Metal‐Free Synthesis of Highly Substituted Pyridines by Formal [2+2+2] Cycloaddition under Mild Conditions

The synthesis of pyridines through direct intermolecular cycloaddition of alkynes and nitriles is a contemporary challenge in organic synthesis. A Brønsted acid mediated formal [2+2+2] cycloaddition of heteroalkynes and nitriles was developed that proceeds under mild conditions. This constitutes a modular approach to highly substituted pyridine cores.     

Regiocontrolled Gold‐Catalyzed [2+2+2] Cycloadditions of Ynamides with Two Discrete Nitriles to Construct 4‐Aminopyrimidine Cores

Reported herein is the novel gold‐catalyzed intermolecular [2+2+2] cycloaddition of ynamides with two discrete nitriles to form monomeric 4‐aminopyrimidines, which are pharmaceutically important structural motifs. The utility of this new cycloaddition is demonstrated by the excellent regioselectivity obtained using a variety of ynamides and nitriles.     

Derivatives of 2-oxo-3(2H)-benzothiazolineacetonitrile and related compounds. II. Synthesis of 2-oxo-alkyl esters of 3(2H)-benzothiazolineacetimidic acids and related products

The reaction of the appropriate 2-benzothiazolinone or 2-benzoxazolinone under basic conditions with (1) 2-chloropropionitrile, (2) acrylonitrile, (3) 4-chlorobutyronitrile or (4) chloroacetonitrile afforded the nitriles 1–8 . The reaction of various nitriles with alcoholic-hydrogen chloride solutions at low temperatures afforded the hydrogen chloride salts of the imino-ester which upon neutralization with potassium carbonate yielded the titled compounds.     

Photocatalyzed [2 + 2 + 2]-cycloaddition of nitriles with acetylene: an effective method for the synthesis of 2-pyridines under mild conditions

The photocatalyzed [2 + 2 + 2]-cycloaddition of nitriles with 2 equiv of acetylene to 2-pyridines can be carried out under mild conditions and represents a valuable extension to common synthetical methods. For the ideal wavelength range (350-500 nm), lamps as well as sunlight can be used. Working at room temperature and in organic solvents such as toluene or hexane as well as in water gives satisfying results in many cases. However, it is also possible to vary the solvent and the reaction temperature of the photocatalyzed synthesis and to choose, with respect to the specific substrate, specific requirements for this particular reaction and general requirements of the method. This simple and selective method derives its potential mainly from the large variety of applicable nitriles. Suitable substrates include (functionalized) aliphatic and aromatic nitriles as well as cyanamides derived from secondary amines.     

P(i-BuNCH2CH2)3N: an efficient ligand for the direct alpha-arylation of nitriles with aryl bromides

A new catalyst system for the synthesis of alpha-aryl-substituted nitriles is reported. The bicyclic triaminophosphine P(i-BuNCH(2)CH(2))(3)N (1b) serves as an efficient and versatile ligand for the palladium-catalyzed direct alpha-arylation of nitriles with aryl bromides. Using ligand 1b, ethyl cyanoacetate and primary as well as secondary nitriles are efficiently coupled with a wide variety of aryl bromides possessing electron-rich, electron-poor, electron-neutral, and sterically hindered groups.     

Synthesis of 2- and 4-imino(1,2-a)pyridopyrimidines from allenic nitriles and 2-aminopyridines

4,4-Dialkylallenyl nitriles and 2-aminopyridines give 2-alkyl-4-iminopyrido(1,2-a)pyrimidines as monohydrates in about 90% yield and 4-monoalkylallenyl nitriles similarly give 4-alkyl-2-imino(1,2-a)pyrimidines.     

One-pot cyclization of dilithiated nitriles with isothiocyanates and epibromohydrin. Synthesis of 2-cyano-1-(hydroxymethyl)cyclopropanes and 2-cyanomethylidene-4-(hydroxymethyl)thiazolidines

The cyclization of dilithiated nitriles with epibromohydrin afforded 2-cyano-1-(hydroxymethyl)cyclopropanes. 2-Cyanomethylidene-(4-hydroxymethyl)thiazolidines were prepared by one-pot cyclization of dilithiated nitriles with isothiocyanates and epibromohydrin.     

