Anthracyclinones. Part 1. A versatile synthesis of the anthracyclinone system using a chiral template derived from a carbohydrate

Condensation of aldehydo-2,3 :4,5-di-O-isopropylidene-D-arabinose (7) with leuco-quinizarin (6a) or 5-hydroxy-leuco-quinizarin (6b) in alkaline solution at 0 °C followed by aerial oxidation gave a good yield of 2-(1-hydroxy-D-arabinityl)quinizarin (8a) and the 5-hydroxy-derivative (8b). Reaction of (8a) with acid furnished the monoisopropylidene derivative (9) and further treatment gave the fully deblocked derivative (10). The monoisopropylidene derivative (9) with periodate, cold alkaline dithionite aerial oxidation, and mild acid treatment gave the novel tetrahydroxy (in ring A) anthracyclinone (12). Structures of the compounds were confirmed by u.v., mass, i.r., and 1H n.m.r. spectroscopy.