nosyloxycarbamate using water as a co-solvent takes place with very high diastereoselectivity, the nucleophilic attack occurring only on the less hindered side of the CN double bond. Interestingly, the presence of water in the reaction medium likely stabilizes the anion intermediate slowing down the successive cyclization reaction and favoring the rotation around the C–N single bond. In fact, as confirmed by
以
水为助溶剂,用壬基氧基
氨基甲酸乙酯将手性α-二
亚胺去对称化的非对映选择性非常高,亲核攻击仅发生在C N双键受阻较小的一侧。有趣的是,反应介质中
水的存在可能使阴离子中间体稳定下来,从而减慢了后续的环化反应并有利于围绕CN单键的旋转。实际上,如通过ROESY实验所证实的,总是始终仅以等摩尔比获得在烷基取代的氮原子的绝对构型方面不同的两种非对映异构体3-(亚
氨基甲基)二
氮丙啶-1-
羧酸酯。最后,所有化合物都可以通过HPLC分离轻松以光学纯净形式获得,可以认为是有趣的手性合成子。