Dynamic stereochemistry of imines and derivatives. Part IX. The mechanism of E–Z isomerization in N-alkylimines

Abstract

Rates of E–Z isomerization in N-alkylimines have been determined by direct thermal stereomutation and by dynamic n.m.r. spectroscopy. Thermal racemization rates of optically active para-disubstituted 2-t-butyl-3.3-diphenyloxaziridines have also been measured, and show a small but consistent correlation with Hammett σ_p. Comparison of the activation parameters for imine isomerization with data for nitrogen inversion in oxaziridines indicates that N-alkylimines isomerize by a planar inversion (lateral shift) mechanism. Barriers determined for an aldimine under optimal conditions are higher than previously reported for imines (ca. 30 kcal mol^–1).