Natural products enantioselective bromination

In looking at vancomycin and teicoplanin, the hydroxyls are but one choice for functionalization reactions. Each natural product also possesses electron-rich arenes, which may be platforms for electrophilic aromatic substitution reactions. In parallel studies of enantioselective and atropisomer-selective bromination reactions [161-164], we were gaining experience with catalyst-controlled bromina-tions, and we wondered whether these might be extended to site-selective reactions. We speculated that an appropriately positioned Lewis base, such as a dimethyl amide unit, could assist in the delivery of electrophilic bromine... 

Section B shows some Hofmann rearrangements. Entry 9, using basic conditions with bromine, provided an inexpensive route to an intermediate for a commercial synthesis of an herbicide. Entry 10, which uses the Pb(OAc)4 conditions (see p. 949), was utilized in an enantiospecific synthesis of the naturally occurring analagesic (-)-epibatidine. Entry 11 uses phenyliodonium diacetate as the reagent. The product is the result of cyclization of the intermediate isocyanate and was used in an enantioselective synthesis of the antianxiety drug (tf)-fluoxetine. 

---