Strategy for the Synthesis of Pyrimidine Derivatives: NbCl5-Mediated Cycloaddition of Alkynes and Nitriles

Metal- and Solvent-Free Synthesis of Substituted Pyrimidines via an NH4I-Promoted Three-Component Tandem Reaction

A facile and practical approach for the preparation of substituted pyrimidines from ketones, NH4OAc, and N,N-dimethylformamide dimethyl acetal has been described. This NH4I-promoted three-component tandem reaction affords a broad range of substituted pyrimidines in acceptable yields under metal- and solvent-free conditions. The present methodology features the advantages of simple and easily available starting materials, metal- and solvent-free conditions, a broad substrate scope with good functional group tolerance, and gram-scale synthesis.

Synthesis of 2,4,6-Trisubstituted Pyrimidines through Copper-Catalyzed [4 + 2] Annulation of α,β-Unsaturated Ketoximes with Activated Nitriles

The copper-catalyzed [4 + 2] annulation of α,β-unsaturated ketoximes with activated nitriles for the rapid construction of 2,4,6-trisubstituted pyrimidines in moderate to good yields has been developed. The reaction features synthetic simplicity, good functional group tolerance, and gram-scale applicability. A plausible mechanism is proposed based on mechanistic investigations.

Catalyzed Methods to Synthesize Pyrimidine and Related Heterocyclic Compounds

This review covers articles published in the period from 2010 to mid-2022 on synthetic advances in the formation of pyrimidine and related heterocyclic compounds. Special emphasis has been given to the different types of cycloadditions, taking into account the number of their components and leading to the formation of the pyrimidine ring. Due to the large number of publications on the Biginelli reaction and related reactions, this will be dealt with in a separate review in the near future.

Applications of Vanadium, Niobium, and Tantalum Complexes in Organic and Inorganic Synthesis

Organometallic catalysis is a powerful strategy in chemical synthesis, especially with the cheap and low toxic metals based on green chemistry principle. Thus, the selection of the metal is particularly important to plan relevant and applicable processes. The group VB metals have been the subject of exciting and significant advances in both organic and inorganic synthesis. In this Review, we have summarized some reports from recent decades, which are about the development of group VB metals utilized in various types of reactions, such as oxidation, reduction, alkylation, dealkylation, polymerization, aromatization, protein synthesis, and practical water splitting.

Acid-controlled multicomponent selective synthesis of 2,4,6-triaryl pyridines and pyrimidines by using hexamethyldisilazane as a nitrogen source under microwave irradiation

An efficient and general protocol for the synthesis of functionalized 2,4,6-triaryl pyridines and pyrimidines was developed from commercially available aromatic ketones, aldehydes and hexamethyldisilazane (HMDS) as a nitrogen source under microwave irradiation. In this multicomponent synthetic route, Lewis acids play an important role in selectively synthesizing six-membered heterocycles, including pyridines (1N) and pyrimidines (2N), by involving [2 + 1 + 2 + 1] or [2 + 1 + 1 + 1 + 1] annulated processes.

Multicomponent syntheses of 5- and 6-membered aromatic heterocycles using group 4-8 transition metal catalysts

In this Perspective, we discuss recent syntheses of 5- and 6-membered aromatic heterocycles via multicomponent reactions (MCRs) that are catalyzed by group 4-8 transition metals. These MCRs can be categorized based on the substrate components used to generate the cyclized product, as well as on common mechanistic features between the catalyst systems. These particular groupings are intended to highlight mechanistic and strategic similarities between otherwise disparate transition metals and to encourage future work exploring related systems with otherwise-overlooked elements. Importantly, in many cases these early- to mid-transition metal catalysts have been shown to be as effective for heterocycle syntheses as the later (and more commonly implemented) group 9-11 metals.

Iron Nitrate-Mediated Selective Synthesis of 3-Acyl-1,2,4-oxadiazoles from Alkynes and Nitriles: The Dual Roles of Iron Nitrate

A direct strategy for the selective synthesis of 3-acyl-1,2,4-oxadiazoles from alkynes and nitriles has been developed under iron(III) nitrate-mediated conditions. The mechanism includes three sequential procedures: iron(III) nitrate-mediated nitration of alkynes leads to α-nitroketones, dehydration of α-nitroketones provides the nitrile oxides, and 1,3-dipolar cycloaddition of nitrile oxides with nitriles produces 3-acyl-1,2,4-oxadiazoles under iron-mediated conditions. Iron(III) nitrate plays dual roles in the nitration of alkynes and the activation of nitriles, while the formation of pyrimidine/isoxazole byproducts can be efficiently inhibited.

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.

Oxidative Coupling with Zr(IV) Supported by a Noninnocent Anthracene-Based Ligand: Application to the Catalytic Cotrimerization of Alkynes and Nitriles to Pyrimidines

We report the synthesis and reactivity of Zr complexes supported by a 9,10-anthracenediyl-linked bisphenoxide ligand, L. Zr^IVLBn₂ (1) undergoes facile photolytic reduction with concomitant formation of bibenzyl and Zr^IVL(THF)₃ (2), which displays a two-electron reduced anthracene moiety. Leveraging ligand-stored reducing equivalents, 2 promotes the oxidative coupling of internal and terminal alkynes to isolable zirconacyclopentadiene complexes, demonstrating the reversible utilization of anthracene as a redox reservoir. With diphenylacetylene under CO, cyclopentadienone is formed stoichiometrically. 2 is competent for the catalytic formation of pyrimidines from alkynes and nitriles. Mechanistic studies suggest that selectivity for pyrimidine originates from preferred formation of an azazirconacyclopentadiene intermediate, which reacts preferentially with nitriles over alkynes.

