An efficient two-step synthesis of 8(H)-9,10,11,12-tetra-hydrodicyclopenta[a,c]phenanthren-7-one, based on the high pressure Diels-Alder cycloaddition of 4-acetoxy-2-cyclopenten-1-one with 1-(1-naphthyl)cyclopentene and a subsequent dehydrogenation-aromatization reaction, is reported. Further, the synthesis of two cyclopenta[c]-phenanthrenes and indeno[c]phenanthrenes is described. Structural analysis of the new products by 1H and 13C NMR spectroscopy is presented. The mutagenic activity of the compounds in Salmonella typhimurium was estimated by Ames' test. Three compounds were shown to be mutagenic for the strain TA 100. The mutagenic activities exhibited by cyclopenta[c]phenanthrenes are compared with those shown by the related cyclopenta[a]phenanthrenes and then discussed with respect to the effect of the cyclopentane ring facing the bay region. Indeno[c]phenanthrenes are mostly inactive. The effect of benzoannulation on the mutagenic activities of cyclopenta[c]phenanthrenes is discussed.