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Synthesis 2008(21): 3504-3508  
DOI: 10.1055/s-0028-1083186
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

An Improved Preparation of 3-Alkoxypyrazoles

Sandrine Guillou, Frédéric J. Bonhomme, Yves L. Janin*
URA 2128 CNRS-Institut Pasteur, 28 rue du Dr. Roux, 75724 Paris cedex 15, France
Fax: +33(1)45688404.; e-Mail: yves.janin@pasteur.fr;
Further Information

Publication History

Received 15 April 2008
Publication Date:
16 October 2008 (online)

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Abstract

The condensation between alkyl acetoacetates and hydrazines constitutes the very well-known Knorr synthetic method leading to pyrazol-3/5-ones. However, contemporary reports describe an alternate reaction pathway leading to low yields of 3/5-alkoxypyrazoles using hydrazine salts. No general method for the selective synthesis of 3-alkoxypyrazoles has been reported to date, hence we focused on this side reaction in an attempt to turn it into the main transformation. Depending on the starting material, various 3-alkoxypyrazoles (methoxy, ethoxy, benzyloxy, isopropoxy, allyloxy) were obtained in up to 56% yield.

Key words

condensation - cyclizations - heterocycles - pyrazoles - Knorr reaction

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