Abstract

--- - The Diels-Alder reaction of the hydroxyquinones 5, 11 and 16 with (E)-1-trimethylsiloxybuta-1,3-diene 3 afforded the corresponding mixture of the regioisomers 6a,b, 12a,b and 17a,b in the ratios 9:1, 8:1 and 11:1, respectively. From these mixtures, the quinones 8, 14 and 19 were obtained by hydrolysis and subsequent oxidation. - The preparation of the diene 22 by chlorotrimethylsilylation of the anion of the ester 21 is described. Diels-Alder reaction of diene 22 with the quinones 23 and 24 yielded the corresponding 6-ethoxybenz[a]anthracenequinones 25 and 26, together with the 6-hydroxybenz[a]anthracenequinones 19 and 20. The quinones 19 and 20, which were isolated in mixtures with the ester 21, undergo selective aerial oxidation under basic conditions to give the corresponding benz[a]anthracene-1,7,12-triones 27 and 28.