B. S. Chekavichus

13C-NMR spectra of substituted 1,4-dihydropyridines

It has been found that the electron shift in the C(2)=C(3) bond, under the influence of the substituent attached to the nitrogen atom and the substituents in the 3- and 5-positions, occurs via a π-inductive mechanism. 4-(1,4-Dihydropyridyl) functional groups behave as electron donating substituents via an inductive mechanism.

Formation of derivatives of 5,6-dihydro-1,3-thiazines in the reaction of acetothioacetic acid ethyl ester under the conditions of the Hantzsch synthesis

Derivatives of 2H-5,6-dihydro-1,3-thiazine are formed by the reaction of acetothioacetic acid ethyl ester with aromatic aldehydes on heating in ethanol in the presence of aqueous ammonia.

Bromination of 4-aryl-3,5-dialkoxycarbonyl-2,6-dimethyl-1,4-dihydropyridines

Abstract4-Aryl-3,5-dialkoxycarbonyl-2,6-dimethyl-1,4-dihydropyridines are brominated by N-bromosuccinimide in methanol at room temperature at the methyl groups at positions 2 and 6 to form mono-, di-, tri-, and tetrabromo derivatives. When the N-unsubstituted bromomethyl-1,4-dihydropyridines are heated they are easily converted to tetrahydrofuropyridines, but in the case of the analogous N-substituted-1,4-dihydropyridines cyclization does not occur. The 2,6-bis(bromomethyl)-substituted products easily replace bromine under the influence of nucleophilic reagents.

Effect of substituents in the dihydropyridine ring on the reactivity of the ester group of 3,5-dialkoxycarbonyl-1,4-dihydropyridines

The reactivity of the ester group of 3,5-dialkoxycarbonyl-1,4-dihydropyridines upon reaction with nucleophilic reagents increases when substituents are absent in the ortho positions relative to the ester group and also in the case of steric disruption of the coplanarity of the β-aminovinylcarbonyl system when substituents are introduced at the nitrogen atom in 2,6-dimethyl derivatives. Mono- and dicarboxylic acids were obtained by hydrolysis of such esters. Thus use of esters of propiolic acid esters and arylamines in the Hantzsch synthesis made it possible to obtain 1-aryl-2,6-unsubstituted derivatives of 1,4-dihydropyridine.

Synthesis and electrochemical oxidation of 1-aryl-3,5-diethoxycarbonyl-2,6-unsubstituted 1,4-dihydropyridines

The possibility of obtaining 1-aryl-3,5-diethoxycarbonyl-2,6-unsubstituted 1,4-dihydropyridines with electronacceptor substituents in the N-phenyl radical was demonstrated. The intermediate products of their formation, viz., 2,4-bis(arylaminomethyiene)-3-phenylglutaric acid esters, were established. The electrochemical oxidation potentials of 1-aryl-2,6-unsubstituted 1,4-dihydropyridines are 100–200 mV higher than those of the 2,6-dimethyl analogs. A linear correlation between the electrochemical oxidation potentials and the Taft σ0 constants of the substituents in the 1-phenyl ring was established.

Formation of a derivative of 3,3,5-tricarbonyl-1,2,3,4-tetrahydropyridine under the conditions of the hantzsch synthesis

An ester of p-nitrobenzoylacetic acid is cyclized under the action of hexamethyl-enetetramine and ammonium acetate to 3,5-diethoxycarbonyl-3-p-nitrobenzoyl-6-p-nitrophenyl-1,2,3,4-tetra-hydropyridine, the structure of which has been established by NMR, UV, IR, and mass spectra and also by its chemical reactions.

ESR spectra of free radicals of 3,3-disubstituted 1,2,3,4-tetrahydropyridines produced during electrochemical reduction

The polarographic properties (potentials, number of electrons, reversibility) of the electrochemical reduction of 3,5-diethoxycarbonyl-3-(p-nitrobenzoyl)-6-(p-nitrophenyl)-1,2,3,4-tetrahydropyridine and its derivatives in dimethylformamide have been determined. In the course of the electrochemical generation, ESR spectra of primary radical anions of p-nitrobenzoyl structure were obtained along with ESR spectra of nitrophenyl-p-substituted free radicals formed as a result of further reduction.

Synthesis and oxidation of 2,6-dimethyl-1,4-dihydropyridine-3, 5-dicarboxylic acid esters

Twenty-six esters of 2,6-dihydropyridine-3,5-dicarboxylic acid were obtained by means of the Hantzsch pyridine synthesis. The synthesized compounds were oxidized by chloranil to the corresponding pyridine derivative.

Voltamperometry of 1,4-dihydropyridine derivatives

Thirty-nine γ-substituted 1,4-dihydropyridine derivatives were subjected to electrochemical oxidation on a rotating platinum microelectrode in acetonitrile, and the Ep (E1/2) values were measured. A satisfactory linear correlation between the Ep and Taft. σ* constants of the substituents in the γ position was observed. A linear correlation of the Ep values with the σ0, α- and σ− constants also exists.

FREE RADICALS IN ELECTROCHEMICAL REDUCTION OF 1-(NITROPHENYL)-3,5-DICARBETHOXY-4-PHENYL-1,4-DIHYDROPYRIDINES

In the primary electrochemical reduction of 1-(nitrophenyl)-3,5-dicarbethoxy-4-phenyl-1,4-dihydropyridine in DMF, free radicals of nitrophenyl type are formed; these are the products of a one-electron reduction of cathode-protonated molecules of the original compound. In alkaline DMF, where cathodic protonation of the initial compound is retarded, union-radicals of the starting material are generated in addition, together with p-nitrophenol free radicals.