A facile synthesis of 1, 5-diketones from 3-acetyl-4-hydroxycoumarin, aldehydes and cyclic-ketones via a one-pot aldol condensation and subsequent Michael addition reaction in presence of a single catalyst of L-proline under mild reaction condition has been developed. Novel 1, 5-diketones were further cyclized to the unexpected 3,4-dihydropyridine rather than generally formed pyridine analogous with ammonium acetate in acetic acid. One-pot, high yields (72-92%) for novel 1,5-diketones and (70-90%) for 3,4-dihydropyridine adduct, easy work-up and purification of products are the key advantages of this method.