Anthracyclinones, part 4. The use of DBN or DBU in a novel extension of the Marschalk reaction leading to Hydroxyglycitylanthraquinones

Abstract

Leuco-quinizarin (1) with propanal, 3-O-(p-chlorobenzyl)-(or 3-O-acetyl)-1,2-O-isopropylidene-α-D-xylo-pentodialdo-1,4-furanose (6a) or (6c), or 3-O-acetyl-3-C-ethynyl-1,2-O-isopropylidene-α-D-ribo-pentodialdo-1,4-furanose (6b) in dimethylformamide solution at 0 °C, under nitrogen with DBN or DBU followed by aerial oxidation, gave a good yield of the crystalline 1-(hydroxypropyl)quinizarin (3), (5S)-3-O-(p-chlorobenzyl)(or 5-O-acetyl)-1,2-O-isopropylidene-5-(quinizarin-2-yl)-α-D-xylo-furanose (7a) and (7e) and 3-O-acetyl-3-C-ethynyl-1,2-O-isopropylidene-5-(quinizarin-2-yl)-α-D-ribofuranose (7c) respectively. Oxidation of (7a) with pyridinium chlorochromate produced the oxo derivative (8) and acid hydrolysis gave the quinizarinylpyranose (9) which with periodate followed by alkali afforded the crystalline (4S)-2-O-(p-chlorobenzyl)-4-(quinizarin-2-yl)-D-threo-pentofuranose (11) and the dehydration product (12). Reduction of (11) with alkaline sodium dithionite produced the crystalline (10S)-8-O-(p-chlorobenzyl)anthracyclinone (14a) and the corresponding deoxy derivative (14b). Structures of the compounds were confirmed by u.v., mass, i.r., c.d., and ¹H n.m.r. spectroscopy.