Asymmetric synthesis. Part 5. Asymmetric reduction of phenyl trifluoromethyl ketone with chiral alkoxy-aluminium and -magnesium halides
Phenyl trifluoromethyl ketone has been asymmetrically reduced with a number of chiral alkoxy-aluminium and -magnesium halides derived from bornan-2-exo- and -endo-ols, p-menthan-3-ol, and 1-phenylethanol. Bornan-2-endo-yloxyaluminium dichloride and p-menthan-3-yloxyaluminium dichloride are highly stereoselective and reduce the ketone to give 2,2,2-trifluoro-1 -phenylethanol with 68 and 77% enantiomeric excess, respectively. The results are discussed in terms of appropriate transition states.