Trimethyl or triethyl phosphite in the Arbuzov reaction with 6-bromomethyl-3,4-dihydropyrimidin-2(1H)-one or analogous 6-bromomethyl-3,4-dihydropyridin-2(1H)-one provided the respective 6-alkylphosphonates in excellent yields. The heterocyclic alkylphosphonates are useful synthons in the Horner–Wadsworth–Emmons reaction for introducing a styryl moiety. Bromination of 6-methyl-4-phenyl-3,4-dihydropyridin-2(1H)-one with NBS in methanol resulted in an unexpected compound, while bromination in chloroform with bromine yielded the expected 6-bromomethyl-3,4-dihydropyridin-2(1H)-one, which undergoes facile nucleophilic substitutions. The intermediates and products are validated by single crystal X-ray diffraction.

A series of new and significative γ-butyrolactone-based phenazines were synthesized through two-step one-pot five-component reactions of 2-hydroxy-1,4-naphthoquinone, a variety of aromatic aldehydes, benzene-1,2-diamine, tetronic acid, and ammonium acetate in glacial acetic acid. The synthesis proceeded via condensation, Michael addition, tautomerization sequence of steps. All the synthesized compounds were fully characterized by spectral data.

A methodology was developed for the synthesis of 1-ethoxy-6-methyl-2H-[1,2]oxazino[3,4-c]quinoline-2,5(6H)-diones from methyl 4-[2-(dimethylamino)phenyl]-5-ethoxy-6-oxo-6H-1,2-oxazine-3-carboxylates by the action of titanium tetrachloride under inert atmosphere. This interaction provides a rare example of demethylation followed by cyclization, yielding several new compounds.

Interaction of imidazol-5-one-based donor–acceptor cyclopropanes with thiourea and thioacetamide was studied. Previously undescribed spirocyclic 2-amino- and 2-iminotetrahydrothiophenes are formed in the reaction.

Series of new potent inhibitors of growth of Staphylococcus aureus Newman, based on 3,4-diphenylpyrazole and 4,5-diphenylisoxazole derivatives were discovered. Structures of interest were selectively modified to check their structure–activity relationship. Studies revealed the most essential groups in the molecule for the antimicrobial activity retention. Active compounds with good MIC range should contain both nonpolar aromatic residues and hydrogen bond donating groups. The best MIC results in selected cases were lower than 1 μg/ml.

A method for the synthesis of 3-nitro-4H-benzo[h]chromenes was developed based on the reaction of 1-naphthoquinone 2-methides generated in situ from Mannich bases with 4-(2-nitrovinyl)morpholine. It was shown that such nucleophiles as morpholine and 4-bromoaniline add to the double bond of the pyran ring.

We provide a generalized overview of stereoselective synthetic strategies used for the preparation of tetrahydropyrimidin-2(1H)-one derivatives, illustrated by the most relevant examples published between years 2012 and 2022. The known methods can be divided into two main groups: intramolecular and intermolecular cyclization of unsaturated acyclic amides/ureas, as well as syntheses on the basis of cyclic precursors.

Single diastereomers of 4-hetaryl-2-pyrrolidone-3(5)-carbo- and 2-[4-hetaryl-2-pyrrolidon-1-yl]acetohydrazides were used in reactions with 2,4-pentanedione, providing (3R*,4S*)-3-, (4R*,5R*)-5-(3,5-dimethyl-1H-pyrazole-1-carbonyl)- and 1-[2-(3,5-dimethyl-1H-pyrazol-1-yl)-2-oxoethyl]-4-hetaryl-2-pyrrolidones. The structures of the synthesized compounds were confirmed by spectral methods and X-ray structural analysis. Some of the obtained compounds were shown to possess nootropic and anxiolytic activity.

The regio- and stereoselectivity of [3+2] cycloaddition reactions of (Z)-1-(anthracen-9-yl)-N-methyl nitrone with analogs of trans-β-nitrostyrene were studied within the molecular electron density theory at the B3LYP/6-31G(d) and MPWB95/6-311G(d,p) theory levels. Analysis of the reactivity indices for presented reactions suggests that nitrone participates as nucleophile, while studied nitroalkenes play a role of electrophiles. According to electron localization function and conceptual density functional theory, kinetic and thermodynamic aspects of processes as well as analysis of all critical structures, the most favored reaction path is the formation of (3RS,4RS,5SR)-3-(anthracen-9-yl)-5-aryl-2-methyl-4-nitroisoxazolidine, independently of simulated solvent.

This minireview summarizes the latest progress in the synthesis of phosphorylated heterocycles via the direct phosphorylation of parent heterocycles, covering four parts: 1) dehydrative cross couplings between P(O)–H compounds and alcohols; 2) cross-dehydrogenative couplings with P(O)–H compounds; 3) phospha-Michael or phospha-Mannich reaction, and 4) electrophilic phosphorylation of heterocycles.

A one-step method for the synthesis of new 5-aminoazolo[1,5-a]pyrimidines was developed. The use of a synthetic equivalent of carbonyl dielectrophile based on Meldrum's acid made it possible to introduce a substituted amino group into position 5 of azolo[1,5-a]-pyrimidines without the use of severe conditions and palladium catalysts. The tolerance of the reaction to various substituents was also investigated. Based on the isolated intermediates, a reaction mechanism of the process was proposed. Moreover, the possibility of synthesizing analogs of biologically active molecules based on the obtained compounds was demonstrated.

