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).