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Bromination of 6‐methoxy‐5,8‐quinolinedione gave the 7‐bromo derivative in quantitative yield. Treatment of the bromo compound with sodium azide followed by hydrogenation yielded 7‐amino‐6‐methoxy‐5,8‐quinolinedione, the A‐B ring portion of the antitumor antibiotic strep tonigrin. The corresponding 2‐methyl homolog was prepared in a similar manner from 6‐methoxy‐2‐methyl‐8‐nitroquinoline, which in turn, was obtained by a Skraup synthesis from 2‐nitro‐anisidine and crotonaldehyde.

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Partial mclhylalion of gallopropiophenonc (4) followed by benzylation and base‐catalyzed condensation with ethyl acetate yielded 3‐(2‐benzyloxy‐3,4‐din]etlK>xy)benzoyl‐2‐butanonc (6). Animation of the latter and subsequent base‐catalyzed cyclization with ethyl cyanoacetate gave 4‐(2‐benzyloxy‐3,4‐dimethoxy)phenyl‐5,6‐dimethyl‐2‐oxo‐1,2‐dihydropyridine (8). Removal of the 2‐oxo group of 8 through chlorination and dechlorination and stepwise conversion of the 5‐cyano and 2‐methyl groups into the 5‐amino and 2‐carboxylic acid groups, respectively, with introduction and removal of protecting groups at proper stages, yielded the C‐D ring moiety of the antitumor antibiotic streptonigrin.