Magnetically Recoverable CuFe 2 O 4 Nanoparticles: Catalyzed Synthesis of Aryl Azides and 1,4-Diaryl-1,2,3-triazoles from Boronic Acids in Water: Magnetically Recoverable CuFe 2 O 4 Nanoparticles

Synthetic strategies of heterocycle-integrated pyridopyrimidine scaffolds supported by nano-catalysts

Nano-catalysts are of special character for the synthesis of organic molecules with high efficiency, and exceptional physicochemical properties. The objective of this study was to present an overview of the literature reports concerning the synthetic strategies supported by nano-catalysts and the biological features of heterocycle-integrated pyridopyrimidine scaffolds. The basic topics include the strategies that were adopted to prepare pyrido[2,3-d]pyrimidines and pyrido[1,2-a]pyrimidines. The synthesis of pyrido[2,3-d]pyrimidines was attained through two-, three-, or four-component reactions. The synthesis of spirocyclic systems, including spiro[indoline-pyridopyrimidine] derivatives and arylation reactions, was investigated. The anticipated mechanisms of the diverse target products, in addition to the preparation of the nanocatalysts, were scrutinized. The privileged antimicrobial characteristics, challenges, literature overview, and future prospectives were consistently investigated.

Copper(I) Chloride Mediated Amination of Halobenzenes via Azides: Scope, Mechanistic Aspects, and C-C Cleavage Reactions

Selective azidation-amination of long-chain alkanoyl halobenzenes with sodium azide, promoted by copper(I) chloride, is reported. The protocol is, apart from CuCl and NaN₃, additive free and allows the isolation of versatile amine-azides. Alkyl cleavage occurs as a side reaction through an unusual Schmidt-type azide insertion adjacent to the carbonyl group, forming alkyl nitriles possibly via radical pathways. Mechanistic studies involving ¹⁵N labeling experiments and test substrates indicate that the reaction occurs via 1-azido-4-alkanoyl benzenes. The amination is applicable for substrates with electron-withdrawing groups and proceeds under mild conditions. The mechanism of the amine formation involves nitrenes. Intermediates were trapped by carrying out the reaction in the presence of the 2,2,6,6-(tetramethylpiperidin-1-yl)oxyl stable radical and characterized by high-resolution mass spectrometry. The intermediates are consistent with earlier mechanistic proposals.

Recent advances in nanoparticles towards sustainability and their application in organic transformations in aqueous media

Nanoparticles (NPs) play a crucial role in organic transformation and are becoming increasingly attractive in the field of catalysis as they show good catalytic activity in organic as well as aqueous media. Numerous NPs have been utilized for several organic transformations in aqueous media, which have led to dedicated efforts for the complete coverage of the application of metal, metal oxide, bimetallic and supported NPs in water-mediated organic transformations in the last decades. This review aims to provide current highlights on the application of various types of metal NPs for organic transformations in aqueous media. The remarkable benefits associated with the catalytic application of NPs in water allows for various transformations to be performed under very mild and green conditions. Lastly, the author's perspectives are briefly considered, including future developments and crucial challenges in the ever-growing field of nanocatalysis.

Supported Metal Catalysts for the Synthesis of N-Heterocycles

Nitrogen-containing heterocycles are important scaffolds for a large number of compounds with biological, pharmaceutical, industrial and optoelectronic applications. A wide range of different methodologies for the preparation of N-heterocycles are based on metal-catalyzed cyclization of suitable substrates. Due to the growing interest in Green Chemistry criteria over the past two decades, the use of supported metal catalysts in the preparation of N-heterocycles has become a central topic in Organic Chemistry. Here we will give a critical overview of all the solid supported metal catalysts applied in the synthesis of N-heterocycles, following a systematic approach as a function of the type of support: (i) metal catalysts supported on inorganic matrices; (ii) metal catalysts supported on organic matrices; (iii) metal catalysts supported on hybrid inorganic-organic matrices. In particular, we will try to emphasize the effective heterogeneity and recyclability of the described metal catalysts, specifying which studies were carried out in order to evaluate these aspects.

Direct Michael addition/decarboxylation reaction catalyzed by a composite of copper ferrite nanoparticles immobilized on microcrystalline cellulose: an eco-friendly approach for constructing 3,4-dihydrocoumarin frameworks

A composite of copper ferrite oxide nanoparticles immobilized on microcrystalline cellulose (CuFe₂O₄@MCC) was synthesized. The synthesized composite was characterized by FESEM with EDS-Mapping, TEM, P-XRD, TEM, and BET analysis and investigated for its catalytic activity toward Tandem Michael addition and decarboxylation of coumarin-3-carboxylic acid with cyclic 1,3-diketones to obtain novel 3,4-dihydrocoumarin derivatives. This protocol was established with wide substrate scope and significant yield. The significant characteristics of this methodology are mild reaction conditions, easy setup procedure, non-toxic, and cost-effectiveness. A gram-scale synthesis with low catalyst loading was also demonstrated.

