation of sulfoximines with iodonium ylides for the synthesis of cyclohexanone-1,2-benzothiazines

A highly efficient Rh(III)-catalyzed cascade C-H activation/annulation of sulfoximines with iodonium ylides under metal-oxidant-free conditions has been reported. The fused cyclohexanone-1,2-benzothiazine scaffold is readily achieved with a one-pot process in this reaction. This protocol exhibits good functional group tolerance and moderate to excellent yields. Additionally, the olefination of the target product illustrates the promising usefulness of this strategy.

Selenonium ylides: synthesis, characterization, and applications to photo-induced cyclopropanation reactions

Carbenes are important and highly reactive intermediates for the synthesis of various complex molecules. They are now an indispensable chemical species in organic chemistry and are used frequently to synthesize complex compounds in drug discovery chemistry. In general, carbenes are synthesized by a combination of transition metal catalysts and diazo compounds or by the decomposition reactions of diazo compounds. This paper reports the development of the visible light for the photochemical generation of carbenes from a novel C,Se-selenonium ylide. Overall, this photochemical carbene generation method using C,Se-selenonium ylide does not require a catalyst, is simple to perform, and enables highly efficient cyclopropanation reactions with alkenes.

Divergent synthesis of fused N-heterocycles via rhodium-catalysed [4+2] cyclization of pyrazolidinones with iodonium ylides

A catalytic system-controlled divergent strategy is developed for the precise synthesis of cinnolines and pyrazolo[1,2-a]cinnolines via rhodium-catalysed [4+2] cyclization of readily available pyrazolidinones and iodonium ylides. A range of cinnolines...

Rh(iii)-Catalyzed C–C coupling of unactivated C(sp3)–H bonds with iodonium ylides for accessing all-carbon quaternary centers

Rhodium-catalyzed inert C(sp3)–H activation/carbene insertion has been realized, leading to the construction of all-carbon quaternary centers.