Assembly of α-(Hetero)aryl Nitriles via Copper-Catalyzed Coupling Reactions with (Hetero)aryl Chlorides and Bromides

CuI/Oxalamide-Catalyzed Coupling Reaction of (Hetero)aryl Halides with Sodium Nitrite

The N,N'-bis(thiophen-2-ylmethyl)oxalamide (BTMO) was found to be an effective ligand for Cu-catalyzed ipso-nitration of (hetero)aryl halides (Br, I), making the coupling reaction with sodium nitrite proceed smoothly at 100-120 °C with 1-5 mol % CuI and BTMO. Electron-rich substrates were the best coupling partners to give the desired coupling products in good to excellent yields at 100 °C. Electron-neutral substrates required heating at 120 °C to get complete conversion, while rather low conversions were observed in the case of electron-poor (hetero)aryl bromides.

Palladium-catalyzed dehydrogenation of α-cyclohexene-substituted nitriles to α-aryl nitriles

The development of a practical, inexpensive, and cyanide-free method for synthesizing α-aryl nitriles remains a challenging goal in synthetic chemistry. Here, we report an approach for synthesizing α-aryl nitriles toward achieving this goal, by which α-cyclohexenyl acetonitriles and α-cyclohexenyl alkenyl nitriles are dehydrogenated to α-aryl nitriles.

Copper-Catalyzed α-Arylation of Nitroalkanes with (Hetero)aryl Bromides/Iodides

α-Aryl substituted nitroalkanes are valuable synthetic building blocks that can be easily converted into α-aryl substituted aldehydes, ketones, carboxylic acids, as well as amines. Herein, an efficient Cu/oxalamide-catalyzed coupling between nitroalkanes and (hetero)aryl halides (Br, I) was developed to direct access highly diverse α-aryl substituted nitroalkanes. Compared with the current state of art, this protocol is more environmentally friendly and practical for synthetic chemists. This approach is characterized by a broad substrate scope on both nitroalkane part (primary nitroalkanes and nitromethane) and sp2 halide part ((hetero)aryl bromides/iodides and alkenyl bromides/iodides). The excellent functional group tolerance was observed, which would enable real world synthetic applications. More importantly, TON of current transformation reached to 3640, when some aryl iodides were used as coupling partners. This represents currently the highest catalyst turnover for transition-metal catalyzed α-arylation of nitroalkanes. Furthermore, the successful application in late-stage modification of complex molecules and synthesis of a known retinoid X receptor (RXR) antagonist exemplified its synthetic potential.

TBHP Mediated C-N Bond Cleavage of Tertiary Amines toward the Synthesis of Oxalamides and α,β-Epoxy Amides

An efficient and convenient method for the synthesis of oxalamides by the reaction of β-ketoamides with tertiary amines and TBHP was developed. A variety of β-ketoamides and tertiary amines substrates were well-tolerated in this transformation. Based on the control experiments, a plausible mechanism for this reaction was proposed that involved the tandem oxidation/amination process. In addition, α,β-epoxy amides could be obtained by adjusting the reaction conditions.

Copper-Catalyzed Asymmetric Arylation of α-Substituted Cyanoacetates Enabled by Chiral Amide Ligands

The (S)-nobin-embodied picolinamide and L-hydroxyproline-derived amide are effective ligands for Cu-catalyzed enantioselective coupling reaction of (hetero)aryl iodides with α-alkyl substituted cyanoacetates. This arylation reaction gave α-(heteroaryl)-α-alkyl cyanoacetates in good to excellent enantioselectivities (up to 95 % ee). A variety of functionalized (hetero)aryl and alkyl groups could be introduced to the quaternary center and therefore provided a valuable tool for preparing enantioenriched compounds with an all-carbon quaternary center tethered with convertible functional groups. The size of both α-alkyl and ester groups was proven as the key factor for asymmetric induction.

Cross-coupling by a noncanonical mechanism involving the addition of aryl halide to Cu(II)

Copper complexes are widely used in the synthesis of fine chemicals and materials to catalyze couplings of heteroatom nucleophiles with aryl halides. We show that cross-couplings catalyzed by some of the most active catalysts occur by a mechanism not previously considered. Copper(II) [Cu(II)] complexes of oxalamide ligands catalyze Ullmann coupling to form the C-O bond in aryl ethers by concerted oxidative addition of an aryl halide to Cu(II) to form a high-valent species that is stabilized by radical character on the oxalamide ligand. This mechanism diverges from those involving Cu(I) and Cu(III) intermediates that have been posited for other Ullmann-type couplings. The stability of the Cu(II) state leads to high turnover numbers, >1000 for the coupling of phenoxide with aryl chloride electrophiles, as well as an ability to run the reactions in air.

