Hydromagnesite as an Efficient Recyclable Heterogeneous Solid Base Catalyst for the Synthesis of Flavanones, Flavonols and 1,4-Dihydropyridines in Water

Recent Progresses in the Multicomponent Synthesis of Dihydropyridines by Applying Sustainable Catalysts Under Green Conditions

The synthesis of dihydropyridines, valuable molecules with diverse therapeutic properties, using eco-friendly heterogeneous catalysts as a green alternative received significant consideration. By selecting appropriate precursors, these compounds can be readily modified to induce the desired properties in the target product. This review focused on synthesising diverse dihydropyridine derivatives in single-pot reactions using magnetic, silica, and zirconium-based heterogeneous catalytic systems. The monograph describes preparation techniques for various catalyst materials in detail. It covers facile and benign magnetic, silica, zirconium-based, and ionic liquid catalysts, exhibiting significant efficacy and consistently facilitating excellent yields in short reaction times and in a cost-effective way. Most of the designated protocols employ Hantzsch reactions involving substituted aldehydes, active methylene compounds, and ammonium acetate. These reactions presumably follow Knoevenagel condensation followed by Michael addition and intra-molecular cyclisation. The multicomponent one-pot protocols using green catalysts and solvents have admirably increased the product selectivity and yields while minimising the reaction time. These sustainable catalyst materials retain their viability for several cycles reducing the expenditure are eco-friendly.

A Facile and Catalyst-Free Microwave-Promoted Multicomponent Reaction for the Synthesis of Functionalised 1,4-Dihydropyridines With Superb Selectivity and Yields

We report a highly efficient green protocol for developing a novel library of 1,2,4-triazole-tagged 1,4-dihydropyridine analogs through the one-pot process from the four-component fusion of the 1H-1,2,4-triazol-3-amine with different chosen aldehydes, diethyl acetylenedicarboxylate, and active methylene compounds in a water medium under microwave irradiation and catalyst-free conditions. Excellent yields (94-97%) of the target products were achieved with high selectivity with a short reaction time (<12 min) at room temperature. The structures of the synthesized pyrimidine analogs were established by NMR and HRMS spectroscopic analysis. Simple workup, impressive yields, no column chromatography, green solvent, rapid reaction, and excellent functional group tolerance are the benefits of this protocol.

A decennary update on applications of metal nanoparticles (MNPs) in the synthesis of nitrogen- and oxygen-containing heterocyclic scaffolds

Heterocycles have been found to be of much importance as several nitrogen- and oxygen-containing heterocycle compounds exist amongst the various USFDA-approved drugs. Because of the advancement of nanotechnology, nanocatalysis has found abundant applications in the synthesis of heterocyclic compounds. Numerous nanoparticles (NPs) have been utilized for several organic transformations, which led us to make dedicated efforts for the complete coverage of applications of metal nanoparticles (MNPs) in the synthesis of heterocyclic scaffolds reported from 2010 to 2019. Our emphasize during the coverage of catalyzed reactions of the various MNPs such as Ag, Au, Co, Cu, Fe, Ni, Pd, Pt, Rh, Ru, Si, Ti, and Zn has not only been on nanoparticles catalyzed synthetic transformations for the synthesis of heterocyclic scaffolds, but also provide an inherent framework for the reader to select a suitable catalytic system of interest for the synthesis of desired heterocyclic scaffold.

Four-Component Fusion Protocol with NiO/ZrO2 as a Robust Recyclable Catalyst for Novel 1,4-Dihydropyridines

Nickel oxide loaded on zirconia (NiO/ZrO₂) as an expedient catalyst is reported for the synthesis of 18 unsymmetrical 1,4-dihydropyridine derivatives. The Lewis acidic nature of the catalyst proved an excellent choice for the one-pot, four-component fusion reaction with excellent yields of 89-98% and a completion time of 20-45 min. Mechanistic studies show that enamine and imine functionalities are the two possible pathways for the formation of 1,4-dihydropyridines with high selectivity. Crystal structures of two novel compounds (5a, 5c) were reported. The catalyst demonstrated reusability up to six cycles. The reaction at room temperature and ethanol as a solvent make this protocol green and economical.

