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

Abstract

Hantzsch first reported in 1882 the one-pot three-component condensation of an aldehyde with ethyl acetoacetate (or 1,3-dicarbonyl compounds) and ammonia (or ammonium acetate) in acetic acid or refluxingalcohol. Yields of the resulting 1,4-dihydropyridinesare usually modest and in recent years, several new efficient methods have been developed including the use of microwaves, ionic liquids, TMSCl–NaI, metal triflates, molecular iodine, SiO2/NaHSO4, SiO2/HClO4, ceric ammonium nitrate, Na- and Cs-norit carbons, tetrabutylammonium hydrogen sulfate, fermentingbaker’s yeast, and organocatalysts.