Copper-Mediated Sequential Cyanation of Aryl C–B and Arene C–H Bonds Using Ammonium Iodide and DMF

Synthesis of All-Benzene Multi-Macrocyclic Nanocarbons by Post-Functionalization of meta-Cycloparaphenylenes

Expanding the diversity of multi-macrocyclic nanocarbons, particularly those with all-benzene scaffolds, represents intriguing yet challenging synthetic tasks. Complementary to the existing synthetic approaches, here we report an efficient and modular post-functionalization strategy that employs iridium-catalyzed C-H borylation of the highly strained meta-cycloparaphenylenes (mCPPs) and an mCPP-derived catenane. Based on the functionalized macrocyclic synthons, a number of novel all-benzene topological structures including linear and cyclic chains, polycatenane, and pretzelane have been successfully prepared and characterized, thereby showcasing the synthetic utility and potential of the post-functionalization strategy.

Recent investigations into deborylative (thio-/seleno-) cyanation of aryl boronic acids

In this review, we intend to summarize the most important discoveries in the deborylative (thio-/seleno-) cyanation of aryl boronic acids from 2006 to the end of 2023. Thus, the review is divided into three parts. The first section focuses exclusively on cyanation of aryl boronic acids into aryl nitriles. The second section covers the available literature on the synthesis of aryl thiocyanates through thiocyanation of respective aryl boronic acids. The third will discuss selenocyanation of aryl boronic acids into aryl selenocyanates.

Kinetic and thermodynamic control of C(sp2)-H activation enables site-selective borylation

Catalysts that distinguish between electronically distinct carbon-hydrogen (C-H) bonds without relying on steric effects or directing groups are challenging to design. In this work, cobalt precatalysts supported by N-alkyl-imidazole-substituted pyridine dicarbene (ACNC) pincer ligands are described that enable undirected, remote borylation of fluoroaromatics and expansion of scope to include electron-rich arenes, pyridines, and tri- and difluoromethoxylated arenes, thereby addressing one of the major limitations of first-row transition metal C-H functionalization catalysts. Mechanistic studies established a kinetic preference for C-H bond activation at the meta-position despite cobalt-aryl complexes resulting from ortho C-H activation being thermodynamically preferred. Switchable site selectivity in C-H borylation as a function of the boron reagent was thereby preliminarily demonstrated using a single precatalyst.

Oxidative Radical Transnitrilation of Arylboronic Acids with Trityl Isocyanide

We report a radical transnitrilation of arylboronic acids with trityl isocyanide in the presence of manganese(III) acetate. Many functional groups can be tolerated in this transformation, and a special positive effect of benzoic acid in this reaction has been observed.

Regiodivergent Cu-Promoted, AcOH-Switchable Distal Versus Proximal Direct Cyanation of 1-Aryl-1H-indazoles and 2-Aryl-2H-indazoles via Aerobic Oxidative C-H Bond Activation

A copper-promoted regiodivergent, AcOH-switchable, distal and proximal direct cyanation of N-aryl-(1H/2H)-indazoles via aerobic oxidative C(sp²)-H bond activation has been developed. The inclusion or exclusion of AcOH as an additive is the foremost cause for the positional switch in the C-CN bond formation method that results in (C-2')-cyanated 2-aryl-2H-indazoles 3a-j, (C-2')-cyanated 1-aryl-1H-indazoles 4a-j [distal], or C-3 cyanated 2-aryl-2H-indazoles 5a-i [proximal] products in good to excellent yields and showed various functional group tolerance. The cyanide (CN^-) ion surrogate was generated via the unification of dimethylformamide and ammonium iodide (NH₄I). The utilization of molecular oxygen (aerobic oxidative strategy) as a clean and safe oxidant is liable for generous value addition. The further pertinence of the developed protocol has been demonstrated by transforming the synthesized cyanated product into numerous other functional groups, which will, undoubtedly, accomplish utilization in the synthetic area of biologically important compounds and medicinal chemistry.

