Hydration of Nitriles to Primary Amides Enabled by the Ghaffar‐Parkins Catalyst

The synthesis and catalytic behavior of the osmium(II) complexes [OsCl2 (η6 -p-cymene)(PR2 OH)] [R=Me (2 a), Ph (2 b), OMe (2 c), OPh (2 d)] in nitrile hydration reactions is presented. Among them, the best catalytic results were obtained with the phosphinous acid derivative [OsCl2 (η6 -p-cymene)(PMe2 OH)] (2 a), which selectively provided the desired primary amides in excellent yields and short times at 80 °C, employing directly water as solvent, and without the assistance of any basic additive (TOF values up to 200 h-1 ). The process was successful with aromatic, heteroaromatic, aliphatic, and α,β-unsaturated organonitriles, and showed a high functional group tolerance. Indeed, complex 2 a represents the most active and versatile osmium-based catalyst for the hydration of nitriles reported so far in the literature. In addition, it exhibits a catalytic performance similar to that of its ruthenium analogue [RuCl2 (η6 -p-cymene)(PMe2 OH)] (4). However, when compared to 4, the osmium complex 2 a turned out to be faster in the hydration of less-reactive aliphatic nitriles, whereas the opposite trend was generally observed with aromatic substrates. DFT calculations suggest that these differences in reactivity are mainly related to the ring strain associated with the key intermediate in the catalytic cycle, that is, a five-membered metallacyclic species generated by intramolecular addition of the hydroxyl group of the phosphinous acid ligand to the metal-coordinated nitrile.

Primary aromatic amides are valuable compounds, which are generally prepared via Beckmann rearrangement of oximes and the hydration of nitriles in organic solvents. We investigated the environmentally friendly catalytic aminocarbonylation in water. Thus, a novel heterogeneous transition-metal catalyst, a polymer-supported terpyridine–palladium(II) complex, was prepared and found to promote azidocarbonylation of aryl iodides with NaN3 and to reduce the generated benzoyl azides in water under CO gas to yield primary aryl amides with high to excellent yield in a one-pot reaction. The catalyst was recovered and reused several times with no loss of catalytic activity.

Activation of nitriles by silver(I) N-heterocyclic carbenes: An efficient on-water synthesis of primary amides

In this paper, we reported an efficient protocol for hydration of aryl(hetero) and alkyl nitriles toward primary amides with 0.1 equiv. NaOH in NH3·H2O-DMSO under mild conditions. Various substituted nitriles are smoothly converted to the corresponding amides with good to excellent isolated yields. Gram-scale reactions were also performed to produce the desired products in high yields. In addition, the excessive hydrolysis of the nitrile to form the corresponding carboxylic acid was also achieved with increasing the amount of NaOH and prolonging the reaction time.

This manuscript summarizes our recent research results on heterogeneously catalyzed aerobic oxidation reactions using supported metal hydroxide catalysts. Metal hydroxide species possess both Lewis acid and Bronsted base sites on the same metal sites, and various kinds of substrates including alcohols, primary amines, nitriles, and terminal alkynes can be activated by the concerted action of the Lewis acid and Bronsted base pair sites. In the presence of a supported ruthenium hydroxide catalyst (Ru(OH) x /Al2O3), oxidative dehydrogenation of alcohols and primary amines efficiently proceeds to afford the corresponding carbonyl compounds (aldehydes and ketones) and nitriles, respectively. In the presence of ammonia (THF solution), Ru(OH) x /Al2O3 can catalyze ammoxidation of primary alcohols to the corresponding nitriles. This ammoxidation proceeds through the sequential reactions of oxidative dehydrogenation of primary alcohols to aldehydes, dehydrative condensation of the aldehydes with ammonia to aldimines, and oxidative dehydrogenation of the aldimines. In addition, formal α-oxygenation of primary amines to the corresponding primary amides can be realized through the Ru(OH) x /Al2O3-catalyzed oxidative dehydrogenation and nitrile hydration. Moreover, a supported copper hydroxide species on a manganese oxide-based octahedral molecular sieve (Cu(OH) x /OMS-2) can act as an efficient and highly durable heterogeneous catalyst for oxidative homocoupling of terminal alkynes to the corresponding diynes. The catalyses for the above-mentioned oxidation reactions are truly heterogeneous, and the catalysts can be reused several times with keeping their high catalytic performance.

