The Anomeric Effect: The Conformational Equilibria of Tetrahydro-1,3-oxazines and 1-Methyl-1,3-diazane

By measurement of CH–NH coupling constants at low temperatures, the N–H axial conformation was shown to be the dominant, or sole, conformation for tetrahydro-1,3-oxazine, tetrahydro-2-methyl-1,3-oxazine, and 1-methyl-1,3-diazane. These results provide further experimental evidence for the generalized anomeric effect. Nuclear Overhauser experiments established the partial axial character of the N-methyl substituent in tetrahydro-3,4,4,6-tetramethyl-1,3-oxazine.The n.m.r. spectral data for a number of tetrahydro-1,3-oxazines and derived salts are tabulated and discussed.