Antitumor agents, 75. Synthesis of cytotoxic anthraquinones digiferruginol and morindaparvin-B

A simple and efficient synthesis of digiferruginol (4) and morindaparvin-B (10) is described. Marschalk reaction of 1-hydroxyanthraquinone afforded 1-hydroxy-2-methylanthraquinone (2). Treatment of 2 with N-bromosuccinimide and benzoyl peroxide led to 1-hydroxy-2-bromomethylanthraquinone (3), which was converted to 4 with AgNO3 in quantitative yield. Methylation of 1,5-dihydroxyanthraquinone yielded a dimethyl ether (6), which was partially demethylated with boron trifluoride to a difluoroboron chelate (7). Treatment of 7 with alkaline HCHO and sodium dithionate gave rise to 1-hydroxy-2-hydroxy-methyl-5-methoxyanthraquinone (9). Cleavage of the 5-methyl ether of 9 with boron tribromide furnished 10.