ABSTRACT
In 1999, we reported a new catalytic asymmetric one-carbon homologation strategy that employed a rhodium catalyzed hydroboration reaction to introduce stereo chemistry.1'2 When followed by homologation with LiCHCl2 and oxidation, 2arylpropionic acids of high enantiomeric purity are generated (Scheme 1). Previously reported catalytic carbon-carbon bond forming reactions for the synthesis of these acids include hydrocarbonylation techniques employing carbon monoxide3'4 or cyanation with hydrogen cyanide.5 These are one-pot procedures; both the hydrometalation and the carbon-carbon bond forming steps are incorporated into a single catalytic cycle. Our approach is unique in that the generation of the required stereo center is separated from the second, stereo specific carbon-carbon bond forming reaction. This has the ad vantage that each step can be optimized individually, and dichloromethane can be used as the carbon source instead of carbon monoxide or hydrogen cyanide. We are currently working towards diversifying this two-step procedure with the aim to extend its scope to the use of different carbon sources.
