Conformational Studies by Dynamic NMR. 97.Structure, Conformation, Stereodynamics and Enantioseparation of Aryl Substituted Norbornanes.

CAN 140:163414 AN 2003:996217 CAPLUS (COPYRIGHT (C) 2008 ACS ON SCIFINDER (R)) ABSTRACT THE STRUCTURE OF A 1,7,7-TRIARYLNORBORNANE (I) HAS BEEN DETD. BY X-RAY DIFFRACTION AND WAS FOUND ESSENTIALLY EQUAL TO THAT PREDICTED BY MOL. MECHANICS CALCNS. RESTRICTED ROTATION OF THE ARYL GROUPS ALSO HAS BEEN OBSD. BY DYNAMIC NMR SPECTROSCOPY IN THIS COMPD. AND IN A NO. OF ANALOGOUSLY SUBSTITUTED NORBORNANES. THE ARYL-NORBORNANE BOND ROTATION BARRIERS WERE MEASURED BY LINE SHAPE ANAL. OF THE 13C NMR SPECTRA OBTAINED AT TEMPS. LOWER THAN -100 °C AND WERE FOUND TO COVER THE RANGE 6.0 TO 7.9 KCAL MOL-1. AN EXCEPTION WAS THE ROTATION INVOLVING THE O-ANISYL GROUP IN II, WHICH OCCURS NEAR AMBIENT TEMP. SINCE THE CORRESPONDING BARRIER IS MUCH HIGHER (14.4 KCAL MOL-1). IN ONE CASE (III) CONFIGURATIONAL ENANTIOMERS COULD BE SEPD. BY CHIRAL HPLC AND THE CORRESPONDING CD SPECTRA RECORDED.