Iron‐Catalyzed Reaction With Carboxylic Acids and Isocyanides to Access <i>N</i> ‐Formylamides

Iron‐catalyzed reactions of carboxylic acids with sterically hindered isocyanides enable access to N ‐formylamides with 100% atom economy. The substrate scope can be extended to aliphatic, aromatic, and α,β‐unsaturated carboxylic acids. Furthermore, the protocol can be smoothly applied in the late‐stage N ‐formylation of acid‐containing drugs, double reaction, and N ‐formylation of alkynyl acids. A library of 41 N ‐formylamides has been constructed, and compound 4i was identified as a promising antioxidant.