Revisit to the Biginelli reaction: a novel and recyclable bioglycerol-based sulfonic acid functionalized carbon catalyst for one-pot synthesis of substituted 3,4-dihydropyrimidin-2-(1H)-ones

Trifluoromethyl-β-dicarbonyls as Versatile Synthons in Synthesis of Heterocycles

Trifluoromethyl group relishes a privileged position in the realm of medicinal chemistry because its incorporation into organic molecules often enhances the bioactivity by altering pharmacological profile of molecule. Trifluoromethyl-β-dicarbonyls have emerged as pivotal building blocks in synthetic organic chemistry due to their facile accessibility, stability and remarkable versatility. Owing to presence of nucleophilic and electrophilic sites, they offer multifunctional sites for the reaction. This review covers a meticulous exploration of their multifaceted role, encompassing an in-depth analysis of mechanism, extensive scope, limitations and wide-ranging applications in diverse organic synthesis, covering the literature from the 21st century. This comprehensive review encapsulates the applications of trifluoromethyl-β-dicarbonyls and their synthetic equivalents as precursors of complex and diverse heterocyclic scaffolds, fused heterocycles and spirocyclic compounds having medicinal and material importance. Their potent synthetic utility in cyclocondensation reactions with binucleophiles, cycloaddition reactions, C-C bond formations, asymmetric multicomponent reactions using classical/solvent-free/catalytic synthesis have been presented. Influence of unsymmetrical trifluoromethyl-β-diketones on regioselectivity of transformation is also reviewed. This review will benefit the synthetic and pharmaceutical communities to explore trifluoromethyl-β-dicarbonyls as trifluoromethyl building blocks for fabrication of heterocyclic scaffolds having implementation into drug discovery programs in the imminent future.

Glycerol based carbon sulfonic acid catalyzed synthesis, in silico studies and in vitro biological evaluation of isonicotinohydrazide derivatives as potent antimicrobial and anti-tubercular agents

The present pathway involves synthesis of isonicotinohydrazide derivatives using isoniazid and diversely substituted aldehydes in the presence of EtOH and catalytic amount of glycerol based carbon sulfonic acid catalyst. The developed pathway has so many merits like excellent yields (91-98%), short reaction time (4-10 min), easy reaction set up, no need of column chromatography, large substrate scope, easily recyclable and reusable catalyst. The synthesized compounds were screened for antimicrobial and anti-tubercular activity and it was observed that compounds possessed high biological potency against the Gram positive and Gram negative bacterial and fungal strains. Regarding anti-tubercular activity, compound 3m exhibited high % inhibition against Mycobacterium tuberculosis H₃₇RV strain. Based on the outcome of in vitro studies, all the synthesized compounds were docked against E. coli (1KZN), C. albicans (1IYL), and M. tuberculosis H ₃₇ Rv strain (2NSD). The synthesized derivatives were docked within the binding site of 1KZN, and 1IYL. However, with 2NSD, apart from 3h, all the derivatives displayed interaction within the binding cavity of the protein. All the crucial interactions with Asn46, Asp73, and Arg136 in 1KZN, His227, Leu451 in 1IYL, and Tyr158 in 2NSD were witnessed in the top-scored docked candidates. Molecular docking studies revealed the importance of the substitution at R position on isonicotinohydrazide scaffold. The nitrogen atoms of hydrazide moiety were involved in forming hydrogen bonding with the active site amino acids, and the substitution at the R position occupy the hydrophobic position in the binding pocket. Also, the functional groups present on the substituted R position were involved in forming hydrogen bonding with the crucial active site residues.

Halloysite Nanotubes as Bimodal Lewis/Brønsted Acid Heterogeneous Catalysts for the Synthesis of Heterocyclic Compounds

Halloysite nanotubes can be used for the preparation of solid catalysts. Owing to their natural availability at low-cost as well as to their large and easy-to-functionalize surface, they can be conveniently activated with mineral acids or derivatized with acidic groups. Nevertheless, the use of HNTs as catalysts in complex transformations is still limited. Herein, we report two strategies to utilize HNT-based materials as solid acidic catalysts for the Biginelli reaction. To this aim, two methods for increasing the number of acidic sites on the HNTs were explored: (i) the treatment with piranha solution (Pir-HNTs) and (ii) the functionalization with phenylboronic acid (in particular with benzene-1,4-diboronic acid: the sample is denoted as HNT-BOA). Interestingly, both strategies enhance the performance of the multicomponent reaction. Pir-HNTs and HNT-BOA show an increased reactivity (72% and 89% yield, respectively) in comparison with pristine HNTs (52%). Additionally, Pir-HNTs can be reused up to five times without significant performance loss. Moreover, the method also displays good reaction scope, as demonstrated by the preparation of 12 different 3,4-dihydropyrimidinones in up to 71% yield. Therefore, the described strategies are promising for enhancing the acidity of the HNTs as catalysts for the organic reaction.

Microwave-assisted synthesis of bioactive tetrahydropyrimidine derivatives as antidiabetic agents

Abstract.

