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■ A Diversity-Oriented Approach to 1H-Pyrazole-4,5-diols, 4-Hydroxy-3H-pyrazol-3-ones, and Phenylhydrazones from Key Intermediate 4-Acetyloxy-3H-pyrazol-3-one

Eiichi Masumoto, Fumi Okabe, Toshihiro Fujioka, Kenji Yamagata, and Hiroshi Maruoka*

*Faculty of Pharmaceutical Sciences, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka 814-0180, Japan

Abstract

An approach to 1H-pyrazole-4,5-diols 4a−d, 4-hydroxy-3H-pyrazol-3-ones 5a−d, and phenylhydrazones 6a−d from key intermediate 4-acetyloxy-3H-pyrazol-3-one 3a is described. 4-Alkylidene-3H-pyrazol-3-ones 1a−c were reacted with m-chloroperbenzoic acid in the presence of potassium carbonate to give the corresponding spiroepoxide-3H-pyrazol-3-ones 2a−c. Treatment of 2a with acid anhydride such as acetic, propionic, butyric, and pentanoic anhydride in the presence of boron trifluoride diethyl etherate led to the corresponding 4-acyloxy-3H-pyrazol-3-ones 3a−d. The reactions of 3a with α-chloroketones, ketones, and/or secondary amines gave the corresponding 4a−d, 5a−d, and 6a−d.