Synlett 2008(7): 1005-1008  
DOI: 10.1055/s-2008-1042923
LETTER
© Georg Thieme Verlag Stuttgart · New York

Selective β-Hydroxyethylation at the N-1 Position of a Pyrazolone: Synthesis of Benzyl 1-(β-Hydroxyethyl)-5-methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazole-4-carboxylate

Aaron Siegmunda, Daniel Retza, Ning Xia, Celia Dominguezb, Roland Bürlia, Longbin Liu*a
a Chemistry Research and Discovery, Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA 91320, USA
b MRSSI/CHDI, Inc., 6080 Center Drive, Suite 100, Los Angeles, CA 90045, USA
e-Mail: lliu@amgen.com;
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Publication History

Received 11 December 2007
Publication Date:
17 March 2008 (online)

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Abstract

Selective 2-hydroxyethylation at the N-1 position of benzyl 5-methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazole-4-carboxylate with epoxides was achieved using either AlMe3 or Mg(ClO4)2 under mild conditions. The epoxide ring opening was both regioselective and stereospecific. Moderate to excellent yields were obtained from mono- and disubstituted epoxides with the exception of cis-dimethyl-2-butene oxide that gave only a trace amount of the product.

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