Inversions in asymmetric conjugate addition reaction of cyclic enones catalyzed by the Cu/NHC-AgX system: Factors affecting the stereoselective formation of both enantiomers
作者:Yuki Nakano、Satoshi Sakaguchi
DOI:10.1016/j.jorganchem.2017.07.025
日期:2017.10
was achieved in a Cu-catalyzed asymmetric conjugate addition (ACA) reaction. The ethylene-bridged, hydroxyamide-functionalized NHC-AgI complex, readily accessible from a chiral β-amino alcohol, was found to be a versatile chiral ligand precursor for dual enantioselective control. The stereocontrol of the catalytic ACA reaction depended on the order of addition of the substrates. To a THF solution containing
在Cu催化的不对称共轭加成(ACA)反应中实现了可切换的对映选择性。可以容易地从手性β-氨基醇得到的乙烯桥联的,羟酰胺官能化的NHC-AgI复合物是用于双重对映选择性控制的通用手性配体前体。催化ACA反应的立体控制取决于底物的添加顺序。向含有CuOTf(6mol%)的THF溶液中,加入NHC-AgI络合物(1b,R 1 = Et,R 2 = Bn,4mol%),和2-环己烯-1-酮(3)添加Et 2 Zn。产生(R)-3-乙基环己酮((R)-4)的对映体选择性为74%(方法A)。与之形成鲜明对比的是,当将3作为最后一种组分添加到THF中的CuOTf(4 mol%),1b(10 mol%)和Et 2 Zn的混合物中(方法B)时,ACA反应得到(S)-4拥有87%的ee。为了深入了解本ACA反应的各个方面,对手性NHC配体前体,底物和NHC骨架进行了全面评估。催化剂ee(ee cat)与产品ee(ee