Used primarily as a protecting group reagent in organic synthesis, particularly for the protection of phenolic hydroxyl groups. It selectively introduces the tert-butoxycarbonyl (Boc) group under mild conditions, which is stable under a variety of reaction conditions but can be easily removed later with acid. This makes it valuable in multi-step syntheses, especially in pharmaceutical and natural product synthesis where precise functional group control is required. Its use helps prevent unwanted side reactions involving phenols during transformations on other parts of a molecule.