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

De Novo Synthesis of α-Ketoamides via Pd/TBD Synergistic Catalysis

Precisely controlling the product selectivity of a reaction is an important objective in organic synthesis. α-Ketoamides are vital intermediates in chemical transformations and privileged motifs in numerous drugs, natural products, and biologically active molecules. The selective synthesis of α-ketoamides from feedstock chemicals in a safe and operationally simple manner under mild conditions is a long-standing catalysis challenge. Herein, an unprecedented TBD-switched Pd-catalyzed double isocyanide insertion reaction for assembling ketoamides in aqueous DMSO from (hetero)aryl halides and pseudohalides under mild conditions is reported. The effectiveness and utility of this protocol are demonstrated by its diverse substrate scope (93 examples), the ability to late-stage modify pharmaceuticals, scalability to large-scale synthesis, and the synthesis of pharmaceutically active molecules. Mechanistic studies indicate that TBD is a key ligand that modulates the Pd-catalyzed double isocyanide insertion process, thereby selectively providing the desired α-ketoamides in a unique manner. In addition, the imidoylpalladium(II) complex and α-ketoimine amide are successfully isolated and determined by X-ray analysis, confirming that they are probable intermediates in the catalytic pathway.

Three-Component Domino Reaction of Thioamide, Isonitriles, and Water: Selective Synthesis of 1,2,4-Thiadiazolidin-3-ones and (E)-N-(1,2-Diamino-2-thioxoethylidene)benzamides

The three-component domino reaction of thioamides, benzyl isocyanide, and water in the presence of a catalytic amount of both Pd(dppf)Cl2 and Cu(OAc)2 afforded novel 1,2,4-thiadiazolidin-3-one cyclic compounds, whereas the same reaction with tertiary alkylisonitriles in the presence of rare earth metal salt [La(OTf)3] resulted in (E)-N-(1,2-diamino-2-thioxoethylidene)benzamide open-chain products. This divergent reaction enabled the one-pot construction of five (N-S, C-S, C-O, and two C-N) or four (C-S, C-N, C-O, and C-C) new chemical bonds. Mechanism studies indicate that the oxygen atom of the product was derived from H2O.

Cyanation with isocyanides: recent advances and perspectives

Cyanation has attracted considerable attention in organic synthesis because nitriles are key structural motifs in numerous important dyes, agrochemicals, natural products and drug molecules. As the fourth generation of cyanating reagents, isocyanides occupy a prominent place in the synthesis of nitriles due to their favorable stability, easy operability and high reactivity. In recent years, three types of cyanation with isocyanides have been established: the cleavage of the C-NC bond of tertiary alkyl isocyanides (Type I), the rearrangement of aryl isocyanides with azides (Type II), and the reductive cyanation of ketones with α-acidic isocyanides (Type III). This review focuses on advances in cyanation with isocyanides with an emphasis on reaction scope, limitations and mechanisms, which could reveal their remarkable value and superiority for accessing various nitriles. In addition, the future development prospects of this specific field are also introduced. We believe that this feature article will serve as a comprehensive tool to navigate cyanation with isocyanides across the vast area of synthetic chemistry.

Triple-Consecutive Isocyanide Insertions with Aldehydes: Synthesis of 4-Cyanooxazoles

An efficient TMSOTf-promoted selective triple consecutive insertions of tert-butyl isocyanide into aldehydes has been developed, affording pharmacological interesting 4-cyanooxazoles in high yields in a one pot manner. The given method encompasses a wide range of substrates with tert-butyl isocyanide serving as sources of critical "CN" and "C-N═C" moieties. The versatile transformations of the resulting 4-cyanooxazoles were demonstrated. The key reaction intermediates for plausible mechanisms were determined.

An Olefin-based Multi-component Reaction to 1,2-Azaborolidine Derivatives

Reaction of the borane FmesBH2·SMe2 [Fmes: 2,4,6-tris(trifluoro-methyl)phenyl] with two molar equivs of a small series of 1-alkenes followed by treatment with two molar equivalents of the bulky isonitrile CN-Xyl (Xyl:...

