Substituted naphthalene-1,2-dihydrodiols

Acid-catalysed dehydrations of substituted naphthalene-cw-l,2-dihydrodiols occur with loss of the 1- or 2-OH groups to form 2- and 1-naphthols, respectively. Effects of substituents MeO, Me, H, F, Br, I, and CN at 3-, 6-, and 7-positions of the naphthalene ring are consistent with rate-determining formation of j8-hydroxynaphthalenium ion (carbocation) intermediates. " The results suggest the conclusion that for naphthalene-cw-l,2-dihydrodiols, the resonance between substituent and reaction site is impaired in the dehydration of 3-substituted arene-l,2-dihydrodiols. 

The conversion of toluene to the cw-dihydrodiol has been examined using inunobilized P. putida UV4, and a dramatic increase in production observed under defined conditions of aeration in a fluidized-bed reactor [48]. The naphthalene dioxygenase enzyme from Pseudomonas fluorescens has been expressed in E. coli, and the resulting biocatalyst used for the conversion of a series of substituted naphthalenes to the diols shown in Fig. 29 [49], while Pseudomonas testosteroni ACS converts 2-naphthoic acid to the diol 40 shown in Fig. 30 [50]. Substituted biphenyls are also substrates for TDO oxidation (Fig. 31) using E. coli JM109 expressing this enzyme [51]. 

Touring studies at NIH, it was discovered that enzymatic hydroxyla-tion of (deuterated or tritiated) substrates leads to a novel and mechanistically important shift of the deuterium or tritium from the point of substitution by oxygen to an adjacent position in the aromatic ring (12). [It has been found recently that arene oxides are likely intermediates in the metabolism of aromatic compounds. They rearrange to phenols with concomitant NIH Shift, and they are enzymatically converted to dihydrodiols and premercapturic acids. In addition, naphthalene oxide has now been demonstrated as an intermediate in the conversion of naphthalene to a-naphthol, frari5-l,2-dihydro-I,2-dihydroxynaphthalene, and... 

The role played by dihydrodiols in the metabolic formation of phenols and their conjugated derivatives from aromatic substances is at present undecided. In theory, upon dehydrating a dihydrodiol, the phenolic hydroxyl should remain at that carbon most activated toward electrophilic substitution (14,625). This criterion of mechanism is satisfied in some instances (i.e., the halogenobenzenes (379, 682) and benzonittile (681). Furthermore, compounds that arise from the metabolism of aromatic hydrocarbons also arise from metabolism of dihydrodiols which are formed from them (94,163). However, hver slices and Uver microsomes capable of forming dihydrodiol from naphthalene form neg%ible amounts of naphthol (95,558). 

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