Synthesis of aminopyridines and aminopyridones by cobalt-catalyzed [2+2+2] cycloadditions involving yne-ynamides: scope, limitations, and mechanistic insights

An in-depth study of the cobalt-catalyzed [2+2+2] cycloaddition between yne-ynamides and nitriles to afford aminopyridines has been carried out. About 30 nitriles exhibiting a broad range of steric demand and electronic properties have been evaluated, some of which open new perspectives in metal-catalyzed arene formation. In particular, the use of [CpCo(CO)(dmfu)] (dmfu=dimethyl fumarate) as a precatalyst made possible the incorporation of electron-deficient nitriles into the pyridine core. Modification of the substitution pattern at the yne-ynamide allows the regioselectivity to be switched toward 3- or 4-aminopyridines. Application of this synthetic methodology to the construction of the aminopyridone framework using a yne-ynamide and an isocyanate was also briefly examined. DFT computations suggest that 3-aminopyridines are formed by formal [4+2] cycloaddition between the nitrile and the intermediate cobaltacyclopentadiene, whereas 4-aminopyridines arise from an insertion pathway.     

Enzymatic nitrile hydrolysis catalyzed by nitrilase ZmNIT2 from maize. An unprecedented β-hydroxy functionality enhanced amide formation

To explore the synthetic potential of nitrilase ZmNIT2 from maize, the substrate specificity of this nitrilase was studied with a diverse collection of nitriles. The nitrilase ZmNIT2 showed high activity for all the tested nitriles except benzonitrile, producing both acids and amides. For the hydrolysis of aliphatic, aromatic nitriles, phenylacetonitrile derivatives and dinitriles, carboxylic acids were the major products. Unexpectedly, amides were found to be the major products in nitrilase ZmNIT2-catalyzed hydrolysis of β-hydroxy nitriles. The hydrogen bonding between the hydroxyl group and nitrogen in the enzyme-substrate complex intermediates that disfavors the loss of ammonia and formation of acyl-enzyme intermediate, which was further hydrolyzed to acid, was proposed to be responsible for the unprecedented β-hydroxy functionality assisted high yield of amide formation.     

Formal [3 + 2] cycloadditions of donor-acceptor cyclopropanes and nitriles

Donor-acceptor cyclopropanes activated with Me3SiOTf cleave to reactive intermediates that can be efficiently intercepted by nitriles in a formal [3 + 2] dipolar cycloaddition reaction. Aliphatic, aromatic, and alpha,beta-unsaturated nitriles are excellent reaction partners, giving synthetically useful 2H-3,4-dihydropyrrole cycloaddition products in high yield.     

Synthesis of New 2-Aminopyrrole Derivatives by Reaction of Furan-2,3-diones 3-Acylhydrazones with CH-Nucleophiles

Recyclization of furan-2,3-diones acylhydrazones under the action of esters, amides and nitriles of cyanoacetic acids gave the corresponding esters, amides and nitriles of 2-amino-1-R-4-oxo-5- (2-oxo-2-aryl/tert-butylethylidene)-4,5-dihydro-1H-pyrrole-3-carboxylic acids.     

Synthesis of Aminopyridines and Aminopyridones by Cobalt‐Catalyzed [2+2+2] Cycloadditions Involving Yne‐Ynamides: Scope,Limitations, and Mechanistic Insights

An in‐depth study of the cobalt‐catalyzed [2+2+2] cycloaddition between yne‐ynamides and nitriles to afford aminopyridines has been carried out. About 30 nitriles exhibiting a broad range of steric demand and electronic properties have been evaluated, some of which open new perspectives in metal‐catalyzed arene formation. In particular, the use of [CpCo(CO)(dmfu)] (dmfu=dimethyl fumarate) as a precatalyst made possible the incorporation of electron‐deficient nitriles into the pyridine core. Modification of the substitution pattern at the yne‐ynamide allows the regioselectivity to be switched toward 3‐ or 4‐aminopyridines. Application of this synthetic methodology to the construction of the aminopyridone framework using a yne‐ynamide and an isocyanate was also briefly examined. DFT computations suggest that 3‐aminopyridines are formed by formal [4+2] cycloaddition between the nitrile and the intermediate cobaltacyclopentadiene, whereas 4‐aminopyridines arise from an insertion pathway.     

Cyclotrimerization of Nitriles Catalyzed by SmI2/Amines: Synthesis of 2,4,6-Trisubstituted-S-Triazines

SmI₂ has been found to catalyze a reaction of cyclotrimerization of nitriles in the presence of amine as cocatalyst to give 2,4,6-trisubstituted-s-triazines effectively under mild reaction conditions. The yield depends on the structure of nitriles.     

