Shaik Karamthulla

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.

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.

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.

“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.

Ultrasound assisted multicomponent reactions: a green method for the synthesis of highly functionalized selenopyridines using reusable polyethylene glycol as reaction medium

A simple and benign one-pot protocol for the synthesis of 2-amino selenopyridine derivatives 4 has been developed using ultrasound assisted multicomponent reactions of aldehydes, malononitrile and benzeneselenol in polyethylene glycol (PEG-400). Under similar reaction conditions, sterically hindered o,o′-disubstituted aromatic aldehydes provide the corresponding functionalized seleno dihydropyridines 5. In this process in total four new bonds (two C–C, one C–N and one C–Se) forms in one pot.

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.

Microwave-assisted synthesis of novel 2,3-disubstituted imidazo[1,2-a]pyridines via one-pot three component reactions

An expeditious one-pot, metal-free, three-component reaction of arylglyoxals, cyclic 1,3-dicarbonyls and 2-aminopyridines in the presence of molecular iodine under microwave irradiation is reported. A wide variety of 2,3-disubstituted imidazo[1,2-a]pyridine derivatives can be synthesized in good to very good yields using this methodology. The salient features of this methodology are: metal-free, short reaction time, good yields, use of microwave heating and no harmful by-products.

Synthesis of Novel 5,6-Disubstituted Pyrrolo [2,3-d]Pyrimidine-2,4-Diones Via One-Pot Three-Component Reactions

A simple and novel method for the synthesis of 5,6-disubstituted pyrrolo[2,3-d]pyrimidine-2,4-diones has been reported using arylglyoxal-based three-component reactions. Under microwave heating conditions, arylglyoxal, 6-amino uracil, or its derivatives reacts with various thiols in acetic acid medium to provide a series of pyrrolo[2,3-d]pyrimidine-2,4-diones (4) having a thioether and an aryl ring in 5 and 6 positions, respectively. On the other hand reaction of arylglyoxal, amino uracil and malononitrile in place of thiols, provided corresponding 5,6-disubstituted pyrrolo[2,3-d]pyrimidine-2,4-diones (5) with selectively converting one of the -CN to -CONH2 group both in conventional (method A) and microwave heating conditions (method B). This methodology is a simple and efficient protocol for the synthesis of diverse 5,6-disubstituted pyrrolo[2,3-d]pyrimidine-2,4-diones from the readily available starting materials in good yields.