The Renaissance of Organo Nitriles in Organic Synthesis

Organic Base-Promoted C-N- and C-O-Coupled Domino Cyclization Strategy: Syntheses of Oxazine-6-ones and 4-Pyrimidinols

Oxazine-6-one and 4-pyrimidinol are two important frameworks in pharmaceutical production. Herein, we disclosed a simple, efficient, inexpensive organic base-promoted and additive-stimulated protocol for the syntheses of variably functionalized oxazine-6-ones and 4-pyrimidinols employing acetonitrile solvent under conventional heating conditions using an oil bath through C-N and C-O coupled domino steps. This simple practicable productive protocol utilizes easily producible cheap precursors, namely, benzimidates or benzamidines, with differently substituted dicyano-olefins, and it comprises step economy, robustness, and moisture insensitive conditions affording high yield that avoids the use of transition-metal catalysts, multistep with multicomponent strategy, and harsh reaction conditions involving hazardous chemicals. This method is scalable into gram-scale production with good yield.

Microwave-Mediated, Catalyst-Free Synthesis of 1,2,4-Triazolo[1,5-a]pyridines from Enaminonitriles

A catalyst-free, additive-free, and eco-friendly method for synthesizing 1,2,4-triazolo[1,5-a]pyridines under microwave conditions has been established. This tandem reaction involves the use of enaminonitriles and benzohydrazides, a transamidation mechanism followed by nucleophilic addition with nitrile, and subsequent condensation to yield the target compound in a short reaction time. The methodology demonstrates a broad substrate scope and good functional group tolerance, resulting in the formation of products in good-to-excellent yields. Furthermore, the scale-up reaction and late-stage functionalization of triazolo pyridine further demonstrate its synthetic utility. A plausible reaction pathway, based on our findings, has been proposed.

Manganese-catalyzed base-free addition of saturated nitriles to unsaturated nitriles by template catalysis

The coupling of mononitriles into dinitriles is a desirable strategy, given the prevalence of nitrile compounds and the synthetic and industrial utility of dinitriles. Herein, we present an atom-economical approach for the heteroaddition of saturated nitriles to α,β- and β,γ-unsaturated mononitriles to generate glutaronitrile derivatives using a catalyst based on earth-abundant manganese. A broad range of such saturated and unsaturated nitriles were found to undergo facile heteroaddition with excellent functional group tolerance, in a reaction that proceeds under mild and base-free conditions using low catalyst loading. Mechanistic studies showed that this unique transformation takes place through a template-type pathway involving an enamido complex intermediate, which is generated by addition of a saturated nitrile to the catalyst, and acts as a nucleophile for Michael addition to unsaturated nitriles. This work represents a new application of template catalysis for C-C bond formation.

Electrohydrogenation of Nitriles with Amines by Cobalt Catalysis

Catalytic hydrogenation of nitriles represents an efficient and sustainable one-step synthesis of valuable bulk and fine chemicals. We report herein a molecular cobalt electrocatalyst for selective hydrogenative coupling of nitriles with amines using protons as the hydrogen source. The key to success for this reductive reaction is the use of an electrocatalytic approach for efficient cobalt-hydride generation through a sequence of cathodic reduction and protonation. As only electrons (e- ) and protons (H+ ) as the redox equivalent and hydrogen source, this general electrohydrogenation protocol is showcased by highly selective and straightforward synthesis of various functionalized and structurally diverse amines, as well as deuterium isotope labeling applications. Mechanistic studies reveal that the electrogenerated cobalt-hydride transfer to nitrile process is the rate-determining step.

Nucleophile-Controlled Trapping of Gold Carbene by Nitriles and Water: Synthesis of 5H-Pyrimido[5,4-b]indoles and 2-Benzylidene-3-indolinones

A gold-catalyzed, nucleophile-controlled cascade reaction of N-(2-azidophenyl-ynyl)methanesulfonamides with nitriles and water is described that provides structurally diverse 5H-pyrimido[5,4-b]indoles and 2-benzylidene-3-indolinones in good to excellent yields. Mechanistic studies indicate that the β-sulfonamido-α-imino gold carbene is the key intermediate which is generated through the gold-catalyzed cyclization of N-(2-azidophenyl-ynyl)methanesulfonamides and undergoes formal [4 + 2] cascade annulation with nitriles and intramolecular SN2' type reaction with water, respectively.

Visible Light-Enhanced [3 + 2] Cycloaddition of N,N-Disubstituted Hydrazines with Organo-Cyanamides: Access to Polysubstituted 1,2,4-Triazol-3-amines

Visible light-enhanced [3 + 2] cycloaddition of N,N-disubstituted hydrazines with N-cyano-N-aryl-p-toluenesulfonamides is an efficient reaction pathway to polysubstituted 1,2,4-triazol-3-amines. The reaction is performed under mild conditions without the addition of any transition metals. This strategy involves a C(sp3)-H bond activation, a cyano cycloaddition, and the formation of two new C═N bonds. The protocol shows the advantages of good functional group tolerance and broad substrate scope. The late-stage modification experiments provide practical applications in the field of organic synthesis and medicinal chemistry.

Pd(II)-Catalyzed Three-Component Synthesis of Furo[2,3-d]pyrimidines from β-Ketodinitriles, Boronic Acids, and Aldehydes

A Pd(II)-catalyzed three-component synthesis of 2,4,6-triarylfuro[2,3-d]pyrimidines from β-ketodinitriles, boronic acids, and aldehydes has been developed. The participation of both nitrile (-CN) groups led to the concurrent construction of furo-pyrimidine via the formation of C-C, C═C, C-O, C-N, and C═N bonds. The compounds show excellent photoluminescence properties with absorption maxima ranging from 348 to 387 nm and emission from 468 to 533 nm. The synthetic utility of the protocol was further demonstrated through a few postsynthetic manipulations.

Access to 2-pyridinones comprising enaminonitriles via AgOAc promoted cascade reactions of thioesters with aminomethylene malononitriles

The facile synthesis of 2-pyridinones containing enaminonitriles from thioesters with aminomethylene malononitriles is achieved through an AgOAc-promoted acylation/cyclization/tautomerization cascade reaction. Control experiments reveal that AgOAc acts as a versatile promoter, activating both thioester and cyano groups while also serving as a Brønsted base in the cascade sequence. Moreover, 2-pyridinones were transformed into biologically significant 2-pyridinone-fused 2-pyrimidones with intriguing fluorescence emission properties.

Visible-Light-Mediated Solvent-Switched Photosensitizer-Free Synthesis of Polyfunctionalized Quinolines and Pyridines

A solvent (2,2,2-trifluoroethanol (TFE) vs ethyl alcohol (EtOH)) switched synthesis of quinolines and pyridines is illustrated from (E)-2-(1,3-diphenylallylidene)malononitriles via a Pd(II)-catalyzed photochemical process. The active catalyst [L₂Pd(0)] generated serves as an exogenous photosensitizer. The process offers predominantly Z-alkenylated quinolines and pyridines in TFE and EtOH, respectively. Furthermore, large-scale synthesis and a few interesting post-synthetic modifications have been demonstrated.