A New Cysteine-Derived Ligand as Catalyst for the Addition of Diethylzinc to Aldehydes: The Importance of a ‘Free’ Sulfide Site for Enantioselectivity
作者:Antonio Braga、Ludger Wessjohann、Elenilson Alves、Claudio Silveira、Gilson Zeni、Helmoz Appelt
DOI:10.1055/s-2005-861801
日期:——
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。