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12.1.2.2.1.4 Variation 4: From 3-Acyldihydrofuran-2(3H)-ones

DOI: 10.1055/sos-SD-012-00002

Stanovnik, B.; Svete, J.Science of Synthesis, (200212130.

3-Acyldihydrofuran-2(3H)-ones can react with hydrazines as masked β-oxo acid derivatives in the presence of sodium ethoxide. Under the influence of a base, the furan ring opens to form β-oxo ester 292, which on treatment with hydrazines gives 4-(2-hydroxyalkyl)pyrazol-5-ols 293 (Scheme 168). This method is closely related to the synthesis of pyrazoles from β-oxo esters due to the intermediacy of 292. Pyrazole derivatives can also be obtained directly from 3-acyldihydrofuran-2(3H)-ones and hydrazines. In this case, the reaction can be explained by initial formation of the hydrazone followed by ring-switching transformation into the pyrazole derivative 293.[‌616‌‌618‌]

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