Pd/Mn Bimetallic Relay Catalysis for Aerobic Aldoxime Dehydration to Nitriles

Stereoselective synthesis of vinyl nitriles through a Ramberg-Bäcklund approach

The applicability of vinyl nitriles in the preparation of pharmaceuticals, polymers, and other valuable materials benefits from robust preparative methodologies. In this work, we present a novel approach for the synthesis of vinyl nitriles based on the Ramberg-Bäcklund olefination reaction (RBR). While there are few examples for accessing functionalized olefins using the RBR, we believe that this methodology embodies useful means for installing privileged vinylnitrile building blocks, such as the acrylonitrile fragment of the US FDA-approved antiviral rilpivirine.

Bioinspired Iron-Catalyzed Dehydration of Aldoximes to Nitriles: A General N-O Redox-Cleavage Method

Inspired by OxdA that operates biocatalytic aldoxime dehydration, we have developed an efficient iron catalyst, Cp*Fe(1,2-Cy₂PC₆H₄O) (1), which rapidly converts various aliphatic and aromatic aldoximes to nitriles with release of H₂O at room temperature. The catalysis involves redox activation of the N-O bond by a 1e^- transfer from the iron catalyst to the oxime. Such redox-mediated N-O cleavage was demonstrated by the isolation of a ferrous iminato intermediate from the reaction of the ketoxime substrate. This iron-catalyzed acceptorless dehydration approach represents a general method for the preparation of nitriles, and it also delivers salicylonitriles by catalyzing the Kemp elimination reaction.

Convenient Synthesis of Pyrazolo[4',3':5,6]pyrano[4,3-c][1,2]oxazoles via Intramolecular Nitrile Oxide Cycloaddition

A simple and efficient synthetic route to the novel 3a,4-dihydro-3H,7H- and 4H,7H-pyrazolo[4′,3′:5,6]pyrano[4,3-c][1,2]oxazole ring systems from 3-(prop-2-en-1-yloxy)- or 3-(prop-2-yn-1-yloxy)-1H-pyrazole-4-carbaldehyde oximes has been developed by employing the intramolecular nitrile oxide cycloaddition (INOC) reaction as the key step. The configuration of intermediate aldoximes was unambiguously determined using NOESY experimental data and comparison of the magnitudes of ¹J_CH coupling constants of the iminyl moiety, which were greater by approximately 13 Hz for the predominant syn isomer. The structures of the obtained heterocyclic products were confirmed by detailed ¹H, ¹³C and ¹⁵N NMR spectroscopic experiments and HRMS measurements.

Cyanide-free synthesis of aromatic nitriles from aldoximes: Discovery and application of a novel heme-containing aldoxime dehydratase

Aromatic nitriles are important structural motifs that frequently existed in pharmaceutical drugs. Due to the convenient synthesis of aldoximes from aldehydes, the dehydration of aldoximes to corresponding nitriles by aldoxime dehydratases (Oxds) is considered as a safe and robust enzymatic production route. Although the Oxd genes are widely distributed in microbial kingdom, so far less than ten Oxds were expressed and further characterized. In this study, we found 26 predicted putative Oxd genes from the GenBank database using a genome mining strategy. The Oxd gene from Pseudomonas putida F1 was cloned and functionally expressed in Escherichia coli BL21 (DE3). The amino acid sequence of OxdF1 shows high identities of 33∼85 % to other characterized Oxds, and contained a ferrous heme as the catalytic site. The optimum reaction pH and temperature of recombinant OxdF1 were 7.0 and 35 °C, respectively. OxdF1 was stable in pH 7.0 potassium phosphate buffer at 30 °C, and its half-life was approximately 3.8 h. OxdF1 can efficiently dehydrate aromatic and heterocyclic aldoximes to nitriles, such as 2-bromobenzaldoxime, 2-chloro-6-fluorobenzaldoxime, thiophene-2-carboxaldoxime, and pyridine-3-aldoxime. Therefore, the recombinant OxdF1 shows a potential application in the cyanide-free synthesis of aromatic nitriles.

