EXPERIMENTS DIRECTED TOWARDS THE SYNTHESIS OF ANTHRACYCLINONES .25. SYNTHESIS OF A VINEOMYCINONE B-2 METHYL-ESTER INTERMEDIATE FROM ANTHRARUFIN

ormyl)-1,5-dimethoxy-2-(2''-oxopropyl)anthrauinone (1), a key intermed iate in Danishefsky's synthesis of vineomycinone B-2 methyl ester (5), has been prepared by a new route from anthrarufin (6) via the interme diate -enyl)-5-(2''-methylprop-2''-enyloxy)anthraquinone (20). An alte rnative synthesis of the diketone (40) has been achieved via Claisen r earrangement of (20) and a subsequent ozonolysis of the resulting bis( methylpropenyl)anthraquinone (26). Other routes to (1) from anthrarufi n have been developed. In one, compound (1) was formed in yields of 10 -16% as an anomalous product from the ozonolysis of (27). Ozonolyses o f mixtures of (27), (37) and (44), obtained by isomerization of (27), afforded (1) in yields of 28-43%. Isomerization of the diphenol (25) w ith palladium(II) chloride bis(acetonitrile) in refluxing chloroform p roceeds at a faster rate than the isomerization of (27), thereby affor ding the mono isomerized diphenol (38) in 37% yield. Methylation of (3 8) affords (37), a known precursor of (1).