Catalytic Cyanation of C-N Bonds with CO2/NH3

Cyanation of benzylic C-N bonds is useful in the preparation of important α-aryl nitriles. The first general catalytic cyanation of α-(hetero)aryl amines, analogous to the Sandmeyer reaction of anilines, was developed using reductive cyanation with CO₂/NH₃. A broad array of α-aryl nitriles was obtained in high yields and regioselectivity by C-N cleavage of intermediates as ammonium salts. Good tolerance of functional groups such as ethers, CF₃, F, Cl, esters, indoles, and benzothiophenes was achieved. Using ¹³CO₂, a ¹³C-labeled tryptamine homologue (five steps, 31% yield) and Cysmethynil (six steps, 37% yield) were synthesized. Both electronic and steric effects of ligands influence the reactivity of alkyl nickel species with electrophilic silyl isocyanates and thus determine the reactivity and selectivity of the cyanation reaction. This work contributes to the understanding of the controllable activation of CO₂/NH₃ and provides the promising potential of the amine cyanation reaction in the synthesis of bio-relevant molecules.

Lewis Acid-Promoted Typical Friedel-Crafts Reactions Using DMSO as a Carbon Source

This study reports a mild and efficient synthetic protocol for the synthesis of symmetrical and unsymmetrical diarylmethanes (DAMs). Using DMSO as the C₁ source and TMSOTf as the Lewis acid promoter, a series of functionalized symmetrical and unsymmetrical DAMs were synthesized in high yields. Gratifyingly, DMSO plays a dual role as a solvent and a C₁ source and can also be replaced with its deuterated counterpart, DMSO-d₆, enabling the incorporation of the -CD₂ moiety into the diarylmethane skeleton. The developed approach has been applied to a wide range of substrates having various functional groups, and this protocol has also been extended to the synthesis of an anti-breast cancer agent and an anticoagulant agent using common feedstock compounds. In addition, the postulated mechanism has been explicitly demonstrated via control experiments.

Synthesis of Unsymmetrical Diarylfumaronitriles via Tandem Michael Addition and Oxidation under K3Fe(CN)6/O2 System

An efficient formal alkenyl C-H cyanation reaction has been developed for the general synthesis of unsymmetrical diarylfumaronitriles in good to excellent yields. The reaction was achieved through tandem Michael addition and an oxidative process. The merits of this transformation include the use of K₃Fe(CN)₆ as a safe and nontoxic cyanide source, without an external noble metal catalyst, oxygen-involved reactions, easily available raw materials, good functional group tolerance, high stereoselectivity, and potential further application of the products.

Open-Air Dual-Diamination of Aromatic Aldehydes: Direct Synthesis of Azolo-Fused 1,3,5-Triazines Facilitated by Ammonium Iodide

A new and practical protocol for the synthesis of medicinally privileged azolo[1,3,5]triazines by simply heating under air has been presented. The in situ generated N-azolo amidines from commercially available aromatic aldehydes and 3-aminoazoles with ammonium iodide undergo the second diamination to accomplish the [3 + 1 + 1 + 1] heteroannulation reaction. This convenient process is appreciated by high efficiency, broad substrate scope, gram-scale synthesis, and operational simplicity under reagent-free conditions.

Application of combined cyanide sources in cyanation reactions

The cyanation reaction is a key transformation due to the wide-ranging applications of nitrile compounds in organic chemistry. Traditionally, the cyanation reaction employs metal cyanides as cyanide sources, which are toxic and environmentally unfriendly. Very recently, many excellent examples of using combined cyanide sources as cyanating agents have been reported. This review summarizes the applications of combined cyano-group sources in a variety of cyanation reactions.

Photo-Promoted Decarboxylative Alkylation of α,β-Unsaturated Carboxylic Acids with ICH2CN for the Synthesis of β,γ-Unsaturated Nitriles

An efficient, catalyst/photocatalyst-free, and cost-effective methodology for the decarboxylative alkylation of α,β-unsaturated carboxylic acids to synthesize β,γ-unsaturated nitriles has been developed. The reaction proceeded in an environmentally benign atmosphere of blue light-emitting diode irradiation with K₂CO₃ and water at room temperature. The methodology worked for a wide range of substrates (22 examples) with up to 83% yield. The protocol is also compatible for gram-scale synthesis.

Photoassisted Charge Transfer Between DMF and Substrate: Facile and Selective N,N-Dimethylamination of Fluoroarenes

A reversible Van der Waals complex formation between the electron-deficient fluorinated aromatic ring and N,N-dimethylformamide (DMF) molecules followed by light irradiation resulted in charge transfer (CT) process. The complex was stabilized by ammonium formate and further decomposed to form the C-N bond. Control experiments revealed that the simultaneous S_N Ar pathway also contributes to product formation. This methodology is mild, metal-free, and effective for the amination of a variety of substrates. The reproducibility of this methodology was also verified on gram-scale reactions. The CT states were supported by control UV/Vis spectroscopy and computational studies.

