Gold-complexes catalyzed oxidative α-cyanation of tertiary amines

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.

Regioselective α-Cyanation of Unprotected Alicyclic Amines

Secondary alicyclic amines are converted to α-aminonitriles via addition of TMSCN to their corresponding imines, intermediates that are produced in situ via the oxidation of amine-derived lithium amides with simple ketone oxidants. Amines with an existing α-substituent undergo regioselective α'-cyanation even if the C-H bonds at that site are less activated. Amine α-arylation can be combined with α'-cyanation to generate difunctionalized products in a single operation.

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.

Iron(III)-catalyzed α-cyanation and carbonylation with 2-pyridylacetonitrile: divergent synthesis of α-amino nitriles and tetrahydroisoquinolinones

Iron-catalyzed oxidative synthesis of N-aryl-substituted tetrahydroisoquinolines (THIQs) toward tetrahydroisoquinoline-based derivatives is reported. A wide range of α-amino nitriles and tetrahydroisoquinolinones are synthesized in moderate to good yields. This approach involves a new organic nitrile source, a cheap iron catalyst under an oxygen atmosphere, and temperature-controlled divergent synthesis and features complete selectivity and operational simplicity.

KOtBu-Mediated Reductive Cyanation of Tertiary Amides for Synthesis of α-Aminonitriles

A simple, mild, catalyst-free, and efficacious KO^tBu-mediated reductive cyanation reaction of tertiary amides under hydrosilylation conditions has been described. A series of α-aminonitriles is obtained in moderate to high yield with good functional group tolerance. The reaction works well with a readily available amide substrate, a cheap and versatile base KO^tBu, and a commercially available hydrosilane (EtO)₃SiH and is convenient for workup and purification.

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.

Direct Synthesis of α-Amino Nitriles from Sulfonamides via Base-Mediated C-H Cyanation

Herein, we disclose a transition-metal-free reaction system that enables α-cyanation of sulfonamides through C-H bond cleavage for the preparation of α-amino nitriles, including difficult-to-access all-alkyl α-tertiary scaffolds. More than 50 substrate examples prove a wide functional group tolerance. Additionally, its synthetic practicality is highlighted by gram-scalability and the late-stage modification of natural compounds. Mechanistic experiments suggest that this process involves in situ formation of an imine intermediate via base-promoted elimination of HF.

Iron-Catalyzed α-C-H Cyanation of Simple and Complex Tertiary Amines

This manuscript details the development of a general and mild protocol for the α-C-H cyanation of tertiary amines and its application in late-stage functionalization. Suitable substrates include tertiary aliphatic, benzylic, and aniline-type substrates and complex substrates. Functional groups tolerated under the reaction conditions include various heterocycles and ketones, amides, olefins, and alkynes. This broad substrate scope is remarkable, as comparable reaction protocols for α-C-H cyanation frequently occur via free radical mechanisms and are thus fundamentally limited in their functional group tolerance. In contrast, the presented catalyst system tolerates functional groups that typically react with free radicals, suggesting an alternative reaction pathway. All components of the described catalyst system are readily available, allowing implementation of the presented methodology without the need for lengthy catalyst synthesis.

Gold(i)-catalysed high-yielding synthesis of indenes by direct Csp3-H bond activation

A catalytic, practical and high-yielding procedure for the synthesis of indenes by direct Csp3-H activation under gold(i) catalysis was developed. The scope of the protocol was determined by synthesizing some electron-neutral, electron-poor as well as electron-rich derivatives including the dibenzofurane and carbazole heterocycles. The mechanism of this reaction was elucidated by theoretical calculations using a ONIOM(M08-HX/mixed-basis:PM6) hybrid scheme. Thereby we found a pericyclic transformation involving a [1,5]-H shift generating a gold(i)-carbene that evolves to the indene derivative. In comparison with several reports, our protocol presents a direct activation of the Csp3-H bond.

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.

