K. Aswin

Thiourea dioxide: An efficient and reusable organocatalyst for the rapid one-pot synthesis of pyrano[4, 3- b ]pyran derivatives in water

Abstract A series of pyrano[4,3- b ]pyran derivatives have been synthesized in excellent yields by the reaction of aromatic aldehydes with malononitrile or cyanoacetate and 4-hydroxy-6-methylpyran-2-one in water at 80 °C, with the transformation being catalyzed by an aqueous solution of thiourea dioxide (TUD). Upon completion of the reaction, the product was isolated by filtration or extraction and the remaining aqueous TUD solution could be reused several times without any discernible impact on its catalytic activity. This procedure offers several advantages over existing procedures, including high yields, operational simplicity, the use of a non-toxic catalyst and solvent, short reaction time and minimum pollution of the environment, making it a useful and attractive process for the preparation of pyrano[4,3- b ]pyran derivatives.

Aqueous media preparation of 2-amino-4,6-diphenylnicotinonitriles using cellulose sulfuric acid as an efficient catalyst

A convenient approach to the synthesis of 2-amino-4,6-diphenylnicotinonitriles via four-component reaction of aromatic aldehydes, acetophenone derivatives, malononitrile and ammonium acetate is described. The reactions were done in water as solvent using cellulose sulfuric acid as catalyst. This simple protocol offer advantages such as shorter reaction times, simple work-up procedure, excellent yields and catalyst recovery.

An eco-friendly catalytic route for one-pot synthesis of 2-amino-6-(2-oxo-2Hchromen-3-yl)-4-arylnicotinonitrile derivatives by silica-supported perchloric acid (HClO4–SiO2) under solvent-free conditions

A facile and environmentally benign synthesis of some 2-amino-6-(2-oxo-2H-chromen-3-yl)-4-arylnicotinonitrile derivatives from the reaction of 3-acetylcoumarin, aromatic aldehydes, and malononitrile under solvent-free condition in the presence of silica-supported perchloric acid (HClO4–SiO2) is described. The ability to reuse the catalyst, the high yields, and ease of purification are the important features of this process.

Silica-supported perchloric acid (HClO4–SiO2): a mild, reusable and highly efficient heterogeneous catalyst for multicomponent synthesis of 1,4-dihydropyridines via unsymmetrical Hantzsch reaction

Facile synthesis of some 1,4-dihydropyridine derivatives via Hantzsch reaction of 5,5-dimethyl-1,3-cyclohexanedione (dimedone), 1,3-diphenyl-2-propen-1-one derivatives and ammonium acetate under solvent-free condition in the presence of silica-supported perchloric acid (HClO4–SiO2) is described. The catalyst is easily prepared, stable, reusable and efficient under the reaction conditions.

Pentafluorophenylammonium triflate (PFPAT) catalyzed facile construction of substituted chromeno[2,3-d]pyrimidinone derivatives and their antimicrobial activity.

A new, simple thermally efficient and solvent-free condensation of 2-amino-3-cyano-6-methyl-4-phenyl-4H-pyran-5-ethylcarboxylate derivatives with coumarin-3-carboxylic acid employing pentafluorophenylammonium triflate (PFPAT) as an inexpensive organocatalyst for the synthesis of a series of ethyl 4,5-dihydro 7-methyl-2-(2-oxo-2H-chromen-3-yl)-4-oxo-5-aryl-3H-chromeno[2,3-d]pyrimidine-6-carboxylate derivatives is described. This method has the advantages of high yields, a cleaner reaction, simple methodology, short reaction times, easy workup, and greener conditions. All the compounds were evaluated for their in vitro antimicrobial activity against different bacterial and fungal strains.

Reusable silica-bonded S-sulfonic acid catalyst for three-component synthesis of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromenes and 2-amino-4H-pyrans in aqueous ethanol

Silica-bonded S-sulfonic acid (SBSSA)-catalyzed, facile, one-pot, three-component coupling of 5,5-dimethyl-1,3-cyclohexanedione (dimedone) or 5,5-dimethyl-1,3-cyclohexanedione, aromatic aldehydes, and malononitrile at reflux temperature is described for preparation of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene derivatives. 2-Amino-3-cyano-6-methyl-4-phenyl-4H-pyran-5-ethylcarboxylate derivatives can also be prepared in good yield under the same experimental conditions by use of ethyl acetoacetate, aldehydes, and malononitrile. The catalyst, silica-bonded S-sulfonic acid, was reused and recycled without any loss of activity or product yield.

