catalytic asymmetric 1,3-dipolarcycloaddition of pyruvate-derived nitrones to α,β-unsaturatedaldehydes was investigated in the presence of various chiral amines. Highly functionalized isoxazolidines containing a quaternary stereocenter were obtained in moderate yields with up to 92% ee. To the best of our knowledge, this is the first example of an enantioselective1,3-dipolarcycloaddition of ketonitrones
Enantioselective 1,3-Dipolar Cycloaddition Reactions of <i>C</i>
-Carboxy Ketonitrones and Enals with MacMillan Catalysts: Evidence of a Nonconcerted Mechanism
作者:Kawther Ben Ayed、Mathieu Y. Laurent、Arnaud Martel、Khalid B. Selim、Souhir Abid、Gilles Dujardin
DOI:10.1002/ejoc.201701307
日期:2017.12.8
Highly diastereo- and enantioselective1,3-dipolarcycloadditions between functional ketonitrones and β-substituted enals are promoted by organocatalysis with the imidazolidinium catalyst of MacMillan. Study of the scope of the reaction shows that high selectivities are conserved by varying the N-protecting group or the ester function. However it is sensitive to sterical interaction with the C-substituent
功能性酮硝酮和 β-取代烯醛之间的高度非对映选择性和对映选择性 1,3-偶极环加成通过 MacMillan 的咪唑啉鎓催化剂的有机催化作用得到促进。对反应范围的研究表明,通过改变 N-保护基团或酯官能团可以保持高选择性。然而,它对与硝酮的 C 取代基的空间相互作用很敏感。反应在所有情况下都以高外选择性进行。在大多数情况下,观察到与协同机制不相容的第三种非对映异构体,尽管数量很少。DFT 计算证明环加成以非协同方式进行,首先将硝酮加入到双键上,然后进行环化。这种机制解释了观察到的次要非对映异构体的形成。此外,该反应的非对映选择性和对映选择性显示为中间热力学控制,非对映体比例受亚胺水解动力学的调节。