Palladium-Catalyzed Cyclocoupling of 2-Halobiaryls with Isocyanides via the Cleavage of Carbon−Hydrogen Bonds

Rhodium(iii)-catalyzed successive C(sp2)–H and C(sp2)–C(sp2) bond activation of aryl oximes: synthetic and mechanistic studies

A rhodium(iii)-catalyzed redox-neutral reaction of aryl oximes and internal alkynes to generate novel N-(2-cyanoaryl) indanone imines.

Palladium catalyzed annulation of 2-iodobiphenyl with a non-terminal alkene enabled by neighboring group assistance

In this work, an efficient palladium catalyzed annulation of 2-iodobiphenyl with a non-terminal alkene was developed. The key factor in this transformation was the formation of a highly reactive oxo-palladacycle intermediate, which was enabled by a neighboring hydroxyl group, and remarkably restrained the β-H elimination process. Mechanistically, control experiments demonstrated that the hydroxyl group may act as an anionic ligand, which was irreplaceable in this reaction. This transformation presented good reactivity and selectivity, and no simple Heck coupling products were detected for all of the explored substrates.

Advances in palladium-catalysed imidoylative cyclization of functionalized isocyanides for the construction of N-heterocycles

Palladium-catalysed isocyanide insertion reactions have witnessed great progress in recent years. In particular, imidoylative cyclization of functionalized isocyanides was successfully developed by taking advantage of the adjustable substituents on the isocyano group, opening a new avenue to access a variety of nitrogen-containing heterocycles. In this review article, we summarize the advances of functionalized isocyanide insertion reactions and highlight the breakthroughs of enantioselective palladium catalysed imidoylation reactions by using this strategy. Additionally, copper-catalysed cyclization reactions of functionalized isocyanides are briefly discussed.

Synthesis of imides via palladium-catalyzed three-component coupling of aryl halides, isocyanides and carboxylic acids

A palladium-catalyzed three-component synthesis of acyclic imides from feedstock aryl halides, carboxylic acids and isocyanides through the intermediacy of isoimides has been developed. The key to the success of this approach was controlled isocyanide slow addition and organic/aqueous biphasic conditions. This transition-metal-catalyzed approach features readily available starting materials, atom- and step-economy, good functional group compatibility and gram-scale synthetic capability. Utilization of this new method is illustrated in the late-stage functionalization of drugs Carprofen, Loxoprofen and Flurbiprofen. This strategy has also been successfully applied in the synthesis of cyclic imides including phthalimide, homophthalimide, and 2H-2-benzazepine-1,3-dione derivatives.

Dimerization–cyclization reactions of isocyanoaryl-tethered alkylidenecyclobutanes via a triplet biradical mediated process

A triplet biradical mediated dimerization–cyclization reaction of isocyanoaryl-tethered alkylidenecyclobutanes to construct macrocyclic skeletons including dihydroquinoline and quinoline units has been reported.

Bimetallic Cu/Pd-catalyzed three-component azide-alkyne cycloaddition/isocyanide insertion: synthesis of fully decorated tricyclic triazoles

The construction of fully decorated 1,2,3-triazole-fused 5-, 6- and 7-membered rings has been disclosed via a bimetallic relay-catalyzed cascade process combining azide-alkyne cycloaddition, C(sp2)-H functionalization of intermediary 1,2,3-triazoles and isocyanide insertion. The salient features of this methodology include simple starting materials, reduced synthetic steps, good substrate scope and high efficiency.

XANES/EPR Evidence of the Oxidation of Nickel(II) Quinolinylpropioamide and Its Application in Csp3 -H Functionalization

An in situ generated oxidation species of nickel quinolinylpropioamide intermediate was produced. Characterization by X-ray absorption near edge structure (XANES) and EPR provides complementary insights into this oxidized nickel species. With aliphatic amides and isocyanides as substrates, a nickel-catalyzed facile synthesis of structurally diverse five-membered lactams could be achieved.

Pd-Catalyzed multicomponent reaction of sulfonyl azides, primary amines and methyl α-isocyanoacetates: highly efficient synthesis of tetrasubstituted imidazolone derivatives

A highly efficient Pd-catalyzed multicomponent reaction of sulfonyl azides, primary amines and methyl α-isocyanoacetates was developed.

α-Oxo-Ketenimines from Isocyanides and α-Haloketones: Synthesis and Divergent Reactivity

The palladium-catalyzed reaction of α-haloketones with isocyanides afforded α-oxo-ketenimines through β-hydride elimination of the β-oxo-imidoyl palladium intermediates. Reaction of these relatively stable α-oxo-ketenimines with nucleophiles such as hydrazines, hydrazoic acid, amines, and Grignard reagent afforded pyrazoles, tetrazole, β-keto amidines, and enaminone, respectively, with high chemoselectivity. Whereas amines attack exclusively on the ketenimine functions, the formal [3+2] cycloaddition between N-monosubstituted hydrazines and α-oxo-ketenimines was initiated by nucleophilic addition to the carbonyl group.

Direct carboxamidation of cyclic 2-diazo-1,3-diketones by Rh2(OAc)4-catalyzed isocyanide insertion–hydrolysis

A novel and efficient strategy for the synthesis of 2-hydroxy-6-oxocyclohex-1-enecarboxamides through a Rh₂(OAc)₄-catalyzed direct carboxamidation of cyclic 2-diazo-1,3-diketones has been developed.

