1,4-Dihydropyridine derivatives as deactivators of singlet oxygen

The constants of deactivation (k_q) of ¹O₂ by 1,4-dihydropyridine (1,4-DHP) derivatives were determined by quenching of the luminescence of singlet oxygen (¹O₂). The k_q values for 1,4-DHP derivatives range from 10⁶ to 10⁷ litersmole^–1-sec^–1 and depend to a considerable extent on the nature of the substituents in the 1,4-DHP ring. The presence of a substituent in the 4 position decreases k_q, while conversion of the 1,4-DHP system to the corresponding pyridine system deprives the compound of its ability to deactivate ¹O₂. As a result of tests of 12 1,4-DHP derivatives it was found that 2,6-dimethyl-3,5-di (phenylcarbamoyl)-1,4-dihydropyridine deactivates ¹O₂ most effectively.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 924–926, July, 1981.     

Fluorescence of 3,5-diethoxycarbonyl-1,4-dihydropyridine derivatives and their anions

The fluorescence spectra of a group of 3,5-diethoxycarbonyl-1,4-dihydropyridine (1,4-DHP) derivatives were investigated. The introduction of electron-acceptor N-substituents and 2,6-methyl groups decreases Q markedly. The fluorescence spectra of 1,4-DHP anions are shifted bathofluorically, and the Q values are higher than for the corresponding 1,4-DHP. The fluorescence spectra have large Stokesian shifts, which are decreased for 1,4-DHP anions. A good correlation exists between the _max values of the fluorescence bands of 1,4-DHP anions and the Hammett _p ⁺ constants of the 4-R-aryl substituents.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 67–70, January, 1988.     

Influence of 1,4-dihydropyridine derivatives on the generation of hydroxyl radicals

It was shown that a series of 1,4-dihydropyridine (1,4-DHP) derivatives in the NAD-H-Cu²⁺ -H₂O₂ system inhibit the formation of the hydroxyl radical (HO), while derivatives of 1,4-DHP with electron-donor substituents in the molecule are themselves capable of generating HO in the presence of Cu²⁺ and H₂O₂.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 519–521, April, 1992.     

FERRIC CHLORIDE HEXAHYDRATE: A CONVENIENT REAGENT FOR THE OXIDATION OF HANTZSCH 1,4-DIHYDROPYRIDINES

A general and practical route for the moderate yield oxidative conversion of readily accessible 1,4-dihydropyridines (1,4-DHPs) to the corresponding pyridines was described using a relatively benign oxidant, i.e. ferric chloride hexahydrate (FeCl₃·6H₂O). The reaction was carried out under mild and convenient condition. However, oxidation of 4-isopropyl-1,4-DHP 1b with FeCl₃·6H₂O afforded the dealkylated pyridine 2a.     

An efficient ‘on-water’ synthesis of 1,4-dihydropyridines using Fe3O4@SiO2 nanoparticles as a reusable catalyst

An ‘on-water’, efficient, high yielding, expeditious method has been developed for the synthesis of 1,4-dihydropyridine (1,4-DHP) derivatives via an one-pot multi-component condensation of dimedone or 4-hydroxycoumarine, aldehydes, and ammonium acetate using Fe₃O₄@SiO₂ nanoparticles as a recyclable heterogeneous catalyst. This method takes advantage of the fact that water, a green solvent is used in combination with Fe₃O₄@SiO₂ nanoparticles as catalyst which can be easily recovered magnetically and reused for further runs.     

N-alkylation of 1,4-dihydropyridine-3,5-dicarboxylic acid esters

Alkylation of the anions of 1,4-dihydropyridines (1,4-DHP) formed by treatment of sodium hydride in aprotic solvents gave 1-alkyl(up to C₆H₁₃)-3,5-bis(ethoxycarbonyl)- and 1-alkyl-3,5-bis(aryloxycarbonyl)-1,4-DHP. The presence of a substituent in the 4 position increases the reactivity of the 1,4-DHP anion in the alkylation reaction. The absorption maximum in the UV spectra of the 1,4-DHP anion is shifted 100 nm bathochromically as compared with the neutral molecule. The longwave absorption maximum in the UV spectra of 1-alkyl-1,4-DHP is shifted hypsochromically as compared with the 1-unsubstituted compounds; this is explained by steric hindrance of the conjugation of the C=O groups with the -electron system of the ring. The introduction of an alkyl group at the nitrogen atom facilitates the electrical oxidation of 1,4-DHP.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1508–1513, November, 1978.     

Reaction of derivatives of 1,4-dihydropyridine with the peroxynitrite anion

The reaction of derivatives of 1,4-dihydropyridine (1,4-DHP) with peroxynitrite anion is an oxidation reaction; no products of nitration were detected. It was found that some 1,4-DHP increase the lifetime of the peroxynitrite anion and the yield of hydroxyl radical in decomposition of the peroxynitrite anion.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 355–357, March, 1998.     

