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Terminal-ring trans-dihydro diol metabolites have been implicated as the ultimate carcinogenic forms of polycyclic aromatic hydrocarbons. Synthesis of these dihydro diols from the related polycyclic phenols in two steps via oxidation to the corresponding o-quinones with either Fremy's salt [(KS03)2N0] or phenylseleninic anhydride followed by stereospecific reduction with lithium aluminum hydride is described. The non-K-region quiñones and trans-dihydro diols of naphthalene, anthracene, phenanthrene, benz[a]anthracene, benzo[a]pyrene, and 7,12-dimethylbenz [o] anthracene are synthesized via this approach. Although poor yields (1-4%) were previously reported for the reduction of non-K-region quiñones, an improved experimental procedure has been developed which affords the trans-dihydro diols free of the isomeric c¿s-dihydro diols in generally good yields. Major byproducts are the corresponding hydroquinones, previously undetected, and the related tetrahydro diols. The latter are the major products of reduction of the poorly soluble quiñones of benzo[a]pyrene and benz [o]anthracene and are shown to arise through further reduction of the dihydro diols. Since the tetrahydro diols are convertible to dihydro diols and the hydroquinones are reoxidizable to quiñones, good overall conversions of quiñones to dihydro diols are attainable. irans-3,4-Dihydroxy-3,4-dihydro-7,12-dimethylbenz[a]anthracene synthesized in

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