Photoredox/palladium-cocatalyzed enantioselective alkylation of secondary benzyl carbonates with 4-alkyl-1,4-dihydropyridines

A photoredox/palladium-cocatalyzed enantioselective alkylation of racemic secondary carbonates with 4-alkyl-1,4-dihydropyridines under visible light irradiation has been developed. The present study provides a method for the preparation of optically active diarylalkanes from racemic diarylmethyl carbonates by a dynamic kinetic asymmetric transformation(DYKAT).This photoredox/palladium dual catalysis strategy expands the scope of the asymmetric Pd-catalyzed benzylic substitution reaction and serves as its potential alternative and complement.     

Recyclization of 1,4-dihydropyridine derivatives in acidic medium

The recyclization of 1,4-dihydropyridines in aqueous-alcoholic hydrochloric acid medium proceeds with cleavage of a C-N bond and pyridine ring opening. Cyclohexenone derivatives are formed as a result of the subsequent intramolecular crotonic condensation of the acyclic intermediate. The leaving carbonyl substituents depart simultaneously with recyclization, depending on the acidity of the reaction medium. Dedicated to Prof. Dr. E. Lukevics on the occasion of his 70th birthday. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 49–58, January, 2007.     

Microwave-assisted combinatorial synthesis of hexa-substituted 1,4-dihydropyridines scaffolds using one-pot two-step multicomponent reaction followed by a S-alkylation

A sequential one-pot two-step protocol for microwave-assisted synthesis of Hantzsch-type hexa-substituted 1,4-dihydropyridines has been developed. The three-component reactions of beta-aroylthioamides with aldehydes and acetonitrile derivatives produce the intermediates in situ followed by a S-alkylation to afford hexa-substituted 1,4-dihydropyridines. The reaction presumably proceeds via a Knoevenagel condensation-Michael addition-cyclocondensation-rearrangement-S N2 reaction sequence. Target compounds were obtained in high yields and simply purified by recrystallization. The novel method is complementary to the classical Hantzsch synthesis in that it is well-suited to the preparation of hexa-substituted 1,4-dihydropyridines.     

2,6-二甲氧基-3-烷基-1,4-苯醌的合成

取代的1,4-苯醌类化合物广泛存在于自然界的植物和动物体内。其中有一部分已证明具有明显生理活性。最重要的取代1,4苯-醌类化合物是泛醌(ubiquinone)和质体醌(plastoquinone)。它们是动物线粒体呼吸链和植物光合作用链中重要的非蛋白电子载体。2,6-二甲氧基-1,4-苯醌(4)存在于许多植物的树皮和木心中。它的生理作用目前还知道得     

Free radicals of electrochemical reduction of derivatives of 3-nitro-1,4-dihydropyridines

By means of ESR, under conditions of eletrochemical generation of particles, the formation of four types of secondary free radicals has been confirmed in the process of electrochemical reduction of molecules of N-unsubstituted derivatives of 3-nitro-1,4-dihydropyridine in dimthylformamide — specifically, a dianion radical of the molecule of the original compound; an anion radical of the corresponding isomeric 4,5-dihydropyridine; a radical of the nitroalkane type; and in addition, for the compound substituted with a nitrobenzene group; a free radical with the nitrobenzene structure. Methods for synthesis of the individual compounds are described, and a scheme is presented for the mechanism of their electrochemical conversion.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 355–364, March, 1995. Original article submitted February 21, 1995.     

Mechanism of disproportionation of 2,2,6,6-tetramethyl-1,4-dioxopiperidinium perchlorate in acidic aqueous medium

The cation of 2,2,6,6-tetramethyl-1,4-dioxopiperidinium perchlorate disproportionates in acidic aqueous medium to give piperidinoxyl and/or 1-hydroxypiperidine, nitrone, and acetone. A mechanism of this reaction was proposed and the rate constants for its particular steps were calculated.     

New synthesis of 4-alkyl-3-cyanocoumarins

A new procedure has been developed for the synthesis of 4-alkyl-6,8-dibromo-7-hydroxy-2-oxo-2H-chromene-3-carbonitriles by bromination of 2-amino-4-alkyl-4H-chromene-3-carbonitriles with bromine in acetic acid, followed by hydrolysis.     

New derivatives of 4-aryl-2,6-dimethyl-3,5-diacetyl-1,4- and 1,2-dihydropyridines

4-Aryl-1,2,6-trimethyl-3,5-diacetyl-1,4-dihydropyridines and the corresponding pyridinium salts, which upon reduction with NaBH₄ form 4-aryl-1,2,6-trimethyl-3,5-diacetyl-1,2-dihydropyridines, were synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 508–513, April, 1983.     

Synthesis of 1,4-dihydropyridines in cyclocondensation reactions (review)

The 1986–1990 literature on the formation of 1,4-dihydropyridines in the Hantzsch synthesis and other cyclocondensation reactions is summarized and correlated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 435–467, April, 1992.     

Systematic HPLC Study of a New Series of 4-Methyl-1,4-dihydropyridines with Antitrombotic Activity

Abstract

A systematic study of a new series of 4-methyl-1,4-dihydropyridine derivatives by HPLC by both photodiode array and electrochemical detectors is reported.

