M. Tisler

Synthesis of pyridazine derivatives—V : Formation of s-triazolo-(4,3-b)-pyridazines and bis-s-triazolo-(4,3-b,3′,4′-f)-pyridazines☆

Abstract 3-Substituted s-triazolo-(4,3-b)-pyridazines (III) and some derivatives have been prepared from II or IV by oxidative or thermal cyclization. The reaction has been extended to the preparation of 3,6-substituted bis-s-triazolo-(4,3-b,3′,4′-f)-pyridazines (VIII)—a new heterocyclic system—also formed with a bis-arylidene derivative of 3,6-dihydrazinopyridazine (X) in one reaction step.Abstract 3-Substituted s-triazolo-(4,3-b)-pyridazines (III) and some derivatives have been prepared from II or IV by oxidative or thermal cyclization. The reaction has been extended to the preparation of 3,6-substituted bis-s-triazolo-(4,3-b,3′,4′-f)-pyridazines (VIII)—a new heterocyclic system—also formed with a bis-arylidene derivative of 3,6-dihydrazinopyridazine (X) in one reaction step.

Synthesis of pyridazine derivatives—VIII : Imidazo(1,2,-b)pyridazines and some tricyclic aza analogs

Abstract 6-Substituted and 3,6-disubstituted imidazo(1,2-b)pyridazines have been prepared. Some of these derivatives were used for convenient syntheses of a new azaheterocycle, imidazo(1,2-b)s-triazolo(3,4-f)pyridazine (V) and its derivatives. Another new heterocyclic system, imidazo(1,2-b)-tetrazolo-(5,1-f)pyridazine (XVI) has also been prepared.

Reactions of some diazoazoles with reactive methylene and other groups

Abstract Reactions of some heteroaromatic diazo compounds with 1,3-dicarbonyl compounds, amines and thiophenol to give bi- and tricyclic heterocycles are studied. Decomposition of heterocyclic diazo compounds, triazenes and related compounds are investigated.

The Tautomerism of Heterocycles: Substituent Tautomerism of Six-Membered Ring Heterocycles

Publisher Summary This chapter reviews the substituent tautomerism of six-membered heterocycles that has appeared since 1976. The most significant development since 1976 is the enormous emphasis on the computational studies. Recent advances in computer technology in combination with increasingly accurate quantum-chemical methods, allow studies of systems of up to 50 atoms on standard personal computers at relatively high levels. Computational chemistry has become increasingly important in traditional heterocyclic chemistry. It discusses the generalized approach to the tautomerism phenomenon and its studies using theoretical, physical spectroscopic, non-spectroscopic, and chemical methods. The chapter also reviews the effect of introduction of an additional heteroatom; inductive substituents, mesomeric substituents, and the effect of benzannulation on the position of the tautomeric equilibrium of azines with various functional groups were investigated by PMO semiempirical calculations.

Δ2-1,2,3-Triazolines

Publisher Summary The 1,2,3-triazolines were first discovered during their studies on the action of organic azides on quinones. Triazolines have assumed considerable importance as intermediates in a number of organic syntheses and recently as a new class of potential anticonvulsant drugs. This chapter presents a comprehensive, unified survey of the methods of synthesis and reactions of Δ 2 -1,2,3-Triazolines. The chemistry of mono-, bi-, and polycyclic triazolines, and that of spiro- and bistriazolines, is considered. A brief account of the chemistry of Δ 3 - and Δ 4 -1,2,3-triazolines is given. Triazoline aromatization to triazoles is achieved by oxidation, isomerization reactions, and elimination of stable molecular fragments, all of which require the presence of free hydrogen at position 4 and/or 5 of the triazoline ring. The aromatization reaction affords a selective, synthetic route for the preparation of triazoles of definitive structure, in as much as azide addition to acetylenes is not regioselective.

