[RhIII(Cp*)]-Catalyzed Cascade Arylation and Chlorination of α-Diazocarbonyl Compounds with Arylboronic Acids and N-Chlorosuccinimide for Facile Synthesis of α-Aryl-α-chloro Carbonyl Compounds

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.

Transition metal-catalyzed reactivity of carbenes with boronic acid derivatives for arylation (alkylation) and beyond

This comprehensive review article discussed the reactivity of carbenes with boronic acid derivatives for the one-pot synthesis of diarylmethanes, difluoromethylated arenes, aryl and alkyl boron compounds, arylacetic acid derivatives, furan derivatives, and many other compounds. We have summarized the arylation, vinylation, and alkylation of carbenes utilizing various transition metals, viz. palladium, rhodium, copper, and platinum, for the construction of carbon-carbon bonds, carbon-boron bonds, and beyond through the cross-coupling strategy. The reason for the increasing popularity of these novel methodologies is their application in the synthesis and late-stage functionalization of biologically active compounds and natural products. Notably, organoboron compounds are exemplified as versatile synthetic intermediates for constructing various bonds.

Rh(III)-Catalyzed Synthesis of Substituted Isoindoles through a Direct C-H Activation/[4 + 1] Annulation and Acyl Migration Cascade of Oxadiazolones with Diazo Compounds

A Rh(III)-catalyzed C-H bond activation for the synthesis of fused 2H-isoindole scaffolds from oxadiazolones with diazo compounds was developed. The reaction proceeded through C-H activation of oxadiazolones/[4 + 1] annulation, intramolecular cyclization, and an unusual acyl migration cascade to afford target scaffolds with good yields. These 2H-isoindole derivatives could be further transformed into intriguing drug privileged scaffolds.

gem-Difunctionalization of α-diazoarylketones with diaryldiselenides and N-halosuccinimides: facile synthesis of α-halo-α-arylseleno ketones

An efficient synthesis of α-halo-α-arylseleno ketones has been developed via gem-difunctionalization of α-diazoarylketones with diaryldiselenides and N-halosuccinimides. With this multicomponent approach, a series of α-halo-α-arylseleno ketones were accessed in excellent yields and chemoselectivities under mild conditions. This transformation is proposed to proceed via the key intermediate arylselenenyl halide that generated from diaryldiselenides/N-halosuccinimides, followed by addition with α-diazoarylketones to give the desired gem-difunctionalization products.

Recent advances in the synthesis of organic chloramines and their insights into health care

Organic nitrogen–chlorine compounds and their derivatives are important heterocyclic motifs, exhibiting applications such as N-chlorinating agents, analytical reagents, disinfectants, antipathogens, and as synthetic intermediates for drugs, polymers, and natural products.

Room Temperature Coupling of Aryldiazoacetates with Boronic Acids Enhanced by Blue Light Irradiation

A visible-light-promoted photochemical protocol is reported for the coupling of aryldiazoacetates with boronic acids. This photochemical reaction shows great enhancement compared to the same protocol performed in the absence of light. Except for a few cases, the room temperature coupling in the dark (thermal process) generally does not work. When it does, it is likely to also involve free carbenes as key intermediates. Alternatively, photochemical reactions show a broad scope, can be performed under air and tolerate a wide variety of functional groups. Reaction-evolution monitoring, DFT calculations and control experiments have been used to evaluate the main aspects of this intricate mechanistic scenario. Biologically active molecules Adiphenine, Benactyzine and Aprophen have been prepared as examples of synthetic applications.

The Fascinating Chemistry of α-Haloamides

The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C-N, C-O and C-S bond forming reactions, and later widely employed in C-C cross-coupling reactions with C(sp3), C(sp2) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates.