Earth-Abundant Bimetallic Nanoparticle Catalysts for Aerobic Ammoxidation of Alcohols to Nitriles

Heterogeneous nitrogen-doped carbon-incarcerated iron/copper bimetallic nanoparticle (NP) catalysts prepared from nitrogen-containing polymers were developed. These catalysts showed activity higher than that of the corresponding monometallic NPs for aerobic ammoxidation of alcohols to nitriles. The important procedure for high activity in the catalyst preparation was found to be a simultaneous reduction of two metal salts.

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.

A convenient reagent for the conversion of aldoximes into nitriles and isonitriles

Described herein is the convenient transformation of aldoximes into nitriles or isonitriles by slightly modifying reaction conditions.

Synthetic Diversity from a Versatile and Radical Nitrating Reagent

We leverage the slow liberation of nitrogen dioxide from a newly discovered, inexpensive succinimide-derived reagent to allow for the C-H diversification of alkenes and alkynes. Beyond furnishing a library of aryl β-nitroalkenes, this reagent provides unparalleled access to β-nitrohydrins and β-nitroethers. Detailed mechanistic studies strongly suggest that a mesolytic N-N bond fragmentation liberates a nitryl radical. Using in situ photo-sensitized, electron paramagnetic resonance spectroscopy, we observed direct evidence of a nitryl radical in solution by nitrone spin-trapping. To further exhibit versatility of N-nitrosuccinimide under photoredox conditions, the late-stage diversification of an extensive number of C-H partners to prepare isoxazolines and isoxazoles is presented. This approach allows for the formation of an in situ nitrile oxide from a ketone partner, the presence of which is detected by the formation of the corresponding furoxan when conducted in the absence of a dipolarophile. This 1,3-dipolar cycloaddition with nitrile oxides and alkenes or alkynes proceeds in a single-operational step using a mild, regioselective, and general protocol with broad chemoselectivity.

Direct Transformation of Nitroalkanes to Nitriles Enabled by Visible-Light Photoredox Catalysis and a Domino Reaction Process

A mild and convenient process for direct transformation of nitroalkanes to the corresponding nitriles was developed using a visible-light photoredox catalysis strategy with household decorative blue LEDs and the additives of Et₃N and DIPIBA (or DIPEA). Application of the process in secondary nitroalkanes bearing a β-alcohol resulted in a domino process of the retro-Henry reaction and the subsequent acetalization, aldol, cyanohydrin, and ring-contraction reactions with stereoselectivities. The photocatalytic reaction was demonstrated by a continuous flow method.

Vilsmeier–Haack reagent mediated synthetic transformations with an immobilized iridium complex photoredox catalyst

The synthesis of amides, nitriles, and anhydrides via reactions under the action of the visible-light-driven in situ generated Vilsmeier–Haack reagent from CBr₄ in DMF.

Utilization of nitriles as the nitrogen source: practical and economical construction of 4-aminopyrimidine and β-enaminonitrile skeletons

A highly practical and economical method for the synthesis of 4-aminopyrimidines and β-enaminonitriles from mixed organonitriles is reported.

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.

Cu(OAc)2/Malononitrile/Water: A Simple Reaction System for Synthesis of Aromatic Nitriles from Aldoximes

A simple method for the preparation of nitriles in moderate to good yield has been achieved by treatment of aromatic and heterocyclic aldoximes with malononitrile in water at reflux in the presence of copper acetate as catalyst. Arylaldoximes with an electron-donating group showed the highest reactivity, their conversion being achievable at room temperature.

Metal-catalyzed 1,3-dipolar cycloaddition reactions of nitrile oxides

In this review recent advances in the metal-catalyzed 1,3-dipolar cycloaddition reactions of nitrile oxides are highlighted, covering references from the period 2000 until August 2018.