Pd-Catalyzed Cyanation of (Hetero)Aryl Halides by Using Biphosphine Ligands

Catalytic Cyanation of C-N Bonds with CO2/NH3

Cyanation of benzylic C-N bonds is useful in the preparation of important α-aryl nitriles. The first general catalytic cyanation of α-(hetero)aryl amines, analogous to the Sandmeyer reaction of anilines, was developed using reductive cyanation with CO₂/NH₃. A broad array of α-aryl nitriles was obtained in high yields and regioselectivity by C-N cleavage of intermediates as ammonium salts. Good tolerance of functional groups such as ethers, CF₃, F, Cl, esters, indoles, and benzothiophenes was achieved. Using ¹³CO₂, a ¹³C-labeled tryptamine homologue (five steps, 31% yield) and Cysmethynil (six steps, 37% yield) were synthesized. Both electronic and steric effects of ligands influence the reactivity of alkyl nickel species with electrophilic silyl isocyanates and thus determine the reactivity and selectivity of the cyanation reaction. This work contributes to the understanding of the controllable activation of CO₂/NH₃ and provides the promising potential of the amine cyanation reaction in the synthesis of bio-relevant molecules.

Nickel-Catalyzed Chemo- and Regioselective Arylcyanation of β,γ-Unsaturated Amides

A nickel-catalyzed intermolecular arylcyanation of 8-aminoquinolinyl β,γ-unsaturated amides is reported. The three-component reaction directly afforded diverse β-cyano γ-aryl amides with exclusive chemo- and regioselectivity. The synthetic practicality of this approach is further demonstrated through multigram scale reaction, expanded transformations of the nitrile product, late-stage modification of complex molecules, and direct drug synthesis.

Tetrasubstituted Peropyrenes Formed by Reductive Aromatization: Synthesis, Functionalization and Characterization

The chromophore class of 1,3,8,10-tetrasubstituted peropyrenes was effectively synthesized from peropyrenequinone via a Zn-mediated reductive aromatization approach. In one step, a symmetric functionalization of the peropyrene backbone introducing silylethers (2,3), pivaloyl (4), triflyl (5) and also phosphinite (6) groups was established. Furthermore, the potential of using 4 and 5 in transition metal catalysed cross couplings was explored leading to 1,3,8,10-tetraaryl (8-11) and tetraalkynyl (7) peropyrenes. The influence of various substituents on the optoelectronic properties of these π-system extended peropyrenes was investigated in solid state by means of X-ray crystallography, in solution by means of UV-Vis and fluorescence spectroscopy and by their redox properties studied via cyclic voltammetry. By comparison with DFT and TD-DFT calculations, it could be elucidated that introduction of a broad variety of substituents in such versatile one or two step procedures leads to peropyrenes with easily tunable HOMO and LUMO energies ranging in a gap window of 0.8 eV. The frontier molecular orbital energies identify the target molecules as promising candidates for hole transporting semiconductors.

Conversions of aryl carboxylic acids into aryl nitriles using multiple types of Cu-mediated decarboxylative cyanation under aerobic conditions

Here, we used malononitrile or AMBN as a cyanating agent to develop efficient and practical protocols for Cu-mediated decarboxylative cyanations, under aerobic conditions, of aryl carboxylic acids bearing nitro and methoxyl substituents at the ortho position as well as of heteroaromatic carboxylic acids. These protocols involved economical methods to synthesize value-added aryl nitriles from simple and inexpensive raw materials. Further diversification of the 2-nitrobenzonitrile product was performed to highlight the practicality of the protocols.

Recent advances and prospects in the palladium-catalyzed cyanation of aryl halides

Aryl nitriles are compounds with wide significance. They have made their own space in various sectors including pharmaceuticals, industries, natural product chemistry, and so on. Furthermore, they are also key intermediates in various transformations in organic chemistry. Transition metal-catalyzed cyanation reactions have proved to be a better replacement for the existing traditional synthetic strategies for aryl nitriles. Palladium is one of the most studied transition metals other than copper and nickel owing to its wide functional group compatibility and catalytic efficacy. There have been drastic developments in the field of palladium-catalyzed cyanation since its discovery in the 1973. This review summarizes the recent developments in the palladium-catalyzed cyanation of aryl halides and covers literature from 2012-2020.

Reductive cyanation of organic chlorides using CO2 and NH3 via Triphos-Ni(I) species

Cyano-containing compounds constitute important pharmaceuticals, agrochemicals and organic materials. Traditional cyanation methods often rely on the use of toxic metal cyanides which have serious disposal, storage and transportation issues. Therefore, there is an increasing need to develop general and efficient catalytic methods for cyanide-free production of nitriles. Here we report the reductive cyanation of organic chlorides using CO₂/NH₃ as the electrophilic CN source. The use of tridentate phosphine ligand Triphos allows for the nickel-catalyzed cyanation of a broad array of aryl and aliphatic chlorides to produce the desired nitrile products in good yields, and with excellent functional group tolerance. Cheap and bench-stable urea was also shown as suitable CN source, suggesting promising application potential. Mechanistic studies imply that Triphos-Ni(I) species are responsible for the reductive C-C coupling approach involving isocyanate intermediates. This method expands the application potential of reductive cyanation in the synthesis of functionalized nitrile compounds under cyanide-free conditions, which is valuable for safe synthesis of (isotope-labeled) drugs.

Nitriles are key intermediates in production of pharmaceuticals, agrochemicals and organic materials. Here, the authors report a nickel-catalyzed reductive cyanation of organic chlorides with CO₂/NH₃ and urea as cyanation reagents to afford a broad range of organic nitriles.

Ruthenium-Catalyzed Site-Selective Trifluoromethylations and (Per)Fluoroalkylations of Anilines and Indoles

Introducing (per)fluoroalkyl groups into arenes continues to be an interesting, but challenging area in organofluorine chemistry. We herein report an ortho-selective C-H perfluoroalkylation including trifluoromethylations of anilines and indoles without the need of protecting groups using Rf I and Rf Br as commercially available reagents. The availability and price of the starting materials and the inherent selectivity make this novel methodology attractive for the synthesis of diverse (per)fluoroalkylated building blocks, for example, for bioactive compounds and materials.

Pd-catalyzed synthesis of α,β-unsaturated ketones by carbonylation of vinyl triflates and nonaflates

A general and highly chemoselective Pd-catalyzed protocol for the synthesis of α,β-unsaturated ketones by carbonylation of vinyl triflates and nonaflates is presented. Applying the specific monophosphine ligand cataCXium® A, the synthesis of various vinyl ketones as well as carbonylated natural product derivatives proceeds in good yields.

A general and practical Ni-catalyzed C-H perfluoroalkylation of (hetero)arenes

A direct perfluoroalkylation of (hetero)arenes using the air- and moisture-stable complex (dppf)Ni(o-tol)Cl was developed (23 examples). The novel procedure allows for the synthesis of various fluorinated products and tolerates sensitive functional groups including aldehydes, free amino groups and several heterocycles.