Investigations of Scope and Mechanism of Nickel-Catalyzed Transformations of Glycosyl Trichloroacetimidates to Glycosyl Trichloroacetamides and Subsequent, Atom-Economical, One-Step Conversion to α-Urea-Glycosides
作者:Matthew J. McKay、Nathaniel H. Park、Hien M. Nguyen
DOI:10.1002/chem.201402433
日期:2014.7.7
to the corresponding α‐trichloroacetamides. The α‐selective nature of the conversion is controlled with a cationic nickel(II) catalyst, [Ni(dppe)(OTf)2] (dppe=1,2‐bis(diphenylphosphino)ethane, OTf=triflate). Mechanistic studies have identified the coordination of the nickel catalyst with the equatorial C2‐ether functionality of the α‐glycosyl trichloroacetimidate to be paramount for achieving an α‐stereoselective
描述了用于制备 α-连接的尿素新糖缀合物和假寡糖的高度立体选择性方法的开发和机理研究。该两步程序首先在镍催化下将糖基三氯乙酰亚胺选择性转化为相应的 α-三氯乙酰胺。转化的 α 选择性由阳离子镍 (II) 催化剂 [Ni(dppe)(OTf) 2 ](dppe=1,2-双(二苯基膦)乙烷,OTf=三氟甲磺酸盐)控制。机理研究已经确定了镍催化剂与赤道 C 2 的配位α-糖基三氯乙酰亚胺酯的-醚官能团对于实现α-立体选择性转化至关重要。交叉实验表明,该反应并非完全以分子内方式进行。该序列的第二步是通过在碳酸铯存在下与多种胺亲核试剂反应,将 α-糖基三氯乙酰胺产物直接转化为相应的 α-尿素糖苷。仅观察到 α-尿素产物的形成,因为反应在异头 C N 键上完全保留立体化学完整性。