Recent Advances in Pyridazine Chemistry

Abstract

This chapter reviews the synthesis, reactivity, uses, physical and spectral properties, biological properties, and crystal structures and molecular complexes of pyridazine. The standard synthesis of pyridazines from γ -keto acids or esters has been applied to the preparation of many derivatives. They can be synthesized using carbonyl compounds, acids, lactones, anhydrides, and related compounds. They can also be synthesized using cycloaddition reactions, heterocycles, carbohydrates, pyridazine 1,2-dioxides, pyridazine glycosides, and several miscellaneous methods. The reactions of pyridazines described are protonation, N -alkylation, N -oxidation, N -amination, substitutions at the pyridazine ring, oxidations and reductions, ring opening reactions, isomerizations, rearrangements, ring contractions, and photoreactions. Several calculations on the electronic structure of pyridazine are also presented. The physical and spectral properties of pyridazine and its derivatives are discussed in the chapter. Ionization constants of hydroxy- and mercaptopyridazines, of amino- and diaminopyridazines and their quaternization products, of methylsulfinylpyridazines, and of pyridazinium ylides are presented. The basicities of a series of pyridazines are determined and correlated with substituent constants using the Hammett free-energy relationship. The magnetic susceptibility of pyridazine is measured, and the rate constant for the reaction of hydrogen atoms with pyridazine is determined. The experimental dipole moment, Kerr constant, and molar Cotton–Mouton constant, obtained at 298°K and 633 nm, are presented.