The synthesis of the potent carcinogen 7,12-dimethylbenzCa]anthracene, DMBA, 4a and its many derivatives has been difficult in the past due to the lack of commercially available starting materials. Of the various methods available for its synthesis (l-4) , the simplest involves the addition of methylmagnesium iodide to a benzcalanthracene-7,12-dione precursor.(2'3) This reaction does not provide easy access to the wide range of DMBA derivatives that are needed for the investigation of its biological activity because of the difficulty in obtaining the appropriately substituted quinones. To make use of this simple Grignard reaction, a facile synthesis of benzralanthracene-7,12-diones was necessary. We have developed such a synthesis by employing a Diels-Alder reaction between styrenes and naphthoquinone. The Diels-Alder type of reaction (5) has been successfully used in the past to prepare numerous naphthoquinones (5) , anthraquinones (71, phenanthraquinones(8) and chrysenequinones.(') There has been only one report of the formation of a benzanthraquinone derivative, 1,2,3,4,-tetrahydro-5-chlorobenz[a]anthracene-7,12-dione, which was formed from the reaction of 1,4_naphthoquinone with a-chlorovinylcyclohexene. (10) However, there have been no reports of the successful reaction of 1,4-naphthoquinones with styrenes, even though considerable work has been done with benzoquinones and styrenes. (11,121 We have been successful in preparing benz[a]anthracene-7,12-dione (3a) in a reasonably good yield from 1,4-naphthoquinone m and styrene (2a). The use of a-methylstyrene (2b) has led to the formation of 5-methylbenz[a]anthracene-7,12-dione m