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Strategy To Prepare 3-Bromo- and 3-Chloropyrazoles
Richard J Fox1, Michael A Schmidt1, Martin D Eastgate1
1Chemical & Synthetic Development, Bristol-Myers Squibb , 1 Squibb Drive, New Brunswick, New Jersey 08903, United States.
Abstract:
A general strategy to prepare substituted 3-bromo- and 3-chloropyrazoles is described. The three-step method involves condensation of crotonates or β-chloro carboxylic acids with hydrazines, followed by halogenation and oxidation. Several condensation and oxidation protocols were developed to enable preparation of a wide variety of 3-halopyrazoles with good to excellent yields and regiocontrol.
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