Suman Pal

Imidazole as organocatalyst for multicomponent reactions: diversity oriented synthesis of functionalized hetero- and carbocycles using in situ-generated benzylidenemalononitrile derivatives

The multicomponent reaction of malononitrile, aldehyde and a third reaction partner such as naphthol/4-hydroxycoumarine/2-hydroxynaphthoquinone/kojic acid/enolizable ketone or thiol in the presence of imidazole as an organocatalyst provides very interesting molecular diversity. In an almost neutral reaction medium, this protocol provides easy access to highly functionalized 2-amino-4H-chromenes, dienes and 2-amino pyridines using in situ-generated aryl/alkylylidenemalononitrile derivatives obtained from the reaction of aldehydes and malononitrile along with various nucleophiles under reflux conditions in ethanol. This methodology is useful for the easy access of a wide range of structurally diverse functionalized molecules having potential application in biological systems.

VCl3 catalyzed imine-based multicomponent reactions for the facile access of functionalized tetrahydropyridines and β-amino carbonyls

A simple, mild, and highly efficient method has been developed for the preparation of functionalized tetrahydropyridines and β-amino carbonyls from the multicomponent reactions involving in situ imines and vanadium (III) chloride as a Lewis acid. The multicomponent reaction of two equivalents of aromatic aldehyde, two equivalents of amine, and one equivalent β-keto ester in the presence of catalytic amount of VCl3 provides highly atom economic five-component tetrahydropyridines in very good yields. The same catalyst was found useful for the efficient synthesis of a wide variety of β-amino ketones using direct-type Mannich reaction of aromatic aldehyde, amine, and aromatic ketones. The notable advantages of this method are simple procedure, short reaction time and good yields, and applicable to broad range of substrates.Graphical AbstractVCl3catalyzed imine based-multicomponent reactions for the facile access of functionalized tetrahydropyridines and β-amino carbonylsSuman Pal, Lokman H Choudhury and Tasneem Parvin

A simple and efficient method for the facile access of highly functionalized pyridines and their fluorescence property studies

In this paper, we have described a simple and convenient method for the one-pot multicomponent reaction of aldehydes, malononitrile and thiols in the presence of a catalytic amount of Bronsted base potassium hydroxide for the efficient synthesis of highly functionalized pyridines. The notable features of this protocol are the simple experimental procedure, short reaction time, broad substrate scope and good yields using a catalytic amount of readily available and cheap base. The photophysical behaviours of the synthesized pyridines have been investigated by UV-Vis and fluorescence spectroscopy and some of the synthesized substituted pyridines exhibit promising fluorescence quantum yields.

Molecular iodine catalyzed one-pot multicomponent reactions for the synthesis of dihydrochromeno[4,3-b]pyrazolo[4,3-e]pyridin-6(7H)-ones

A simple and concise method catalyzed by molecular iodine has been reported for the synthesis of a series of dihydrochromeno[4,3-b]pyrazolo[4,3-e]pyridin-6(7H)-ones (1) using a multicomponent domino reaction of aromatic aldehydes, 4-hydroxycoumarin derivatives and 3-aminopyrazoles. The same catalyst was also found useful for the four component reaction of aromatic aldehydes, 4-hydroxycoumarin, benzoylacetonitrile and hydrazine hydrate. The notable advantages of this method are: good yields, no column chromatography, environmentally friendly catalyst and applicability for diversity oriented synthesis of substituted dihydrochromeno pyrazolo pyridin-6(7H)-one scaffolds using both three and four component reactions.

PEG-mediated one-pot multicomponent reactions for the efficient synthesis of functionalized dihydropyridines and their functional group dependent DNA cleavage activity.

Polyethylene glycol (PEG) has been found to be an inexpensive, non-toxic and useful medium for the one pot synthesis of highly functionalized dihydropyridines using multicomponent reactions (MCRs) at room temperature under catalyst free conditions. The notable features of this protocol are: mild reaction condition, applicability to wide range of substrates, reusability of the PEG and good yields. The interaction of the synthesized compounds with pUC19 plasmid DNA was also analyzed. Some of the synthesized compounds showed interesting functional group dependent nuclease activity for plasmid DNA cleavage under physiological conditions.

