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 ra cemates, 5a-c and 6a-c, each containing electron-deficient and electro n-rich aromatic systems, were prepared and studied chromatographically on a chiral stationary phase derived from the N,N-diallyl amide of na proxen. The endo stereoisomers, 5a-c, contain the aforementioned cleft s 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. Fo r comparative purposes, chromatographic data are provided for the enan tiomers of both the selector used in the commercially available CSP 1 and its trans isomer.