New chiral sulfides and disulfides were synthesized from readily available and inexpensive cysteine by straightforward methods in order to elucidate the relative importance of the various donor atoms (N, O, S) available in free or alkylated form resulting in covalent or dative bonds to the metal, respectively. Their application in the addition of diethylzinc to aldehydes provides secondary alcohols with up to 99% ee, and S-configuration, when catalytic amounts of disulfide ligands with the ability to form an S-Zn bond were used. In contrast to this, benzyl alcohols with the opposite absolute configuration R could be achieved, albeit with decreased yield and enantioselectivity, by the use of alkylated sulfide ligands.
新型手性
硫化物和二
硫化物是通过简单的方法从易得且廉价的半胱
氨酸合成的,目的是阐明各种供体原子(N、O、S)在游离或烷基化形式下与
金属形成共价或配位键的相对重要性。它们在
二乙基锌与醛的加成反应中的应用,能够提供高达99% ee的二级醇,并且具有S-构型,当使用具有形成S-Zn键能力的催化量二
硫化物配体时。与此相反,通过使用烷基化
硫化物配体,可以得到绝对构型为R的
苄醇,尽管产率和对映选择性有所降低。