Heterocycles from α-Aminonitriles

TFA-catalyzed solvent-free dearomative cyanidation of isoquinoline using (Boc)2O as an acylation agent

A TFA-catalyzed dearomative cyanidation of isoquinoline is described, which provides a series of 1-cyanoisoquinolines in high yields under solvent-free conditions. This protocol is operated under mild and environmentally friendly conditions, utilizing readily available and cost-effective starting materials. The reaction features broad functional group compatibility, 100 mmol scale synthesis ability and operational simplicity, making it a significant potential approach for the synthesis of various biologically interesting isoquinolines via α C-cyanation.

Mn-Catalyzed Aerobic Oxidative α-Cyanation of Tertiary Amines Using Azo/Hydrazide Redox

Azo compounds such as diethyl azodicarboxylate have been used in oxidative coupling reactions to generate iminium ions from tertiary amines. However, the requirement of stoichiometric amounts of azo compounds limits their large-scale applications. Herein, we present an aerobic oxidative α-cyanation of tertiary amines using catalytic amounts of an azo compound or hydrazine. The developed protocol provides a practical and ecofriendly route for α-cyanated tertiary amines, using molecular oxygen as the terminal oxidant.

Light-Induced Metal-Free Generation of Cyanocarbenes from Alkynyl Triazenes for the Synthesis of Nitrile Derivatives

The chemistry of alkynyl triazenes is an emerging field for organic chemists and especially acid-induced nucleophilic functionalizations, either directly, or after a prior reaction towards aromatic triazenes under extrusion of nitrogen, paved the way for fruitful strategies. In contrast, the chemical behavior of alkynyl triazenes upon irradiation with light is still unknown. Herein we present the first photoactivation of alkynyl triazenes that triggers an uncommon reactivity pattern involving the cleavage of the N1-N2 bond of the triazene moiety resulting in a unique approach to cyanocarbenes from a readily available, stable, and insensitive precursor. This allows to access various nitrile compounds without the use of a toxic cyanating agent by exploiting the reactivity pattern of carbenes. By variation of the reaction conditions and light sources, different substitution patterns can be obtained selectively in good yields under mild and metal-free conditions, thus introducing the alkynyl triazene unit as a photo accessible methylene nitrile synthon. Using this synthon, subclasses like α-alkoxynitriles, α-aminonitriles and α-cyanohydrazones become easily available. These exhibit synthetically valuable substitution patterns for the synthesis of pharmaceuticals, intermediates for total synthesis and amino acid synthesis.

Polyaromatic Group Embedded Cd(II)-Coordination Polymers for Microwave-Assisted Solvent-Free Strecker-Type Cyanation of Acetals

In this work, two new 1D Cd(II) coordination polymers (CPs), [Cd(L1)(NMF)₂]_n (1) and [Cd(L2)(DMF)(H₂O)₂]_n·n(H₂O) (2), have been synthesized, characterized and employed as catalysts for the microwave-assisted solvent-free Strecker-type cyanation of different acetals. Solvothermal reaction between the pro-ligand, 5-{(pyren-1-ylmethyl)amino}isophthalic acid (H₂L1) or 5-{(anthracen-9-ylmethyl)amino}isophthalic acid (H₂L2), and Cd(NO₃)₂.6H₂O in the presence of NMF or DMF:THF solvent, produces the coordination polymer 1 or 2, respectively. These frameworks were characterized by single-crystal and powder X-ray diffraction analyses, ATR-FTIR, elemental and thermogravimetry analysis. Their structural analysis revealed that both CPs show one-dimensional structures, but CP 1 has a 1D double chain type structure whereas CP 2 is a simple one-dimensional network. In CP 1, the dinuclear {Cd₂(COO)₄} unit acts as a secondary building unit (SBU) and the assembly of dinuclear SBUs with deprotonated ligand (L1^2-) led to the formation of a 1D double chain framework. In contrast, no SBU was observed in CP 2. To test the catalytic effectiveness of these 1D compounds, the solvent-free Strecker-type cyanation reactions of different acetals in presence of trimethylsilyl cyanide (TMSCN) was studied with CPs 1 and 2 as heterogenous catalysts. CP 1 displays a higher activity (yield 95%) compared to CP 2 (yield 84%) after the same reaction time. This is accounted for by the strong hydrogen bonding packing network in CP 2 that hampers the accessibility of the metal centers, and the presence of the dinuclear Cd(II) SBU in CP 1 which can promote the catalytic process in comparison with the mononuclear Cd(II) center in CP 2. Moreover, the recyclability and heterogeneity of both CPs were tested, demonstrating that they can be recyclable for at least for four cycles without losing their structural integrity and catalytic activity.

