Augmentation of Enantioselectivity by Spatial Tuning of Aminocatalyst: Synthesis of 2-Alkyl/aryl-3-nitro-2<i>H</i>-chromenes by Tandem Oxa-Michael–Henry Reaction
作者:Rahul Mohanta、Ghanashyam Bez
DOI:10.1021/acs.joc.9b03366
日期:2020.4.3
The asymmetric oxa-Michael addition of salicylaldehyde to conjugated nitroalkenes often suffers from poor reactivity and selectivity and a long reaction time. Because of the formation of an iminium ion with aminocatalyst, the nucleophilicity of the phenolic hydroxy group in salicylaldehyde reduces further to make the oxa-Michael reaction reversible. Here, we report a structurally simple and easily
水杨醛向共轭硝基烯烃的不对称氧杂-迈克尔加成反应通常具有较差的反应性和选择性以及较长的反应时间。由于与氨基催化剂形成亚胺离子,因此水杨醛中酚羟基的亲核性进一步降低,从而使氧杂-迈克尔反应可逆。这里,我们报告一个结构简单且容易接近升-脯氨酸衍生aminocatalyst,苯基升-脯氨酰胺,为水杨醛的不对称串联氧杂迈克尔-亨利反应与共轭硝基烯,得到2-烷基/芳基-3-硝基-2- ħ -色烯在较短的反应时间内具有出色的对映选择性。