A. T. Gubaidullin

Tautomerism of aza cycles: II. Synthesis and structure of 5-substituted 3-(2-hydroxyethylsulfanyl)-1H-1,2,4-triazoles and their salts. Preference of the 1H,4H-1,2,4-triazolium tautomers

New complexing agents, potentially tautomeric 3-(2-hydroxyethylsulfanyl)-1H-1,2,4-triazole, its 5-methyl-and 5-phenyl-substituted analogs, and some their salts, were synthesized, and their structure was discussed on the basis of the 1H and 13C NMR, IR, and mass spectra, X-ray diffraction data, and published data. In keeping with the rule formulated previously for N-unsubstituted 1,2,4-triazoles having dissimilar substituents, the synthesized compounds were found to exist as 3-(2-hydroxyethylsulfanyl)-5-R-1H-1,2,4-triazole tautomers (3-RA-5-RD-1H-1,2,4-triazoly). They are protonated at the nitrogen atom in position 4 of the triazole ring. The 1H and 13C NMR spectra of these compounds in trifluoroacetic acid suggest the presence of two forms due to equilibrium between the neutral and protonated species. Analysis of the crystallographic data for the triazolium salts and published data showed preference of the 1H,4H-1,2,4-triazolium tautomer.

Quinoxaline-benzimidazole rearrangement in the synthesis of benzimidazole-based podands

Alkylation of 3-benzoylquinoxalin-2(1H)-one with 1,5-dibromo-3-oxapentane, 1,8-dibromo-3,6-dioxaoctane, and α,ω-dihaloalkanes with different lengths of the polymethylene chain gave the corresponding quinoxaline podands. In the reaction with 1,2-dibromoethane, the N,O-rather than N,N′-alkylation product was obtained. The reaction of the obtained quinoxaline-based podands with benzene-1,2-diamine followed the quinoxaline-benzimidazole rearrangement pattern with formation of 2-(3-phenylquinoxalin-2-yl)benzimidazole-based podands.

Synthesis and Functionalization of 3-Ethylquinoxalin-2(1H)-one

A new and effective procedure was developed for the synthesis of 3-ethylquinoxalin-2(1H)-one from o-phenylenediamine and ethyl 2-oxobutanoate. The latter was prepared by the Grignard reaction of diethyl oxalate with ethylmagnesium bromide or iodide. The ethyl group in 3-ethylquinoxalin-2(1H)-one can readily be converted into various functional groups: α-bromoethyl, α-thiocyanato, α-azidoethyl, α-phenylaminoethyl, acetyl, and bromoacetyl. The reaction of 3-(bromoacetyl)quinoxalin-2(1H)-one with thiourea and hydrazine-1,2-dicarbothioamide gives the corresponding 3-(2-amino-4-thiazolyl) derivatives.

New synthesis of diterpenoid (16S)-dihydrosteviol

A new procedure has been developed for the synthesis of diterpenoid (16S)-dihydrosteviol [(16S)-13-hydroxy-ent-kauran-19-oic acid] by acid hydrolysis (0.7% hydrochloric acid) of SWETA food sweetener and subsequent reduction of the resulting mixture of caurenoids with hydrazine hydrate over Raney nickel. The molecular geometry of (16S)-dihydrosteviol, as well as of Δ15-steviol (13-hydroxy-ent-kaur-15-en-19-oic acid), was determined for the first time by X-ray analysis.

Tautomerism of aza cycles: I. Structure of 3(5)-butylsulfanyl-5(3)-methyl(phenyl)-1H-1,2,4-triazole tautomers in crystal. Preference of the 3-RA-5-RD-1H-tautomer of 3(5)-mono-and 3,5-disubstituted 1,2,4-triazoles

The X-ray diffraction study of potentially tautomeric 3(5)-butylsulfanyl-5(3)-methyl-1H-1,2,4-triazole and its 5(3)-phenyl-substituted analog showed that these compounds in crystal have the structure of 3-butylsulfanyl-5-methyl(phenyl)-1H-tautomers. Analysis of our experimental and published data indicated that 3(5)-monosubstituted 1,2,4-triazoles and 3,5-disubstituted derivatives having nonequivalent substituents in crystal as exist as a tautomer in which the electron-acceptor substituent (RA) occupies the 3 position, while the electron-donor substituent (RD) resides in the 5 position, i.e., as 3-RA-5-RD-1H-1,2,4-triazoles. Symmetric 3,5-disubstituted 1,2,4-triazoles could give rise to tautomeric equilibrium between the 1H-and 2H-structures even in crystal.

Synthesis and Properties of Phosphabetaine Structures: III. Phosphabetaines Derived from Tertiary Phosphines and α,β-Unsaturated Carboxylic Acids. Synthesis, Structure, and Chemical Properties

Methods of synthesis of acylate phosphabetaines by reactions of triphenylphosphine with methacrylic, cinnamic, and p-methoxycinnamic acids are developed. The phosphabetaine form is proposed to exist in equilibrium with the σ5-oxaphospholane form. The features of methylation of the phosphabetaines are discussed.

3-Indolizin-2-ylquinoxalines and the derived monopodands

The reactions of 3-acetylquinoxalin-2-one with methyl-and benzylpyridines in the presence of iodine produce the corresponding 3-(2-alkylpyridinioacetyl)quinoxalin-2(1H)-one iodides. Treatment of the latter with triethylamine affords the corresponding 3-indolizin-2-ylquinoxalin-2-ones. Due to the presence of the endocyclic carbamoyl group, the reactions of these compounds with bisalkylating reagents give quinoxaline-containing monopodands and monoalkylation products containing spacers with different lengths and of different nature.

Synthesis and Properties of Phosphabetaine Structures: II. Synthesis and Molecular Structure of 3-(Triphenylphosphonio)propanoate and Its Alkylation Products

The structure of 3-(triphenylphosphonio)propanoate was studied, and the ability of proton-donor reagents to stabilize the betaine structure was demonstrated. The phosphobetaines are alkylated by alkyl halides to form (alkoxycarbonyl)alkyltriphenylphosphonium halides and acylated by acetyl bromides. Some features of the latter reactions were revealed.

Synthesis and properties of phosphabetaine structures: IV. 3-(triphenylphosphonio)propanoate in reactions with dipolar electrophilic reagents

Reactions of 3-(triphenylphosphonio)propanoate with heterocumulenes, such as phenyl isocyanate and dicyclohexylcarbodiimide, we studied under the assumption that they proceed by nucleophilic addition and 1,4-dipolar cycloaddition schemes. Quantum-chemical calculations show that the σ5-phosphorane cycloadduct of the betaine with isocyanate is thermodynamically preferred over its isomeric zwitter-ionic adduct. However, the experimental evidence suggests that the reaction with phenyl isocyanate involves nucleophilic addition of the betaine to isocyanate followed by hydrolysis to firm finally a complex of the starting betaine with diphenylurea. The structure of the complex was established by X-ray diffraction analysis. The revealed above controversy is explained by a high protophilicity of betaine structures, which is also confirmed by the results of the reaction of the betaine with carbodiimide.

Synthesis, Structure and Reactivity of Carboxylate Phosphabetaines

Abstract Triphenylphosphoniumethylcarboxylate 1 has been obtained in the reaction of triphenylphosphine with acrylic acid.