Sulfonated carbons from agro-industrial residues: simple and efficient catalysts for the Biginelli reaction

An eco-friendly catalyst prepared from rice husk was used to synthesize dihydropyrimidinones (DHPMs) and achieved a yield of 92%.

A Brønsted acidic ionic liquid anchored to magnetite nanoparticles as a novel recoverable heterogeneous catalyst for the Biginelli reaction

In this study, simple and effective methods were used for the preparation of an ionic liquid that immobilized magnetite nanoparticles. Fe₃O₄ nanoparticles were prepared via a chemical co-precipitation method. Then, a SiO₂ shell was coated on the magnetic core via the Stober method. Finally, CPTES (chloropropyltriethoxysilane) and morpholine were coated on the SiO₂ shell. Morpholine sulfate, an acidic ionic liquid, was successfully bound to magnetite nanoparticles (Mag@Morph-AIL) and this was used as an efficient catalyst for the preparation of 3,4-dihydropyrimidinones. Compared to previous works, the easy separation of the nanocatalyst using an external magnet and the recyclability, non-toxicity, versatility, and high stability of the catalyst, combined with low reaction times and excellent yields, make the present protocol very useful for the synthesis of the title products. The synthesized products and catalyst were confirmed via ¹H-NMR, ¹³C-NMR, FT-IR, scanning electron microscope, X-ray diffraction, and elemental analysis.

Chiral Separation of 3,4-dihydropyrimidin-2(1H)-ones and 3,4-di -hydropyrimidin- 2(1H)-thiones Enantiomers by HPLC on Chiralcel®OD-H

Objective:

Ten racemic 3,4-dihydropyrimidin-2(1H)-ones and 3,4-dihydropyrimidin- 2(1H)-thiones were separated by liquid chromatography on Chiralcel®OD-H column containing cellulose tris(3, 5-dimethylphenylcarbamate).

Methods:

The enantioseparation was carried out using Chiralcel®OD-H polysaccharide-type chiral stationary phase to resolve such enantiomers under normal-phase mode.

Results:

Complete separations of the 3,4-dihydropyrimidin-2(1H)-ones and 3,4-dihydropyrimidin- 2(1H)-thiones derivatives with good resolution (RS= 1.04-2.80) were achieved within a short time (10-15 min).

Conclusion:

An optimal baseline separation (Rs> 1.5) was achieved using Chiralcel®OD-H under normal-phase mode. Structure-retention relationships have also been discussed.

Oxidative Dehydrosulfurative Cross-Coupling of 3,4-Dihydropyrimidine-2-thiones with Alkynes for Access to 2-Alkynylpyrimidines

A reaction method is described for the one-step synthesis of 2-alkynylpyrimidines from 3,4-dihydropyrimidin-1H-2-thiones (DHPMs) via dehydrosulfurative Sonogashira cross-coupling with concomitant oxidative dehydrogenation using a Pd/Cu catalytic system. Together with the ready availability of DHPMs possessing various substituents at the C4-C6 positions, this transformation offers rapid and general access to diverse 2-alkynylpyrimidine derivatives.

Selective ultrasonic assisted synthesis of iron oxide mesoporous structures based on sulfonated melamine formaldehyde and survey of nanorod/sphere, sphere and core/shell on their catalysts properties for the Biginelli reaction

Sulfonated melamine-formaldehyde including iron oxide nanoparticles were synthesized by sulfonation of melamine-formaldehyde and then Fe₃O₄ nanoparticles were bounded onto the surface of sulfonated melamine-formaldehyde (SMF). Two different iron oxide nanostructures including nanorods/spheres and nanospheres on sulfonated melamine-formaldehyde (SMF/Fe₃O₄) were obtained only by modifying the time of radiation from 4 to 8 h in our synthetic method. Furthermore core/shell (Fe₃O₄@SMF) was prepared by entrapping Fe₃O₄ magnetic nanoparticles as the core and sulfonated melamine-formaldehyde as the outer shell. The prepared components were characterized via, Fourier transform infrared spectroscopy (FT-IR), titration, X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) analysis, Barret-Joyner-Halenda (BJH) analysis, vibrating sample magnetometer (VSM), energy-dispersive X-ray (EDX) spectroscopy, and thermal gravimetric analysis (TGA). According to obtained results, the synthesized products had a thermal stability near 180 °C, particle-size distribution around of 20-140 nm and surface area between 6 and 10 m²/g. In this study, vapor was used as a heat source. These effective and magnetically recoverable catalysts were employed for the synthesis of numerous 3,4-dihydropyrimidin-2(1H)-ones by utilizing aldehydes, ethylacetoacetate and urea. Functional easiness, excellent yields, short reaction time, the simplicity of work-up or filter, and thermal stability of these catalysts created them as appropriate heterogeneous systems and acceptable alternative to different heterogeneous catalysts.

Recent developments in the synthesis and applications of dihydropyrimidin-2(1H)-ones and thiones

Dihydropyrimidin-2(1H)-ones/thiones (DHPMs) are important heterocyclic compounds owing to their excellent biological activities and have been widely utilized in pharmaceutical applications. Recently, numerous DHPM derivatives have been prepared. This review covers the synthesis of DHPMs and improved procedures for the preparation of DHPMs from 1995 to 2016.

