Nuclear Magnetic Resonance Evidence for High Barrier of Conformational Inversion in Hexahydro-3,3,7,7-tetramethyl-1,2-oxazepine-5-one

Variable temperature proton n.m.r. spectra indicate an activation energy of 19.0 ± 0.5 kcal/mol for conformational equilibration in hexahydro-3,3,7,7-tetramethyl-1,2-oxazepine-5-one. It is suggested that the rate process involves slow conformational interconversion of the seven-membered ring and not slow inversion at the nitrogen atom. The synthesis of several related 1,2-oxazepines is described.