Electrochemical Aminoxyl-Mediated α-Cyanation of Secondary Piperidines for Pharmaceutical Building Block Diversification

Secondary piperidines are ideal pharmaceutical building blocks owing to the prevalence of piperidines in commercial drugs. Here, we report an electrochemical method for cyanation of the heterocycle adjacent to nitrogen without requiring protection or substitution of the N-H bond. The reaction utilizes ABNO (9-azabicyclononane N-oxyl) as a catalytic mediator. Electrochemical oxidation of ABNO generates the corresponding oxoammonium species, which promotes dehydrogenation of the 2° piperidine to the cyclic imine, followed by addition of cyanide. The low-potential, mediated electrolysis process is compatible with a wide range of heterocyclic and oxidatively sensitive substituents on the piperidine ring and enables synthesis of unnatural amino acids.

Selective Synthesis of Aryl Nitriles and 3-Imino-1-oxoisoindolines via Nickel-Promoted C(sp2)-H Cyanations

An efficient nickel-promoted selective monocyanation of benzamides with TMSCN via 8-aminoquinoline directed ortho C-H activation has been developed. Varieties of functionalized ortho-cyanated (hetero)aryl nitriles can be selectively synthesized in moderate to good yields. These cyanation products can be easily transformed into various 3-imino-1-oxoisoindolines in a one-pot procedure. The mild reaction conditions, use of cheap and commercially available reagents, wide functional group tolerance, and operational convenience make this protocol practical to the synthetic community.

A Computational Mechanistic Investigation into Reduction of Gold(III) Complexes by Amino Acid Glycine: A New Variant for Amine Oxidation

Density functional theory (DFT) was utilized to explore the reduction of gold(III) complexes by the amino acid glycine (Gly). Interestingly, when the nitrogen atom of Gly coordinates to the gold(III) center, its C^α -hydrogen atom becomes so acidic that it can be easily deprotonated by a mild base like water. The deprotonation converts the amino acid into a potent reductant by which gold(III) is reduced to gold(I) with a moderate activation energy. To our knowledge, this is the first contribution suggesting that primary amines are oxidized to imines via direct α-carbon deprotonation. This finding may provide new insights into the mechanistic interpretation of amine oxidations catalyzed/mediated by a center with high cathodic reduction potential. This work also provides a rationalization behind why gold(III) complexes with amine-based polydentate ligands are reluctant to undergo a redox process. Gold(III) reduction occurs most efficiently if the C^α proton leaves in the plane of the C^α , N and Au atoms. Chelation prevents this alignment, resulting in the gold(III) complex being unreactive toward reduction. It has been experimentally found that gold(III) is capable of oxidizing Gly to glyoxylic acid (GA) as the initial product. The latter, in the presence of another gold(III) complex, has been reported to undergo oxidative decarboxylation to afford CO₂ and HCOOH. This process is found to be mediated by formation of a geminal diol intermediate produced by reaction of water with the aldehyde functional group of the coordinated GA.

Ligand Effect on Bonding in Gold(III) Carbonyl Complexes

We quantitatively assess the Dewar-Chatt-Duncanson (DCD) components of the Au(III)-CO bond and the charge density polarization at the CO, in a series of neutral, cationic, and dicationic bis- and monocyclometalated gold(III) complexes via charge-displacement (CD) analysis. A striking feature concerns the very small net electron charge flux from CO to the metal fragment which is unexpectedly stable toward both the charge of the complex and the oxidation state of gold (I, III). All systems exhibit a similar trend for the σ charge rearrangement in the region of the carbonyl bond, where, by contrast, the π back-donation trend variation is large, which is strictly correlated to the change in CO bond distance and the shift in CO stretching frequencies, in close analogy with the gold(I) carbonyl complexes. In the whole series of gold(III) compounds, a large Au(III) ← CO σ donation is measured (from 0.19 to 0.31 electrons), as well as a significant Au(III) → CO π back-donation (from -0.09 to -0.22 electrons), which however is not generally able to completely balance the polarization of the CO π electrons in the direction from oxygen to carbon (C ← O) induced by the presence of the metal fragment [LAu(III)]^0/+1/+2. Surprisingly, all the gold(III) complexes in the series are characterized by a very small anisotropy in the Au(III) → CO in-plane and out-of-plane π back-donation components, in sharp contrast with the marked anisotropy found before for the experimentally characterized [(C^N^C)Au(III)CO]⁺ complex. A first attempt to figure out a rationale on the bonding/reactivity relationship for Au(III)-CO is made by performing a comparative study with an isostructural [(N^N^C)Pt(II)CO]⁺ complex in a model water-gas shift (WGS) reaction.

