One-pot Synthesis of 5-oxo-hexahydroquinoline and 1,4-dihydropyridine derivatives through the Hantzsch four component condensation in the presence of cellulose-sulfuric acid as efficient hetergenous catalyst

Heterogeneous solid acid catalysts for the synthesis of fine chemicals have attracted considerable attention from both environmental and economical points. They have opened new perspectives in synthetic organic chemistry not only in terms of yield and selectivity, but also concerning the work-up, recyclability, and mild reaction conditions. In particular cellulose-sulfuric acid is an efficient biodegradable and recyclable solid acid catalyst which has been used in the one-pot synthesis of quinolines [1] and xanthenes [2]. The catalyst simply was prepared by the reaction of chlorosulfuric acid with commercially available cellulose and the by product, HCl gas, is easily removed from the reaction vessel. On the other hand 4-substituted-1,4-dihydropyridines(1,4-DHPs) are analogues of NADH coenzymes and an important class of drugs [3-5]. These compounds possess a variety of biological activities. Classical methods for the synthesis of 1,4-dihydropyridines are one–pot condensation of an aldehyde with ethyl acetoacetate, ammonium acetate and 1,3-diones in the presence of Lewis acids. At present study we employed cellulose-sulfuric acid as reusable, eco-friendly and green catalyst in the reaction of dimedone &1,3-cyclohexandione or α-β unsaturated 1,3-dicarbonyl compound, arylaldehyde, ethyl acetoacetate and ammonium acetate in refluxing ethanol to furnish new derivatives of 4-aryl-1,4-dihydropyridines in high yields.