Conformational assignments and a nitrogen inversion process in some 3-acyloxy-1,3-oxazinanes by NMR and X-ray analysis

Abstract

The stereochemistry of the preferred conformers of several 3-acyloxy-1,3-oxazinanes has been established by NMR spectroscopy. A strong anomeric effect stabilizes the conformation having an equatorial orientation of the lone pair on nitrogen. A nitrogen inversion process was found to be the rate-limiting process in the conformational equilibria. The range of ΔG ^‡ values was found to be 60–71 kJ mol^–1. Solid state structures as determined by X-ray diffraction confirm the findings of the NMR study.