Organocatalytic methods for chemoselective O-tert-butoxycarbonylation of phenols and their regeneration from the O-t-Boc derivatives

Carbon tetrabromide (CBr4) catalyzes O-tert-butoxycarbonylation of functionalized phenols without any side reactions (bromination, addition of CBr3 to a double bond, and formation of symmetrical diaryl carbonates, cyclic carbonates, or carbonic-carbonic anhydrides). The parent phenols are regenerated from the O-t-Boc derivatives by the catalyst system CBr4-PPh3 without affecting other protecting groups (aryl alkyl ether, alkyl ester, and thioacetal) or competitive side reaction such as bromination, nitrene (from NO2) and alpha,alpha-dibromoolefine (with CHO/COMe) formation, and transesterification (with CO2Me/Et) taking place.