An appropriate one-pot synthesis of 3,4-dihydropyrano[c]chromenes and 6-amino-5-cyano-4-aryl-2-methyl-4H-pyrans with thiourea dioxide as an efficient, reusable organic catalyst in aqueous medium

Abstract An efficient, convenient method for the synthesis of 3,4-dihydropyrano[3,2-c]chromene derivatives by one-pot, three-component reaction of aldehydes, malononitrile/cyanoacetate, and 4-hydroxycoumarin in the presence of a catalytic amount of thiourea dioxide, an efficient, reusable organic catalyst, is described. A variety of 3,4-dihydropyrano[3,2-c]chromene derivatives were obtained, and 6-amino-5-cyano-4-phenyl-2-methyl-4H-pyran-3-carboxylic acid ethyl esters were obtained by condensation of aldehydes, malononitrile and ethyl acetoacetate in the presence of thiourea dioxide in aqueous medium. The salient features of the protocol are mild reaction conditions, high yields, short reaction time, safety, high atom-economy, eco-friendly standards, easy isolation of products, no column chromatographic separation and reusability of the catalyst.

An efficient one-pot synthesis of 1,4-dihydropyridine derivatives through Hantzsch reaction catalysed by melamine trisulfonic acid

Abstract The classical Hantzsch reaction is one of the simplest and most economical methods for the synthesis of biologically important and pharmacologically useful 1,4-dihydropyridine derivatives. Melamine trisulfonic acid (MTSA) under thermal condition is proven to act as a very efficient catalyst for a one-pot synthesis of 2-amino-4-phenyl-3-cyano-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline derivatives in excellent yields from aldehydes, dimedone, malononitrile and ammonium acetate under solvent-free conditions. The present environmentally benign procedure for the synthesis of 1,4-dihydropyridines is suitable for library synthesis and it will find application in the synthesis of potent biologically active molecules. The process presented here is operationally simple, environmentally benign and has excellent yield. Furthermore, the catalyst can be recovered conveniently and reused efficiently.

Synthesis and in vitro microbiological evaluation of novel series of 8-hydroxy-2-(2-oxo-2 H -chromen-3-yl)-5-phenyl-3 H -chromeno [2,3- d ]pyrimidin-4(5 H )-one derivatives catalyzed by reusable silica-bonded N -propylpiperazine sulfamic acid

Abstract Silica-bonded propylpiperazine-N-sulfamic acid is employed as a recyclable catalyst for the synthesis of a series of 8-hydroxy-2-(2-oxo-2H-chromen-3-yl)-5-phenyl-3H-chromeno[2,3-d]pyrimidin-4(5H)-one derivatives by the condensation of 2-amino-3-cyano-7-hydroxy-4-phenyl-4Hchromene derivatives with coumarin-3-carboxylic acid. The heterogeneous catalyst was used for four runs. This method has the advantages of high yields, a cleaner reaction, simple methodology, short reaction times, and easy work-up. All the compounds were evaluated for their in vitro antimicrobial activity against different bacterial and fungal strains.

Poly(4-vinylpyridinium)hydrogen sulfate: A novel and efficient catalyst for the synthesis of 13-aryl-indeno[1,2-b]naphtha[1,2-e]pyran-12(13H)-ones under solvent-free conditions

Abstract An facile and efficient protocol for the synthesis of 13-aryl-indeno[1,2- b ]naphtha[1,2- e ]pyran-12(13 H )-ones has been developed that proceeds via the one-pot three-component sequential reaction of an aromatic aldehyde with β-naphthol and 2 H -indene-1,3-dione under solvent-free conditions in the presence of a poly(4-vinylpyridinium)hydrogen sulfate (P(4-VPH)HSO 4 ) catalyst. The catalyst can be reused several times, making this procedure facile, practical, and sustainable. The simple experimental procedure, solvent-free reaction conditions, use of an inexpensive catalyst, short react time, and excellent yields are some of the major advantages of this methodology.