Conformational Studies by Dynamic NMR. 86. Structure, Stereodynamics, and Cryogenic Enantioseparation of the Stereolabile Isomers of <i>o</i>-Dinaphthylphenyl Derivatives

Static and dynamic stereochemistry of the hydrocarbon comprising a phenyl ring bearing two α-naphthyl substituents in the <i>ortho</i> positions, i.e., 1,2-di-(4-methyl-naphth-1-yl)-benzene<b> 1</b>, has been studied by a combination of variable temperature NMR, cryogenic HPLC, and MM calculations. Whereas in solution both <i>syn</i> (meso) and <i>anti</i> (chiral) forms were observed and the corresponding interconversion barrier was determined (Δ<i>G</i><sup>⧧</sup> = 19.5 kcal mol<sup>-1</sup>), only the diastereoisomer <i>anti</i> was found to be present in the crystalline state (X-ray diffraction). When the molecule is rendered asymmetric by introduction of a nitro group in the phenyl ring as in 1,2-di-(4-methyl-naphth-1-yl)-4-nitrobenzene <b>2</b>, the chiral <i>syn</i> and <i>anti</i> diastereoisomers are simultaneously present both in solution and in the solid state, albeit in different proportions. Cryogenic chromatography on a HPLC chiral stationary phase at −20 °C allowed the stereolabile diastereoisomers and the corresponding enantiomers to be separated.