Synthesis of Functionalized Tetrahydropyridines by SnCl4-Mediated [4+2] Cycloaddition between Donor–Acceptor Cyclobutanes and Nitriles

Cycloadditions of strained carbocycles promoted by Lewis acids are powerful methods to construct heterocyclic frameworks. In fact, the formal [3+2] cycloadditions of donor–acceptor (DA) cyclopropanes with nitriles has seen particular success in synthesis. In this work, we report on the first [4+2] cycloaddition of nitriles with DA cyclobutanes by Lewis acid activation. Tetrahydropyridine derivatives were obtained in up to 91 % yield from various aryl-activated cyclobutane diesters and aliphatic or aromatic nitriles.     

Catalytic Chemo- and Regioselective Radical Carbocyanation of 2-Azadienes for the Synthesis of α-Amino Nitriles

α-Amino nitriles are versatile structural motifs in a variety of biologically active compounds and pharmaceuticals and they serve as valuable building blocks in synthesis. The preparation of α- and β-functionalized α-amino nitriles from readily available scaffolds, however, remains challenging. Herein is reported a novel dual catalytic photoredox/copper-catalyzed chemo- and regioselective radical carbocyanation of 2-azadienes to access functionalized α-amino nitriles by using redox-active esters (RAEs) and trimethylsilyl cyanide. This cascade process employs a broad scope of RAEs and provides the corresponding α-amino nitrile building blocks in 50–95 % yields (51 examples, regioselectivity >95 : 5). The products were transformed into prized α-amino nitriles and α-amino acids. Mechanistic studies suggest a radical cascade coupling process.     

2-(2-hydroxyphenyl)-2-adamantanol in Ritter reaction

2-Substituted 4H-1,3-benzoxazines were obtained by the condensation of 2-(2-hydroxyphenyl)-2-adamantanol with aromatic and aliphatic nitriles in trifluoroacetic acid. With acetonitrile the classic product of Ritter reaction, a secondary amide, was isolated.     

Synthesis of 2-aryl- and 2-hetaryloxazoles from the oxazolines and oxazolidines

Treatment of 2-phenyl-, 2-(2-furyl)-, and 2-(2-thienyl)oxazolines with nickel peroxide has been found to give, in addition to the dehydrogenation products (2-substituted oxazoles), the fragmentation products (amides of benzoic, furan-2-carboxylic, and thiophen-2-carboxylic acids). This fragmentation appears to give initially the nitriles, which are then converted into the amides by the nickel peroxide. Catalytic dehydrogenation of 2-phenyloxazoline gives low yields of 2-phenyloxazole, the principal product being benzonitrile. Treatment of the Schiff's bases obtained from ethanolamine and aldehydes (benzaldehyde, furfural, and thiophen-2-aldehyde) with nickel peroxide gives trace amounts of the oxazoles, the principal products being the aldehydes, with smaller amounts of the nitriles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 822–825, June, 1986.     

Catalytic oxidative conversion of aldehydes into nitriles using NH3·H2O/FeCl2/NaI/Na2S2O8: A practical approach to febuxostat

A novel approach to convert aldehydes into nitriles using NH₃·H₂O/FeCl₂/NaI/Na₂S₂O₈ has been developed. Both alkyl and aryl nitriles were obtained in good to excellent yields. Electron-withdrawing and electron-donating groups, such as fluoro, chloro, bromo, nitro, ester, cyano, trifluoromethyl and alkoxy were tolerated. Notably, febuxostat and its intermediate, ethyl 2-[3-cyano-4-(2-methylpropoxy)phenyl]-4-methyl-5-thiazolecarboxylate, were obtained in excellent yields.     

Nitroenamines—III: Synthesis of 3,3-diamino-2-nitroacrylonitriles from 1,1-diamino-2-nitroethylenes

A novel fragmentation of an isothiazoline ring is reported. Nitroketene aminals 1 react with benzoyl isothiocyanate to form the adducts 3. These adducts can be converted to the 3,3-diamino-2-nitroacrylonitriles 2 in two discrete steps—first to an isothiazoline (4,7) by oxidation, and then to the nitriles by base-induced fragmentation; alternatively the adducts (3c, 11) can be directly treated with alkaline hydrogen peroxide to provide the nitriles in one step.     

Synthesis of substituted imidazolines via [3+2]-cycloaddition of aziridines with nitriles

An efficient synthesis of 2,4-disubstituted 1H-imidazolines from aziridines and nitriles in the presence of BF₃-Et₂O or triethyloxonium tetrafluoroborate has been described. The reaction proceeds via a [3+2]-cycloaddition reaction. Most of the nitriles successfully underwent cycloaddition reactions with aziridines even at room temperature in a very short time.