Kavita Singhal

One-pot Green Synthesis for Pyrimido[4,5-d]pyrimidine Derivatives

Abstract Water has been used efficiently as a solvent for the reaction of barbituric acid, aldehyde and urea or thiourea to yield pyrimido[4,5-d]pyrimidines. This environmentally benign procedure leads to high yields of products of greater purity in a single step using water.

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.

Synthesis for Pyridopyrimidinones

Abstract An improved clean methodology has been developed for the synthesis of pyrido[2,3‐d]pyrimidin‐4‐ones through a simple one‐pot reaction of chalcones, ketones, and ammonium acetates via a [3+2+1] ring annulation. This dry media methodology, where the three components absorbed over solid inorganic support under microwave irradiation, afforded the desired product in a short reaction time.

Molecular iodine: A highly efficient catalyst for the regioselective synthesis of novel 1,2,4-triazepines

Triazepines represent a class of reactive seven membered heterocycles with three nitrogen atoms. Like azepines and diazepines, triazepines are also associated with various pharmacological properties. Out of four isomeric systems [1,2,3], [1,2,4], [1,2,5] and [1,3,5], 1,2,4-triazepine core has received utmost attention because of the diverse applications associated with their derivatives. 1,2,4-Triazepines with amino group at position-3 have been of special interest because of the antifungal and antibacterial properties associated with them. Their thioxo analogues have also been reported to be associated with some interesting properties. Monocyclic triazepines are much less studied than their condensed analogues. Very few methods of their synthesis have been cited in literature viz. by reaction of bis-acetylenic ketones with amidrazones, β-isothiocyanato pentane-2-ones with hydrazone hydrate, nitrileimines with β-alanine and from α,β-unsaturated ketones via cyclization of their isothiocyanate derivatives. However, all these procedures are multistep and suffer from some drawbacks viz. harsh reaction conditions such as long refluxing hours, use of strong acid or base catalysts and formation of side products resulting in low yields. Since 3-amino-1,2,4-triazepine core is an important biodynamic lead and can further be used as a synthon to generate medicinally relevant imidofused triazepines, therefore, the development of a simple, efficient eco-benign and low-cost protocol seemed warranted. Recently, molecular iodine has received considerable attention as an inexpensive, non-toxic, readily available catalyst for various organic transformations affording the corresponding products with high selectivity in excellent yields. We have already reported its efficient use for the synthesis of some bioactive heterocycles such as imidazoles and diazepines. In continuation to our efforts towards the application of molecular iodine for various organic transformations, we herein wish to report a novel, one-pot methodology that leads to regioselective synthesis for the titled compounds. This protocol involves a reaction between α,β-unsaturated ketones and aminoguanidine hydrochloride using iodine as a powerful catalyst. The reaction is modular, facile and high yielding and hence constitutes an example of “click chemistry” wherein compounds 1a-h are spring loaded towards multiple nucleophilic additions to afford the products expeditiously.

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.