Pragati Rai

Synthesis of fused pyridines in the presence of thiamine hydrochloride as an efficient and reusable catalyst in aqueous conditions

Efficient and straightforward synthesis of fused pyridine derivatives was achieved from electron-rich amino heterocycles and Knoevenagel products derived from aldehyde and malononitrile under aqueous media at 90 °C in the presence of thiamine hydrochloride as a reusable, green catalyst. The strategy in this protocol involves addition on an activated olefinic bond formed in situ by Knoevenagel condensation between an aromatic aldehyde and an active methylene compound. The Michael product on subsequent cyclo condensation yielded fused pyridine in high yield. It offers several advantages such as inexpensive, easily available and recyclable catalyst, simple operational procedure, excellent yield and use of aqueous medium that is considered to be relatively eco-friendly. Vitamin B1 was recovered and reused thrice.

Chitosan: an efficient promoter for the synthesis of 2-aminopyrimidine-5-carbonitrile derivatives in solvent free conditions

Reusable chitosan without any post-modification, with active –NH2 and –OH groups, was found to be a highly efficient and renewable heterogeneous catalyst for the rapid and convenient synthesis of 2-aminopyrimidine-5-carbonitrile derivatives from guanidines, aldehydes and cyanoketones, under mild reaction conditions at 85 °C in good yields. Undoubtedly this methodology gives a facile and straightforward pathway to construct 2-aminopyrimidine-5-carbonitrile derivatives in an eco-friendly fashion.

Molecular iodine catalysed domino cyclization in aqueous medium: a simple and efficient synthetic route to 1,4-dihydropyridazines

A facile, efficient and environmentally friendly approach has been developed for the diverse synthesis of 1,4-dihydropyridazines from (E)-2-benzylidene-1-phenylhydrazine and α,β-unsaturated aldehyde under aqueous condition using molecular iodine as a green and recoverable catalyst. This procedure features low cost and easily available starting materials, an inexpensive and recoverable catalyst, short reaction time, reliable scalability, excellent yield and mild reaction conditions, as well as use of aqueous medium. The scope of this method was thoroughly explored under three different reaction conditions resulting in the generation of a library of title compounds. In view of the various advantages of the present investigation, this methodology gives a convenient and straightforward pathway to construct 1,4-dihydropyridazines in an eco-friendly fashion.

Sustainable construction: admicellar catalysed synthesis of pyrimido[4,5-b]quinolines in an aqueous system

A simple and highly efficient strategy has been documented for the rapid and convenient synthesis of 1-methyl-5-phenylbenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone from aldehydes, 2-hydroxynaphthalene1,4dione and 6-aminouracil in the presence of nano ZnO under an aqueous admicellar system at 80 °C. Results show that nano ZnO is a potential catalyst for the synthesis of pyrimido[4,5-b]quinoline. Nano ZnO was recovered and reused efficiently several times for the synthesis of the desired product which is an essential parameter of green synthesis. The reported method represents an eco-friendly alternative to classical protocols. Nano size of ZnO was confirmed by EDS, transmission electron microscopy (TEM) and XRD techniques.

S-Nanoparticle/SDS: an efficient and recyclable catalytic system for synthesis of substituted 4H-pyrido[1,2-a]pyrimidines in aqueous admicellar medium

A novel and green methodology has been described for the synthesis of substituted 4H-pyrido[1,2-a]pyrimidines under admicellar catalysis by sulfur nano-particles that can be efficiently recycled up to the fifth run. The greenness of the procedure was well established, as organic solvent was avoided in the reaction media as well as in the preparation of catalyst.

ZnO nanoparticle–β-cyclodextrin: a recyclable heterogeneous catalyst for the synthesis of 3-aryl-4H-benzo[1,4]thiazin-2-amine in water

A combination of ZnO nanoparticles and β-cyclodextrin was used as an efficient and green catalytic system for the synthesis of 3-aryl-4H-benzo[1,4]thiazin-2-amine via a one-pot, three-component reaction of an o-amino thiophenol, aromatic aldehydes and isocyanides in good to excellent yields at 60 °C in water. The nano size of ZnO was confirmed by transmission electron microscopy (TEM), XRD and UV-visible spectral techniques. A high catalytic activity and easy recovery and reuse for several cycles with consistent activity are additional eco-friendly attributes of this catalytic system.

MoO2Cl2(DMF)2 catalyzed microwave assisted reductive cyclisation of nitroaromatics into dibenzodiazepines

The paper describes a gentle and highly efficient protocol for the synthesis of dibenzodiazepines by reductive cyclisation of nitroaniline to dibenzodiazepines under microwave irradiation catalyzed by MoO2Cl2(DMF)2 involving Ph3P as reducing agent. This synergic approach results in the transformation of nitroaromatics into dibenzodiazepines in high yield and is applicable to the construction of a wide variety of dibenzo(di/ox)azepines and other structurally related heterocycles.

A green route for the synthesis of pyrrolo[2,3-d]pyrimidine derivatives catalyzed by β-cyclodextrin

Herein, we present the synthesis of pyrrolo[2,3-d]pyrimidine derivatives, which are important heterocyclic scaffolds in the field of synthetic and pharmaceutical research, via biomimetic catalysis. This strategy involves the use of β-cyclodextrin as a reusable promoter and water as an eco-friendly reaction medium. The merits of this protocol are high atom economy, mild reaction conditions, good yields of desired products in short reaction times, and reusable reaction medium.

Oligosaccharide Assisted Approach: An Efficient and Facile Access to Isochromeno [4,3-b] Indoles Derivatives in the Presence of Beta Cyclodextrin

A completely eco-friendly and straightforward protocol for the biologically important isochromeno[4,3-b]indoles derivatives has been developed employing beta cyclodextrin in aqueous medium. This documented strategy includes the elimination of hazardous catalysts and volatile organic solvents. Additionally this protocol highlights environmentally benign reaction conditions, short reaction times, operational simplicity, easy workup and purification procedure and good yield of products.Graphical Abstract