Ultrasound promoted one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones/thiones using dendrimer-attached phosphotungstic acid nanoparticles immobilized on nanosilica

A highly efficient and improved synthetic methodology for the preparation of 3,4-dihydropyrimidin-2(1H)-ones and thiones in the Biginelli reaction by condensation of β-dicarbonyl compounds, urea/thiourea and aromatic aldehydes using Dendrimer-PWAⁿ as a nanocatalyst under ultrasonic irradiation is reported. Compared with classical Biginelli reaction conditions, this new method has the advantage of easy reaction condition, short reaction time, excellent yields, recyclable green catalyst, reduced environmental impacts and absence of any tedious workup or purification. The catalyst can be easily recovered by filtration and reused for eight consecutive reaction cycles without significant loss of activity. Also, SEM and DLS images of the catalyst after reaction cycle were investigated.

An Efficient, Eco-friendly and Sustainable One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones Directly from Alcohols Catalyzed by Heteropolyanion-Based Ionic Liquids

Efficient, eco-friendly and sustainable access to 3,4-dihydropyrimidin-2(1H)-ones directly from alcohols under microwave and solvent-free conditions has been reported. The practical protocol involves heteropolyanion-based catalyzed oxidation of alcohols to aldehydes with NaNO₃ as the oxidant followed by cyclocondensation with dicarbonyl compounds and urea or thiourea in a two-step, one-pot manner. Compatibility with different functional groups, good to excellent yields and reusable catalysts are the main highlights. The utilization of alcohols instead of aldehydes is a valid and green alternative to the classical Biginelli reaction.

1,3,5-Tris(2-hydroxyethyl)isocyanurate functionalized graphene oxide: a novel and efficient nanocatalyst for the one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones

The preparation and characterization of a novel 1,3,5-tris(2-hydroxyethyl)isocyanurate functionalized graphene oxide (GO–THEIC) nanomaterial and its catalytic application for the Biginelli reaction are described.

Cu–EDTA-modified APTMS-Fe3O4@SiO2 core–shell nanocatalyst: a novel magnetic recoverable catalyst for the Biginelli reaction

A novel copper–ethylenediamine tetracarboxylate modified core–shell magnetic catalyst is introduced.

Bioglycerol-derived carbon−SO3H as a recyclable catalyst for the synthesis of tetrahydro-β-carbolines

A variety of aldehydes undergo smooth coupling with N-tosyltryptamine in the presence of carbon−SO3H in ethanol at 80 °C to furnish the corresponding tetrahydro-β-carbolines in excellent yields with high selectivity. The coupling of tryptamine with isatins affords the respective spiro-tetrahydro-β-carbolines in good yields. The use of a recyclable solid acid catalyst makes this method simple, convenient, and cost-effective.

A novel one pot four-component reaction for the efficient synthesis of spiro[indoline-3,4′-pyrano[2,3-c]pyrazole]-3′-carboxylate and trifluoromethylated spiro[indole-3,4′-pyrano[2,3-c]pyrazole] derivatives using recyclable PEG-400

A novel, simple and efficient synthetic protocol has been developed via a one pot, four-component reaction using recyclable PEG-400.

The combined role of catalysis and solvent effects on the Biginelli reaction: improving efficiency and sustainability

The traditional Biginelli reaction is a three-component condensation between urea, benzaldehyde and an acetoacetate ester to give a dihydropyrimidinone. An investigation into catalytic and solvent effects has returned the conclusion that the diketo-enol tautomerisation equilibrium of the dicarbonyl reactant dictates the yield of the reaction. Whereas the solvent is responsible for the tautomerisation equilibrium position, the catalyst only serves to eliminate kinetic control from the reaction. Generally, to preserve reaction efficiency and improve sustainability, bio-derivable p-cymene was found to be a useful solvent. The metal-enolate intermediate that results from the application of a Lewis acidic catalyst often cited as promoting the reaction appears to hinder the reaction. In this instance, a Brønsted acidic solvent can be used to return greater reactivity to the dicarbonyl reagent.

Bi-SO3H Functionalized Ionic Liquid Based on DABCO: New and Efficient Catalyst for Facile Synthesis of Dihydropyrimidinones

A simple and efficient method for the one-pot Biginelli condensation reaction of aldehydes,β-dicarbonyl compounds, and urea or thiourea employing [DABCO](SO3H)2Cl2as a novel ionic liquid catalyst is described.

Mechanistic studies on Lewis acid catalyzed Biginelli reactions in ionic liquids: evidence for the reactive intermediates and the role of the reagents

This paper describes the use of common Lewis acids supported in imidazolium-based ionic liquids as the catalysts to promote the Biginelli reaction. The ionic liquid effect and the reaction mechanism are discussed on the basis of nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI-MS), and theoretical calculations. Indeed, the results showed that the ionic medium plays a fundamental role in the synthesis of biologically active dihydropyrimidinones due to the stabilization of the charged intermediates proposed in the mechanism. When conducted in an ionic liquid as solvent, the reaction mechanism is more complex than in other Lewis acid catalyzed Biginelli reactions.