Indium-Catalyzed Reductive Bromination of Carboxylic Acids Leading to Alkyl Bromides

Toshimitsu Moriya , Shinichiro Yoneda , Keita Kawana , Reiko Ikeda , Takeo Konakahara , and Norio Sakai * 

http://pubs.acs.org/doi/abs/10.1021/ol302168q 

This is a potentially really useful transformation, that is milder and somewhat more FG-tolerant than the two-step procedure involving LAH and PBr3.  This reaction tolerates phenols, aryl halides, thioethers, and olefins -- however, it is also more sensitive to the electron-rich/poor nature of the carbonyl group.   For instance, p-MeO-benzoic acid did not react at all.  The proposed mechanism is shown below. Also, reaction is moisture sensitive (and is quenched by water)!