 the 
 catalytic asymmetric synthesis of alkyl fluorides , particularly 
 -fluorocarbonyl compounds , has been the focus of substantial 
 effort in recent years . 
 while significant progress has been described 
 in the formation of enantioenriched secondary alkyl fluorides , advances 
 in the generation of tertiary alkyl fluorides have been more limited . 
 here 
 , we describe a method for the catalytic asymmetric coupling of 
 aryl alkyl ketenes with commercially available n - fluorodibenzenesulfonimide 
 ( nfsi ) and c6f5ona to furnish tertiary -fluoroesters . 
 
 mechanistic studies are consistent with the hypothesis that the addition 
 of an external nucleophile ( c6f5ona ) is critical 
 for turnover , releasing the catalyst ( ppy * ) from an n - acylated 
 intermediate . 
 the available data can be explained by a reaction pathway 
 wherein the enantioselectivity is determined in the turnover - limiting 
 transfer of fluorine from nfsi to a chiral enolate derived from the 
 addition of ppy * to the ketene . 
 the structure and the 
 reactivity of the product of this proposed elementary step , an -fluoro - n - acylpyridinium salt , have been examined . 
Supplementary Material