Cycloaddition of nitrones to diethyl arylmethylene malonates occurred with very high selectivity to furnish 3,5-trans-2,3,5-triaryl-4,4-dicarbethoxy isoxazolidines. This is in contrast with the nitrone cycloadditions to other α,β-conjugated carbonyl derivatives where two diastereoisomeric (and on occasion regioisomeric) cycloadducts are generally obtained.