An efficient and controlled site-selective annulation of 3,5-diethoxycarbonyl 4-hydrazonyl pyrazoles is described. The relative proportion of the products is affected by hydrazone intermediate configuration, reaction temperature, and Lewis acid employed. At a temperature of 110-120 °C, the reaction preferentially afforded 1-pyrazolo[3,4-]pyridazin-7(6)-ones, whereas using Yb(OTf) in MeCN reflux, 2-pyrazolo[3,4-]pyridazin-7(6)-ones were favored. Computational investigations were performed to clarify the mechanism and the origin of the regiodivergence.
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Controlled Pyrazole-Hydrazone Annulation: Regiodivergent Synthesis of 1- and 2-Pyrazolo[3,4-]pyridazinones.
J Org Chem
August 2023
Chemistry Departament, State University of Maringa, Maringa, Parana 87020-900, Brazil.
An efficient and controlled site-selective annulation of 3,5-diethoxycarbonyl 4-hydrazonyl pyrazoles is described. The relative proportion of the products is affected by hydrazone intermediate configuration, reaction temperature, and Lewis acid employed. At a temperature of 110-120 °C, the reaction preferentially afforded 1-pyrazolo[3,4-]pyridazin-7(6)-ones, whereas using Yb(OTf) in MeCN reflux, 2-pyrazolo[3,4-]pyridazin-7(6)-ones were favored.
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