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Updated: Jul 23, 2025
![Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions](/_next/image?url=https%3A%2F%2Fcloudfront.jove.com%2FCDNSource%2Fteasers%2F60786.jpg&w=3840&q=50)
Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Controlled Pyrazole-Hydrazone Annulation: Regiodivergent Synthesis of 1H- and 2H-Pyrazolo[3,4-d]pyridazinones
Fernanda Andreia Rosa1, Andrey Petita Jacomini1, Michael Jackson Vieira da Silva1
1Chemistry Departament, State University of Maringa, Maringa, Parana 87020-900, Brazil.
Abstract:
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 1H-pyrazolo[3,4-d]pyridazin-7(6H)-ones, whereas using Yb(OTf)3 in MeCN reflux, 2H-pyrazolo[3,4-d]pyridazin-7(6H)-ones were favored. Computational investigations were performed to clarify the mechanism and the origin of the regiodivergence.
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