A new sequential defluorination route to α-fluoro-α,β-unsaturated ketones from trifluoromethyl ketones

α-Fluoro-α,β-unsaturated ketones were prepared from trifluoromethyl ketones via a sequence involving Mg metal promoted successive double defluorination. Trifluoromethyl ketones were transformed to β,β-difluoroenol silyl ethers which were then coupled with aldehydes and ketones to β-hydroxy-α,α-difluoroketones. A second Mg-promoted defluorination of the hydroxyketones followed by acid-catalyzed hydrolysis of γ-hydroxy-β-fluoroenol silyl ethers provided α-fluoro-α,β-unsaturated ketones as a final product.