Rhodium-Catalyzed Direct C–H Bond Cyanation of Arenes with Isocyanide

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.

Direct C-H Cyanation by ICN Formed In Situ: Nannozinone B

A novel method for C-H cyanation of different pyrans, pyrroles, indoles, and acyclic nucleophilic double bonds using TMSCN, NIS, and Zn(OTf)₂ as a catalyst is described. The transformation is conducted under mild conditions tolerating a variety of functional groups. Zn(OTf)₂ is likely to serve a dual catalytic role as an activator for TMSCN and for the cyanogen iodide generated in situ. Optimization, the substrate scope, and mechanistic observations are reported. Furthermore, this method is applied in the first total synthesis of the natural product nannozinone B.

Multicomponent Reaction of Isocyanide, Ditelluride, and Mn(III) Carboxylate: Synthesis of N-Acyl Tellurocarbamate

A multicomponent reaction of isocyanides, ditellurides and manganese(III) carboxylates under mild reaction conditions leads to the synthesis of various N-acyl tellurocarbamates. This method demonstrates good functional tolerance and broad substrate scope and, as a result, is especially suitable for the postfunctionalization of complicated molecules such as drugs. The given method can be further extended to the synthesis of selenocarbamates.

Directing group strategies in catalytic sp2 C–H cyanations: scope, mechanism and limitations

Directing group strategy in transition metal catalyzed sp² C–H bond cyanation has contributed to the direct conversion of hydrocarbons to cyano-containing compounds. Recent developments in transition metal-mediated sp² C–H bond cyanation using this strategy are reviewed.

Transition-metal-free direct C-3 cyanation of quinoxalin-2(1H)-ones with ammonium thiocyanate as the “CN” source

A practical protocol for TBHP-mediated oxidative C–H cyanation of quinoxalin-2(1H)-ones utilizing ammonium thiocyanate as the cyanide source has been developed under metal free conditions.

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

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.

Rhodium-Catalyzed C(sp2 )- or C(sp3 )-H Bond Functionalization Assisted by Removable Directing Groups

In recent years, transition-metal-catalyzed C-H activation has become a key strategy in the field of organic synthesis. Rhodium complexes are widely used as catalysts in a variety of C-H functionalization reactions because of their high reactivity and selectivity. The availability of a number of rhodium complexes in various oxidation states enables diverse reaction patterns to be obtained. Regioselectivity, an important issue in C-H activation chemistry, can be accomplished by using a directing group to assist the reaction. However, to obtain the target functionalized compounds, it is also necessary to use a directing group that can be easily removed. A wide range of directed C-H functionalization reactions catalyzed by rhodium complexes have been reported to date. In this Review, we discuss Rh-catalyzed C-H functionalization reactions that are aided by the use of a removable directing group such as phenol, amine, aldehyde, ketones, ester, acid, sulfonic acid, and N-heteroaromatic derivatives.

Palladium-Catalyzed Multicomponent Reaction of Alkynes, Carboxylic Acids, and Isocyanides: A Direct Approach to Captodative Olefins

A palladium-catalyzed multicomponent reaction of alkynes, carboxylic acids, and isocyanides has been developed with the assistance of silver salt under mild conditions. Highly functionalized captodative olefins are synthesized efficiently by this method, which can find many applications as versatile synthons in organic synthesis.

Rhodium(iii)-catalyzed aromatic C–H cyanation with dimethylmalononitrile as a cyanating agent

Safe, bench-stable, and commercially available DMMN was used as a cyanating reagent in Rh(iii)-catalyzed aromatic C–H bond direct cyanation in the presence of copper oxide as a promotor.

Theoretical studies on Rh(iii)-catalyzed regioselective C-H bond cyanation of indole and indoline

Density functional theory calculations were carried out to study the reaction mechanism of the Rh(iii)-catalyzed regioselective C-H cyanation of indole and indoline with N-cyano-N-phenyl-para-methylbenzenesulfonamide (NCTS). This mechanism involves four major steps: C-H activation, cyano group insertion, β-N elimination, and regeneration of active species. How different indole and indoline substrates affect the regioselectivity of C-H bond cyanation has been examined and analyzed in detail. Our calculation results indicate that the regioselectivity of C-H bond cyanation of indole depends on the nucleophilicity of carbon atoms in C-Rh(iii) bonds to the cyano group. For indoline, it can be attributed to the different hybridization platforms of the C-H bond activation.

