Recyclization reactions of heterocycles

The direction of recyclization during hydrazination of isoquinolinium salts is practically independent of the substituent attached to nitrogen and the reaction conditions and leads to compounds with an N-aminoisoquinoline structure.See [1] for communication XIV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 961–965, July, 1974.     

Recyclization reactions of heterocycles

2-Thioxo-4-oxazolidone and thiazolidines containing heteroatom substituants (O, S, and NH) in the 2 and 4 positions are converted to benzimidazole derivatives on reaction with o-phenylenediamine. The direction of these recyclizations depends on the nature of the heteroatom substituents in the 2 and 4 positions of the heteroring.See [1] for communication XX.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 666–668, May, 1978.     

Recyclization reactions of heterocycles XVIII. Synthesis and recyclization of thiazolium and benzothiazolium salts

A number of thiazolium salts were obtained, and their reaction with hydrazine was studied. On reaction with hydrazine the aryl-substituted thiazolium salts are recyclized to dihydro-l, 2, 4-triazines, whereas on reaction with monoalkylhydrazines they are converted to 4H, 5H-1, 2-4-triazinium salts; thiazolium salts are converted to hydrazidohydrazones on reaction with phenylhydrazine. Recyclization to the dihydro-sym-tetrazine system was observed for 2-phenyl-substituted benzothiazolium tosylate.See [1] for communication XVII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 635–640, May, 1976.     

Molecular design of heterocycles. I. Recyclization graphs and structural hierarchy of the transformations of heterocycles

A new method for modeling the processes involved in the transformation of the ring of heterocyclic systems by means of recyclization graphs, the vertexes and ribs of which correspond only to the atoms and skeletal bonds that enter into the starting or final heteroring, is proposed. An analysis of the structures of such graphs and the use of various types of labels for the ribs and vertexes make it possible for the first time to construct a convenient and flexible hierarchy of recyclizations from the principle of the structural similarity in their recyclization graphs. The effectiveness of the approach is illustrated by examples of the classification of known interconversions of azoles and azines and by the prediction of new recyclizations.Plenary paper presented at the 5th All-Union Conference on the Chemistry of Nitrogen-Containing Heterocyclic Compounds, Chernogolovka, October 22–25, 1991.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 808–828, June, 1992.     

Recyclization reactions. 26. Recyclization of heteroarenium salts by action of acid anhydride in the presence of base

When oxazolium, 1,3,4-thia- and -selenadiazolium, or pyrilium salts react with acid anhydride in the presence of base, they are recyclized to pyrrol, pyrazole, and benzene derivatives, respectively. The typical features of recyclization involving anhydride in a number of five-membered and six-membered systems are discussed.For Communication 25, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1689–1695, December, 1988.     

Recyclization reactions of 2-(1-benzoylpyrrolidin- 2-ylidene)malononitrile

Acylation of pyrrolidin-2-ylidenemalononitrile with benzoyl chloride leads to the formation of 2-(1-benzoylpyrrolidin-2-ylidene)malononitrile. The obtained product was used as starting material in the synthesis of γ-aminopropylpyrazoles and pyrimidines.     

Catalyst-free synthesis of N-rich heterocycles via multi-component reactions

Efficient and straightforward methods for the synthesis of 5-substituted 1H-tetrazoles via multi-component reaction of α-dicarbonyl compounds, 2,3-diaminomaleonitrile and sodium azide without any catalyst has been reported. These general protocols provide a wide variety of N-rich heterocyclic compounds (1H-tetrazole-5-yl) pyrazines and di(1H-tetrazole-5-yl) pyrazines, in good to excellent yields.     

Synthesis of highly condensed heterocycles using radical reactions

Using radical chemistry novel highly condensed heterocycles have been synthesized. The mechanism for their formation is discussed.     

Recyclization reactions. 30. Interaction of 3-acetonyl-2,4-thiazolidinedione with nucleophiles

3-Acetonyl-2,4-thiazolidinedione, upon interaction with phenylhydrazine or benzoylhydrazine, forms anti-hydrazones that are recyclized in an alkaline medium to 1-aminoimidazol-2-ones.For Communication 29, see [11].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 412–414, March, 1993.     

Acetylene derivatives of heterocycles,some reactions of 3-ethynylpyrazole

3-Ethynylpyrazole, which possesses two mobile hydrogen atoms, takes part in the Favorskii and Iotsich reactions at the acetylene group and in the Mannich reaction at the acetylene group and the nitrogen atom. It has been found that the pyrazoles are also capable of undergoing aminoalkylation at the nitrogen atom under the action of isobutyraldehyde and secondary amines. The intermediate product of the condensation of isobutyraldehyde with 3-ethynylpyrazole is unstable and exists in equilibrium with the initial compounds.     

Addition reactions of heterocycles. VII. Pyrrole and C-Acetyl-N-phenylnitrilimine

The addition reaction of C-acetyl-N-phenylnitrilimine to pyrrole has been investigated. The products obtained show that the reaction proceeds via two distinct pathways. The 1,3-addition reaction leads to the non-cyclic-adduct III, whereas the 1,3-cycloaddition reaction gives a mixture of regioisomeric Δ₂-pyrroline IV and V, and Δ₁ -pyrroline VI and VII mono-cycloadducts. These latter compounds cannot be isolated because they undergo a further 1,3-cycloaddition reaction leading to the N-substituted bis-adducts X and XI, and to the bis-adduets XII and XIII. The stereochemical assignment for X, XI, XII and XIII is provided by nmr data which suggest also that in X and XI the rotation around the exocyclic N-C bond is relatively slow on the instrument time scale.     

Catalytic synthesis and reactions of nitrogen heterocycles (Review)

Studies at the Latvian Institute of Organic Synthesis and literature data from 1984–1994 on organic catalysis in the chemistry of N-heterocycles are reviewed. 77 to prospects for further developments in catalytic reactions of N-heterocycles are examined.