Publisher Summary This chapter discusses the synthesis of condensed 1,2,4-triazolo[3,4-z]- heterocycles. The synthesis of condensed 1,2,4-triazolo[3,4-z]- heterocycles is arranged according to the complexity of the ring directly fused to the 1,2,4-triazole nucleus (irrespective of other rings that might be fused to it) beginning with those rings having one nitrogen atom in a five-membered ring and proceeding with those that are more complex. The heterocycles are arranged in the following order according to their types of heteroatoms: nitrogen, oxygen, sulfur, and other elements. Consideration is given to the possible alternative nomenclature of some 1,2,4- triazoles[3,4-z]heterocycles such as heterocyclo[n,m-c] 1,2,4-triazoles (n,m are numbers indicating linkage positions of the heterocycle to the traizole ring) in order to comply with the nomenclature rules of the IUPAC.

Synthesis of Condensed 1,2,4-Triazolo[3,4-z] Heterocycles

Publisher Summary 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.

Recent Advances in Pyridazine Chemistry

The organic chemistry of hypervalent organoiodine compounds has been an area of unprecedented development. This surge in interest in the use of hypervalent iodine compounds has mainly been owing to their highly selective oxidizing properties, environmentally benign character and commercial availability. Hypervalent iodine reagents have also been used as an alternative to toxic heavy metals, owing to their low toxicity and ease of handling. Hypervalent organoiodine(III) reagents are versatile oxidants that have been successfully employed to extend the scope of selective oxidative transformations of complex organic molecules in synthetic chemistry. This Focus Review concerns the tandem in situ generation and 1,5-electrocyclization of N-heteroaryl nitrilimines into fused triazoles. We describe the importance of recently developed hypervalent-organoiodine(III)-catalyzed oxidative cyclization reactions, building towards the conclusion that hypervalent iodine chemistry is a promising frontier for oxidative cyclization, in particular of hydrazones, for the synthesis of fused triazoles.

Hypervalent-Iodine(III)-Mediated Oxidative Methodology for the Synthesis of Fused Triazoles.

Data on the synthesis of thiazoles systems condensed with heterocycles are classified. The principal directions in the practical application of these substances are briefly discussed.

L. Kramberger

Papers

Heterocycles. CXXVII. Action of sulfur on some heterocyclic compounds. Formation of thioamides, oxidative cyclization and thiation