Palladium-Catalyzed Cyanothiolation of Internal Alkynes Using Organic Disulfides and tert-Butyl Isocyanide

Despite the availability of selective synthetic approaches to multifunctionalized substituted olefins, the cyanothiolation of internal alkynes has been much less explored. Herein, we show that nonactivated internal alkynes can be successfully cyanothiolated with diaryl disulfides and tert-butyl isocyanide in the presence of a Pd catalyst (e.g., Pd(PPh₃)₄) with the release of isobutene and arenethiol to afford β-thiolated alkenyl cyanides in yields of 34-89%.

Copper catalyzed cyanation through CC bond cleavage of gem-aryl dibromide followed by second cyanation of iodoarene by a released CN unit

A new approach for the synthesis of aryl cyanides through CC cleavage of styrenyl gem-dibromide has been achieved.

Recent developments and applications of cyanamides in electrophilic cyanation

This review summarizes the recent developments and applications of readily accessible cyanamides in the electrophilic cyanation of various nucleophiles.

Ruthenium catalyzed remote C4-selective C–H functionalisation of carbazoles via σ-activation

We report the C4-selective C–H alkylation of carbazole derivatives furnished with a pyrimidine directing group at C1.

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.

Transition Metal-Participated Synthesis and Utilization of N-containing Heterocycles: Exploring for Nitrogen Sources

This account aims to describe our recent efforts on the synthesis and utilization of N-containing heterocycles, where transition metals participate in the synthesis. A variety of nitrogen sources, including amines, amides, hydrazones, pyrimidines, isocyanides, and copper nitrate, have been disclosed for the synthesis of diverse bioactive and pharmacologically interesting N-containing heterocycles under the participation of transition metals. The well-known nitrogen sources, such as amines and amides, were used for the construction of indoles, isatins, and quinolones. Dihydrophthalazines, isoquinolines, indazoles, and pyrazoles were obtained from hydrazones, while various pyrimidine-containing heterocycles were afforded through regioselective C-H functionalizations using pyrimidine as the directing group. Recent research has focused on the chemistry of isocyanides to achieve several kinds of heterocyclic compounds with high efficiency under the catalysis of transition metals (Pd, Rh, Mn, Cu), through oxidative cyanation reactions, sequential isocyanide insertions into C-H, N-H, or O-H bonds, and tandem radical annulation. More recently, an efficient route to isoxazolines has been reported using copper nitrate as a novel nitrogen source.

Manganese(ii)-catalyzed modular synthesis of isoquinolines from vinyl isocyanides and hydrazines

An efficient manganese(ii)-catalyzed oxidative radical cascade reaction was developed from vinyl isocyanides and hydrazines leading to the modular synthesis of multi-substituted isoquinolines, phenanthridines and pyrrolo[1,2-a]quinoxalines.

C–H bond cyanation of arenes using N,N-dimethylformamide and NH4HCO3 as a CN source over a hydroxyapatite supported copper catalyst

Copper dispersed on Ca₅(PO₄)₃OH has been identified as an excellent heterogeneous catalyst for the in situ generation of ‘CN’ from NH₄HCO₃ and N,N-dimethylformamide, in the C–H bond activation of 2-phenylpyridine.

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.

Silver-Catalyzed Cross-Coupling of Isocyanides and Active Methylene Compounds by a Radical Process

Isocyanides are versatile building blocks, and have been extensively exploited in C-H functionalization reactions. However, transition-metal-catalyzed direct C-H functionalization reactions with isocyanides suffer from over-insertion of isocyanides. Reported herein is a radical coupling/isomerization strategy for the cross-coupling of isocyanides with active methylene compounds through silver-catalysis. The method solves the over-insertion issue and affords a variety of otherwise difficult to synthesize β-aminoenones and tricarbonylmethanes under base- and ligand-free conditions. This report presents a new fundamental C-C bond-forming reaction of two basic chemicals.