LiBr as an Efficient Catalyst for One-pot Synthesis of Hantzsch 1,4-Dihydropyridines under Mild Conditions (original) (raw)
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2014
An efficient Hantzsch synthesis of various substituted 1,4-dihydropyridines from an aldehyde, a β-dicarbonyl compound and ammonium acetate using p-toluenesulfonic acid in a solvent-free condition in the absence of any other co-catalyst is described. The process is simple and environmentally benign and the catalyst is commercially available and inexpensive. This method has the advantages of excellent yield (80-96%) and short reaction time (5-20 min.). Irradiation of a typical 1,4-dihydropyridine leads to the corresponding pyridine.
A Review: Alternative Methods of Preparing 1, 4- Dihydropyridine Derivatives by Hantzsch Reaction
Journal of Scientific Research
1, 4-dihydropyridines and its derivatives are an important class of heterocyclic scaffolds of low molecular weight. Dihydropyridines act as calcium-channel blockers. They have been used for the treatment of a variety of cardiovascular diseases due to their potential antihypertensive, anti-angina, vasodilator, and cardiac depressant activities. They show antibacterial, anticancer, anti-leishmanial, anticoagulant, anticonvulsant, anti-tubercular, antioxidant, antiulcer, and neuroprotective properties. The reaction to produce 1, 4-dihydropyridines (1, 4-DHPs) was reported by Arthur Hantzsch. This review article will throw light on some green attempts done to improve the synthesis of 1, 4-Dihydropyridine derivatives via Hantzsch reaction.
Hantzsch 1,4-dihydropyridines (1,4-DHPs) are useful as vasodilators, bronchodilator and anti-hypertensive, hepta-protective, anti-tumor, anti-mutagenic, gero-protective and antidiabetic agents. 1 Nifedipine, nitrendipine and nimodipine for example have found commercial utility as calcium channel blockers. 2-4 A number of DHP calcium antagonists have been introduced for the treatment of congestive heart failure 5,6 some DHPs have been introduced as a neuroprotectant and cognition enhancer. In addition, a number of DHPs with platelet anti-aggregatory activity have also been discovered. 1,4-DHPs have been synthesized by the Hantzsch reaction 8 which involves the cyclocondensation of aldehydes with compounds containing methylene group activated by carbonyl groups (ethyl or methyl acetoacetate, acetylacetone) and ammonium acetate/ammonia/primary amine 9 under long reflux in acetic acid or ethanol. Recently, several improved procedures for the synthesis of 1,4-DHPs have been reported by using CAN, 10 silica gel/NaHSO 4 , 11 Sc(OTf) 3 , 12 microwave-assisted synthesis with catalysts, ionic liquids, and reflux at high temperature. However, there are several drawbacks associated with the reported methodologies. Reactions carried out under solvent-free conditions offer several advantages such as formation of cleaner products, simpler work-up, enhanced selectivity and pronounced reaction rates. Polyethylene-glycols (PEGs) are known to function as efficient phase-transfer catalysts in a variety of organic reactions. 20,21 In addition, PEGs are non-toxic, thermally stable and inexpensive compared to conventional phase-transfer catalysts such as crown ethers or quaternary ammonium salts. We now report a solvent-free synthesis of 1,4-dihydropyridines using a catalytic amount of anhydrous lithium carbonate and PEG400.
A new three-component domino synthesis of 1,4-dihydropyridines
Tetrahedron, 2007
Cerium ammonium nitrate (CAN) catalyzed the three-component domino reaction between aromatic amines, a,b-unsaturated aldehydes, and ethyl acetoacetate, providing an efficient new entry into 1,4-dihydropyridines. This new reaction requires very mild reaction conditions, has water as the only side product and is complementary to the classical Hantzsch synthesis in that it is well suited to the preparation of N-aryl-5,6-unsubstituted dihydropyridines. Experiments in the presence of a radical trap suggest that a one-electron oxidative mechanism can be excluded and that CAN acts as a Lewis acid.