One-step, synthesis of Hantzsch esters and polyhydroquinoline derivatives using new organocatalyst

Construction of 1,4-Dihydropyridines: The Evolution of C4 Source

The field of cascade cyclization for the construction of 1,4-dihydropyridines (1,4-DHPs) has been continuously expanding during the last decades because of their broad-spectrum biological and synthetic importance. To date, many methods have been developed, mainly including the Hantzsch reaction, Hantzsch-like reaction and newly developed cascade cyclization, in which various synthons have been successively developed as C4 sources of 1,4-DHPs. This review presents the cascade cyclization synthesis strategy for the construction of 1,4-DHPs according to various C4 sources from carbonyl compounds, alkenyl fragments, alcohols, aliphatic amines, glycines and other C4 sources.

Organocatalyzed Heterocyclic Transformations In Green Media: A Review

Background:

Since the discovery of metal-free catalysts or organocatalysts about twenty years ago, a number of small molecules with different structures have been used to accelerate organic transformations. With the development of environmental awareness, to obtain highly efficient scaffolds, scientists have directed their studies towards synthetic methodologies that minimize or preferably eliminate the formation of waste, avoid toxic solvents and reagents and use renewable starting materials as far as possible.

Methods:

In this connection, the organocatalytic reactions providing efficiency and selectivity for most of the transformations have become an endless topic in organic chemistry since several advantages from both practical and environmental standpoints. Organocatalysts contributing to the transformation of reactants into products with the least possible waste production, have been serving the concept of green chemistry.

Results and Conclusion:

Organocatalysts have been classified based on their binding capacity to the substrate with covalent or noncovalent interactions involving hydrogen bonding and electrostatic interaction. Diverse types of small organic compounds including proline and its derivatives, phase-transfer catalysts, (thio)urease, phosphoric acids, sulfones, N-oxides, guanidines, cinchona derivatives, aminoindanol, and amino acids have been utilized as hydrogen bonding organocatalysts in different chemical transformations.

Amine-functionalized graphene oxide nanosheets (AFGONs): an efficient bifunctional catalyst for selective formation of 1,4-dihydropyridines, acridinediones and polyhydroquinolines

We report here selective formation of functionalized 1,4-dihydropyridines (DHP), acridinediones and polyhydroquinolines in high yields using amine-functionalized graphene oxide nanosheets (AFGONs) as the bifunctional catalyst. The method overcomes the limitations of previous protocols affording a mixture of DHP and pyridine derivatives using graphene oxide as the catalyst. The mild reaction conditions are found compatible with a wide range of functional groups. It is presumed that a cooperative effect between the acidic and basic functionalities present in AFGONs may have exerted high catalytic efficiency as well as prevented further oxidation to pyridine derivatives. A plausible mechanism is proposed on the basis of some control experiments. The reactions can be scaled up conveniently, and the catalyst can be recycled for five consecutive runs without loss of its activity.

Introduction of a novel nanosized N-sulfonated Brönsted acidic catalyst for the promotion of the synthesis of polyhydroquinoline derivatives via Hantzsch condensation under solvent-free conditions

In this research NS-C₄(DABCO-SO₃H)₂)·4Cl as a new nano sized N-sulfonic acid was prepared and characterized using different types of methods including FT-IR, ¹H NMR, ¹³C NMR, mass, XRD, TGA, SEM and AFM analysis.

Synthesis and characterization of novel silica-coated magnetic nanoparticles with tags of ionic liquid. Application in the synthesis of polyhydroquinolines

A novel, green and recoverable silica-coated magnetic nanoparticle immobilized ionic liquid, was designed, synthesized, fully characterized and was used for the synthesis of polyhydroquinoline derivatives.

Ultrasound-mediated synthesis of 4-substituted 1,4-dihydropyridine-3,5-dicarboxylates catalyzed by 1-carboxymethyl-3-methylimidazolium tetrafluoroborate under solvent free condition

4-Substituted 1,4-dihydropyridine-3,5-dicarboxylates (4) have been synthesized by the solvent-free reaction of aldehyde, methyl propiolate and ammonium carbonate catalyzed by ionic liquid 1-carboxymethyl-3-methylimidazolium tetrafluoroborate under ultrasonic irradiation. The effects of changes in the ultrasonic power, temperature, catalysts and reactants on the synthesis of 4-substituted 1,4-dihydropyridine-3,5-dicarboxylates (4) are discussed. With the optimized reaction conditions, various aldehydes were used to synthesize 1,4-dihydropyridines (4) under the influence of ultrasound irradiation. Compared with the conventional thermal methods, the remarkable advantages of this method are the simple experimental procedure, shorter reaction time (2-10min) and high yield of product (76-95%). Furthermore, the green catalytic system can be recycled specific times without significantly decreasing the yields and reaction rates.