Preparation of 1,2-bis(pyrazol-1-yl)benzene: “Modern” Cross-Coupling vs. the “Classic” Nucleophilic Substitution Approach

Several potential methods for the preparation of 1,2-bis(pyrazol-1-yl)benzene, a prospective ligand for transitional metals, starting from 1,2-dihalobenzenes and pyrazole have been studied. Cross-couplings of 1,2-dichloro-, - dibromo- and -diiodobenzenes with pyrazole using palladium and copper catalysts were unsatisfactory because of dehalogenation side reactions or a lack of reactivity. On the other hand, nucleophilic aromatic substitution of fluorine in 1,2- difluorobenzene under the action of sodium pyrazolide gave a good yield of the desired product.