Microwave-Assisted Synthesis of Diversely Substituted Quinoline-Based Dihydropyridopyrimidine and Dihydropyrazolopyridine Hybrids

An efficient, catalyst-free, and one-pot three-component procedure for the synthesis of novel and nitrogen rich dihydropyrido[2,3-d]pyrimidines and dihydro-1H-pyrazolo[3,4-b]pyridines bearing a quinoline pharmacophore fragment is provided. Reactions proceeded in DMF under microwave irradiation of three-component mixtures of formyl-quinoline derivatives, primary heterocyclic amines and cyclic 1,3-diketones. Interestingly, when conventional heating at reflux was used for the starting 5-amino-1-phenylpyrazole, the corresponding aromatized pyrazolopyridines were obtained as the main products. Single crystal X-ray analysis confirmed unequivocally the structure of both the dihydro- and aromatized products.