Relay Rh(ii)/Pd(0) dual catalysis: synthesis of α-quaternary β-keto-esters via a [1,2]-sigmatropic rearrangement/allylic alkylation cascade of α-diazo tertiary alcohols

A relay Rh(ii)/Pd(0) dual catalysis that enables domino [1,2]-sigmatropic rearrangement/allylic alkylation of α-diazo tertiary alcohols is described. This transformation represents a highly efficient method for the one-pot synthesis of α-quaternary β-keto-esters under mild conditions, in which two separate C-C σ-bonds at the carbenic center were formed in a straightforward manner.

Comparative solution and structural studies of half-sandwich rhodium and ruthenium complexes bearing curcumin and acetylacetone

Half-sandwich organometallic complexes of curcumin are extensively investigated as anticancer compounds. Speciation studies were performed to explore the solution stability of curcumin complexes formed with [Rh(η⁵-C₅Me₅)(H₂O)₃]²⁺. Acetylacetone (Hacac), as the simplest β-diketone ligand bearing (O,O) donor set, was involved for comparison and its Ru(η⁶‑p‑cymene), Ru(η⁶‑toluene) complexes were also studied. ¹H NMR, UV-visible and pH-potentiometric titrations revealed a clear trend of stability constants of the acac complexes: Ru(η⁶‑p‑cymene) > Ru(η⁶‑toluene) > Rh(η⁵-C₅Me₅). Despite this order, the highest extent of complex formation is seen for the Rh(η⁵-C₅Me₅) complexes at pH 7.4. Formation constant of [Rh(η⁵-C₅Me₅)(H₂curcumin)(H₂O)]⁺ reveals similar solution stability to that of the acac complex. Additionally, structures of two complexes were determined by X-ray crystallography. The in vitro cytotoxicity of curcumin was not improved by the complexation with these organometallic cations.

[RhIII(Cp*)]-catalyzed arylfluorination of α-diazoketoesters for facile synthesis of α-aryl-α-fluoroketoesters

Here we describe the Cp*Rh(iii)-catalyzed cascade arylfluorination reactions of α-diazoketoesters with arylboronic acids and N-fluorobenzenesulfonimide for one-pot C(sp3)-C(aryl) and C(sp3)-F bond formation. The arylfluorination reaction can be accomplished with remarkable chemo- and regioselectivity. Our mechanistic investigation showed that the Rh-catalyzed arylfluorination of diazoacetates occurred by (1) transmetalation of arylboronic acids to form an arylrhodium(iii) complex, (2) coupling of diazomalonates with the arylrhodium(iii) complex to form carbene-rhodium, (3) migratory carbene insertion to form a diketonato-rhodium(iii) complex - probably via rearrangement of the putative σ-alkylrhodium(iii) complex, and (4) electrophilic fluorination of the diketonato-rhodium to form the α-aryl-α-fluoromalonates.

Mn-Catalyzed Electrochemical Chloroalkylation of Alkenes

The heterodifunctionalization of alkenes is an efficient method for synthesizing highly functionalized organic molecules. In this report, we describe the use of anodically coupled electrolysis for the catalytic chloroalkylation of alkenes-a reaction that constructs vicinal C-C and C-Cl bonds in a single synthetic operation-from malononitriles or cyanoacetates and NaCl. Knowledge of the persistent radical effect guided the reaction design and development. A series of controlled experiments, including divided-cell electrolysis that compartmentalized the anodic and cathodic events, allowed us to identify the key radical intermediates and the pathway to their electrocatalytic formation. Cyclic voltammetry data further support the proposed mechanism entailing the parallel, Mn-mediated generation of two radical intermediates in an anodically coupled electrolysis followed by their selective addition to the alkene.

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.

Iridium-catalyzed [4 + 2] annulation of 1-arylindazolones with α-diazo carbonyl compounds: access to indazolone-fused cinnolines

An Ir-catalyzed tandem strategy for the synthesis of indazolone-fused cinnolines by [4 + 2] annulation of 1-arylindazolones with α-diazo carbonyl compounds.

