A novel synthesis of 1,3,5-trisubstituted pyrazoles through a spiro-pyrazoline intermediate via a tandem 1,3-dipolar cycloaddition/elimination

Tetrahedron Letters

Volumn 50, Issue 3, 2009, Pages 291-294

  Dadiboyena, Sureshbabu ^a   Valente, Edward J ^b   Hamme II, Ashton T ^a  

^a Jackson State University   (United States)

^b MISSISSIPPI COLLEGE   (United States)

Author keywords

Cycloaddition; Heterocycles; Regioselectivity; Ring fragmentation; Spirocycles; Tandem reactions

Indexed keywords

2 METHYLENE 1,3,3 TRIMETHYLINDOLINE; ALKENE; HYDRAZONE DERIVATIVE; IMINE; NITRILE; PYRAZOLE DERIVATIVE; PYRAZOLINE DERIVATIVE; SPIRO COMPOUND; UNCLASSIFIED DRUG;

ARTICLE; CHEMICAL STRUCTURE; CYCLIZATION; CYCLOADDITION; ELIMINATION REACTION; HUISGEN CYCLIZATION; RING OPENING; SYNTHESIS; X RAY CRYSTALLOGRAPHY;

EID: 57149131220     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/j.tetlet.2008.10.145     Document Type: Article

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12. General cycloaddition procedure: A solution of the 2-methylene-1,3,3-trimethylindoline (3 mmol) and the hydrazonyl chloride (3 mmol) in 10 mL of either dry chloroform or dichloromethane was treated with triethylamine (0.46 mL, 3.3 mmol). The reaction mixture was stirred at rt until the disappearance of the starting materials, as evidenced by TLC. After the reaction was complete, the solvent was evaporated under reduced pressure. For pyrazoles 4, 5, and 6, the crude products were purified by triturating with hexanes. For Spiro-pyrazolines 8, 9, and 10, the crude products were purified by flash column chromatography over silica gel by using 4:1, 9:1, and 7:3 hexanes-ethyl acetate eluant systems, respectively.
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14. Structural information for pyrazole (4) has been deposited with the CCDC as 701051, available free of charge from www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CambridgeCrystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033).
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16. +): 436.1347; found: 436.1344.