Pratibha Rai

An environmentally friendlier approach—ionic liquid catalysed, water promoted and grinding induced synthesis of highly functionalised pyrazole derivatives

Grinding induced synthesis of highly functionalised pyrazoles derivatives by use of malanonitrile, phenyl hydrazine and diversified aldehyde. Ionic liquid is used as a catalyst with water, and no by-products form. A high yield is obtained and simple handling are the benefits of the adopted route, and this route fulfils all shades of green chemistry.

Efficient iodine-catalyzed one pot synthesis of highly functionalised pyrazoles in water

An efficient one pot multi-component sequential reaction of phenyl hydrazine, malanonitrile and a diverse range of aldehydes to afford highly functionalised pyrazoles is reported. The reaction proceeds in water using molecular iodine as a catalyst, with no by-product formation, and involves simple operation requiring no column chromatography. Thus, this protocol fulfils all of the criteria that define green chemistry.

Visible light induced, catalyst free, convenient synthesis of chromene nucleus and its derivatives using water–ethanol mixture as a solvent

A highly efficient, green, eco-friendly, one pot protocol has been demonstrated for the synthesis of 2-imino-2H-chromene-3-carbonitrile (3), 2-aminochromene (4) and chromeno(2,3-b)pyridines (5). The synthesis of the chromene nucleus has been carried out under visible light irradiation in a water–ethanol mixture at room temperature using salicylaldehyde and malononitrile in different proportions. The adopted method shows significant advantages such as mild and clean reaction conditions, eco-friendly procedures, absence of catalysts and a short reaction time. This protocol involves the use of CFL as the visible light source and shows high selectivity in the presence of a mixture of ethanol and water. The reaction proceeds with good to excellent yield.

Visible light triggered, catalyst free approach for the synthesis of thiazoles and imidazo[2,1-b]thiazoles in EtOH : H2O green medium

The development of a visible light promoted, mild and greener approach for the synthesis of highly functionalized thiazoles and imidazo[2,1-b]thiazoles under photochemical activation in EtOH : H2O green medium is demonstrated. The characteristic feature of the present protocol is the utilization of visible light (an omnipresent, nontoxic, environmentally benign and inexpensive reagent) to form C–S and C–N bonds and circumvent the use of catalysts or photosensitizers. The reported protocol is the first example of visible light promoted synthesis of thiazoles and imidazo[2,1-b]thiazoles with various attractive features like being catalyst free, eco-efficient and possessing cost effectiveness, short reaction time, excellent yields and sustainability to fulfill the parameters of green chemistry.

Chitosan/ionic liquid forms a renewable and reusable catalyst system used for the synthesis of highly functionalized spiro derivatives

Chitosan, a reusable heterogeneous catalyst, can be combined with an ionic liquid as a green solvent to generate a highly efficient catalyst system for our densely functionalised and diversified target molecule. The reaction is completed with a good to excellent yield. This procedure demonstrates an eco-friendly catalyst system and eliminates the use of toxic transition metal catalysts, bases and volatile organic solvents, which adversely affect the environment and human beings.

Molecular iodine: a green and inclusive catalyst for the synthesis of highly functionalized 1,3,5-trisubstituted pyrazoles in aqueous medium

A library of 1,3,5-trisubstituted pyrazoles was synthesized in excellent yields from the reaction of aldehyde, phenylhydrazine and alkynes in the presence of iodine via an eco-friendly, simple process performed in aqueous medium. This single pot transformation generates new CN, C–C, C–N bonds and proceeds by a domino reaction involving the formation of Schiff base, Mannich addition and finally intramolecular cyclisation.

Oxidative organophotoredox catalysis: a regioselective synthesis of 2-nitro substituted imidazopyridines and 3-substituted indoles, initiated by visible light

We have established a mild, metal-free, one pot, visible light-catalyzed procedure for a highly regioselective synthesis of 2-nitro-3-arylimidazo [1,2-a] pyridines via nitroalkene and 2-aminopyridine under an open atmosphere involving a photoredox catalyst, Eosin Y, which is an inexpensive organic dye that has been employed as a photo sensitizer in the conversion. This protocol serves as an example of green chemistry, due to the fact that molecular oxygen and visible light have been utilized effectively for the transformation. The procedure involves intramolecular C–N heterocyclization, followed by aerobic oxidation and C–C bond formation at room temperature. This green protocol has also been successfully extended to the regioselective synthesis of 3-substituted indoles via indole and nitroalkene by a free radical pathway.

β-Cyclodextrin: A Biomimetic Catalyst used for the Synthesis of 4H-chromene-3-carbonitrile and Tetrahydro-1H-xanthen-1-one Derivatives

An efficient and facile protocol has been documented for the synthesis of 4H-chromene and xanthen-1-one derivatives via a three component one pot reaction of salicyladehyde, malononitrile/dimedone and indole utilizing biomimetic catalyst. Affiliation between biomimetic and organocatalyst exhibits a versatile and high catalytic activity emerging to be a sustainable alternative to other catalysts. The significant features of this protocol are compatibility with various types of indole and active-methylene compound, accomplishment of high yields, cleaner reaction condition and avoidance of the use of costly catalysts. Recyclability of β-cyclodextrin a “biomimetic catalyst” is a significant feature of this protocol.Graphical Abstract

An eco-efficient, domino synthesis of highly functionalized spiro-oxindole derivatives catalyzed by an organocatalyst in an aqueous medium

Here we report a multicomponent domino reaction for the synthesis of a combinatorial library of spiro-oxindole derivatives with a pyrido[2,3-d]pyrimidine moiety by a one pot, eco-efficient three component reaction involving isatin, 6-aminouracil and acetyl acetone which is catalyzed by an organocatalyst in water as the reaction medium. A heterocyclic molecule which contains a highly functionalized bioactive spiro-oxindole and a pyrido[2,3-d]pyrimidine ring in one nucleus is very important due to its bioactive nature. This method avoids the use of costly and toxic catalysts and organic solvents which show a number of side effects on the environment and human beings. The simplicity and versatility of this eco-efficient method is described.

A green and clean pathway: one pot, multicomponent, and visible light assisted synthesis of pyrano[2,3-c]pyrazoles under catalyst-free and solvent-free conditions

A mild, eco-efficient and metal-free synthetic protocol for the production of biologically significant scaffold dihydropyrano[2,3-c]pyrazoles via reaction between ethylacetoacetate (1), hydrazine hydrate (2), aromatic aldehydes (3) and malononitrile (4) as reactants and exploiting visible light as a reaction promoter has been developed. Cost effectiveness, nontoxicity, being catalyst-free and solvent-free, the easy-availability of reactants and non-involvement of specific glasswares and a photo-reactor system are some of the significant traits of the present protocol. The scope of the current methodology is further extended by using diethyl acetylene dicarboxylate (6) as a reactant in place of ethylacetoacetate.