Facile Total Syntheses of Idarubicinone‐7‐β‐D‐glucuronide: Convenient Preparations of AB‐Ring Synthon Using Some Carboxylic Acid Derivatives

Regiospecific syntheses of idarubicinone coupled with D‐glucuronic acid are described. Cyclization of dimethoxybenzene with carboxylic acid derivatives in polyphosphoric acid (PPA) in one step afforded the naphthalenones 7, which were transformed to the (±)‐idarubicinone 3b by general methods. Esterification of (±)‐3b with (S)‐(+)‐O‐acetylmandelic acid with subsequent separation and deprotection gave (+)‐3b and (−)‐3b. Reaction of separated two stereoisomers with acetobromo‐α‐D‐glucuronic acid methyl ester respective followed by hydrolysis using lithium hydroxide and amberite cation exchange resin furnished two kinds of idarubicinone‐7‐β‐D‐glucuronide (20 and 21) that are coupled at C‐7 position of idarubicinone.