Addition regioselective d'organometalliques α-insatures ou α-fonctionnels au chlorure de n-ethoxycarbonylpyridinium : synthese de dihydro-1,2 (ou -1,4) pyridines 2-(ou 4-)substituees.

α-unsaturated and α-functional organometallics easily react with 1-ethoxycarbonylpyridinium chloride to lead to 1,2 (or 1,4) substituted dihydropyridines. From these dihydropyridines, either pyridines or piperidines can be prepared.     

Synthesis of Functionalized 1‐Benzamido‐1,4‐dihydropyridines via a One‐Pot Two‐Step Four‐Component Reaction

The one‐pot four‐component reaction of benzohydrazide, acetylenedicarboxylate, aromatic aldehydes and malononitrile in ethanol with triethylamine as base catalyst afforded functionalized 1‐benzamido‐1,4‐dihydropyridines in satisfactory yields. Under similar conditions, picolinohydrazide or nicotinohydrazide can also be successfully utilized in the reactions to give corresponding functionalized 1,4‐dihydropyridines. ¹H NMR data indicated that an equilibrium of cis/trans‐conformations exist in 1‐benzamido‐1,4‐dihydropyridines.     

Enantioselective C3-Allylation of Pyridines via Tandem Borane and Palladium Catalysis

Herein, we report a one-pot method for enantioselective C−H allylation of pyridines at C3 via tandem borane and palladium catalysis. This method involves borane-catalyzed pyridine hydroboration to generate dihydropyridines, then palladium-catalyzed enantioselective allylation of the dihydropyridines with allylic esters, and finally air oxidation of the allylated dihydropyridines to afford the products. This method enables the introduction of an allylic group at C3 with excellent regio- and enantioselectivities.     

Silica Chloride/NaNO 2 as a Novel Heterogeneous System for the Oxidation of 1,4-Dihydropyridines Under Mild Conditions via In Situ Generation of NOCl

A combination of silica chloride and sodium nitrite in the presence of wet SiO 2 were used as an effective oxidizing agent for the oxidation of dihydropyridines to their corresponding pyridine derivatives under mild and heterogeneous conditions in moderate to excellent yields.     

Metal-free Brønsted acids catalyzed synthesis of functional 1,4-dihydropyridines

Brønsted acids catalyze the addition of β-enaminoacrylates to α,β-unsaturated aldehydes leading to substituted dihydropyridines in moderate to good yields under mild conditions. The first example of an enantioselective synthesis of a dihydropyridine is also reported.     

Aromatization of Hantzsch Ester 1,4‐Dihydropyridines with Iodine under Normal Conditions and Ultrasound Irradiation

A variety of Hantzsch ester 1,4‐dihydropyridines are efficiently oxidized to their corresponding pyridine compounds with iodine under normal conditions and ultrasound irradiation. The reactions were carried out in refluxing CH₃CN.     

An Efficient,Three-component One-pot Preparation of 1,4-Dihydropyridines Containing Novel Substituted Pyrazole under Sulfamic Acid Catalysis

An efficient approach to 1,4‐dihydropyridines containing novel substituted pyrazole is achieved via three‐component reaction of pyrazolyl aldehyde, β‐ketoester, and ammonium acetate in one‐pot under sulfamic acid catalysis.     

Ionic Liquid [EMIM]OAc under Ultrasonic Irradiation towards Synthesis of 1,4‐DHP's

The ionic liquid 1‐ethyl‐3‐methylimidazole acetate ([EMIM]OAc) was found to be a mild and effective catalyst for the efficient, one‐pot, three‐component synthesis of 1,4‐dihydropyridines from arylaldehydes, ethylacetoacetate/acetylacetone and ammonium acetate at room temperature under sonication. The developed method has many advantages, including devoid of harmful catalysts, reacting at room temperature, higher yields in a simple methodology or operational convenience.     

Aromatization of Various 1,4‐Dihydropyridines by Tetrabutylphosphonium Dichromate (TBPDC) under Conventional Heating and Microwave Irradiation

Tetrabutylphosphonium dichromate (TBPDC) has been found an efficient oxidizing agent for the aromatization of various 1,4‐dihydropyridines to their pyridine derivatives in refluxing acetonitrile and also under microwave irradiation. Short reaction times and clean workup are the advantages of this method.     

KHSO4 Supported Onto Bentonite,A Versatile Reagent for Aromatization of Hantzsch 1,4‐Dihydropyridines

Aromatization of Hantzsch 1,4‐dihydropyridines was promoted by KHSO₄, a relatively green chemical, supported onto bentonite to yield the corresponding pyridine derivatives in excellent yields. The reaction was carried out under mild and convenient conditions.     