Composites of copper ferrite oxide nanoparticles immobilized on microcrystalline cellulose were synthesized and studied for their catalytic activity toward the preparation of novel 3,4-dihydrocoumarin derivatives.

General Approach to N6,C5'-Difunctionalization of Adenosine

Among the C6-halo purine ribonucleosides, the readily accessible 6-chloro derivative has been known to undergo slow S_NAr reactions with amines, particularly aryl amines. In this work, we show that in 0.1 M AcOH in EtOH, aryl amines react quite efficiently at the C6-position of 2',3',5'-tri-O-(t-BuMe₂Si)-protected 6-chloropurine riboside (6-ClP-riboside), with concomitant cleavage of the 5'-silyl group. These two-step processes proceeded in generally good yields, and notably, reactions in the absence of AcOH were much slower and/or lower yielding. Corresponding reactions of 2',3',5'-tri-O-(t-BuMe₂Si)-protected 6-ClP-riboside with alkyl amines proceeded well but without desilylation at the primary hydroxyl terminus. These differences are likely due to the acidities of the ammonium chlorides formed in these reactions, and the role of AcOH was not desilylation but possibly only purine activation. With 50% aqueous TFA in THF at 0 °C, cleavage of the 5'-silyl group from 2',3',5'-tri-O-(t-BuMe₂Si)-protected N⁶-alkyl adenosine derivatives and from 6-ClP-riboside was readily achieved. Reactions of the 5'-deprotected 6-ClP-riboside with alkyl amines proceeded in high yields and under mild conditions. Because these complementary methodologies yielded N⁶-aryl and -alkyl adenosine derivatives containing a free 5'-hydroxyl group, a variety of product functionalizations were undertaken to yield N⁶,C5'-doubly modified nucleoside analogues.

Green and efficient three-component synthesis of 4H-pyran catalysed by CuFe2O4@starch as a magnetically recyclable bionanocatalyst

The development of simple, practical and inexpensive catalysis systems using natural materials is one of the main goals of pharmaceutical chemistry as well as green chemistry. Owing to the ability of easy separation of nanocatalyst, those goals could be approached by applying heterogeneous bionanocatalyst in combination with magnetic nanoparticles. Starch is one of the most abundant natural polymers; therefore, preparing bionanocatalyst from starch is very valuable as starch is largely available and inexpensive. An ecologically benign and efficacious heterogeneous nanocatalyst was prepared based on a biopolymer, and its attributes and morphology were specified by using Fourier transform infrared spectra, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), thermal analysis and vibrating sample magnetometer measurements; followed by studying catalytic behaviour of bionanocomposite in a multicomponent reaction to synthesize of 4H-pyran derivatives. 4H-pyran is extremely valuable in pharmaceutical chemistry, and the development of methods for synthesis of different derivatives of 4H-pyran is momentous. Revealing environmentally benign nature, mild condition, easy work-up, low cost and non-toxicity are some of the advantages of this protocol. Besides, the bionanocomposite was recovered using an external magnetic bar and could be re-used at least six times with no further decrease in its catalytic activity.

Sonochemically Synthesized Spin-Canted CuFe2O4 Nanoparticles for Heterogeneous Green Catalytic Click Chemistry

Heterogeneous green catalysis by using magnetically separable nanometal-oxide catalysts has become a subject of prime focus recently. PXRD (powder X-ray diffraction), FESEM (field emission scanning electron microscopy), and HRTEM (high-resolution tunneling electron microscopy) with IR and Raman spectroscopy are applied to analyze the structural and microstructural properties of nanosized (∼15.3 nm) CuFe₂O₄ synthesized by both sonochemical and mechanochemical processes. The sonochemical process provides a better uniformity of sizes of the nanoparticles (NPs). Rietveld refinement with the PXRD pattern reveals the inverse spinel-like architecture of CuFe₂O₄ NPs. The Raman spectra also indicate the phase purity of the synthesized material. The static magnetic measurements are performed at different magnetic fields and temperature ranges from 300 to 5 K, which confirms the existence of the ferrimagnetic phase mixed with some finer superparamagnetic (SPM) nanophases within the sample. Unsaturated magnetization is observed even at an applied 5 T magnetic field for the presence of spin-canting nature in the partially inverted copper ferrite phases at the surfaces of the nanoparticles. Now, these coupled magnetic CuFe₂O₄ NPs are used as a heterogeneous catalyst for three-component Huisgen 1,3-dipolar cycloaddition click reaction in aqueous media. By this catalyst system, we were able to couple alkyl halide, epoxide, or boronic acid with alkynes efficiently to furnish 1,4-disubstituted 1,2,3-triazoles in excellent yields within very short reaction time. The test for heterogeneity, reusability, and reproducibility of the catalyst has also been performed successfully without prominent decrease in yield up to the fifth cycle.

