Assessment was made of the effectiveness of different boron Lewis acids in mediating the trifluoromethylation of reactive enolate anions with S- and Se-(trifluoromethyl)chalcogen salts. Treatment of potassium or lithium enolates derived in situ from carbonyl compounds or enol trimethylsilyl ethers with S-(trifluoromethyl)dibenzothiophenium triflate (1) in the presence of 2-phenyl-1,3,2-benzodioxaborole (4) produced trifluoromethylated carbonyl compounds in high yields. In this manner, various α-CF 3 ketones, γ-CF 3 -α,β-unsaturated ketones, and an α-CF3 ester were synthesized. Perfluorooctylation was similarly conducted using S-(perfluorooctyl)dibenzothiophenium triflate and 4. Thus, a balance of the reactivity of the reactants was essential for these electrophilic perfluoroalkylations. The deprotonation of 2-methylcyclohexanone with KN(SiMe 3 ) 2 followed by trifluoromethylation gave the 6-trifluoromethylated product regioselectively. In the trifluoromethylation of potassium enolate 16 of 4,4a,5,6,7,8-hexahydro-4a-methyl-2(3H)-nanphthalenone, the use of bulky 2-mesitylphenanthro[9,10-d]-1,3,2-dioxaborole (15) led to the diastereoselective formation of the thermodynamically less stable CF 3 -isomer 17β. For enantioselective trifluoromethylation, optically active (S)-4-phenyldinaphth[2,1-d:1',2'-f][1,3,2]dioxaborepin (19) and its 3,3'-diphenyl derivative 20 were synthesized. The trifluoromethylation of the potassium enolate of propiophenone with 1 in the presence of 20 afforded optically active α-CF 3 -propiophenone in 45% ee yield. Thus, a new and versatile method for selective trifluoromethylation has been developed