On the relevance of face-to-edge pi-pi interactions to chiral recognition

Several chiral selectors have been developed in our laboratory on the premise that a cleft having an electron-deficient aromatic system as a ''wall'' and an electron-rich aromatic system as a ''floor'' would be conducive to chiral recognition. As a test of this hypothesis, six racemates, 5a-c and 6a-c, each containing electron-deficient and electron-rich aromatic systems, were prepared and studied chromatographically on a chiral stationary phase derived from the N,N-diallyl amide of naproxen. The endo stereoisomers, 5a-c, contain the aforementioned clefts whereas the exo stereoisomers, 6a-c, do not. The enantiomers of the former show much larger separation factors than do the enantiomers of the latter, supportive of the importance of the preorganized cleft. For comparative purposes, chromatographic data are provided for the enantiomers of both the selector used in the commercially available CSP 1 and its trans isomer.