Iodine-mediated C-N and N-N bond formation: a facile one-pot synthetic approach to 1,2,3-triazoles under metal-free and azide-free conditions

A novel strategy towards the synthesis of 1,4-disubstituted 1,2,3-triazoles via C–N and N–N bond formation has been demonstrated under transition metal-free and azide-free conditions. These 1,2,3-triazoles were obtained in a regioselective manner from commercially available anilines, aryl alkenes/aryl alkynes and N-tosylhydrazines using I₂ under O₂ atmosphere. Broad substrate scope, milder reaction conditions, good to moderate yields and clean protocol are the notable features of the method. Moreover, this protocol is amenable for the generation of a library of medicinally important key building blocks.

A novel strategy towards the synthesis of 1,4-disubstituted 1,2,3-triazoles via C–N and N–N bond formation has been demonstrated under transition metal-free and azide-free conditions.

DBU-Promoted Cu(OAc)•H2O-Catalysed Coupling Reactions of Aryl Iodides and Sodium Azide

An efficient and simple protocol for the synthesis of aryl azides by the coupling of aryl iodides with sodium azide, in good to excellent yields in DMSO at 95 °C under catalysis by Cu(OAc)2-H2O and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), has been established. The optimised loadings of Cu(OAc)2-H2O and DBU were 10 mol% and 15 mol% respectively.

Regioselective Zn(OAc)2-catalyzed azide–alkyne cycloaddition in water: the green click-chemistry

A new method of azide–alkyne cycloaddition (AAC) in the presence of Zn(OAc)₂ as an inexpensive and environmentally friendly catalyst in neat water has been developed.

Copper(I)-Phosphinite Complexes in Click Cycloadditions: Three-Component Reactions and Preparation of 5-Iodotriazoles

The remarkable activity displayed by copper(I)–phosphinite complexes of general formula [CuBr(L)] in two challenging cycloadditions is reported: a) the one‐pot azidonation/cycloaddition of boronic acids, NaN₃, and terminal alkynes; b) the cycloaddition of azides and iodoalkynes. These air‐stable catalysts led to very good results in both cases and the expected triazoles could be isolated in pure form under ‘Click‐suitable’ conditions.

Unsymmetrical Aryl(2,4,6-trimethoxyphenyl)iodonium Salts: One-Pot Synthesis, Scope, Stability, and Synthetic Studies

Diaryliodonium salts have recently attracted significant attention as metal-free-arylation reagents in organic synthesis, and efficient access to these salts is critical for advancement of their use in reaction discovery and development. The trimethoxybenzene-derived auxiliary is a promising component of unsymmetrical variants, yet access remains limited. Here, a one-pot synthesis of aryl(2,4,6-trimethoxyphenyl)iodonium salts from aryl iodides, m-CPBA, p-toluenesulfonic acid, and trimethoxybenzene is described. Optimization of the reaction conditions for this one-pot synthesis was enabled by the method of multivariate analysis. The reaction is fast (<1 h), provides a high yield of product (>85% average), and has broad substrate scope (>25 examples) including elaborate aryl iodides. The utility of these reagents is demonstrated in moderate to high yielding arylation reactions with C-, N-, O-, and S-nucleophiles including the synthesis of a liquid crystal molecule.

Magnetically separable CuFe2O4/reduced graphene oxide nanocomposites: as a highly active catalyst for solvent free oxidative coupling of amines to imines

Solvent free aerobic oxidative coupling of amines to imines in presence of CuFe₂O₄/RGO nanocomposites.

Synthesis of symmetrical N,N′-alkylidene bis-amides catalyzed by silica coated magnetic NiFe2O4 nanoparticle supported polyphosphoric acid (NiFe2O4@SiO2-PPA) and its application toward silver nanoparticle synthesis for electrochemical detection of glucose

For the first time, a new and facile Ag@PM-b-B nanocomposite electrochemical sensor was successfully developed for the detection of glucose. Also, the magnetically recoverable catalyst was easily recycled at least ten times without significant loss of catalytic activity.

One-pot three-component synthesis of 1,2,3-triazoles using magnetic NiFe2O4–glutamate–Cu as an efficient heterogeneous catalyst in water

A magnetic NiFe₂O₄ supported glutamate–copper catalyst is prepared and applied for the synthesis of a wide variety of 1,2,3-triazoles in water at room temperature.

Magnetically separable CuFe2O4 nanoparticles as a recoverable catalyst for the addition reaction of C(sp3)–H bond of azaarenes to aldehydes

A green and efficient method for CuFe₂O₄-catalyzed C(sp³)–H functionalization of 2-alkyl azaarenes has been developed. The catalyst can be magnetically recycled and reused for eight times without significant decrease in catalytic activity.

Magnetically recoverable and reusable CuFe2O4 nanoparticle-catalyzed synthesis of benzoxazoles, benzothiazoles and benzimidazoles using dioxygen as oxidant

A green and efficient strategy for the synthesis of benzoxazoles, benzothiazoles and benzimidazoles has been developed by using inexpensive, readily available, dioxygen-stable and recyclable CuFe₂O₄ as the nanocatalyst.