A New Approach to the Synthesis of Polyfunctionally Substituted 1,8-Naphthyridin-2-one Derivatives from 6-Azidopyridones: A Novel Thermal Decomposition to 6-Aminopyridones

Azidation of the chloroaldehyde 2, which was obtained from the 6-hydroxy-2-pyridones 1, afforded the 6-azido-2-pyridones 3. Compound 3 can be converted to the corresponding 6-amino-2-pyridones 5, by the reaction with triphenylphosphine via phosphazenes and subsequent hydrolysis (Staudinger reaction). This obtained amine 5 reacts with ethyl cyanoacetate in an ethanolic solution containing piperidine to give 7-amino-6-carbethoxy-3-cyano-1,4-dimethyl-1,8-naphthyridin-2(1H)-one (9). Reaction of 9 with dimethylformamide dimethyl acetal, triethylorthoformate and hydrazine hydrate furnished the new 1,8-naphthyridin-2-ones 10, 11 and 12, respectively, in good yields. On the other hand, refluxing 9 with piperidine or morpholine, as secondary amines, did not afford the corresponding 1,8-naphthyridin-2-ones 13, but instead it undergoes a thermal decomposition under these reaction conditions to yield the unexpected 6-amino-3-cyano-1,4-dimethyl-pyridin-2(1H)-one (14).

new synthesis - 1,8-naphthyridin-2-ones - thermal decomposition - 6-amino-3-cyano-1,4-dimethyl-pyridin-2(1H)-one