Transition-Metal-Catalyzed Diarylation of Isocyanides with Triarylbismuthines for the Selective Synthesis of Imine Derivatives

The transition-metal-catalyzed diarylation of isocyanides with triarylbismuthines was investigated in detail, and rhodium catalysts such as [RhCl(nbd)]₂ were found to selectively afford N-alkyl diaryl ketimines. On the other hand, palladium-catalyzed diarylation proceeded with the incorporation of two molecules of isocyanide, preferentially yielding N,N’-dialkyl or N,N’-diaryl α-diimines. In addition, a cascade synthesis of 2,3-diarylquinoxalines starting from the palladium-catalyzed diarylation of isocyanides with triarylbismuthines was successfully achieved.

Nickel-promoted oxidative domino Csp3-H/N-H bond double-isocyanide insertion reaction to construct pyrrolin-2-ones

The first nickel-catalyzed oxidative domino C_sp3-H/N-H double isocyanide insertion reaction of acetamides with isocyanides has been developed for the synthesis of pyrrolin-2-one derivatives. A wide range of acetamides bearing various functional groups are compatible with this reaction system by utilizing Ni(acac)₂ as a catalyst. In this transformation, isocyanide could serve as a C1 connector and insert into the inactive C_sp3-H bond, representing an effective way to construct heterocycles.

Recent Advances in Palladium-Catalyzed Isocyanide Insertions

Isocyanides have long been known as versatile chemical reagents in organic synthesis. Their ambivalent nature also allows them to function as a CO-substitute in palladium-catalyzed cross couplings. Over the past decades, isocyanides have emerged as practical and versatile C1 building blocks, whose inherent N-substitution allows for the rapid incorporation of nitrogeneous fragments in a wide variety of products. Recent developments in palladium catalyzed isocyanide insertion reactions have significantly expanded the scope and applicability of these imidoylative cross-couplings. This review highlights the advances made in this field over the past eight years.

Palladium-catalyzed double coupling reaction of terminal alkynes with isocyanides: a direct approach to symmetrical N-aryl dialkynylimines

A novel and efficient one-pot synthesis of symmetrical N-aryl dialkynylimines via palladium-catalyzed and copper-promoted isocyanide insertion, cross-coupling and elimination has been developed. This method features readily available starting materials, mild reaction conditions and high atom efficiency as well as simple one-pot operation, which make this strategy highly attractive. Moreover, 2-iodobenzo[f]quinoline derivatives can be obtained via electrophilic cyclization of N-aryl dialkynylimines.

Cellulose-Supported Sulfonated Magnetic Nanoparticles: Utilized for One-pot Synthesis of α-Iminonitrile Derivatives

ntroduction: An instrumental strategy for α-iminonitrile derivatives preparation by Fe3O4@cellulose-OSO3H (MCSA) as an eco-friendly nanocatalyst and oxidative agent in aerobic condition, is presented.

MATERIALS AND METHODS

Through this method, a one-pot three-component condensation reaction of various aldehydes, primary amines and trimethylsilylcyanide (TMSCN) were applied to synthesize the desired products. It was performed in absolute ethanol and under a mild condition by using the presented nanocatalyst. High reaction yields were obtained through using the presented magnetic agent, as well. Moreover, the threecomponent reactions were executed using accessible and economical precursors. The convenient separation and recyclability of the used nanocatalyst were also precisely investigated.

RESULTS AND DISCUSSION

In this research, we identified novel α-iminonitrile derivatives using 1H NMR, 13C NMR, CHN, and FT-IR analyses, as well. In order to determine the well-known derivatives, we used FT-IR method as well as comparing their melting points with those of reported.

CONCLUSION

In summary, an extremely efficient method was used for the environmentally-friendly synthesis of α-iminonitrile derivatives that are important bioactive substances. The catalytic oxidative coupling reaction afforded the products via a one-pot three-component condensation reaction of various aldehydes, primary amines and TMSCN with great reaction yields, in ethanol under mild conditions.

Catalytic formation of N3-substituted quinazoline-2,4(1H,3H)-diones by Pd(ii)EN@GO composite and its mechanistic investigations through DFT calculations

Modified GO based palladium composite was synthesized for catalytic synthesis of N3-substituted ouinazoline-2,4(1H,3H)-diones and the mechanistic route was theoretically investigated.

