Melamine trisulfonic acid as an efficient catalyst for the synthesis of 2,6-dimethyl-4-substituted-1,4- dihydropyridine-3,5-diethyl/dimethylcarboxylate derivatives via Hantzsch reaction in solvent free condition

A facile and highly efficient one-pot synthesis of 1,4-dihydropyridine derivatives (1,4- DHPs) is reported via three component condensation reaction of aldehydes, ethyl acetoacetate or methyl acetoacetate and ammonium acetate using environmentally benign melamine trisulfonic acid (MTSA) as a catalyst in solvent free condition at 60 C. The method presented here is applied to the tenets of green chemistry to the generation of biologically interesting products under solvent-free media that is less expensive and less toxic than those with organic solvents. Also, the catalyst is recyclable and could be reused without significant loss of activity. Even after three runs for the reaction, the catalytic activity of MTSA was almost the same as that of the freshly used catalyst. The method also offers several advantages including high yields and simple work-up procedure.