Fe3O4@SiO2@ADMPT/H6P2W18O62: a novel Wells–Dawson heteropolyacid-based magnetic inorganic–organic nanohybrid material as potent Lewis acid catalyst for the efficient synthesis of 1,4-dihydopyridines

A novel Wells–Dawson heteropolyacid-based magnetic Inorganic–organic nanohybrid, Fe₃O₄@SiO₂@ADMPT/H₆P₂W₁₈O₆₂, was fabricated and used as a green, efficient, eco-friendly, and highly recyclable catalyst for the one-pot and multi-component synthesis of 1,4-Dihydopyridine (1,4-DHP) derivatives from the reaction of various aromatic aldehydes with ethyl acetoacetate and ammonium acetate with good to excellent yields and in a short span of time. The nanohybrid catalyst was prepared by the chemical anchoring of Wells–Dawson heteropolyacid H₆P₂W₁₈O₆₂ onto the surface of functionalized Fe₃O₄ nanoparticles with 2,4-bis(3,5-dimethylpyrazol)-triazine (ADMPT) linker. These nanocatalysts were identified by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and vibrating sample magnetometer (VSM). This protocol is developed as a safe, cost-effective and convenient alternate method for the synthesis of 1,4-DHP derivatives utilizing an eco-friendly, and a highly reusable catalyst.     

Rapid, efficient, room temperature aromatization of Hantzsch-1,4-dihydropyridines with vanadium(V) salts: superiority of classical technique versus microwave promoted reaction

The aromatization of 1,4-dihydropyridines (1,4-DHPs) employing group 4 (Zr and Hf) and 5 (V, Nb, Ta) elements of periodic system has been studied. The reaction with VOCl₃ in dichloromethane at room temperature afforded products, substituted pyridines, in high-to-excellent yield. For the first time, the formation of charge-transfer complexes (CTCs) has been evidenced in preorganization step between 1,4-DHP and oxidant before electron transfer. The CTC has been formed only in neutral solvents such as dichloromethane and is characterized by intensive coloration. The aromatization of 1,4-DHP with V₂O₅ in refluxing acetic acid has found to be superior over microwave promoted reaction in solventless media. The only reasonable explanation was found in polymeric structure of V₂O₅, which slowly transfer energy of microwaves needed for the activation of the reactants. The solvent polarity dependent oxidative dealkylation of 4-n-propyl-1,4-DHP has been discovered. Unexpectedly, the reaction in acetic acid afforded only 33% of dealkylated product compared to 91% obtained in dichloromethane under the same reaction conditions.     

[3 + 3] Cycloaddition of aza-oxyallyl cations with 1,4-dithiane-2,5-diols for the construction of 3-thiomorpholinones

Abstract

Base-mediated [3?+?3] cycloaddition reaction of in-situ formed aza-oxyallyl cations and 1,4-dithiane-2,5-diols has been achieved under mild reaction conditions. This strategy provides direct and efficient access to prepare desired thiomorpholin-3-one derivatives in moderate-to-high yields. The approach features broad substrates scope and short reaction time. Moreover, the resulting products can be readily converted into other useful heterocyclic compounds including 2H-1,4-thiazin-3(4H)-ones and thiomorpholine-3,5-diones.     

Reductive ability of 1,4-dihydropyridine derivatives in relation to ions of trivalent iron

3,5-Dicarbonyl derivatives of 2,6-dimethyl-1,4-dihydropyridine (1,4-DHP) can reduce Fe³⁺ to Fe²⁺ depending on the nature of the substituents at position 4 and in the 3,5-ester group. This ability is less pronounced for the 1,4-DHP derivatives investigated than for ascorbic acid, but among derivatives possessing antioxidant activity it is less than that of the known antioxidants ionol (BOT) and trolox. Latvian Institute of Organic Synthesis, Riga, LV-1006, Latvia Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 661–663, May, 1999.     

An umpolung approach to the hydroboration of pyridines: a novel and efficient synthesis of N-H 1,4-dihydropyridines

The first inverse hydroboration of pyridine with a diboron(4) compound and a proton source has been realized under simple basic and catalyst-free conditions. This process consists of a formal boryl anion addition to pyridine, which produces an N-boryl pyridyl anion complex, and the subsequent protonation of the anion complex. This process enables a simple and efficient method for the synthesis of multi-substituted N-H 1,4-dihydropyridine (1,4-DHP) derivatives that are difficult to prepare using established methods. Furthermore, this method allows for facile preparation of 4-deuterated 1,4-DHPs from an easily accessible deuterium ion source. This inverse hydroboration reaction represents a new mode for pyridine functionalization.

Umpolung of pyridine hydroboration was achieved by the reaction between pyridine and diboron(4) with a base and a proton source.     