From Isocyanides to Iminonitriles via Silver-mediated Sequential Insertion of C(sp3)-H Bond

Heterocycles are prevalent constituents of many marketing drugs and biologically active molecules to meet modern medical challenges. Isocyanide insertion into C(sp³)–H bonds is challenging especially for the construction of quaternary carbon centers. Herein, we describe an efficient strategy for the synthesis of α-iminonitrile substituted isochromans and tetrahydroisoquinolines (THIQs) with quaternary carbon centers through silver-triflate-mediated sequential isocyanide insertion of C(sp³)–H bonds, where isocyanide acts as the crucial “CN” and “imine” sources. The produced α-iminonitriles have extensive applications as valuable synthetic building blocks for pharmacologically interesting heterocycles. This protocol could be further applied for the synthesis of iminonitrile-decorated phenanthridines and azapyrene. Interestingly, a remarkable aggregation-induced emission (AIE) effect was first observed for an iminonitrile-decorated pyrene derivative, which may open a particular area for iminonitrile applications in materials science.

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Iminonitrile formation via sequential C(sp³)-H bond isocyanide insertion

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Construction of quaternary center

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Isocyanide as both "imine" and "CN" sources

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Valuable synthetic building blocks and novel AIEgen

Synthesis of imidazo[1,2-c]thiazoles through Pd-catalyzed bicyclization of tert-butyl isonitrile with thioamides

Building new biological molecules is challenging. Herein, imidazo[1,2-c]thiazoles were synthesized as a new class of heterobicyclic analogs through Pd-catalyzed cascade bicyclization from isonitriles with thioamides. The bicyclic scaffolds were constructed by inserting three molecules of isonitrile into two molecules of thioamide and then cyclizing them in a one-pot procedure. In vitro antitumor studies of these new compounds were conducted by using the MTT assay, and compound 3c showed excellent inhibitory effects against HepG2 at 7.06 ± 0.68 μM.

Palladium-Catalyzed Diarylation of Isocyanides with Tetraarylleads for the Selective Synthesis of Imines and α-Diimines

Using tetraaryllead compounds (PbAr₄) as arylating reagents, isocyanides undergo selective diarylation in the presence of palladium catalysts such as Pd(OAc)₂ or Pd(PPh₃)₄ to afford imines and/or α-diimines based on the isocyanide employed. With aliphatic isocyanides, imines are obtained preferentially, whereas α-diimines are formed in the case of electron-rich aromatic isocyanides. The differences in imine/α-diimine selectivity can be attributed to the stability of imidoylpalladium intermediates formed in this catalytic reaction. Compared with other arylating reagents, tetraaryllead compounds are excellent candidates for use in the selective transformations to imines and/or α-diimines, especially in terms of inhibiting the oligomerization of isocyanides, which results in a lower product selectivity in many transition-metal-catalyzed reactions of isocyanides.

A facile tandem decyanation/cyanation reaction of α-iminonitriles toward cyano-substituted amides

A new tandem decyanation/cyanation reaction of α-iminonitriles has been developed. A variety of cyano-substituted aryl amides and heteroaryl amides are synthesized in good yields. Both electron-rich and electron-deficient groups are compatible with the standard conditions. This reaction features a nonmetallic cyano source, tandem decyanation and cyanation reaction, waste utilization of the HCN from the hydrolysis of α-iminonitriles, formation of two important functional groups in one-step operation, etc.

Cascade double isocyanide insertion and C-N coupling of 2-iodo-2'-isocyano-1,1'-biphenyls

A palladium-catalyzed double isocyanide insertion using 2-iodo-2'-isocyano-1,1'-biphenyls followed by copper-catalyzed intramolecular C-N coupling, delivering a unique heterocyclic structure containing both phenanthridine and carbazole scaffolds, has been developed. In this cascade process, four chemical bonds, including two C-C, one C-O, and one C-N bonds are formed consecutively without isolating an intermediate. The strategy of using a functionalized isocyanide in double insertion provides a quick approach for constructing heterocyclic systems with high bond-forming efficiency.

