Stereochemical Assignment of (E)-and (Z)-2-(l-Naphthyl)-l-phenylpropene and Their Photocyclization to 5-Methylchrysene

Dehydration of 2-(l-naphthyl)-l-phenyl-2-propanol (3) gave varying ratios of (E)-2-(l-naphthyl)-l-phenyl-propene (4), (Z)-2-(l-naphthyl)-l-phenylpropene (5), and 2-(l-naphthyl)-3-phenylpropene (6), depending upon conditions and choice of reagent. Assignment of configuration to these alkenes by UV and 1H NMR spectroscopy was equivocal, but unambiguous assignment was made through comparison of chemical shifts in the NMR spectra of the cis diols and the corresponding cyclic phenylboronates prepared from 4 and 5. Photocyclization of 4 or 5 gave 5-methylchrysene (1), whereas 6 was inert.