Transition-Metal-Catalyzed Cross-Couplings through Carbene Migratory Insertion

Transition-metal-catalyzed cross-coupling reactions have been well-established as indispensable tools in modern organic synthesis. One of the major research goals in cross-coupling area is expanding the scope of the coupling partners. In the past decade, diazo compounds (or their precursors N-tosylhydrazones) have emerged as nucleophilic cross-coupling partners in C-C single bond or C═C double bond formations in transition-metal-catalyzed reactions. This type of coupling reaction involves the following general steps. First, the organometallic species is generated by various processes, including oxidative addition, transmetalation, cyclization, C-C bond cleavage, and C-H bond activation. Subsequently, the organometallic species reacts with the diazo substrate to generate metal carbene intermediate, which undergoes rapid migratory insertion to form a C-C bond. The new organometallic species generated from migratory insertion may undergo various transformations. This type of carbene-based coupling has proven to be general: various transition metals including Pd, Cu, Rh, Ni, Co, and Ir are effective catalysts; the scope of the reaction has also been extended to substrates other than diazo compounds; and various cascade processes have also been devised based on the carbene migratory insertion. This review will summarize the achievements made in this field since 2001.

Silver-catalyzed geminal aminofluorination of diazoketones with anilines and N-fluorobenzenesulphonimide

A silver-catalyzed three-component reaction of diazoketones, anilines and NFSI is developed. The reaction provides a new method for gem-aminofluorination of acceptor diazo compounds with aniline as the nitrogen source and NFSI as the fluorine source.

Catalyst-Free Halogenation of α-Diazocarbonyl Compounds with N-Halosuccinimides: Synthesis of 3-Halooxindoles or Vinyl Halides

A novel catalyst-free halogenative cyclization of N-aryl diazoamides with N-halosuccinimides (NXS) is reported for the synthesis of 3-halooxindoles through a carbene-free mechanism. N-Aryl diazoamides reacted with NXS under mild and catalyst-free conditions to afford the corresponding 3-halooxindoles in good yields. This transformation is proposed to proceed through diazonium ion formation followed by intramolecular Friedel-Crafts alkylation.

Aminofluorination: transition-metal-free N-F bond insertion into diazocarbonyl compounds

Gem-aminofluorination of diazocarbonyl compounds has been achieved for the first time. This reaction proceeds under mild conditions and does not require any transition-metal promoter or catalyst. Treatment of diazoesters with N-fluorobenzenesulfonimide (NFSI), which serves as both a fluorine and nitrogen source, results in the facile construction of C-N and C-F bonds, providing aminofluorination products in moderate to excellent yields. Kinetic studies and DFT calculations have provided valuable insight into the potential mechanism for this novel N-F bond insertion.

Synthesis of isoquinolines via Rh-catalyzed C–H activation/C–N cyclization with diazodiesters or diazoketoesters as a C2 source

Synthesis of isoquinolines based on efficient C–C and C–N bond formation through Rh(iii)-catalyzed C–H functionalization and subsequent intramolecular cyclization is reported. Diazodiesters serving as a C₂ source in the newly formed heterocycles are first demonstrated.

NBS-mediated dinitrogen extrusion of diazoacetamides under catalyst-free conditions: practical access to 3-bromooxindole derivatives

A synthetically useful reaction via NBS-mediated dinitrogen extrusion of N-aryl diazoacetamides under catalyst-free conditions is disclosed, which gives the 3-bromooxindoles in high to excellent yields with high selectivity via a non carbene process.

Cp*Rh(iii)-catalyzed electrophilic amination of arylboronic acids with azo compounds for synthesis of arylhydrazides

A [Cp*Rh(iii)]-catalyzed electrophilic amination of arylboronic acids with azocarboxylates for the synthesis of mono- and di-arylhydrazides was developed.

Domino reactions of diazodicarbonyl compounds with α,β-unsaturated δ-amino esters: a convenient way towards 2-oxopiperidines, dihydropyridinones and isoquinolinediones

Thermal decomposition of a series of diazodicarbonyl compounds in the presence of α,β-unsaturated δ-amino esters and sodium hydride gives rise to a variety of nitrogenous heterocycles.