Multicomponent cyclocondensations between 5-aminopyrazoles, barbituric acids, and aromatic aldehydes under conventional thermal heating, microwave irradiation, or ultrasonic irradiation were studied and the temperature regime was found to be the main factor in controlling their chemoselectivity. At high temperatures the starting materials react in two different ways yielding pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrimidines or their dihydro analogues depending on the nature of the N-substituent in the 5-aminopyrazole. Treatment at room temperature results in a new four-component reaction giving previously undisclosed heterocyclic compounds, 4,6-diaryl-1,4,6,7-tetrahydro-2′H-spiro[pyrazolo[3,4-b]pyridine-5,5′-pyrimidine]s. Facile multipurpose three-component selective procedures to new spiroheterocycles are proposed.

The present review is devoted to heterocyclizations of α,β-unsaturated carbonyl compounds which result in the formation of three-membered partially hydrogenated nitrogen containing heterocyclic systems – aziridinyl ketones, biand tricyclic aziridines. Scientists are interested in these classes of heterocyclic compounds first of all by their photochromic properties and high sensitivity towards UV-VIS irradiation. From the other hand, these compounds are interesting from the viewpoint of classical problems of organic chemistry, among them reactivity, chemo- and regio-selectivity, stereochemistry and many other. The main aim of the publication is a comprehensive review and organization of the known literature data devoted to the reactions of α,β-unsaturated ketone derivatives utilized in the synthesis of aziridines and their chemical and photochemical properties. The first part of the review deals with synthesis and chemical properties of aziridinyl ketones. Two main groups of the reactions leading to target compounds – one-pot synthesis directly from unsaturated carbonyl compounds and step-by-step pathway including their initial modification – are described as well as chemical transformation of azyridinyl ketones. In the second section several synthetic pathways to bi- and tricyclic aziridines like dihyrdoazireno[1,2-c]imidazoles, tetrahydroazireno[ 1,2-a]pyrazines and dihydroazireno[1,2-a]quinoxalines are described and some aspects of stereo- and regoselectivity of appropriate reactions are discussed. The last part of the review is concerned with chemical behavior of aziridinyl aniles in numerous organic reactions including photochemical transformations, cycloadditions, rearrangements, cross-couplings and other. Stereochemistry of such processes and their mechanisms are touched as well.

A microwave-assisted synthesis of pyrazoloquinolizinones by a 3-CR of aminopyr­azoles, aldehydes and 1,3-diketones is described. The reaction, carried out under strongly basic conditions directly affords the pyrazoloquinolizi­nones with the stereogenic centers in trans relationship. The scope of the reaction was insufficiently explored.

Number of novel derivatives of dihydrotriazolo-and-tetrazolopyrimidines containing carboxamide group in position 6 were obtained by multicomponent Biginelli-type reaction. The structures of all synthesized compounds were proved by NMR and MS spectral methods. The method of three-component Biginelli-type reaction is well suited for the synthesis of new promising dihydroazolopyrimidines providing a scaffold for screening of biological activity.

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The tautomerism of 1,4-diazepines fused with pyrimidine rings was studied by means of nmr spec-troscopy, X-ray analysis and quantum chemical calculations. It was found that in the case of 6,8-diphenyl-pyrimido[4,5-b][1,4]diazepin-4-ols (7a - e) the enamine form is more stable than the diimine form. This result is rationalized with the electron-withdrawing effect of the 4-hydroxypyrimidine ring and with the formation of intermolecular hydrogen bonds. In contrast to 7a - e, the 6,8-diaryl-2,3,4,7-tetrahydro-1,3-dimethyl-1H-pyrimido[4,5-b][1,4]diazepine-2,4-diones (9a, c, f) exist in the diimine form.