N-acyloxyiminium species, which are more reactive toward soft carbon nucleophiles than nitrones. Addition of chiral enolates to the N-acyloxyiminium species gave N-hydroxy-β-amino acid derivatives highly diastereoselectively. Reversal of diastereoselectivity was observed between the boron enolates and titanium enolates. Using this method all of the four stereoisomers of α-methyl-β-phenylalanines can be prepared as
硝酮和酰基卤的反应产生 N-酰氧基
亚胺鎓物种,其对软碳亲核试剂的反应性高于硝酮。将手性烯醇化物添加到 N-酰氧基
亚胺鎓物种中,可产生高度非对映选择性的 N-羟基-β-
氨基酸衍
生物。在
硼烯醇化物和
钛烯醇化物之间观察到非对映选择性的逆转。使用这种方法,α-甲基-β-苯丙
氨酸的所有四种立体异构体都可以制备为对映体纯形式。