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Organocatalytic Methods for ChemoselectiveO-tert-Butoxycarbonylation of Phenols and Their Regeneration from theO-t-Boc Derivatives
November 07 2008
November 07 2008
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Abstract
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.