L-Proline as an efficicent catalyst for the multi-component synthesis of 6-amino-4-alkyl/aryl-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles in water

Tetrahedron Letters

Volumn 52, Issue 25, 2011, Pages 3228-3231

  Mecadon, Hormi ^a   Rohman, Md Rumum ^a   Kharbangar, Iadeishisha ^a   Laloo, Badaker M ^a   Kharkongor, Icydora ^a   Rajbangshi, Mantu ^a   Myrboh, Bekington ^a  

^a NORTH EASTERN HILL UNIVERSITY   (India)

Author keywords

Environmentally benign; Four component reaction; l Proline; Water

Indexed keywords

6 AMINO 4 ALKYL ARYL 3 METHYL 2,4 DIHYDROPYRANO[2,3 C]PYRAZOLE 5 CARBONITRILE; ACETOACETIC ACID; ACETOACETIC ACID ETHYL ESTER; ALDEHYDE; ALUMINUM OXIDE; BASIC ALUMINUM OXIDE; CYANIDE; GAMMA ALUMINUM OXIDE; HYDRAZINE; KF ALUMINUM OXIDE; MALONONITRILE; PROLINE; UNCLASSIFIED DRUG; WATER;

ARTICLE; CATALYST; CHEMICAL COMPOSITION; CHEMICAL REACTION KINETICS; COMPARATIVE STUDY; ENVIRONMENTAL FACTOR; FOUR COMPONENT SYNTHESIS; SYNTHESIS;

EID: 79956214376     PISSN: 00404039     EISSN: 18733581     Source Type: Journal    
DOI: 10.1016/j.tetlet.2011.04.048     Document Type: Article

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25. We thank the referee for suggesting this mechanism.
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27. General experimental procedure for the synthesis of 6-amino-4-alkyl/aryl- 3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles (5). Method A: to a pre-stirred mixture of ethyl acetoacetate (1) (0.26 mL, 2.0 mmol), hydrazine hydrate (2) (0.13 mL, 2.5 mmol) in water (4 mL) was added aldehydes (3) (2.0 mmol) and malononitrile (4) (0.13 g, 2.0 mmol) followed by l-proline (10 mol %). The reaction mixture was then refluxed for 10-20 min. On completion of the reaction (monitored by TLC), it was cooled. The solid mass was filtered through a sintered funnel and washed thoroughly with water. The crude residue was crystallized from ethanol/water (9.5:0.5), or purified by column chromatography over silica gel (100-200 mesh) using methanol/dichloromethane (2:8) as the eluent to afford pure compound 5. The same procedure was followed when γ-alumina, basic alumina, and KF-alumina were employed as catalysts. On completion of the reaction (monitored by TLC), water was evaporated in vacuo. Work-up was carried out after diluting the residue with boiling mixture of ethyl acetate and methanol (7:3) and filtering off the catalyst followed by removal of the combined filtrate to give the crude mass and purified by crystallization or column chromatography as mentioned above. Method B: method A was followed except for the ethanol (4 mL) used as solvent. Work-up was carried out by filtering the reaction mass and washing thoroughly the residue with boiling mixture of ethyl acetate and methanol (7:3) followed by removal of the combined filtrate under vacuum to give the crude mass, which was purified by crystallization or column chromatography as mentioned above.
28. 4O: C, 60.53; H, 6.47; N, 25.67%; found: C, 60.41; H, 6.39; N, 25.40.