Enantioselective trifluoromethylthiolation of 4-substituted pyrazolones catalyzed by amide-based phase transfer catalysts

We successfully developed the first enantioselective trifluoromethylthiolation of 4-substituted pyrazolones catalyzed by amide-based Cinchona alkaloids with N-trifluoromethylthiosaccharin. A broad variety of chiral CF3S-pyrazolones were obtained in excellent yields with high enantioselectivities. Controlled experiments showed that the multiple hydrogen bonding interactions and the steric hindrance at NH-position were indispensable for high enantioselectivity and reactivity. Furthermore, these amide-based phase transfer catalysts could be easily recovered and reused for such a reaction with almost original reactivity and enantioselectivity.