A new family of polystyrene-supported cis-4-hydroxydiphenylprolinol silyl ethers has been prepared, and the resulting polymers have been evaluated as organocatalysts to promote the tandem reaction between N-protected hydroxylamines and α,β-unsaturated aldehydes in batch and flow. The new PS-supported catalysts compare favorably with well-established immobilized Jørgensen-Hayashi catalysts, affording 5-hydroxyisoxazolidines as single diastereoisomers with high enantioselectivities and good yields (up to 83% yield, up to 99% ee).