Intercepted-Knoevenagel condensation for the synthesis of unsymmetrical fused-tricyclic 4H-pyrans

4H-Pyrans (4H-Pys) and 1,4-dihydropyridines (1,4-DHPs) are important classes of heterocyclic scaffolds in medicinal chemistry. Herein, an indium(III)-catalyzed one-pot domino reaction for the synthesis of highly functionalized 4H-Pys, and a model of 1,4-DHP is reported. This alternative approach to the challenging Hantzsch 4-component reaction enables the synthesis of fused-tricyclic heterocycles, and the mechanistic studies underline the importance of an intercepted-Knoevenagel adduct to achieve higher chemoselectivity towards these types of unsymmetrical heterocycles.

CuO@Fe2O3 catalyzed C1-alkynylation of tetrahydroisoquinolines (THIQs) via A3 coupling and its decarboxylative strategies

C1-alkynylation of tetrahydroisoquinoline (THIQ) with wide substrate scope was achieved via A3 coupling strategy from the reaction among THIQ, aldehydes and alkynes using CuO@Fe₂O₃ as a nanocatalyst under green reaction conditions.

Copper NPs supported on hematite as magnetically recoverable nanocatalysts for a one-pot synthesis of aminoindolizines and pyrrolo[1,2-a]quinolines

Copper mixed oxide NPs supported on a hematite surface were achieved using a facile hydrothermal method in a single step. The catalytic potential of the Cu@Fe₂O₃ NPs was explored for the synthesis of aminoindolizines and pyrrolo[1,2-a]quinolines.

MoO2Cl2 catalyzed efficient synthesis of functionalized 3,4-dihydropyrimidin-2(1H)-ones/thiones and polyhydroquinolines: recyclability, fluorescence and biological studies

MoO₂Cl₂ catalyzed Biginelli, Hantzsch reactions exploring spectroscopic and biological properties of novel compounds.

CuI nanoparticles mediated expeditious synthesis of 2-substituted benzimidazoles using molecular oxygen as the oxidant

2-Substituted benzimidazoles from o-diaminobenzenes and aldehydes using CuI nanoparticles as a heterogeneous nano-catalyst and O₂ as an oxidant were synthesised in excellent yields.

Facile construction of 3-indolochromenes and 3-indoloxanthenes via EDDF catalyzed one-pot three component reactions

EDDF–ethylene glycol, an ambiphilic catalytic system has been employed for the mild and rapid synthesis of various 3-indolochromenes and 3-indoloxanthenesviaa one-pot MCR. Besides recyclability of the catalyst, the present method circumvents the formation of any by-products.

Design and fabrication of mesoporous heterogeneous basic catalysts

Recent advances in mesoporous solid bases were reviewed, and fundamental principles of how to fabricate efficient basic catalysts were highlighted.

Cu(0)@Al2O3/SiO2 NPs: an efficient reusable catalyst for the cross coupling reactions of aryl chlorides with amines and anilines

The C–N cross coupling reaction of aryl chlorides with various alkyl/aryl amines catalyzed by copper nanoparticles impregnated on alumina/silica support (Cu(0)@Al₂O₃/SiO₂) was investigated and the catalyst showed excellent reactivity and efficacy.

Alginic acid: a highly efficient renewable and heterogeneous biopolymeric catalyst for one-pot synthesis of the Hantzsch 1,4-dihydropyridines

Alginic acid was found to be an efficient, environmentally benign, easily recoverable and low-cost catalyst for clean synthesis of 1,4-dihydropiridine derivatives (DHPs).

Multicomponent diversity-oriented synthesis of symmetrical and unsymmetrical 1,4-dihydropyridines in recyclable glycine nitrate (GlyNO3) ionic liquid: a mechanistic insight using Q-TOF, ESI-MS/MS

Glycine nitrate (GlyNO₃) ionic liquid has been explored for the synthesis of symmetrical and unsymmetrical 1,4-DHPs in good-to-excellent yields with mechanistic studies using Q-TOF and ESI-MS/MS.

Functionalized superparamagnetic Fe3O4 as an efficient quasi-homogeneous catalyst for multi-component reactions

Tetrabutylammonium valinate [NBu₄][Val] ionic liquid functionalized Fe₃O₄ NPs (VSF) was used as an efficient “quasi-homogeneous” catalyst for multi-component synthesis of 1,4-dihydropyridines and 2-amino-4-(indol-3-yl)-4H-chromenes at room temperature.