Review: 62 refs.

In this study, a new green synthetic route to primary amides, that is, aerobic oxidative amidation of primary alcohols or aldehydes with ammonia, has been developed. In the presence of a cryptomelane-type manganese oxide-based octahedral molecular sieve (OMS-2), various kinds of structurally diverse primary alcohols or aldehydes including aromatic, olefinic, heteroaromatic, and aliphatic ones can be converted into the corresponding primary amides in moderate to high yields (20 examples from primary alcohols and 11 examples from aldehydes). Furthermore, gram-scale amidation is also effective, and the analytically pure primary amides can easily be isolated. The present catalysis by OMS-2 is truly heterogeneous in nature, and the retrieved OMS-2 catalyst can be reused several times (at least 12 times for the amidation of 2-pyridinemethanol). Though the formation rates of the corresponding primary amide are gradually decreased by repeating reuse experiments, OMS-2 can be regenerated by calcination. The present OMS-2-catalyzed amidation of primary alcohols is composed of four relay steps: (i) oxidative dehydrogenation of primary alcohols, (ii) dehydrative condensation of aldehydes with ammonia, (iii) oxidative dehydrogenation of aldimines, and (iv) hydration of nitriles to form the corresponding primary amides. All steps (i)–(iv) can be promoted by the presence of OMS-2.

Selective hydration of nitriles to primary amides as well the base-catalyzed synthesis of 2-substituted 4(1H)-quinazolinones via reaction of 2-aminobenzonitrile with carbonyl compounds using macroporous Amberlyst A26 OH in H2O–EtOH is described. The latter reaction proceeds via tandem hydration of 2-aminobenzonitrile, condensation of the in situ generated 2-aminobenzamide with carbonyl compounds, and cyclization of the imine intermediate to give the quinazolinone derivatives.

Selective hydration of nitriles to primary amides as well the base-catalyzed synthesis of 2-substituted 4(1H)-quinazolinones via reaction of 2-aminobenzonitrile with carbonyl compounds using macroporous Amberlyst A26 OH in H2O–EtOH is described. The latter reaction proceeds via tandem hydration of 2-aminobenzonitrile, condensation of the in situ generated 2-aminobenzamide with carbonyl compounds, and cyclization of the imine intermediate to give the quinazolinone derivatives.

Review: 160 refs.

A general and practical methodology for the hydration of nitriles to primary amides enabled by manganese catalyst is presented. The described protocol shows broad substrate scope with good functional group tolerance, including a wide range of (hetero)aromatic and aliphatic nitriles, thus afforded the corresponding amides in good to excellent isolated yields under mild conditions. Preliminary mechanistic studies indicated that metal‐ligand cooperation (MLC) mode was involved in this catalytic process.

Metal-catalyzed nitrile hydration reactions: The specific contribution of ruthenium

The hydration of nitriles is an important transformation because the resulting primary amides present a huge number of applications in synthetic organic chemistry, as well as industrial and pharmaceutical interest. Metallic compounds (complexes, oxides, and nanoparticles) are known to catalyze the hydration of nitriles by activating the nitrile substrate, the water molecule, or both partners, upon coordination. In this Minireview article, the application of metal‐based catalysts in the hydration of α‐ and β‐hydroxynitriles and cyanamides is comprehensively discussed. Compared to more classical organonitriles, little attention has been paid to the hydration of these particular class of substrates despite the synthetic relevance of the respective carboxamides, i. e. α‐/β‐hydroxyamides and ureas. Transfer hydration strategies, in which a water surrogate is employed to convert the C≡N group into the C(=O)NH2 one, are also covered.

Ruthenium(II) carbonyl complexes containing pyridoxal thiosemicarbazone and trans-bis(triphenylphosphine/arsine): Synthesis, structure and their recyclable catalysis of nitriles to amides and synthesis of imidazolines

CeO2-catalyzed one-pot selective synthesis of N-alkyl amides from nitriles, amines and water