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

6-(1'-Formyl)-1,5-dimethoxy-2-(2''-oxopropyl)anthrauinone (1), a key intermediate in Danishefsky's synthesis of vineomycinone B-2 methyl ester (5), has been prepared by a new route from anthrarufin (6) via the intermediate 1-methoxy-2-(2-methylprop-2'-enyl)-5-(2''-methylprop-2''-enyloxy)anthraquinone (20). An alternative synthesis of the diketone (40) has been achieved via Claisen rearrangement of (20) and a subsequent ozonolysis of the resulting bis(methylpropenyl)anthraquinone (26). Other routes to (1) from anthrarufin have been developed. In one, compound (1) was formed in yields of 10-16% as an anomalous product from the ozonolysis of (27). Ozonolyses of mixtures of (27), (37) and (44), obtained by isomerization of (27), afforded (1) in yields of 28-43%. Isomerization of the diphenol (25) with palladium(II) chloride bis(acetonitrile) in refluxing chloroform proceeds at a faster rate than the isomerization of (27), thereby affording the mono isomerized diphenol (38) in 37% yield. Methylation of (38) affords (37), a known precursor of (1).