Syntheses of angucyclinones related to ochromycinone. III - An 11-hydroxy isomer and some reduced analogues

The boron triacetate assisted Diels Alder reaction between racemic 5,5-dime thyl-3-vinylcyclohex-2-enyl acetate and 5-hydroxynaphthoquinone yields the racemic 11-hydroxy-3,3-dimethyl-7,12-dioxo-1,2,3,4,6,6a,7,12,12a,12b-decahy drobenzo[a]anthracen-1-yl acetate as the sole stereoisomer by regio- and st ereo-selective cis endo addition. Aromatization of the Diels Alder adduct f ollowed by hydrolysis of the acetate and oxidation of the resultant 1-hydro xy group gives the target angucyclinone, 11-hydroxy-3,3-dimethyl-1,2,3,4,7, 12-hexahydrobenzo[a]anthracene-1,7,12-trione, in an overall yield of 37% fr om 5-hydroxynaphthoquinone. The regio- and stereo-selectivity of the Diels Alder addition is confirmed by a combination of C-13 n.m.r. spectroscopy an d X-ray crystallography.