Cu/Oxalic Diamide-Catalyzed Coupling of Terminal Alkynes with Aryl Halides

N¹-(2,6-Dimethylphenyl)-N²-(pyridin-2-ylmethyl)oxalamide (DMPPO) was revealed to be a more effective ligand for copper-catalyzed coupling reaction of (hetero)aryl halides with 1-alkynes than previously reported ones. Only 3 mol % CuCl and DMPPO are required to make the coupling complete at 100 °C (for bromides) and 80 °C (for iodides). Both (hetero)aryl and alkyl substituted 1-alkynes worked well under these conditions, leading to the formation of internal alkynes in great diversity.

Boron Lewis Acid Catalysis Enables the Direct Cyanation of Benzyl Alcohols by Means of Isonitrile as Cyanide Source

The development of an efficient and straightforward method for cyanation of alcohols is of great value. However, the cyanation of alcohols always requires toxic cyanide sources. Herein, an unprecedented synthetic application of an isonitrile as a safer cyanide source in B(C₆F₅)₃-catalyzed direct cyanation of alcohols is reported. With this approach, a wide range of valuable α-aryl nitriles was synthesized in good to excellent yields (up to 98%). The reaction can be scaled up and the practicability of this approach is further manifested in the synthesis of an anti-inflammatory drug, naproxen. Moreover, experimental studies were performed to illustrate the reaction mechanism.

Computer-Driven Development of Ylide Functionalized Phosphines for Palladium-Catalyzed Hiyama Couplings

Palladium-catalyzed couplings of silicon enolates with aryl electrophiles are of great synthetic utility, but often limited to expensive bromide substrates. A comparative experimental study confirmed that none of the established ligand systems allows to couple inexpensive aryl chlorides with α-trimethylsilyl alkylnitriles. In contrast, ylide functionalized phosphines (YPhos) led to encouraging results. A statistical model was developed that correlates the reaction yields with ligand features. It was employed to predict catalyst structures with superior performance. With this cheminformatics approach, YPhos ligands were tailored specifically to the demands of Hiyama couplings. The newly synthesized ligands displayed record-setting activities, enabling the elusive coupling of aryl chlorides with α-trimethylsilyl alkyl nitriles. The preparative utility of the catalyst system was demonstrated by the synthesis of pharmaceutically meaningful α-aryl alkylnitriles, α-arylcarbonyls and biaryls.

Ligand-Promoted Rosenmund–von Braun Reaction

Two picolinamide ligands were found to have significant accelerating effect to classical Rosenmund–von Braun reaction, making the coupling of (hetero)aryl bromides with CuCN occur at 100–120 °C with good to excellent yields in most cases. A large number of functional groups and heterocycles were tolerated under these conditions, thereby providing a convenient and reliable approach for diverse synthesis of aryl nitriles.

High Nitrile Yields of Aerobic Ammoxidation of Alcohols Achieved by Generating •O2- and Br• Radicals over Iron-Modified TiO2 Photocatalysts

Catalytic ammoxidation of alcohols into nitriles is an essential reaction in organic synthesis. While highly desirable, conducting the synthesis at room temperature is challenging, using NH₃ as the nitrogen source, O₂ as the oxidant, and a catalyst without noble metals. Herein, we report robust photocatalysts consisting of Fe(III)-modified titanium dioxide (Fe/TiO₂) for ammoxidation reactions at room temperature utilizing oxygen at atmospheric pressure, NH₃ as the nitrogen source, and NH₄Br as an additive. To the best of our knowledge, this is the first example of catalytic ammoxidation of alcohols over a photocatalyst using such cheap and benign materials. Various (hetero) aromatic nitriles were synthesized at high yields, and aliphatic alcohols could also be transformed into corresponding nitriles at considerable yields. The modification of TiO₂ with Fe(III) facilitates the formation of active ^•O₂^- radicals and increases the adsorption of NH₃ and amino intermediates on the catalyst, accelerating the ammoxidation to yield nitriles. The additive NH₄Br impressively improves the catalytic efficiency via the formation of bromine radicals (Br^•) from Br^-, which works synergistically with ^•O₂^- to capture H^• from C_α-H, which is present in benzyl alcohol and the intermediate aldimine (RCH═NH), to generate the active carbon-centered radicals. Further, the generation of Br^• from the Br^- additive consumes the photogenerated holes and OH^• radicals to prevent over-oxidation, significantly improving the selectivity toward nitriles. This amalgamation of function and synergy of the Fe(III)-doped TiO₂ and NH₄Br reveals new opportunities for developing semiconductor-based photocatalytic systems for fine chemical synthesis.

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.

Palladium-Catalyzed Direct Decarbonylative Cyanation of Aryl Carboxylic Acids

The direct transformation of aryl carboxylic acids to aryl nitrile compounds is an interesting topic because carboxylic acids are not only abundant in nature but are also inexpensive and stable. Here, the synthesis of a series of aryl nitriles by palladium-catalyzed decarbonylative cyanation of carboxylic acids without base has been achieved. The successful decarbonylative cyanation of drug molecules and Gram-scale reaction to verify the practicality and operability of this method are analyzed.

