SYNTHESES OF ANGUCYCLINONES RELATED TO OCHROMYCINONE

Two synthetic approaches have been investigated for the syntheses of m odel angucyclinones related to ochromycinone. The first involves a Die ls-Alder/Friedel-Crafts strategy in which the Diels-Alder adduct forme d between dimethyl acetylenedicarboxylate and 3-ethenyl-5,5-dimethylcy clohex-2-en-1-one was converted into oxo-5,6,7,8-tetrahydronaphthalene -1,2-dicarboxylic anhydride, which was then reacted with benzene in a Friedel-Crafts reaction. Acid-catalysed cyclization of the Friedel-Cra fts products gave hyl-3,4-dihydrobenz[a]anthracene-1,7,12(2H)-trione ( 3) in poor yield. Angucyclinones related to (3) are formed (in 40-50% overall yield) by aromatization of the adduct formed between the appro priate 1,4-naphthoquinone and )-2-methoxyethenyl]5,5-dimethylcyclohex- 2-en-1-one (this dienone reacts with itself by a Diels-Alder process t o yield an adduct which decomposes to thyl-3,4,7,8-tetrahydroanthracen e-6(2H,5H)-dione). When the substituted 1,4-naphthoquinone is unsymmet rical, a boron triacetate assisted Diels-Alder reaction gives a single regioisomer (e.g. X-ray investigations indicate that 8-hydroxy-3,3-di methyl-3,4-dihydrobenz[a] anthracene-1,7,12 (2H)-trione is the product from 5-hydroxy-1,4-naphthoquinone). An X-ray structural study of the Diels-Alder adduct in the above reaction confirms the operation of an endo cyclization.