The trihydroxyanthraquinone derivative of formula 10 is reduced, as by treating with a reducing agent such as stannous chloride or sodium borohydride, to produce, 1,4,8-trihydroxy-3-(2,3-dicarboxypropyl)-9,10-(H)-anthr-9-one having the following formula: ##STR15## Cyclization to the desired naphthacene structure is achieved by use of a condensation catalyst such as hydrogen fluoride, polyphosphori