Organocatalytic Enantioselective Synthesis of Oxindole‐4‐Aminopyrazolone Derivatives via Mannich Reaction of 3‐Substituted Oxindoles With Pyrazolinone Ketimines

ABSTRACT The organocatalyzed Mannich reaction between pyrazolinone ketimines and 3‐aryl‐substituted oxindoles mediated by a hidroquinine‐derived squaramide is reported. This method enables the synthesis of a diverse set of oxindole‐4‐aminopyrazolone derivatives bearing vicinal tetrasubstituted stereocenters, affording products in good yields (up to 95%), with excellent diastereoselectivity (> 20:1) and moderate enantioselectivity (up to 85:15 er) under mild conditions.