Numerous lines of evidence have now implicated 7,8-diol-9,10-epoxides as metabolically formed ultimate carcinogens from the environmental contaminant benzo[alpyrene. ly2 In an attempt to generalize the concept of diol epoxides3 as ultimate carcinogens, we have attempted to predict which of the several possible diol epoxides of a given polycyclic hydrocarbon would show the highest biological activity. Comparison of existing carcinogenicity data for alkyl and halogen substituted hydrocarbons4 as well as perturbational molecular orbital calculations5 predict that diol epoxides on saturated angular benzo-rings in which the epoxide forms part of the "bay-region" of the hydrocarbon6 will have the highest biological activity. To test this prediction, we have recently synthesized dihydrodiols7 and diol epoxides8 of benzo[a]anthracene. Studies of the mutagenicity 9,1@ and carcinogenicity 11 of these compounds have born out the prediction in that the 3,4-dihydrodiol and its diol epoxides were markedly more active than the other isomeric dihydrodiols, diol epoxides, or the parent hydrocarbon. The present report describes the synthesis of dihydrodiols from chrysene and dibenzo[a,h]anthracene in order to further test the "bay-region" theory. A general approach which has been successfully from polycyclic hydrocarbons 7,12,13 is shown below: utilized in the synthesis of dihydrodiols la-d 2a-d In order to apply this approach, ketones related to chrysene and dibenzo[a,h]anthracene were re-. B ?,-3a-d quired. Of these the 1-keto-(la)" and 4-keto-1,2,3,4_tetrahydrochrysene (lb)'> and 1-keto-. --1,2,3,4-tetrahydrodibenzo[a,h]anthracene (&)16 were known. In order to synthesize the remaining 4-keto-1,2,3,4-tetrahydrodibenzo[a,h]anthracene (Id), 8-keto-8,9,10,11-tetrahydrobenzo[a]-anthracene17 was converted to 4-(8-benzo[a]anthryl)-butyric acid (mp 167-169", 39%.overall yield from ketone) in a manner analogous to that used in the synthesis of 4-(1-phenanthryl)-butyric acid.14 The procedure consisted of a Reformatsky reaction between the ketone and methyl 19. A