(Chemical Equation Presented) Cycloadditions of C,N-diarylnitrones to β-nitrostyrenes occurred to yield two diastereoisomeric cycloadducts, the 3,4-trans-4,5-trans substituted isoxazolidine derivatives being formed selectively as the major products. These were characterised by spectroscopic and X-ray data. Conformational studies were carried out by X-ray crystallography and Molecular Modelling.