Direct Transformation of Nitrogen-Containing Methylheteroarenes to Heteroaryl Nitrile by Sodium Nitrite

The cyanation reaction of methylheteroarenes with acetyl chloride and sodium nitrite via the radical process in high yields is reported. According to the control experiments, the reaction mechanism underwent radical progress. It is very useful in the pharmacy industry due to its metal-free and easy treatment conditions.

Copper-Catalyzed Reactions of Aryl Halides with N-nucleophiles and Their Possible Application for Degradation of Halogenated Aromatic Contaminants

This review summarizes recent applications of copper or copper-based compounds as a nonprecious metal catalyst in N-nucleophiles-based dehalogenation (DH) reactions of halogenated aromatic compounds (Ar-Xs). Cu-catalyzed DH enables the production of corresponding nonhalogenated aromatic products (Ar-Nu), which are much more biodegradable and can be mineralized during aerobic wastewater treatment or which are principally further applicable. Based on available knowledge, the developed Cu-based DH methods enable the utilization of amines for effective cleavage of aryl-halogen bonds in organic solvents or even in an aqueous solution.

Oxalamide/Amide Ligands: Enhanced and Copper-Catalyzed C-N Cross-Coupling for Triarylamine Synthesis

Triarylamines are privileged core structures that are found in versatile optoelectronic materials. New methods are constantly being sought for their preparation. Herein, a new protocol for triarylamine synthesis is presented where a wide range of diarylamines couple smoothly with aryl bromides mediated by a copper oxalamide (or amide) catalytic system. Notably, a new non-C₂-symmetric 1-isoquinolinamide-based N,N-/N,O-bidentate ligand was introduced that could tolerate bulky diarylamines. Plenty of known optoelectronic functional molecules could be synthesized in good to excellent yields. The practicality of this C-N cross-coupling was illustrated by the gram-scale synthesis of a patented thermally activated delayed fluorescence emitter for organic light-emitting diodes.

Cyanomethylation of the Benzene Rings and Pyridine Rings via Direct Oxidative Cross-Dehydrogenative Coupling with Acetonitrile

A novel and efficient approach for the amine-directed dehydrogenative C(sp²)-C(sp³) coupling of arylamines with acetonitrile was reported by using FeCl₂ as the catalyst. Substituted anilines, aminopyridines, naphthylamines, and some nitrogen-containing heterocyclic arylamines react with inactive acetonitrile to form the corresponding arylacetonitriles in moderate to good yields. This protocol features nontoxic iron catalysis, efficient atom economy, nonprefunctionalized starting materials, good regioselectivity, and excellent compatibility of functional groups and aromatic rings, providing a novel, straightforward, and green approach toward arylacetonitriles.

Rapid and Simple Access to α-(Hetero)arylacetonitriles from Gem-Difluoroalkenes

A scalable cyanation of gem-difluoroalkenes to (hetero)arylacetonitrile derivatives was developed. This strategy features mild reaction conditions, excellent yields, wide substrate scope, and broad functional group tolerance. Significantly, in this reaction, aqueous ammonia offers a "N" source for the "CN" reagent and entirely avoids the use of toxic cyanating reagents or metal catalysis. Hence, we provide a green and alternative method for the synthesis of arylacetonitriles.

Copper-Catalyzed Ullmann-Type Coupling and Decarboxylation Cascade of Arylhalides with Malonates to Access α-Aryl Esters

We have developed a high-efficiency and practical Cu-catalyzed cross-coupling to directly construct versatile α-aryl-esters by utilizing readily available aryl bromides (or chlorides) and malonates. These gram-scale approaches occur with turnovers of up to 1560 and are smoothly conducted by the usage of a low catalyst loading, a new available ligand, and a green solvent. A variety of functional groups are tolerated, and the application occurs with α-aryl-esters to access nonsteroidal anti-inflammatory drugs (NSAIDs) on the gram scale.

Copper(i)-catalyzed asymmetric intramolecular C-arylation with ureas as the additives: highly enantioselective formation of spirooxindoles

A cooperative catalytic strategy is developed for a copper-catalyzed asymmetric intramolecular C-arylation reaction with ureas as the co-catalysts. By forming hydrogen bonds with 1,3-dicarbonyl structures, ureas can activate the substrates, stabilize the carbanion intermediates and the products, and fix the syn-configurations of 1,3-dicarbonyl structures. They help enhance the reactivity, prevent side reactions and improve the enantioselectivities.

Copper(i)–catalyzed intramolecular asymmetric C-arylation of acyclic β-ester amides: enantioselective formation of chiral oxindoles

A highly efficient intramolecular asymmetric C-arylation of acyclic β-ester amides is demonstrated.