Revisiting the synthesis of aryl nitriles: a pivotal role of CAN

Facilitated by the dual role of Ceric Ammonium Nitrate (CAN), herein we report a cost-effective approach for the cyanation of aryl iodides/bromides with CAN-DMF as an addition to the existing pool of combined cyanation sources. In addition to being an oxidant, CAN acts as a source of nitrogen in our protocol. The reaction is catalyzed by a readily available Cu(ii) salt and the ability of CAN to generate ammonia in the reaction medium is utilized to eliminate the additional requirement of a nitrogen source, ligand, additive or toxic reagents. The mechanistic study suggests an evolution of CN- leading to the synthesis of a variety of aryl nitriles in moderate to good yields. The proposed mechanism is supported by a series of control reactions and labeling experiments.

Cyanation: a photochemical approach and applications in organic synthesis

This review summarises the photocatalytic cyanation strategies to construct C(sp²)–CN, C(sp³)–CN and X–CN (X = N, S) bonds.

C–CN bond formation: an overview of diverse strategies

Aim for cyanation: a comprehensive overview on various approaches on C–CN bond formation in arenes/heteroarenes by activated halides/pseudohalide, directed, non-directed, electro-catalyzed, photoredox-catalyzed, and radical approaches.

Three types of copper derivatives formed by CuCl2·2H2O interaction with (Z)-3-aryl-2-(methylthio)-5-(pyridine-2-ylmethylene)-3,5-dihydro-4H-imidazol-4-ones

The reactions of (Z)-3-aryl-2-(methylthio)-5-(pyridine-2-ylmethylene)-3,5-dihydro-4H-imidazol-4-ones (3) with CuCl2·2H2O in the presence of a reducing solvent (alcohol or dimethylformamide (DMF)) produce three types of Cu-containing compounds: two Cu complexes with a composition of CuII(3)Cl2 (4) and CuI(3)Cl (5) as well as a salt (3 + H)+CuICl2- (6) in a 4 : 5 : 6 ratio depending on the substituent at the N(3) nitrogen atom of the ligand moiety. In non-reducing solvents (dimethyl sulfoxide (DMSO) and CHCl3/acetone), only complexes 4 were formed, All three Cu derivatives (4, 5, and 6) were characterized by single-crystal X-ray diffraction, UV/vis spectroscopy, and electrochemistry data. Convenient electrochemical and UV-vis spectral criteria were recorded, which made it possible to distinguish between the different Cu-containing compounds. Based on the electron spectroscopy and electron paramagnetic resonance (EPR) data, a possible scheme for the formation of compounds 4-6 was proposed, including the initial coordination of copper(ii) chloride with an organic ligand, the subsequent reduction of the resulting complex 4 by DMF with the formation of salt 6, and the further transition of salt 6 into the complex 5.

Reductive cyanation of organic chlorides using CO2 and NH3 via Triphos-Ni(I) species

Cyano-containing compounds constitute important pharmaceuticals, agrochemicals and organic materials. Traditional cyanation methods often rely on the use of toxic metal cyanides which have serious disposal, storage and transportation issues. Therefore, there is an increasing need to develop general and efficient catalytic methods for cyanide-free production of nitriles. Here we report the reductive cyanation of organic chlorides using CO₂/NH₃ as the electrophilic CN source. The use of tridentate phosphine ligand Triphos allows for the nickel-catalyzed cyanation of a broad array of aryl and aliphatic chlorides to produce the desired nitrile products in good yields, and with excellent functional group tolerance. Cheap and bench-stable urea was also shown as suitable CN source, suggesting promising application potential. Mechanistic studies imply that Triphos-Ni(I) species are responsible for the reductive C-C coupling approach involving isocyanate intermediates. This method expands the application potential of reductive cyanation in the synthesis of functionalized nitrile compounds under cyanide-free conditions, which is valuable for safe synthesis of (isotope-labeled) drugs.

Nitriles are key intermediates in production of pharmaceuticals, agrochemicals and organic materials. Here, the authors report a nickel-catalyzed reductive cyanation of organic chlorides with CO₂/NH₃ and urea as cyanation reagents to afford a broad range of organic nitriles.

