Asymmetric α-electrophilic difluoromethylation of β-keto esters by phase transfer catalysis.

An efficient and enantioselective C difluoromethylation of β-keto esters has been achieved by phase-transfer catalysis. This procedure is applicable to different kinds of β-keto esters with a series of cinchona-derived C-2' aryl-substituted phase-transfer catalysts. The reaction gives the corresponding products in good enantioselectivities (up to 83% ee) and yields (up to 92%) with high C/O regioselectivities (up to 98:2). Moreover, the C/O selectivity of β-keto esters could be easily reversed and controlled. The enantioselective difluoromethylation could be scaled up and the C-difluoromethylation product could be derived into useful chiral CF2H-containing compounds.