NMR Studies of Hindered Rotation. The Diels-Alder Adduct of Phencyclone withN-n-Propylmaleimide: Restricted Motion of Bridgehead Phenyls

Abstract

Abstract The Diels-Alder adduct of phencyclone and N-n-propylmaleimide has been studied in CDCl3 solution at ambient temperatures by one-and two-dimensional 1H NMR (300 MHz) and 13C NMR (75 MHz) techniques. Clear evidence is presented from slow exchange limit (SEL) spectra for hindered rotation of the bridgehead phenyls in the adduct. Full 1H spectral assignments have been made via selective homonuclear decoupling and high resolution COSY experiments. The number of signals in the aryl region of 13C NMR spectra also indicated slow rotation about the C(sp2)-C(sp3) bond to the unsubstantiated bridgehead phenyls. Striking evidence of magnetic anisotropic effects, seen from 1H NMR, permits stereochemical assignment of the adduct as endo.