anti‐selective Mannichreaction of aldehydes with N‐sulfonyl imines has been developed by using a 4‐hydroxypyrrolidine in combination with an external Brønstedacid. The catalyst design is based on three elements: the α‐substituent of the pyrrolidine, the 4‐hydroxy group, and the Brønstedacid, the combination of which is essential for high chemical and stereochemical efficiency. The reaction works with