[5]HELOL phosphite: A helically grooved sensor of remote chirality

Even when the first center of chirality is far from a functional group, the stereochemistries of chiral molecules can be sensed if the functional group is attached to a phosphorus embedded within the groove of a nonracemic helicene. The sensor used was a phosphite ester of [5]HELOL, structure 6, and P-31 NMR spectroscopy was the method of analysis. Although there are seven methylene between the hydroxyl and the first center of chirality, the P-31 NMRs could distinguish the enantiomers of 8-phenylnonanol with baseline resolution. However, to achieve this resolution, the solvent has to be chosen appropriately. The probe can also analyze the enantiomers of other alcohols, amines, phenols, and, when they were coupled to 2-aminophenol, carboxylic acids. The sensitivity to remote chiral centers of the moieties analyzed is attributed to their confinement to the helical groove.