Nickle Catalysis Enables Access to Thiazolidines from Thioureas via Oxidative Double Isocyanide Insertion Reactions

An efficient synthesis of thiazolidine-2,4,5-triimine derivatives was developed via Ni-catalyzed oxidative double isocyanide insertion to thioureas under air conditions, in which thioureas play three roles as a substrate, a ligand, and overcoming isocyanide polymerization. The reaction is featured by employing a low-cost and low loading Ni(acac)₂ catalyst, without any additives, and high atom economy. This is the first example to directly apply a Ni(II) catalyst in oxidative double isocyanide insertion reactions.

Cyanide-Free Ce(III)-Catalyzed Highly Efficient Synthesis of α-Iminonitriles from 2-Aminopyridines and Nitroalkenes via Intermolecular Dehydration Reaction

A direct and rapid method for the synthesis of α-iminonitriles achieved good to excellent yields. A novel intermolecular dehydration reaction between 2-aminopyridines and nitroalkenes is reported via a rare-earth-metal catalyst. The merits of this transformation include cyanide-free protocol, short reaction time, simple operation, water as the only byproduct, commercially available reagents, good functional group tolerance, etc. Moreover, nitroalkenes are demonstrated as a new "CN" source in this transformation.

Synthesis of 2,3-Difunctionalized Benzofuran Derivatives through Palladium-Catalyzed Double Isocyanide Insertion Reaction

A novel palladium-catalyzed tandem cyclization of 1-(allyloxy)-2-ethynylbenzene derivatives with isocyanides in the presence of water has been developed. The key intermediates, benzofuran-3-α-carbonyl aldehydes, were obtained through a simple acid hydrolysis process and could serve as precursors for structurally diverse 2,3-difunctionalized benzofuran derivatives such as important 2-benzofurylquinoxalines, benzofuran-3-α-ketoesters and benzofuryl ynediones. This transformation features convenient operation, simple and commercially available starting materials, broad functional-group compatibility, and moderate to good reaction yields.

Palladium-catalyzed oxidative coupling of arylboronic acid with isocyanide to form aromatic carboxylic acids

A valuable palladium-catalyzed oxidative coupling of aryl- and alkenyl borides with isocyanide for the synthesis of corresponding carboxylic acids has been developed. With wide substrate scopes and good functional group tolerance, this reaction offers corresponding carboxylic acids in moderate to excellent yields.

Palladium-Catalyzed Incorporation of Two C1 Building Blocks: The Reaction of Atmospheric CO2 and Isocyanides with 2-Iodoanilines Leading to the Synthesis of Quinazoline-2,4(1H,3H)-diones

A Pd-catalyzed insertion and cycloaddition of CO₂ and isocyanide into 2-iodoanilines under atmospheric pressure has been developed and affords quinazoline-2,4(1H,3H)-diones through the formation of new C-C, C-O, and C-N bonds under mild conditions. This reaction provides a new and practical method not only for the construction of quinazoline-2,4(1H,3H)-diones but also for the efficient utilization of carbon dioxide.

Assembly of Polysubstituted Maleimides via Palladium-Catalyzed Cyclization Reaction of Alkynes with Isocyanides

An efficient and convenient palladium-catalyzed cyclization reaction of alkynes with isocyanides is described herein. This protocol allows the practical synthesis of many valuable polysubstituted maleimide derivatives after hydrolysis with a broad scope of substrates and mild reaction conditions. C-C, C═O, and C-N bonds were constructed in this transformation with isocyanide serving as both C and N sources.

Palladium-Catalyzed Synthesis of 5-Iminopyrrolones through Isocyanide Double Insertion Reaction with Terminal Alkynes and Water

With the combination of Pd(dppf)Cl₂ and Cu(OAc)₂, a variety of 5-iminopyrrolones were synthesized in moderate to good yields from terminal alkynes, isocyanide, and water via isocyanide double insertion and cycloaddition reaction. A plausible reaction mechanism for this process is depicted. Furthermore, selected compounds 3c, 3e, and 3h exhibited good activities against HepG2 (human liver cancer), NCI-H460 (human lung cancer), and SK-OV-3 (human ovarian cancer) cell lines with IC₅₀ values in the range of 10.63-22.63 μmol L^-1.

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.

α-Iminonitrile: a new cyanating agent for the palladium catalyzed C–H cyanation of arenes

An efficient palladium-catalyzed C–H cyanation reaction of arenes using α-iminonitrile as a new cyanating reagent has been developed.