Paired Electrolysis for Decarboxylative Cyanation: 4-CN-Pyridine, a Versatile Nitrile Source

A decarboxylative cyanation of amino acids under paired electrochemical reaction conditions has been developed. 4-CN-pyridine was found to be a new and effective cyanation reagent under catalyst-free conditions. Mechanistic studies support a nucleophilic reaction pathway, and the cyanation protocol can be applied to diverse substrates including N,N-dialkyl aniline and indole derivatives.

Photochemical α-Aminonitrile Synthesis Using Zn-Phthalocyanines as Near-Infrared Photocatalysts

While photochemical transformations with sunlight almost exclusively utilize the UV-vis part of the solar spectrum, the majority of the photons emitted by the sun have frequencies in the near-infrared region. Phthalocyanines show high structural similarity to the naturally occurring light-harvesting porphyrins, chlorins, and mainly bacteriochlorins and are also known for being efficient and affordable near-infrared light absorbers as well as triplet sensitizers for the production of singlet oxygen. Although having been neglected for a long time in synthetic organic chemistry due to their low solubility and high tendency toward aggregation, their unique photophysical properties and chemical robustness make phthalocyanines attractive photocatalysts for the application in near-infrared-light-driven synthesis strategies. Herein, we report a cheap, simple, and efficient photocatalytic protocol, which is easily scalable under continuous-flow conditions. Various phthalocyanines were studied as near-infrared photosensitizers in oxidative cyanations of tertiary amines to generate α-aminonitriles, a synthetically versatile compound class.

Designing and Construction of Polyaromatic Group Containing Cd(II)-based Coordination Polymers for Solvent-free Strecker-type Cyanation of Acetals

In the present work, we have synthesized and characterized two novel Cd(II) coordination polymers, [Cd4(L1)4(DMF)6]n.3n(DMF) (1) and [Cd2(L2)2(DMF)3]n.2n(DMF) (2), and studied their catalytic application. They were synthesized via solvothermal reaction...

Electrochemically promoted oxidative α-cyanation of tertiary and secondary amines using cheap AIBN

The electrochemical α-cyanation of tertiary and secondary amines has been developed by using a cheap cyanide reagent, azobisisobutyronitrile (AIBN). The CN radical, generated through n-Bu₄NBr-meidated electrochemical oxidation, participates in a novel α-cyanation reaction under exogenous oxidant-free conditions.

Cyanation of glycine derivatives

We report a catalytic oxidative C-H cyanation of glycine derivatives using a simple copper(i) catalyst with NFSI as an oxidant via a radical process to furnish α-cyano glycine derivatives, which are useful intermediates for organic synthesis. CuCl acted as both a one-electron reductant and a transition-metal catalyst in this transformation. NFSI served as a one-electron oxidant and generated a N-centered radical as a H-abstractor. The reaction displayed broad substrate scope and mild reaction conditions.

Flow Photochemistry as a Tool in Organic Synthesis

Photochemical transformations of molecular building blocks have become an important and widely recognized research field in the past decade. Detailed and deep understanding of novel photochemical catalysts and reaction concepts with visible light as the energy source has enabled a broad application portfolio for synthetic organic chemistry. In parallel, continuous-flow chemistry and microreaction technology have become the basis for thinking and doing chemistry in a novel fashion with clear focus on improved process control for higher conversion and selectivity. As can be seen by the large number of scientific publications on flow photochemistry in the recent past, both research topics have found each other as exceptionally well-suited counterparts with high synergy by combining chemistry and technology. This review will give an overview on selected reaction classes, which represent important photochemical transformations in synthetic organic chemistry, and which benefit from mild and defined process conditions by the transfer from batch to continuous-flow mode.

Evidence and exploitation of dicationic ammonium-nitrilium superelectrophiles: direct synthesis of unsaturated piperidinones

Exploiting superacid activation, the reactivity of aminonitriles was enhanced through the transient formation of highly reactive ammonium-nitrilium superelectrophiles. Demonstrated by using in situ low-temperature NMR experiments and confirmed by X-ray diffraction analysis, these dications can be intramolecularly trapped by non-activated alkenes to generate unsaturated piperidinones, including enantioenriched ones, in a straightforward way.

Diastereocontrolled Formal Syntheses of (±)-Lepadiformines A, B, and C and the Divergent Synthesis of 2-epi-Lepadiformine C through Unexpected Double Consecutive Epimerizations

We describe here the diastereocontrolled formal racemic syntheses of tricyclic marine alkaloids, lepadiformines A, B, and C as well as their C2 epimers, featuring divergent and stereoselective syntheses of the N-acetyl-8a-cyanodecahydroquinoline frameworks and the base-mediated intramolecular cyclization to establish the spiral quaternary center of the tricyclic framework from sterically well-defined α-aminonitrile 2. The approach allows us to accomplish the tricyclic core structure efficiently from readily available starting materials through simple operations. An unexpected pair of consecutive epimerizations at two contiguous stereocenters is observed on the basis of single-crystal X-ray analyses of the intermediates and derivatives. The findings have been successfully applied to the total synthesis of 2-epi-lepadiformine C. The epimerization mechanism has been elucidated through a series of deuterium-labelling-controlled experiments.

