Abstract
Ring transformations and ring expansions of ka-acetyl-5a, 6a-dihydro-6a-ethoxy-carbonyl-6H-cyclopropa [e] pyrazolo [1, 5a] pyrimidines (3, 4 and 5) are described. For example, treatment of 4a with potassium hydroxide in ethanol gave 4-acetyl-1-(4-cyanopyrazol-3-yl)-5-methylpyrrole-2-carboxylic acid (7a), the structure of which was confirmed by X-ray crystal structure determination. On the other hand, it was found that 3a reacted with ethanol, with ethanol in the presence of potassium hydroxide, or with acetic acid to give 7, 8-dihydro-8-ethoxy (or acetoxy)-4H-pyrazolo [1, 5-a] [1, 3] diazepines (17, 11 or 24, respectively) in moderate yields. Furthermore, when aqueous dioxane was used as the reaction medium, 3a was transformed to ethyl 6-pyrazolo [1, 5-a] pyrimidinepyruvate (22), which was found to exist as a mixture of keto and enol tautomers. The mechanism of formation of these products is discussed.