New trends and applications in cyanation isotope chemistry

In this review, newly developed cyanation methods are evaluated in regards to their usefulness in synthetic isotope chemistry. In combination with already established protocols in ^13/14 C- or ¹¹ C-isotope chemistry, this manuscript should help isotope scientists to choose the best possible method for their scientific cyanation problem, but with the main focus on ¹⁴ C-applications. Perhaps, most promising of the described novel cyanation reaction is the decarboxylation-cyanation-hydrolysis approach which makes a 1-step late-stage functionalization procedure possible.

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 Highly Efficient Heterogeneous Ruthenium-Catalysed Oxidative α-Cyanation of Tertiary Amines Leading to α-Aminonitriles

Oxidative α-cyanation of tertiary amines was achieved by using an MCM-41-immobilised N-alkylethylenediamine ruthenium(III) complex (MCM-41-2N-RuCl3) as catalyst in MeOH at 60 °C in the presence of H2O2 as oxidant and NaCN in acetic acid as a cyanide source to afford the corresponding α-aminonitriles in good yields. The new heterogeneous ruthenium catalyst can easily be prepared by a simple two-step procedure from commercially readily available and inexpensive reagents. It can be recovered by filtration of the reaction solution and reused at least 7 times without significant loss of activity.

Room temperature decarboxylative cyanation of carboxylic acids using photoredox catalysis and cyanobenziodoxolones: a divergent mechanism compared to alkynylation

The one-step conversion of aliphatic carboxylic acids to the corresponding nitriles has been accomplished via the merger of visible light mediated photoredox and cyanobenziodoxolones (CBX) reagents. The reaction proceeded in high yields with natural and non-natural α-amino and α-oxy acids, affording a broad scope of nitriles with excellent tolerance of the substituents in the α position. The direct cyanation of dipeptides and drug precursors was also achieved. The mechanism of the decarboxylative cyanation was investigated both computationally and experimentally and compared with the previously developed alkynylation reaction. Alkynylation was found to favor direct radical addition, whereas further oxidation by CBX to a carbocation and cyanide addition appeared more favorable for cyanation. A concerted mechanism is proposed for the reaction of radicals with EBX reagents, in contrast to the usually assumed addition elimination process.

Iridium-Catalyzed Reductive Strecker Reaction for Late-Stage Amide and Lactam Cyanation

A new iridium-catalyzed reductive Strecker reaction for the direct and efficient formation of α-amino nitrile products from a broad range of (hetero)aromatic and aliphatic tertiary amides, and N-alkyl lactams is reported. The protocol exploits the mild and highly chemoselective reduction of the amide and lactam functionalities using IrCl(CO)[P(C₆ H₅ )₃ ]₂ (Vaska's complex) in the presence of tetramethyldisiloxane, as a reductant, to directly generate hemiaminal species able to undergo substitution by cyanide upon treatment with TMSCN (TMS=trimethylsilyl). The protocol is simple to perform, broad in scope, efficient (up to 99 % yield), and has been successfully applied to the late-stage functionalization of amide- and lactam-containing drugs, and naturally occurring alkaloids, as well as for the selective cyanation of the carbonyl carbon atom linked to the N atom of proline residues within di- and tripeptides.

Iron-catalysed sequential reaction towards α-aminonitriles from secondary amines, primary alcohols and trimethylsilyl cyanide

We have developed a one-pot iron-catalysed sequential reaction of secondary amines with primary alcohols, trimethylsilyl cyanide and TBHP under mild reaction conditions to give the corresponding α-aminonitriles.

Iron-catalyzed direct α-arylation of α-amino carbonyl compounds with indoles

A mild and general α-arylation of α-amino carbonyls with indoles catalyzed by Fe(ClO4)3 has been developed. C-H activation is smoothly fulfilled by using TBHP as the oxidant with good yields. Two hydrogen dissociations make this transformation more environmentally benign because of high atom efficiency.