Synthesis of intermediates related to 11-deoxyanthracyclinones

A series of Diels-Alder adducts has been synthesised from 4a,9a-epoxy-4a,9a-dihydroanthracene-1,4,9,10-tetraone (5), and the naphthacene (9b) has subsequently been converted into the epoxides (9d) and (9e). Catalytic hydrogenolysis of the ethanonaphthacene (9a) gave after work-up in air the 6,11 -dione (11), whereas hydrogenolysis of the methanonaphthacene (9f) gave a condensed leuco quinizarin derivative (13). Catalytic hydrogenolysis of the ethylenedioxynaphthacene (9e) gave the partially reduced trihydroxy derivative (15), the structure of which was established by converting it in two steps into the known trione (6a). Compound (9e) was also transformed oxidatively into the condensed quinizarin derivative (16), and by base-promoted methylation into a compound believed to be the dione (6d); the latter was deprotected to give the trione (6e).