Synthesis of 3-ethoxyisoxazole derivatives and 3-ethoxy-1H-pyrazole derivatives from β-oxo thionoesters

Article abstract of DOI:10.1246/bcsj.73.1861

3-Ethoxyisoxazoles and 3-ethoxy-1H-pyrazoles were obtained in high yields from β-oxo thionoesters. The reaction of the ethyl β-oxo thionoesters with hydroxylamine hydrochloride in the presence of triethylamine at room temperature for 2 h gave the ethyl 3-oxopropiohydroximates and their hemiacetals, which were easily converted to the 3-ethoxyisoxazoles by refluxing for 3 h at pH 3-5. On the other hand, the reaction of the ethyl β-oxo thionoesters with hydrazine derivatives in the presence of triethylamine for 3-8 h at room temperature directly yielded the 3-ethoxy-1H-pyrazoles.