The First Catalytic Highly Enantioselective Alkylation of Ketimines—A Novel Approach to Optically Active Quaternaryα-Amino Acids
作者:Steen Saaby、Kimitaka Nakama、Mette Alstrup Lie、Rita G. Hazell、Karl Anker Jørgensen
DOI:10.1002/chem.200305302
日期:2003.12.15
anchoring was synthesized and allowed to react with various silylketene acetals in the presence of 5-10 mol % of a chiral Zn(OTf)(2)-(R,R)-Ph-pybox-aqua complex. The corresponding optically active quaternary alpha-amino acid derivatives were obtained in high yields and with enantioselectivities ranging from 34 % up to 95 % ee. The catalyst was studied by (1)H NMR spectroscopy and X-ray crystallography
合成了一系列具有固有保护基团锚定的新型酮亚胺,并使其在5-10 mol%手性Zn(OTf)(2)-(R,R)-Ph-pybox-水族情结。相应的旋光性季α-氨基酸衍生物以高收率获得,其对映选择性为34%至95%ee。通过(1)H NMR光谱和X射线晶体学研究了该催化剂,并且在溶液中鉴定了两种物质的动态平衡。它们是均手性的1:2金属-配体络合物和1:1的金属-配体络合物,其中后者有望成为非对映和对映选择性反应的实际催化剂。由于形成了催化失活的1:2金属-配体杂手性络合物,观察到了强烈的正非线性效应。基于DFT计算和产品的绝对立体化学,提出了亚氨基亲电子体和H(2)O单分子与手性Lewis酸配合物的同时配位。亚胺-氮原子在八面体络合物的轴向位置上的配位可以说明面部选择性以及观察到的非对映选择性。