The interactions of alkyl 3-bromo-3-nitroacrylates with 1,2-diaminoethane, 1,2-diaminopropane, 1,2-diaminocyclohexane, and 2-aminoethanol were shown to provide a convenient route for the synthesis of six-membered heterocycles – (3Z)-3-(nitromethylidene)-piperazin-2-ones and (3Z)-3-(nitromethylidene)morpholin-2-one. The structures of the synthesized heterocycles were characterized by a range of spectral methods and by X-ray structural analysis.

Cyclization of 1-hydrazinyl-3,3-dimethyl-3,4-tetrahydro-5H-benzo[c]azepine with ethyl orthoformate gave 5,5-dimethyl-6,7-dihydro-5Hbenzo[c]-1,2,4-triazolo[3,4-a]azepine, and its reaction with acetic acid afforded 3,5,5-trimethyl-9,10-dimethoxy-6,7-dihydro-5Н-benzo[c]-1,2,4-triazolo[3,4-a]azepine. Nitrosation of 1-hydrazino-3,3-dimethyl-3,4-tetrahydro-5H-benzo[c]azepine led to the formation of substituted 6,7-dihydro-5H-benzo[c]tetrazolo[5,1-a]azepines.

A comparative analysis was performed for 13C NMR chemical shifts of C-4 and C-4a (or C-5) atoms in previously synthesized pyrido[2,3-d]-pyrimidin-5-ones, pyrido[2,3-d]pyrimidin-7-ones, pyrimido[4,5-d]pyrimidines, and 5-acetylpyrimidines containing methylsulfanyl, methylsulfonyl, butoxy, and amino groups at position 4. It was possible to determine the type of heteroatom (sulfur, oxygen, or nitrogen) bonded to the C-4 carbon atom on the basis of chemical shifts observed for C-4a carbon atom in the spectra of fused heterocycles or C-5 carbon atom in the spectra of pyrimidines. At the same time, the chemical shift values of C-4a (or C-5) atoms practically did not depend on the particular sulfur-containing functionality: sulfanyl or sulfonyl group. A significant upfield shift was observed for the C-4 atom in 13C NMR spectra of sulfones compared to the spectra of compounds containing a methylsulfanyl moiety.

This theoretical study, performed using density functional theory at the B3LYP/6-311+G(d,p) level, shows that the most likely route to obtain 3-phenyl[1,2,4]oxadiazolo[4,5-a]benzimidazole from the reaction of 2-chlorobenzimidazole with benzonitrile oxide implies the presence of anionic species. A concerted [3+2] cycloaddition reaction on the imidoyl group of 2-chlorobenzimidazole is not possible. The presence of a polar protic solvent (MeOH) favors the reaction. The analysis of the Wiberg indices shows that the transition states are earlier in MeOH than in THF or gas phase. Finally, topological analysis of the electron localization function indicates that the formation of the N4–C3 and C5–O bonds and the breaking of the C5–Cl bond in the preparation of 3-phenyl[1,2,4]oxadiazolo[4,5-a]benzimidazole are marked for each by the presence of an asynaptic basin V(Asyn) and proceed through tetrahedral intermediates, indicating the nonconcerted nature of the mechanism. These results are in good agreement with the experimental results.

A new spiropyran containing a cationic 3Н-indolium substituent and methoxy groups at positions 5 and 5” of the indoline cycles was synthesized. Hydrolysis of this compound was observed during crystallization from EtOH, leading to the formation of protonated merocyanine form of spiropyran containing a free formyl group. The hydrolysis product was characterized by X-ray structural analysis, the intermolecular interactions in crystal were studied with the CrystalExplorer 21.5 software suite. Quantum-chemical modeling based on the Fukui function distribution was used to establish the preferred site for nucleophilic attack, and a mechanism for hydrolysis was proposed.

3-Alkyl- and 3-aryl-substituted [2,2'-dithiophene]-5-carboxylate esters, as well as naphtho[2,1-b:3,4-b']dithiophene-2-carboxylates were used in the synthesis of 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives. The obtained compounds were characterized with regard to their electrochemical and photophysical properties. The replacement of alkyl side chains with aryl substituents led to a substantial decrease of luminescence quantum yield and narrowing the energy gap between HOMO and LUMO, as well as a bathochromic shift of the absorption and emission peaks in the absorption and luminescence spectra. Changing from 3-aryldithiophene- to naphtho[2,1-b:3,4-b']-dithiophene-substituted 1,3,4-oxadiazoles and 1,3,4-thiadiazoles led to a slight increase of quantum yields, while the positions of LUMO and HOMO changed insignificantly.

The two diastereoisomers of 6-(3,4-epoxy-4-methylcyclohexyl)-2-methylhepta-2,5-dien-4-one were synthesized in the [2+1] cycloaddition reaction of α-atlantone, isolated compound from Cedrus atlantica essential oil, with m-chloroperbenzoic acid in CH2Cl2. The chemoselectivity of this cycloaddition reaction has been both experimentally and theoretically studied within the molecular electron density theory. Parr functions and electron localization function analysis of the reagents correctly predicted the experimental chemoselectivity with the most favorable interaction at C3'=C4' bond. These reactions follow a two-stage one-step mechanism.

The data on the use of carbocationic catalysis in the synthesis of heterocyclic compounds presented in the literature over the last 5–10 years are summarized and analyzed. Particular attention is paid to the discussion of reaction mechanisms and the problem of selectivity.