Synthetic studies of the antitumor antibiotic streptonigrin. II. Synthesis of the C‐D ring portion of streptonigrin

Abstract

Abstract 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.