In Situ-Generated Niobium-Catalyzed Synthesis of 3-Pyrroline Derivatives via Ring-Closing Metathesis Reactions

An active in situ-generated Nb complex was used as a catalyst in the ring-closing metathesis reaction of N,N-diallyl-p-toluenesulfonamide to afford the corresponding 3-pyrroline derivative. The Nb complex was formed from NbCl₅, trimethylsilyl chloride, Zn, and PhCHCl₂ in tetrahydrofuran. The Nb complex displayed high catalytic activity toward ring-closing metathesis reactions.

FeCl3-Assisted Niobium-Catalyzed Cycloaddition of Nitriles and Alkynes: Synthesis of Alkyl- and Arylpyrimidines Based on Independent Functions of NbCl5 and FeCl3 Lewis Acids

NbCl₅-catalyzed [2 + 2 + 2] cycloaddition of nitriles with alkynes was used to synthesize pyrimidine derivatives. In this reaction, the use of individual Lewis acids, namely NbCl₅ and FeCl₃, is a key strategy for achieving the reaction using a catalytic amount of NbCl₅. The roles of the two Lewis acids were investigated using FT-IR spectroscopy. The results showed that NbCl₅ served as an efficient Lewis acid catalyst for nitrile activation, whereas FeCl₃ showed stronger Lewis acidity toward pyrimidines, releasing NbCl₅ into the catalytic cycle.

Crystal structure of 4-(1H-imidazol-1-yl)-6-pyrimidinylferrocene, C17H14FeN4

C17H14FeN4, monoclinic, P21/c, a = 11.8213(11) Å, b = 10.3610(10) Å, c = 11.8552(11) Å, α = γ = 90°, β = 101.1540(10)°, V = 1424.6(2) Å3, Z = 4, R gt (F) = 0.0233, wR ref (F 2 ) = 0.0653, T = 296(2) K.

Theoretical study on Au(i)-catalyzed [2 + 2 + 2] cycloadditions of ynamides with two discrete nitriles

The Au-catalyzed [2 + 2 + 2] cycloadditions of ynamides with two discrete nitriles were theoretically studied with the aid of DFT calculations.

Synthesis of α-amino acidato derivatives of niobium and tantalum pentahalides and their conversion into iminium salts

Dinuclear complexes of formula Nb2Cl9[O2CCH(R)NR'R″2-κO,κO] (R = CH2CHMe2, R' = R″ = H, 1a; R = CH2Ph, R' = R″ = H, 1b; R = CH2CH2SCH3, R' = R″ = H, 1c; R = R' = H, R″ = Me, 1d; R = CH2Ph, R' = R″ = Me, 1e; Nb2Cl9[O2C⌈CH(CH2)3NH⌉], 1f) were prepared by allowing NbCl5 to react in dichloromethane with the appropriate α-amino acid in 1:2 amino acid/Nb molar ratio. The 1:1 reactions between MX5 (M = Nb, Ta; X = Cl, Br) and a series of α-amino acids resulted in the formation of the iminium salts [(R)CH═NR'R″2][MX6] (R = CH2Ph, R' = R″ = Me: M = Nb, X = Cl, 2a; M = Nb, X = Br, 2b; M = Ta, X = Cl, 2c; M = Ta, X = Br, 2d; R = CH2Ph, R' = R″ = H, M = Nb: X = Cl, 3a; X = Br, 3b; R = CH2CHMe2, R' = R″ = H, M = Nb, X = Cl, 4; R = R' = H, R″ = Me, M = Nb, X = Cl, 5). The formate/amino acidate derivative NbCl3(O2CH)[O2CCH(CH2Ph)NMe2], 6, was isolated and identified as coproduct of the 1:1 reaction between NbCl5 and N,N-dimethyl-l-phenylalanine, leading to 2a. All of the compounds were characterized by analytical and spectroscopic methods and by X-ray diffractometry in the cases of 2a, 2b, and 2d. Moreover, density functional theory studies were carried out to shed light on mechanistic and structural aspects.

KOtBu-promoted synthesis of multi-substituted 4-aminopyrimidines from benzonitriles and aliphatic amides

Multi-substituted 4-aminopyrimidines were prepared from commercially-available benzonitriles and aliphatic amides in transition-metal-free conditions. With KO^tBu as the only promoter, target pyrimidines were isolated in moderate to excellent yields.

Greener [3+3] tandem annulation–oxidation approach towards the synthesis of substituted pyrimidines

An efficient and practical method using choline hydroxide has been developed for the production of a wide range of substituted pyrimidines.

The iron-catalyzed construction of 2-aminopyrimidines from alkynenitriles and cyanamides

Several cycloaddition catalysts and reagents were surveyed for their effectiveness toward cyclizing alkynenitriles with cyanamides. Catalytic amounts of FeI2, (iPr)PDAI and Zn were found to effectively catalyze the [2+2+2] cycloaddition of a variety of cyanamides and alkynenitriles to afford bicyclic 2-aminopyrimidines.