Synthesis of some 3‐substituted quino[3,2‐c][1,8]naphtyridines . A new heterocyclic ring system

Isatoic acid reacts with 7‐mcthyl‐2,3‐dihydro‐1,8‐naphthyridin‐4(1 H ) one ( 8 ) to give 3‐methyl‐5,6‐dihvdroquino[3,2‐ c ][1,8]naphthyriclin‐7‐carboxylic acid ( 9a ), which was transformed into the 3‐methylquino[3,2‐ c ][1,8]naphthyridine ( 7a ) by refluxing with copper chromite in quinoline. The same product ( 7a ) was also obtained by aromatization of the 3‐methyl‐5,6‐dihydroquino‐[3,2‐ c ][1.8]naphthvridine ( 10a ), prepared by condensation of the ketone ( 8 ) and o ‐aminobenzaldehyde. Other 3‐substituted quino[3,2‐ c ][1,8]naphthyridines ( 7b,c,d,e ), which contain a new heterocyclic, ring structure, have been prepared using o‐aminobenzaldehyde and 7‐sub‐stituted‐2,3‐dihv dro‐1,8‐naphthyridin‐4(1 H ) ones ( 12 and 13 ) as starting materials. Also, the preparation of the parent nucleus ( 7f ) is described.