Synthesis of 4‐Amino‐substituted‐6‐hydroxy and 11‐hydroxynaphtho[2,3‐ g ]quinoline‐5,12‐diones, and the unexpected formation of disubstituted imidazo[4,5,l‐ i,j ]naphtho[2,3‐ g ]quinolin‐7‐ones

4‐Chloroquinoline‐5,8‐dione ( 8a ) and 6‐bromo‐4‐chloroquinoline‐5,8‐dione ( 8b ) were reacted with homophthalic anhydride to give tetracyclic compounds 10 and 11 respectively. The 6,11‐dihydroxy derivative 12 was prepared in low yield by photochemical addition of benzocyclobutenedione to 4‐chloroquinoline‐5,8‐dione ( 8a ) and in better yield through a Friedel‐Crafts reaction of phthalic anhydride with 4‐chloro‐5,8‐dimethoxyquinoline ( 7a ). Whereas 4‐chloro‐6‐hydroxynaphtho[2,3‐ g ]quinoline‐5,12‐dione ( 11 ) was substituted by amines in the usual way to the corresponding 4‐amino‐substituted derivatives, 4‐chloro‐11‐hydroxynaph‐tho[2,3‐ g ]quinoline‐5,12‐dione ( 10 ) led to a mixture of 4‐amino derivatives and the unexpected 2,6‐disubstituted‐imidazo[4,5,l‐ I‐j ]naphtho[2,3‐ g ]quinolin‐7‐ones, 13a‐b .