Herein, we report a sustainable and efficient method for the synthesis of structurally diverse phthalimidines from 2-formylbenzoic acid and primary amines using an iridium-catalyzed reductive lactamization strategy. The advantages of this method, such as the use of water-ethanol as a solvent, broad substrate scope, high catalyst efficiency (S/C up to 10000), good scalability, and easy purification, enable it to be a practical approach to phthalimidines. It is suggested that iridium hydride formation is involved in the rate-limiting step. Synthetic applications for the late-stage functionalization of medicinally relevant molecules are also demonstrated.