Substituent Effect on the Photolability of 4‐Aryl‐1,4‐Dihydropyridines

The electronic nature of substituents attached to the 4‐aryl moiety of 1,4‐dihydropyridines strongly affects the photophysical and photochemical behavior of these family of compounds. The presence of an electron donor substituent on the 4‐aryl moiety (or the absence of electron‐withdrawing ones) modifies the luminescence lifetimes (τ < 100 ps) and diminishes the photodecomposition quantum yields. For electron‐withdrawing substituents, the photodegradation quantum yield is affected by the media, changing more than two orders of magnitude as the polarity is increased. Studies in micellar media allow us to conclude that 4‐aryl‐1,4‐dihydropyridines are located near to the interface; however, the surface charge of micelles has no effect on the photodegradation rate constant or the photoproducts profile. The main conclusion of this work is that the photolability of 4‐aryl‐1,4‐dihydropyridines can be significantly reduced by the incorporation of antioxidant moieties.     

Synthesis of novel 2-chloro-1,4-dihydropyridines by chlorination of 2-hydroxy-1,4-dihydropyridines with phosphorus oxychloride

Novel 2-chloro-1,4-dihydropyridine derivatives were synthesized by chlorination of 2-hydroxy-1,4-dihydropyridines with POCl3. The dihydropyridines chlorinated at position 2 exhibited more potent vasodilative and hypotensive activities than the dihydropyridines (nicardipine and nitrendipine) with a methyl group at position 2.     

Catalyst‐Free One‐Pot Synthesis of Ketene Imines under Ultrasound Irradiation

An efficient and simple procedure for the synthesis of ketene imines via a one‐pot three‐component reaction of cyclohexyl isocyanide, diethyl acetylenedicarboxylate, and 1,4‐dihydropyridines under ultrasonic irradiation is described. The remarkable advantages are the simplicity of the experimental procedures, high yields, and short reaction times.     

Unusual Oxidative Dealkylation of Certain 4-Alkyl-1,4-Dihydropyridines With MnO2/Bentonite Using Microwave Irradiation,in the Absence of Solvent (II)

Several Hantzsch 4-alkyl-1,4- dihydropyridines have been oxidized to the corresponding aromatic systems. An unexpected mixture of 4-alkyl pyridines and/or dealkylated pyridines are formed.     

Highly Site Selective Formal [5+2] and [4+2] Annulations of Isoxazoles with Heterosubstituted Alkynes by Platinum Catalysis: Rapid Access to Functionalized 1,3‐Oxazepines and 2,5‐Dihydropyridines

Platinum‐catalyzed formal [5+2] and [4+2] annulations of isoxazoles with heterosubstituted alkynes enabled the atom‐economical synthesis of valuable 1,3‐oxazepines and 2,5‐dihydropyridines, respectively. Importantly, this Pt catalysis not only led to unique reactivity dramatically divergent from that observed under Au catalysis, but also proceeded via unprecedented α‐imino platinum carbene intermediates.     

Ytterbium-catalyzed synthesis of dihydropyridines

The reaction of anilines, benzaldehydes, and ethyl 3,3-diethoxypropionate in the presence of Yb(OTf)₃ proceeded under mild reaction conditions to give dihydropyridines (DHPs). We have found that the reaction depended on the solvent and the DHPs were obtained selectively in 1,4-dioxane as a solvent. Various 2,6-unsubstituted DHPs were synthesized in one pot in satisfactory yields.     

Dihydropyridine-based MCRs. New reaction pathways in the interaction with ethyl glyoxalate and non-aromatic amines

The Lewis acid-catalyzed interaction of dihydropyridines with ethyl glyoxalate and primary aliphatic amines yields, depending on the reaction conditions, bicyclic aminals or rearranged tetrahydropyridines in one-pot multicomponent reactions.     

One pot synthesis of nitrogen-containing polycyclic delta-lactones by double nucleophilic addition of bis(trimethylsilyl)ketene acetals to pyridines

Pyridine and bis(TMS)ketene acetals (TMS = trimethylsilyl) react successively with methylchloroformate and iodine (or peracids) to give, via functionalized dihydropyridines, bicyclic nitrogen-containing lactones which have been characterized by X-ray crystallography.     

Microwave-assisted ammonium formate-mediated synthesis of Hanstzch dihydropyridines under solvent-free conditions – a green protocol

Abstract

Microwave-assisted ammonium formate-mediated eco-friendly synthesis of structurally varied Hantzsch dihydropyridines under solvent-free conditions has been successfully accomplished with good yield, minimization of toxic reagents and organic solvents in the process. The elimination of the inorganic support decreased the disposal problem and the extremely small reaction time minimized energy dissipation.     

Microwave‐assisted synthesis of phenylenedi(4′,4“‐tetrahydroquinoline) and di(4′,4”‐tetrahydropyridine) derivatives

The synthesis of bifunctional pyridine and quinolione derivatives were investigated using terephthalic and isophthalic aldehydes as a precursor. The reaction proceeds under microwave irradiation with good yield (70–92%) and short reaction time (7–9 min.). We provide a rapid and efficient method of synthesizing a range of bifunctional monocyclic and bicyclic products related to 1,4‐dihydropyridines (1,4‐DHPs).