Syntheses of Angucyclinones Related to Ochromycinone. III. An 11-Hydroxy Isomer and Some Reduced Analogues

Abstract

The boron triacetate assisted Diels Alder reaction between racemic 5,5-dimethyl-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-decahydrobenzo[a]anthracen-1-yl acetate as the sole stereoisomer by regio- and stereo-selective cis endo addition. Aromatization of the Diels Alder adduct followed by hydrolysis of the acetate and oxidation of the resultant 1-hydroxy 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% from 5-hydroxynaphthoquinone. The regio- and stereo-selectivity of the Diels Alder addition is confirmed by a combination of ¹³C n.m.r. spectroscopy and X-ray crystallography.