The optimum mobile phase was acetonitrile 0.05 M phosphate buffer pH 3 (55/45, v/v) at a flow-rate of 1.5 mL/min.

Compounds I–VIII were determined with UV detection at 250 nm and by electrochemical detection at + 1200 mV.

Retention times varied between 3.0 and 14.0 minutes in the optimal experimental conditions.

Good linear relationships between the peak areas and concentration were found, with limits of quantification ranging between 1 x 10^?8 M and 1 x 10^?6 M. Repeatability studies showed average variation coefficients lower than 1% for a photodiode array detector. No significant differences between the detectors in sensitivity and selectivity were found.

Also, we used different degradation trials to test the selectivity of the methods. Results of these experiments revealed that the developed methods exhibited a good selectivity.     

Electronic structures and reactivities of derivatives of 1,4-dihydropyridines. 3. Enthalpies of elementary processes in the 1,4-dihydronicotinamide series

The heat effects of the elementary processes involved in electron and hydrogen transfer with the participation of 1,4-dihydropyridines were calculated by the semiempirical MINDO/3 method. The effect of a number of side and parallel processes on the kinetic principles is discussed in the case of the oxidation of 1-methyl-1,4-dihydronicotinamide. The calculated and experimental data are compared.See [1] for Communication 2.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 63–66, January, 1988.     

Reactivity of bis-vinylphosphates obtained from imide derivatives. Synthesis of 2,6-disubstituted 1,4-dihydropyridines

The Pd-catalyzed functionalization of lactam-derived vinyl phosphates has become an important tool in the last decade for the synthesis of nitrogen-containing heterocycles. By using this method, we were able to introduce alkenyl, aryl and heteroaryl groups on bis-vinylphosphate derivatives to provide efficient access to 2,6-disubstituted 1,4-dihydropyridines.     

Electrochemical oxidation of C4-vanillin- and C4-isovanillin-1,4-dihydropyridines in aprotic medium: Reactivity towards free radicals

This work reports the electrochemical oxidation of two new synthetic C4-vanillin and -isovanillin-1,4-dihydropyridines in aprotic medium. Its reactivity with alkylperoxyl radicals ABAP-derived at pH 7.4 is also studied. Voltammetry, coulometry, controlled-potential electrolysis, UV–visible spectroscopy and GC–MS techniques were employed to collect data that permitted us to study its oxidation. Effect of TBA-OH addition on the oxidation was electrochemically and spectroscopically followed. In aprotic medium, the oxidation mechanism involves the formation of the pyridine derivative, which was generated by controlled-potential electrolysis (CPE) at 1270 mV and identified by GC–MS technique as the final product of the electrolysis. Spectroelectrochemical experiments also support the formation of the pyridine derivative from the oxidation of both 1,4-dihydropyridines. Direct reactivity of synthesized compounds towards alkylperoxyl radicals ABAP-derived was determined. Results reveal that the inclusion of vanillin radical or its positional isomer, isovanillin in the 4-position of the dihydropyridine ring produced a significant positive effect on the reactivity towards alkylperoxyl radicals, even compared with commercial dihydropyridine drugs with a well-known antioxidant ability. Scavenging mechanism involves the electron-transfer and the formation of a pyridine derivative, which was identified by GC–MS.     

New method of synthesis of 3-alkyl-4-piperidones

A new method is presented for the synthesis of 3-substituted 4-piperidones by alkylation of lithium derivatives of 4-(-phenylethylimino) piperidines using alkyl halides.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 372–374, March, 1986.     

Synthesis of 4-alkyl-3-pyridinols from 3-benzyloxypyridine

The addition of Grignard reagents to the 1-phenoxycarbonyl salt of 3-benzyloxypyridine and a catalytic amount of cuprous iodide afforded 4-alkyl-3-benzyloxy-1-phenoxycarbonyl-1,4-dihydropyridines in good yield. The crude dihydropyridines were aromatized with o-chloranil to give 4-alkyl-3-benzyloxypyridines, which were debenzylated with hydrogen and 10% palladium on carbon to provide 4-alkyl-3-pyridinols.     

Catalytic aromatization of Hantzsch 1,4-dihydropyridines by ferric perchlorate in acetic acid

Catalytic oxidation of Hantzsch 1,4-dihydropyridines is described using a catalytic amount of ferric perchlorate in acetic acid at room temperature.     

Synthesis of 2-alkyl-1,2,4-benzotriazin-3(2h)-ones and 2-alkyl-1,4-dihydro-1,2,4-benzotriazin-3(2h)-ones

A preparative method for the synthesis of 2-alkyl-1,2,4-benzotriazin-3(2H)-ones 3 was developed. The method involves treatment with sodium cyanate of 2-alkylbenzotetrazinium tetrafluoroborates, which exist in solutions in equilibrium with o-(alkylazo)aryldiazonium tetrafluoroborates. Reduction of compounds 3 with zinc in acetic acid afforded 2-alkyl-1,4-dihydro-1,2,4-benzotriazin-3(2H)-ones. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 346–349, February, 2006.