Light-Sensitive Protecting Groups for Amines and Alcohols: The Photosolvolysis of N-Substituted 7-Nitroindolines

Representative examples of primary and secondary amines were protected as urea derivatives 4 of 5-bromo-7-nitro-indoline and even more efficiently as ureas 8 derived from 5,7-di-nitroindoline, via high-yield reactions with carbamoyl chlorides 3 and 7, respectively. Deprotection of 4 or 8 was achieved in high yields by UV irradiation at room temperature in Pyrex vessels under neutral conditions and exclusion of air. In a similar manner the di-nitroindolines serve as protecting groups for alcohols and phenols; the derived carbamates 5 and 9 can likewise be deprotected photochemically in high yields.