Nitrogen inversion process in some camphor-based isoxazolidines

A series of isoxazolidines has been prepared via asymmetric nitrone cycloaddition reactions of a camphor-based methylenenitrone with several alkenes. The H-1 NMR spectra of the N(2) and C(5)-disubstituted isoxazolidines in CDCl3 at low temperatures revealed the predominant or exclusive presence of the diasteromer having trans disposition of the substituents. The presence of hydroxyl substituent on the camphor moiety permits H-bonding with the N or O of the isoxazolidine ring. The effect of H-bonding - intramolecular in CDCl3 and intermolecular in CD3OD - on the population ratio of the invertomers and nitrogen inversion process has been investigated. The nitrogen inversion barriers are determined using complete line-shape analysis, and their dependence on solvent is discussed.