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Synfacts 2008(11): 1150-1150  
DOI: 10.1055/s-0028-1083488
Synthesis of Heterocycles
© Georg Thieme Verlag Stuttgart ˙ New York

AgNO3-Catalyzed 5-endo-dig Cyclizations to Form Pyrazole N-Oxides and Pyrazoles

Contributor(s): Victor Snieckus, Johnathan Board
S. J. Hayes, D. W. Knight*, M. O’Halloran, S. R. Pickering
Cardiff University, GSK, Irvine, UK
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Publication History

Publication Date:
23 October 2008 (online)

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Significance

Reported is the silver nitrate catalyzed 5-endo-dig cyclization of N-nitrosaminepropargylamines to form pyrazole N-oxides in excellent yields. Deoxygenation of these N-oxides was achieved, also in excellent yield, using the established protocol of PCl3 in refluxing, ethanol-free, chloroform. The N-nitrosamines were prepared in moderate to good yield through addition of an alkyne to an imine and subsequent N-nitrosation. A reasonable, yet tentative, mechanism for the cyclization is proposed.