O‐Acylation of 3‐Methylpyrazol‐5‐ones with Acylisothiocyanates
作者:Mykhaylo V. Vovk、Andrij V. Bol'but、Pavlo S. Lebed'
DOI:10.1081/scc-120030702
日期:2004.12.31
Abstract 3‐Methylpyrazol‐5‐ones 1 react by the O‐acylation pattern with acylisothiocyanates 2 in the solvent mixture ethanol–dioxane in the presence of the equimolar amount of potassium hydroxide to produce 5‐acyloxy‐3‐methyl‐1H‐pyrazoles 3.
The unusual formation of 1-acyl-1,2-dihydro-3H-pyrazol-3-ones starting from 3-acyloxypyrazoles by Fries-type rearrangement is described. Under normal conditions, acylation of 2,4-dihydro-3H-pyrazol-3-ones 1 and 2 with acid chlorides or anhydrides in the presence of triethylamine gave the corresponding 3-acyloxypyrazoles 3a-f and 4a-f. Treatment of 3a-c and 4a-f with Lewis acid, e.g. titanium(IV) chloride