L-proline catalyzed multicomponent reactions: facile access to 2H-benzo[g]pyrazolo[3,4-b]quinoline-5,10(4H,11H)-dione derivatives

A series of 2H-benzo[g]pyrazolo[3,4-b]quinoline-5,10(4H,11H)-dione derivatives has been synthesized from the three component reactions of 2-hydroxy-1,4-naphthoquinone, aldehydes, and aminopyrazoles in the presence of a catalytic amount of L-proline. This domino reaction proceeds smoothly in good to excellent yields and offers several advantages including no column chromatography, a simple reaction procedure, metal-free reaction conditions and being applicable to a broad range of aldehydes.

One-Pot Multicomponent Reactions for the Efficient Synthesis of Highly Functionalized Dihydropyridines

Abstract An efficient, atom-economic, one-pot protocol has been developed for the synthesis of highly functionalized dihydropyridines via four-component reactions of aromatic aldehydes, arylamines, malononitrile, and dimethylacetylenedicarboxylate in the presence of sodium hydroxide in ethanol. This domino reaction proceeded smoothly in good to excellent yields and offered several advantages, including short reaction time, simple experimental procedure, and applicability to a broad range of substrates. Supplemental materials are available for this article. Go to the publishers online edition of Synthetic Communications® to view the free supplemental file. GRAPHICAL ABSTRACT

“On-water” synthesis of novel trisubstituted 1,3-thiazoles via microwave-assisted catalyst-free domino reactions

A clean, efficient and catalyst-free multicomponent domino reaction of arylglyoxals, cyclic 1,3-dicarbonyls and thioamides in aqueous media under microwave conditions is reported. A wide variety of trisubstituted thiazoles can be synthesized in good to very good yields using this green protocol. The salient features of this methodology are: catalyst-free reaction, water as reaction medium, short reaction time, good yields, use of microwave heating, and no harmful by-products.

Synthesis of novel spiro[indoline-3,7′-pyrrolo[1,2-c]imidazole]-6′-carbonitrile derivatives in water using a regioselective sequential three component reaction

A novel and straightforward method for the synthesis of pharmacologically promising spiro[indoline-3,7′-pyrrolo[1,2-c]imidazole]-6′-carbonitrile derivatives has been developed by a sequential three component one-pot reaction of isatin, malononitrile and hydantoin or thiohydantoin derivatives catalyzed by Et3N in water, an environmentally friendly reaction medium. This method provides clean and efficient access of privileged spirooxindole derivatives tethered with pyrrolizidine moiety from the readily available starting materials.

Multicomponent reactions for facile access to coumarin-fused dihydroquinolines and quinolines: synthesis and photophysical studies

A simple and straightforward method for facile access to coumarin-fused dihydroquinolines (4) has been developed using the microwave-assisted multicomponent reactions of 4-hydroxycoumarin, aldehydes and aromatic amines in water catalyzed by bismuth triflate. Under solvent-free and conventional heating conditions, the same combination provided the corresponding coumarin-fused quinolines (5). An alternative and rapid method for the conversion of (4) to (5) with very good yields was also developed using N-bromosuccinamide. Single-crystal X-ray crystallographic analysis of one of the products (4q) showed that the products are regioselective and that the reactions proceed via 1,2-addition followed by 6π-electrocyclization instead of a Skraup–Doebner–von Miller type reaction. Substituted quinoline carboxylic acid derivatives (7) were synthesized selectively from (4) by ring opening of the coumarin moiety followed by aromatization using NaOH/DMSO under reflux conditions. Considering the presence of the polycyclic conjugated structure of the synthesized compounds 4 and 5 with the coumarin moiety, preliminary photophysical studies were carried out and promising quantum yields were observed along with a maximum quantum yield (∅f = 0.65) for 4j.