Synthesis of Functionalized Pyrano[3,2-c]pyridines and Their Transformations to 4-Hydroxy-3[(1E)-N-hydroxyalkanimidoyl]pyridones

Reaction of 4-hydroxy-6-methyl-2(1H)-pyridones 1a and 4-hydroxy-1,6-dimethyl-2(1H)-pyridones 1b with diethyl malonates 2a-e leads to the formation of pyrano[3,2-c]pyridines 4a-j. Degradation of 4a-i affords the corresponding ketones 6a-i. Condensation of ketones 6a-i with hydroxyl amine or phenyl hydrazine hydrochloride is described.