An “One-Pot” Synthesis of Substituted 3-Benzoylamino-5-oxo-5, 6, 7, 8-Tetrahydrocoumarins

Abstract A new simple “one-pot” synthesis of some 3-benzoylamino-5-oxo-5, 6, 7, 8-tetrahydrocoumarins from 1, 3-cyclohexanediones, hippuric acid, acetic anhydride and triethyl orthoformate or other one-carbon synthetic equivalent is described.

Über Ringöffnungen einiger Azolo-und Azinoazine

Ring opening reactions of tetrazolo[1.5—a]pyridines, imidazo[1.2—b]pyridazines, s-triazolo[4.3—b]pyridazines and pyrimido[1.2—b]pyridazines are reported. The reaction takes place at the six-membered ring of azoloazines and the formed monocyclic compounds may subsequently isomerize at the double bonds or new cycles may be formed.ZusammenfassungEs wird über Ringöffnungen von Tetrazolo[1,5—a]pyridinen, Imidazo[1,2—b]pyridazinen, s-Triazolo[4,3—b]pyridazinen und Pyrimido[1,2—b]pyridazinen berichtet. Die Reaktion verläuft stets am Sechserring der Azoloazine und bei den entstandenen monocyclischen Verbindungen kann nachfolgend einecis—trans-Isomerisierung stattfinden, oder es kommt zu einem neuen Ringschluß.

RECENT ADVANCES IN THE CHEMISTRY OF PYRIDAZINES

Publisher Summary This chapter provides an overview of further advances in pyridazine chemistry. The chapter illustrates that many bioactive natural products containing pyridazine rings as a part of their molecules have been discovered and their structures determined. Many new synthetic approaches and unusual transformations of pyridazines are described in the chapter. The chapter discusses other aspects, which have been the subject of intensive investigations, from a theoretical standpoint, of biological activities. With the resurgence of pyridazine derivatives as novel bioactive molecules these were the subject of intensive synthetic and medicinal studies. This chapter discusses the chemistry of pyridazine complexes with inorganic ions or compounds and their biological activities. Several pyridazine derivatives were prepared from haloalkyl or cyanoalkyl ketones. A great number of pyridazines can be prepared from preformed hydrazones or related compounds. Hydrazones of 1,2-diketones, when treated with ethyl cyanoacetate, can be transformed into cyanopyridazinones.

Cyanoamino compounds in synthesis syntheses of some heterocycles

Transformations of some heterocyclic cyanoamino compounds leading to various heterocyclic systems are described.s-Triazolo (1,5-α)azines are obtained either in a direct synthetic approach or via the substituted aminotetrazoles, substituted 3-amino-5-oxo-1,2,4-oxadiazolines, and fromN-ethoxycarbonylN′-heteroaryl thioureas orN-heteroarylN′-hydroxyguanidine. The cyanoamino group reacts also witho-difunctional benzenes to give the corresponding substituted derivatives of benzimidazole, benzoxazole or benzothiazole.ZusammenfassungUmwandlungen von einigen heterocyclischen Cyanoamino-Verbindungen in verschiedene heterocyclische Systeme werden beschrieben.s-Triazolo-(1,5-a)azine konnten in einem direkten Syntheseschritt oder über die substituierten Aminotetrazole, substituierten 3-Amino-5-oxo-1,2,4-oxadiazoline und ausN-Ethoxycarbonyl-N′-Heteroaryl-Thioharnstoffen oderN-Heteroaryl-N′-Hydroxyguanidin erhalten werden. Die Cyanoamino-Gruppe reagiert auch mit einigeno-disubstituierten Benzolderivaten; es wurden damit Derivate von Benzimidazol, Benzoxazol oder Benzothiazol dargestellt.

Syntheses and transformations of some heterocyclic hydroxylamines

Abstract Syntheses of some hydroxylaminoazines, their quaternized derivatives or N-oxides and N-amino compounds are described. Several transformations of these compounds and cyclization reactions are presented.