Copper-mediated selective cyanation of indoles and 2-phenylpyridines with ammonium iodide and DMF

Weakly coordinating tert-amide assisted Rh(III)-catalyzed C4-cyanation of indoles: application in photophysical studies

A rhodium(III)-catalyzed indole C4-selective cyanation is described using the bench-stable, user-friendly electrophilic cyanation agent N-cyano-N-phenyl-p-toluenesulfonamide (NCTS) as a coupling partner. A suitably positioned weakly coordinating tert-amide group was utilized for this site selectivity. The developed protocol proceeded with a broad scope. [Cp*Rh(MeCN)3][SbF6]2 was found to be an effective Rh(III) catalyst for this transformation. An initial study was carried out to know the photophysical properties of the C4-cyanated indole frameworks.

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.

Lentinuses A-B, two alkaloids from the marine-derived fungus Lentinus sajor-caju with potent anti-pulmonary fibrosis activity

By adding natural amino acids into the medium as sole nitrogen source, twenty-four compounds, including two new alkaloids lentinuses A-B (1-2) with a rare oxazinone core in marine natural products, one new natural product 3-acetamido-4-phenylfurazan (3), 9β-ergosterol (22) were firstly discovered from a marine fungus, and twenty known compounds (4-21, 23-24) were isolated from the marine-derived fungus Lentinus sajor-caju. The chemical structures of all these compounds were elucidated by HRMS, NMR spectroscopy and X-ray diffraction. Compounds 1-24 were evaluated for their inhibitory activity against TGF-β1-induced collagen accumulation in human fetal lung fibroblasts (HFL1). Compounds 2, 3, 12, 22, and 23 showed potent activity against TGF-β1-induced collagen accumulation and low toxicity to HFL1 cells. The binding mode of lentinus B (2) with TGF-β1 receptor was then performed by using Schrödinger software, and the result showed that lentinus B possesses a strong binding force such as hydrogen bonding and hydrophobic interactions to the protein, which may provide a theoretical basis to design more potent anti-fibrotic drugs in the future.

Magnetically separable triazine-based Cu(ii)-vitamin B5 complex in nitromethane toward efficient heterogeneous cyanation reaction of aryl halides

In the current study, a highly efficient heterogeneous copper catalyst has been developed by supporting copper acetate on a magnetically separable triazine-vitamin B₅ system. After the successful characterization of the prepared nanoparticles by various techniques such as FT-IR, FE-SEM, EDX/MAP, XRD, TEM, TGA, VSM, and ICP-OES, the catalytic efficiency of them were evaluated in the cyanation reaction of aryl halides in the presence of nitromethane as a non-toxic and cost-effective cyanation source. The cyanation products were obtained in desirable yields. Notably, the magnetic nanocatalyst can be easily recovered and reused at least five times without a significant decrease in its performance.

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.

One-Pot Modified Madelung Synthesis of 3-Tosyl- and 3-Cyano-1,2-disubstituted Indoles

A One-pot, two-step procedure for the synthesis of 1,2-disubstituted-3-tosyl and 1,2-disubstituted-3-cyanoindoles from the corresponding N-(o-tolyl)benzamides is reported. The developed procedure is operationally simple, does not utilize any transition metals, and provides variably substituted indoles in good yields from readily available starting materials.

Rapid 'on-column' preparation of hydrogen [11C]cyanide from [11C]methyl iodide via [11C]formaldehyde

Hydrogen [11C]cyanide ([11C]HCN) is a versatile 11C-labelling agent for the production of 11C-labelled compounds used for positron emission tomography (PET). However, the traditional method for [11C]HCN production requires a dedicated infrastructure, limiting accessibility to [11C]HCN. Herein, we report a simple and efficient [11C]HCN production method that can be easily implemented in 11C production facilities. The immediate production of [11C]HCN was achieved by passing gaseous [11C]methyl iodide ([11C]CH3I) through a small two-layered reaction column. The first layer contained an N-oxide and a sulfoxide for conversion of [11C]CH3I to [11C]formaldehyde ([11C]CH2O). The [11C]CH2O produced was subsequently converted to [11C]HCN in a second layer containing hydroxylamine-O-sulfonic acid. The yield of [11C]HCN produced by the current method was comparable to that of [11C]HCN produced by the traditional method. The use of oxymatrine and diphenyl sulfoxide for [11C]CH2O production prevented deterioration of the molar activity of [11C]HCN. Using this method, compounds labelled with [11C]HCN are now made easily accessible for PET synthesis applications using readily available labware, without the need for the 'traditional' dedicated cyanide synthesis infrastructure.

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.

Copper-mediated oxidative C-H/N-H activations with alkynes by removable hydrazides

The efficient copper-mediated oxidative C-H alkynylation of benzhydrazides was accomplished with terminal alkynes. Thus, a heteroaromatic removable N-2-pyridylhydrazide allowed for domino C-H/N-H functionalization. The approach featured remarkable functional group compatibility and ample substrate scope. Thereby, highly functionalized aromatic and heteroaromatic isoindolin-1-ones were accessed with high efficacy with rate-limiting C-H cleavage.

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.

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.

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.

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.

Terminal methyl as a one-carbon synthon: synthesis of quinoxaline derivatives via radical-type transformation

An iron-promoted method for the construction of pyrrolo[1,2-a]quinoxaline derivatives has been developed. Various solvents with terminal methyl group, including ethers, amines and dimethyl sulfoxide, were utilized as carbon sources for the synthesis.

Cu(OAc)2-Mediated benzimidazole-directed C–H cyanation using 2-(4-methylpiperazin-1-yl)acetonitrile as the cyano source

The C–H activation catalytic system was originally applied to the C(sp²)–H cyanation of aryls/heteroaryls to synthesize 2-(1H-benzo[d]imidazol-2-yl)aryl nitriles.

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.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Metal-Free Direct C-H Cyanation of Alkenes

A metal‐free and direct alkene C−H cyanation is described. Directing groups are not required and the mechanism involves electrophilic activation of the alkene by a cyano iodine(III) species generated in situ from a [bis(trifluoroacetoxy)iodo]arene and trimethylsilyl cyanide as the cyanide source. This C−H functionalization can be conducted on gram scale, and for noncyclic 1,1‐ and 1,2‐disubstuted alkenes high stereoselectivity is achieved, thus rendering the method highly valuable.

Beyond a solvent: triple roles of dimethylformamide in organic chemistry

N,N-Dimethylformamide (DMF) is frequently used as an aprotic solvent in chemical transformations in laboratories of academia as well as in those of chemical industry. In the present review, we will reveal that DMF is actually something much more than a solvent. It is a unique chemical since, as well as being an effective polar aprotic solvent, it can play three other important roles in organic chemistry. It can be used as a reagent, a catalyst, and a stabilizer.

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.

Cyanation of aromatic/vinylic boronic acids with α-cyanoacetates

A protocol is reported to achieve safe and convenient aromatic and vinylic cyanation of boronic acids (as well as halides) with α-cyanoacetates, avoiding the use of toxic cyanide salts.