Electrocatalytic Three-Component Synthesis of 4-Bromopyrazoles from Acetylacetone, Hydrazine and Diethyl Bromomalonate
Si‐Yu Mu, Hongxia Li, Zhilin Wu, Junmei Peng, Jinyang Chen, Wei‐Min He
Abstract
Pyrazoles are the most important five-membered N-heterocycles as they are present in many natural products and synthetic drugs.Among various pyrazole derivatives, 4-bromopyrazoles have attracted great attention because they not only display significant biological activities and physicochemical properties but also serve as valuable synthons in organic chemistry.In this manuscript, an efficient and eco-friendly method for the synthesis of various 4-bromopyrazoles through threecomponent reaction of hydrazine, acetylacetone and 2-bromomalonate was reported and the proposal reaction mechanism was revealed.According to the mechanism, hydrazine reacts with acetylacetone to afford pyrazole firstly, which then converts to 4-bromopyrazole through bromination.This method could also be well applicable for the bromination of other heterocyclic compounds.Given the high oxidation state of diethyl 2-bromomalonate, the peroxidation can be avoided through the electrolysis process, thus the excess amount of brominating agent was not be required.