Study of inversion isomerism in some 4,5-cis-substituted-2-isoxazolidineethanols by NMR spectroscopy

A series of β-phenyl-2-isoxazolidineethanols having cis-disposed substituents at C(4) and C(5) has been prepared by asymmetric nitrone cycloaddition reactions and their NMR spectra recorded over a wide range of temperatures. The spectra in CDCl3 at low temperatures indicate the presence of two interconverting invertomers for some of the tri-substituted isoxazolidines. The effect of H-bonding - intramolecular in CDCl3 and intermolecular in CD3OD - on the population ratio of the nitrogen invertomers has been investigated. The nitrogen inversion barriers are determined using complete line-shape analysis, and their dependence on solvent is discussed.