An umpolung reaction of α-iminonitriles and its application to the synthesis of aminomalononitriles

An umpolungN-alkylation reaction of α-iminonitriles with Grignard reagents gaveN-alkylated α-aminonitriles in good yields.

Metal-free dehydrosulfurization of thioamides to nitriles under visible light

A visible light-mediated dehydrosulfurization of thioamides to nitriles is demonstrated, using an organic dye as a photocatalyst and air as an oxidant.

Synthesis of α-amino nitriles through one-pot selective Ru-photocatalyzed oxidative cyanation of amines

A new family of Ru(ii) photocatalysts exhibits excellent performance in the efficient and eco-friendly one-pot preparation of α-amino nitriles from primary and secondary amines.

Recent developments in dehydration of primary amides to nitriles

Various dehydration methods available for the direct conversion of amides to the corresponding nitriles have been reviewed.

Chemoselective Synthesis of α-Amino-α-cyanophosphonates by Reductive Gem-Cyanation-Phosphonylation of Secondary Amides

A novel approach to α-amino-α-cyanophosphonates has been developed. The method features a Tf₂O-mediated reductive geminal cyanation/phosphonylation of secondary amides. Mild reaction conditions, high bond-forming efficiency, inexpensive readily available starting materials, and good to excellent yields with wide functional group compatibility constitute the main advantages of this method. The protocol can be run on a gram scale.

Aroyl and acyl cyanides as orthogonal protecting groups or as building blocks for the synthesis of heterocycles

α-Cyanoketones represent a synthetically attractive scaffold possessing bifunctional reactivity which enabled synthesis of a diversity of products. This involves reaction of nucleophiles with electrophilic carbonyl carbon performing an efficient and regioselective way to acylation reaction, cycloaddition of activated cyano function with dipolarophiles, metal-catalyzed cross-dehydrogenative coupling carbocyanation across C-C multiple bonds as well as hydrocyanation. This review provides the recent developments in the chemistry of α-cyanoketones which will be beneficial for researchers and scientists in such field.

Oxidative cyanation of N-aryltetrahydroisoquinoline induced by visible light for the synthesis of α-aminonitrile using potassium thiocyanate as a “CN” agent

A novel method for the synthesis of α-aminonitrile, through visible-light-induced oxidative cyanation of N-aryltetrahydroisoquinoline with potassium thiocyanate, has been developed.

Thiocyanate radical mediated dehydration of aldoximes with visible light and air

This work describes the first example of dehydration of aldoximes by an in situ generated radical-based hydrogen abstraction reaction.

Copper-catalyzed amination of an α-C(sp3)–H bond in inactivated ethers to synthesize α-aminonitriles

A copper-catalyzed functionalization of inert cyclic ethers was developed to provide α-aminonitriles via a cascade oxidation/amination/ring-opening/cyanation reaction.

A metal-free direct C (sp3)–H cyanation reaction with cyanobenziodoxolones

Metal-free direct C(sp³)–H cyanation reaction: cyanobenziodoxolones as cyanating reagents and oxidants.

Copper-catalyzed synthesis of α-amino nitriles through methyl transfer from DMF to aromatic amines

A copper-catalyzed activation of C(sp³)–H bonds of DMF at room temperature was developed, which results in methyl transfer to aromatic amines for efficient synthesis of exceedingly valuable α-amino nitriles.

A rapid flow strategy for the oxidative cyanation of secondary and tertiary amines via C-H activation

An efficient continuous flow protocol has been developed for bond C-H activation which promotes the α-cyanation of secondary and tertiary amines using magnetic nano-ferrites.

The reductive decyanation reaction: an overview and recent developments

This review presents an overview of the reductive decyanation reaction with a special interest for recent developments. This transformation allows synthetic chemists to take advantages of the nitrile functional group before its removal. Mechanistic details and applications to organic synthesis are provided.

Highly enantioselective metallation-substitution alpha to a chiral nitrile

We report the deprotonation of a chiral nitrile and reaction of the resulting chiral organometallic species with a variety of electrophiles to give highly enantiomerically enriched 2-substituted nitrile products. The nitrile was treated with TMPMgCl and the resulting anion, an asymmetric alpha cyano Grignard species, was found to be configurationally stable at low temperature for a short time (half-life several minutes at -104 °C).

Deconjugative alkylation/Heck reaction as a simple platform for dihydronaphthalene synthesis

A simple platform for carbocycle synthesis by Knoevenagel adduct deconjugative alkylation/“pairing” reaction is described.

Intramolecular aminocyanation of alkenes promoted by hypervalent iodine

Hypervalent iodine-promoted aminocyanation of unactivated alkenes has been developed and the orientation of cyanation on the double bond can be controlled.