Enantioselective organocatalytic epoxidation using hypervalent iodine reagents
作者:Sandra Lee、David W.C. MacMillan
DOI:10.1016/j.tet.2006.07.055
日期:2006.12
A rare example of a hypervalentiodine reagent participating in a 1,4-heteroconjugate addition reaction is reported for the organocatalytic, asymmetric epoxidation of α,β-unsaturated aldehydes using imidazolidinone catalyst 1. Development of an ‘internal syringe pump’ effect via the slow release of iodosobenzene from an iminoiodinane source provides high levels of reaction efficiency and enantiomeric
据报道,使用咪唑烷酮催化剂1可以使α,β-不饱和醛发生有机催化,不对称环氧化,这是参与1,4-杂合物加成反应的高价碘试剂的一个罕见例子。通过从亚碘碘烷源缓慢释放碘代苯来开发“内部注射泵”效应,可在缺电子烯烃的不对称环氧化中提供高水平的反应效率和对映体控制。进行了15 N NMR研究,以阐明在原型氧化剂存在下导致催化剂耗竭的反应途径。这些NMR研究也为亚氨基碘烷作为内部缓释氧化剂的应用提供了机理基础,以规避这些催化剂的消耗途径。
Proposal for structure revision of pinofuranoxin A through total syntheses of stereoisomers
The relative configuration of the epoxide functionality in pinofuranoxin A (1), α-alkylidene-β-hydroxy-γ-methyl-γ-butyrolactone with trans-epoxy side chain isolated by Evidente et al. in 2021, was revised by DFT-based spectral reinvestigations and stereo-controlled synthesis. The present investigation demonstrates the difficulty of the configurational elucidation of the stereogenic centers on the conformationally
Evidente 等人分离出具有反式环氧侧链的呋喃呋喃辛 A ( 1 )、α-亚烷基-β-羟基-γ-甲基-γ-丁内酯中环氧化物官能团的相对构型。 2021年,通过基于DFT的光谱重新研究和立体控制合成进行了修订。目前的研究表明,构象灵活的无环侧链上的立体中心的构型阐明很困难。 Sharpless 的对映选择性环氧化和二羟基化在构型的重新研究中非常有效。由于我们的合成使所有非对映体可用,这些在下一步的结构-生物活性关系研究中将非常有效。 图解摘要
An Organocatalytic Approach to 2-Hydroxyalkyl- and 2-Aminoalkyl Furanes
The first enantioselective methodology for the synthesis of electron-poor 2-hydroxyalkyl- and 2-aminoalkyl furanes is demonstrated in this study. It utilizes a highly stereoselective organocatalytic one-pot reaction cascade: epoxidation or aziridination of alpha,beta-unsaturated aldehydes followed by Feist-Benary reaction of various 1,3-dicarbonyl compounds to give the target furanes. This efficient multibond forming reaction cascade benefits from low catalyst loadings and readily available starting materials. Furthermore, the possibility to interrupt the reaction sequence at the stage of the corresponding optically active 2-hydroxyalkyl- and 2-aminoalkyl 2,3-dihydrofuranes with three stereogenic centers is also presented. Finally, models which account for the formation of the optically active 2,3-dihydrofuranes are proposed.
Base-Induced Heterochiral Dimerization of an Oxiranyl Carbaldimine: Stereoselective Synthesis of a Highly Functionalized Aziridine
Treatment of the oxiranyl carbaldimine with base (LDA or LDA/KOtBu) leads in an one-step procedure to the polyfunctionalized aziridine, This highly diastereoselective reaction is explained by a new type of an Aza-Darzens reaction, in which one enantiomer of the starting material is deprotonated to form an oxiranyl anion, which attacks the imine carbon atom of the other enantiomer (mutual kinetic resolution by double diastereofacial selection).