Overcoming Selectivity Issues in Reversible Catalysis: A Transfer Hydrocyanation Exhibiting High Kinetic Control

Reversible catalytic reactions operate under thermodynamic control, and thus, establishing a selective catalytic system poses a considerable challenge. Herein, we report a reversible transfer hydrocyanation protocol that exhibits high selectivity for the thermodynamically less favorable branched isomer. Selectivity is achieved by exploiting the lower barrier for C-CN oxidative addition and reductive elimination at benzylic positions in the absence of a cocatalytic Lewis acid. Through the design of a novel type of HCN donor, a practical, branched-selective, HCN-free transfer hydrocyanation was realized. The synthetically useful resolution of a mixture of branched and linear nitrile isomers was also demonstrated to underline the value of reversible and selective transfer reactions. In a broader context, this work demonstrates that high kinetic selectivity can be achieved in reversible transfer reactions, thus opening new horizons for their synthetic applications.

Acyl Cyanides as Bifunctional Reagent: Application in Copper-Catalyzed Cyanoamidation and Cyanoesterification Reaction

Cu-catalyzed domino decyanation and cyanation reaction of acyl cyanides with amines or alcohols have been developed. The cyano sources were generated in situ via C-CN cleavage yielding the corresponding cyano substituted amides or esters in moderate to excellent yields. This approach features a cheap copper catalyst, domino decyanation and cyanation reaction, readily available starting materials, broad substrate scope, operational simplicity, and the potential for further transformation of the cyano group.

Nickel-Catalyzed Transformation of Alkene-Tethered Oxime Ethers to Nitriles by a Traceless Directing Group Strategy

Nickel-catalyzed transformation of alkene-tethered oxime ethers to nitriles using a traceless directing group strategy has been developed. A series of alkene-tethered oxime ethers derived from benzaldehyde and cinnamyl aldehyde derivatives were converted into the corresponding benzonitriles and cinnamonitriles in 46-98% yields using the nickel catalyst system. Control experiments showed that the alkene group tethered to an oxygen atom on the oximes via one methylene unit plays a key role as a traceless directing group during the catalysis.

Recent advances in C–CN and C–H bond activation of green nitrile (MeCN) for organo-complexation, cyanation and cyanomethylation

The use of green and inexpensive organic nitrile (MeCN) as a cyano and cyano-methyl source for organo-complexation, cyanation, and cyanomethylation is reviewed.

An aerobic and green C-H cyanation of terminal alkynes

This study describes a benign C-H cyanation of terminal alkynes with α-cyanoesters serving as a nontoxic cyanide source. In situ generation of the key copper cyanide intermediate is proposed by a sequence of α-C-H oxidation and copper-mediated β-carbon elimination of α-cyanoesters, releasing the α-ketoester byproduct observed experimentally. The ensuing reaction of copper cyanide with terminal alkynes delivers preferentially cyanoalkynes and surpasses the possible Glaser type dimerization of terminal alkynes or the undesired accumulation of HCN under protic conditions. The presence of the co-oxidant K2S2O8 is crucial to this selectivity, probably by promoting oxidative transmetalation and the resulting formation of the Cu(iii)(acetylide)(CN) intermediate. All the reagents and salts used are commercially available, cheap and nontoxic, avoiding the use of highly toxic cyanide salts typically required in cyanation studies. The scope of this reaction is demonstrated with a set of alkynes and α-cyanoesters. The application of this method to late-stage functionalization of the terminal alkyne group in an estrone derivative is also feasible, showing its practical value for drug design.

Palladium-catalyzed cyanation of aryl halides with in situ generated CN− from ClCF2H and NaNH2

An efficient Pd-catalyzed cyanation of aryl halides with in situ generated CN⁻ anions is described.

Copper- and DMF-mediated switchable oxidative C–H cyanation and formylation of imidazo[1,2-a]pyridines using ammonium iodide

The cyanation and formylation of imidazo[1,2-a]pyridines were developed under copper-mediated oxidative conditions using ammonium iodide and DMF as a nontoxic combined cyano-group source and DMF as a formylation reagent.

One-pot regioselective C-H activation iodination-cyanation of 2,4-diarylquinazolines using malononitrile as a cyano source

A one-pot cyanation of 2,4-arylquinazoline with NIS and malononitrile has been developed. The one-pot reaction includes two steps. The Rh-catalyzed selective C-H activation/iodization of 2,4-diarylquinazoline with NIS, and then Cu-catalyzed cyanation of the corresponding iodinated intermediate with malononitrile to selectively give 2-(2-cyanoaryl)-4-arylquinazolines or 2-(2,6-dicyanoaryl)-4-arylquinazolines in good to excellent yields.

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.