Palladium-catalyzed β-selective C(sp2)–H carboxamidation of enamides by isocyanide insertion: synthesis of N-acyl enamine amides

An efficient synthesis of N-acyl enamine amides via palladium-catalyzed alkene C–H activation and isocyanide insertion has been developed.

Metal-catalyzed C–H functionalization involving isocyanides

This review demonstrates the metal-catalyzed incorporation of isocyanides into C–H functionalization to establish complicated reactions utilizing synergistic effects.

Ketenimines from Isocyanides and Allyl Carbonates: Palladium-Catalyzed Synthesis of β,γ-Unsaturated Amides and Tetrazoles

The reaction of allyl ethyl carbonates with isocyanides in the presence of a catalytic amount of Pd(OAc)₂ provided ketenimines through β-hydride elimination of the allyl imidoylpalladium intermediates. The insertion of the isocyanide into the π-allyl Pd complex proceeded via an unusual η¹ -allyl Pd species. The resulting ketenimines were hydrolyzed to β,γ-unsaturated carboxamides during purification by flash column chromatography on silica gel or converted in situ into 1,5-disubstituted tetrazoles by [3+2] cycloaddition with hydrazoic acid or trimethylsilyl azide.

Rh(I) -Catalyzed Intramolecular Carbonylative C-H/C-I Coupling of 2-Iodobiphenyls Using Furfural as a Carbonyl Source

Synthesis of fluoren-9-ones by a Rh-catalyzed intramolecular C-H/C-I carbonylative coupling of 2-iodobiphenyls using furfural as a carbonyl source is presented. The findings indicate that the rate-determining step is not a C-H bond cleavage but, rather, the oxidative addition of the C-I bond to a Rh(I) center.

Palladium-Catalyzed Construction of Amidines from Arylboronic Acids under Oxidative Conditions

A valuable palladium-catalyzed three-component coupling reaction for the synthesis of amidines has been developed. Using arylboronic acids, isocyanides, and anilines as the reactants under oxidative conditions, various amidines were isolated in good yields with good functional group tolerances.

Palladium-catalyzed chemoselective synthesis of indane-1,3-dione derivatives via tert-butyl isocyanide insertion

A simple and efficient strategy for the synthesis of indane-1,3-dione derivatives through a palladium(0)-catalyzed reaction incorporating tert-butyl isocyanide has been developed. In addition, by applying this protocol as the key step, indenopyrazole derivatives can be easily synthesized in high yields in a one-pot procedure. This methodology is tolerant of a wide range of substrates and applicable to library synthesis.

Palladium-Catalyzed Synthesis of α-Iminonitriles from Aryl Halides via Isocyanide Double Insertion Reaction

An efficient one-pot synthesis of α-iminonitriles from readily available aryl halides via palladium-catalyzed double isocyanide insertion and elimination has been developed, without using various hypertoxic cyanides and excess oxidants. Furthermore, the utility of this reaction was demonstrated by the rapid total synthesis of quinoxaline and the reaction of functional groups exchanged with aryl halides.

Palladium-Catalyzed Domino Synthesis of 4-Amino-3-acyl-2- naphthols via Isocyanide Chemoselective Insertion

A novel and efficient strategy for the synthesis of sterically hindered 4-amino-3-acyl-2-naphthols through a palladium-catalyzed coupling reaction involving isocyanide chemselective insertion and domino isomerization has been developed. The methodology, which is in accordance with the principle of "atom and step economy", efficiently constructs 4-amino-3-acyl-2-naphthols in moderate to good yields.

Palladium-catalyzed intramolecular C(sp(2))-H imidoylation for the synthesis of six-membered N-heterocycles

A new strategy for the construction of phenanthridine and isoquinoline scaffolds, starting from arenes containing a pending isocyanide moiety under palladium catalysis, has been developed. This process involves sequential intermolecular isocyanide insertion to an aryl palladium(II) intermediate and intramolecular aromatic C-H activation as key steps. Alkyl palladium(II) intermediate lacking β-hydrogen is also applicable to this reaction, generating unique bisheterocyclic scaffolds with three C-C bonds being formed consecutively.

Pd-catalyzed isocyanide insertion/nucleophilic attack by indole C-3/desulfonylation in the same pot: a direct access to indoloquinolines of pharmacological interest

A Pd-catalyzed new cascade reaction furnished indoloquinolin based small molecules as potential cytotoxic agents.

Palladium(0)-catalyzed single and double isonitrile insertion: a facile synthesis of benzofurans, indoles, and isatins

A palladium(0)-catalyzed cascade process consisting of isonitrile insertion and α-Csp(3)-H cross-coupling can be achieved for the synthesis of benzofurans and indoles. The construction of isatins by a Pd-catalyzed cascade reaction incorporating double isonitrile insertion, amination, and hydrolysis has also been achieved. The key features of this work include diverse heterocycle synthesis, phosphine-ligand-free reaction conditions, a one-pot procedure, simple and commercially available starting materials, broad functional-group compatibility, and moderate to good reaction yields.