Organocatalyzed regioselective and enantioselective synthesis of 1,4- and 1,2-dihydropyridines

Abstract

Herein, we introduce one of the first examples of asymmetric organocatalyzed synthesis of 1,2-dihydropyridines, affording enantioselective access to and partially solving regioselectivity challenges in the synthesis of dihydropyridines. We demonstrate that through modification of organocatalysts both 1,2- and 1,4-dihydropyridines (1,2- and 1,4-DHPs) can be obtained with high regioselectivity (ratio of 1,2-DHP/1,4-DHP from 95/5 to 0/100) and enantioselectivity (33% ee for 1,2-DHPs and up to 98% ee for 1,4-DHPs) in good yields (up to 87%).     

Efficient and Convenient Synthesis of 1,4-Benzoxazines, 1,4-Benzothiazines,Spiro-1,4-benzoxazines,and Spiro-1,4-benzothiazines

An efficient, convenient synthesis of 1,4-benzoxazines, 1,4-benzothiazines, spiro-1,4-benzoxazines, and spiro-1,4-benzothiazines derivatives was accomplished in good yields via the novel intramolecular cyclization mediated by mild base K₂CO₃ in ethanol solvent. A variety of substrates can participate in the process with good yields, making this methodology have broad applicability. All the structures of synthesized compound have been confirmed by spectral analysis.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications ^® to view the free supplemental file.     

Homo-1,4-addition to cyclo-octa-1,4-diene and cyclohepta-1,4-diene

Cyclo-octa-1,4-diene and cyclohepta-1,4-diene give the bicyclic derivatives IIa–b and IVa–b on reaction with Br₂-CCl₄ or I₂-AgClO₄-MeOH respectively. Cyclo-octa-1,4-diene also undergoes homo-1,4-addition in the Prevost reaction with I₂-AgOAc or I₂-AgOCOPh in benzene.     

Synthesis and Characterization of Nitrogen and Sulfur Containing 1,4-Naphthoquinones

Abstract

New N,S-disubstituted naphthoquinones were synthesized by reactions of S- and N-nucleophiles with 2,3-dichloro-1,4-naphthoquinone. 2-(Hexadecylthio)-3-(phenylamino)-naphthalene-1,4-dione 5a was synthesized by reaction of 2-chloro-3-(phenylamino)-naphthalene-1,4-dione 3a with hexadecanethiol 4a. The structures of the new synthesized naphthoquinone derivatives were determined by micro analyses and spectroscopic methods (FT-IR, ¹H NMR, ¹³C NMR, MS, and UV/Vis.). Photo- and electrochemical properties of selected compounds were investigated by using fluorescence spectroscopy and the cyclovoltammetry method.     

Phenyliodine(III) Diacetate/I2-Mediated Domino Approach for Pyrrolo[1,4]Thiazines and 1,4-Thiazines by a One-Pot Morin Rearrangement of N,S-Acetals

An efficient domino transformation using a phenyliodine(III) diacetate (PIDA)/I₂ combination towards Morin 1,4-thiazine compounds has been developed starting from N,S-acetals. The latter leads to “one-step” regioselective methylene insertion without the need for traditional sulfoxide intermediates in good yields. The reaction involves easily accessible N,S-acetals obtained from cost-effective basic ketones and cysteamine as starting materials. This process ultimately leads to 1,4-thiazines related to natural product and fused derivatives necessary for further QSAR study.     

Synthesis of Bis‐1,4‐Dihydropyridine Derivatives

Abstract

A series of bis‐1,4‐dihydropyridine derivatives were synthesized by the reaction of p‐phenylenedialdehyde or m‐phenylenedialdehyde and active methylene compounds.     

Me3SiCl and Et3SiI‐promoted one‐pot synthesis of 1,4‐dihydropyridine derivatives

An efficient synthesis of 1,4‐dihydropyridine derivatives has been achieved by the one‐pot cyclocondensation reaction of methyl 3‐aminocrotonate and a range of aldehydes in the presence of chlorotrimethylsilane as a promoter under solvent‐free conditions. The cyclocondenstion reaction requires a very short time and takes place in good to excellent yields. Furthermore iodotriethylsilane, generated in situ by the reaction of triethylsilane and methyl iodide in the presence of palladium chloride, has been investigated for the synthesis of 1,4‐dihydropyridine derivatives. This facile and efficient method affords high yields for the preparation of 1,4‐dihydropyridines at room temperature and short reaction times. Copyright © 2009 John Wiley & Sons, Ltd.     

Iodinated 1,4-naphthoquinones

Iodination of 5-amino- and 6-amino-1,4-naphthoquinones with I₂ and HIO₃ in aqueous dioxane occurs only at the benzoid ring. Depending on the reaction conditions, either aminoiodo- or aminodiiodonaphthoquinones are produced. Diazotization of these compounds followed by reduction or replacement of the diazo group with iodine affords mono- or polyiodo derivatives of 1,4-naphthoquinone. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1465–1469, June, 2005.