Separation and Identification of Residual Diastereomers in a Maximally Labeled Triarylamine

Residual diastereoisomerism in a maximally labeled triarylamine, methyl N-(biphenyl-2-yl)-N-(l-naphthyl)anthranilate, has been demonstrated for the first time. The two stereoisomers were obtained by manual separation of crystals, and their structures were determined by X-ray analysis. Both isomers are molecular propellers, with the three ortho substituents on the triphenylamine skeleton pointing toward the apex of the nitrogen pyramid. Interconversion of the residual diastereomers requires ∆G^± = 17.8 kcal/mol. It is noted that the central nitrogen atom in these systems is a nonstereogenic chiral center.