One-Pot Synthesis of 1,4-Dihydropyridines via Hantzsch Reaction Using Nano-kaolin/BF3/Fe3O4 as a Green Catalyst under Solvent-Free Conditions

1,4-Dihydropyridine derivatives exhibit a large range ofbiological activities. They have beenused as anticonvulsant, antidepressive, antianxiety, analgesic, antitumoral, hypnotic, vasodilator,bronchodilator and anti-inflammatoryagents [1]. Some of them, such as amlodipine, felodipine,isradipine, lacidipine and nifedipine are effective drugsas calcium-channel blockersfor the treatment ofcardiovascular diseases and hypertension.1,4-dihydropyridinesare alsogood precursors of the correspondingsubstituted pyridine derivatives and constitute usefulreducingagents for imines in the presence of a catalyticamount of lewis acid [2]. Hantzschfirst reported in 1882 theone-pot three-component condensation of an aldehydewith ethylacetoacetate (or 1,3-dicarbonyl compounds) and ammonia (or ammonium acetate) in aceticacid or refluxingalcohol [3]. Yields of the resulting 1,4-dihydropyridinesare usually modestand in recent years, several newefficient methods have been developed including the useofmicrowaves, ionic liquids, TMSCl–NaI, metal triflates, molecular iodine, SiO2/NaHSO4,SiO2/HClO4, ceric ammonium nitrate, Na- and Cs-norit carbons, tetrabutylammonium hydrogensulfate, fermentingbaker’s yeast, and organocatalysts [4].In this study, we report our results for the synthesis of 1,4-dihydropyridines by a one-pot cyclocondensationof aldehyde with ethyl acetoacetate and ammonium carbonate using nanokaolin/BF3/Fe3O4 as a magnetic catalyst under solvent-free conditions (Fig.1). The advantagesof this study involve in use of solvent-free conditions, an easy experimental work-up system,rapidity, recyclable catalyst and green process.