Cobalt-Bisoxazoline-Catalyzed Asymmetric Kumada Cross-Coupling of Racemic α-Bromo Esters with Aryl Grignard Reagents

The first cobalt-catalyzed asymmetric Kumada cross-coupling with high enantioselectivity has been developed. The reaction affords a unique strategy for the enantioselective arylation of alpha-bromo esters catalyzed by a cobalt-bisoxazoline complex. A variety of chiral alpha-arylalkanoic esters were prepared in excellent enantioselectivity and yield (up to 97% ee and 96% yield). The arylated products were transformed into alpha-arylcarboxylic acids and primary alcohols without erosion of ee. The new enantioenriched alpha-arylpropionic esters synthesized herein are potentially useful in the development of nonsteroidal anti-inflammatory drugs. This method was conducted on gram-scale and applied to the synthesis of highly enantioenriched (S)-fenoprofen and (S)-ar-turmerone.