Chiral quaternary ammonium phenoxides were prepared readily from commercially available cinchona alkaloids and employed as novel useful asymmetric organocatalysts. Among these chiral quaternary ammonium phenoxides, a cinchonidine-derived phenoxide that possesses a sterically hindered N(1)-3,5-bis[3,5-bis(trifluoromethyl)phenyl]benzyl group was the most effective for asymmetric trifluoromethylation. In the presence of a catalytic amount of Lewis bases, such as cinchonidine-derived quaternary ammonium phenoxides, catalyzed the reaction of various ketones with (trifluoromethyl)trimethylsilane to afford the corresponding trifluoromethylated adducts in high yields and with moderate to high enantioselectivities.
手性四级
铵酚氧化物是通过商业可得的
金雀花
生物碱制备的,并作为新型有用的非对称有机催化剂。在这些手性四级
铵酚氧化物中,来源于
金雀花碱的
酚氧化物,具有空间位阻的N(1)-3,5-双[3,5-双(三
氟甲基)苯基]苄基,是用于非对称三
氟甲基化的最有效的催化剂。在存在少量路易斯碱(如来源于
金雀花碱的四级
铵酚氧化物)的条件下,催化了各种酮与(三
氟甲基)三甲基
硅烷的反应,从而以高产率和中到高的对映选择性获得相应的三
氟甲基化加合物。