Shweta Rastogi

A Convenient K2CO3 Catalysed Regioselective Synthesis for Benzopyrano[4,3-c]pyrazoles in Aqueous Medium

This synthetic approach features heterocondensation reaction between in situ generated 3-arylidene-2,4-chromanediones and N-substituted hydrazine moiety avoiding the use of organic solvents at any stage. Water as solvent is taken for the synthesis of selective benzopyranopyrazole derivatives under microwaves (MWs). Hydroxy coumarin moiety is employed for this ecofriendly strategy.

Reaction of Coumarin Derivatives with Nucleophiles in Aqueous Medium

A series of heterocycles was synthesized by the reaction of α,β -unsaturated ketones of benzopyrans or coumarins with various nucleophiles in aqueous medium bearing two points of diversity. Compared to an identical library generated by conventional parallel synthesis, a microwaveassisted procedure dramatically decreased reaction times from hours to minutes, and yields of products and intermediates were improved remarkably. This synthetic approach is ecofriendly in nature which features water as solvent, microwave irradiation, and usage of a “green” catalyst (K2CO3).

An aqua mediated facile synthesis of conformationally restricted p olycyclic dihydropyridines

An economically and environmentally benign synthesis of 4-substituted-dihydropyridines (DHPs) is described from readily accessible 4-hydroxy coumarin with aldehydes and ammonium nitrate that are accelerated by exposure to microwaves. The reaction completes within a few minutes with good yields. The mechanistic detail of methodology includes Michael type addition of �-aminobenzopyran-2-one across the double bond of arylidine formed by the condensation of 4hydroxycoumarin with aldehyde in aq. medium. The main advantages of the protocol reported here is absence of use of strong acid or expensive catalyst, good yields, easy work-up and almost no effluent generation.

Solvent-free synthesis of 2,4,6-triaryl pyridines

A modified method to prepare 1,3,5-triarylpyridines by a [3+2+1] ring annulation reaction is described. Three-component condensation of neat reactants when subjected to microwaves afforded the required product in shorter reaction time with higher yield in comparison to conventional methodologies. The microwave accelerated reaction technique without external solvent renders the whole synthesis into a truly ecofriendly protocol.

A Novel Route to the Niementowski Reaction

The Niementowski reaction has been extended to synthesize 3-substituted/2,3-disubstituted4(3H)quinazolinones instead of the 2-substituted derivatives. The methodology is environmentally benign and completely eliminates the need of solvent from the reaction. Neat reactants were cyclocondensed under microwaves to afford, in good yield, the desired product in less irradiation time as compared to the classical technique. The reaction time was reduced from hours to minutes along with yield enhancement. The rate enhancement and high yield are attributed to the coupling of solvent-free conditions with microwaves.