An efficient and selective method for the synthesis of spiro-fused (C5)-isoxazolino-(C4)-pyrazolones (C) is reported. The process consists of utilizing the Baylis-Hillman reaction-or a quicker, stepwise MAC procedure-to give I followed by 1,3-dipolar cycloaddition and Swern oxidation to give beta-ketoesters H, which were condensed with hydrazine derivatives to provide hydrazones that underwent cycloelimination. These novel spiro-fused (C5)-isoxazolino-(C4)-pyrazolones were confirmed by spectroscopic analysis as well as single-crystal X-ray of 5. We also concluded that all condensations/cycloeliminations, except with hydrazine itself, were more effective with catalysts or higher reaction temperatures. For example, TiCl(4) was an efficient catalyst for hydrazone formation and cycloelimination with methylhydrazine, while phenyl-, benzyl-, and (4-methoxyphenyl)hydrazine reacted effectively without catalyst in refluxing xylene.
Synthesis of Spiro-Fused (C5)-Isoxazolino-(C4)-pyrazolones (1- 7,4]-2,8-dien-6-ones) via 1,3-Dipolar Cycloaddition and Cycloelimination.-An efficient and selective route to title compounds is reported. They are of biological interest. -(SAMMELSON, ROBERT E.; GURUSINGHE, CHAMINDRA D.; KURTH, JEFFREY M.; OLMSTEAD, MARILYN M.; KURTH, MARK J.; J. Org. Chem. 67 (2002) 3, 876-882; Dep. Chem., Univ. Calif., Davis, CA 95616, USA; EN)
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