Construction of Vicinal Quaternary Centers via Iridium-Catalyzed Asymmetric Allenylic Alkylation of Racemic Tertiary Alcohols
作者:Mayuko Isomura、David A. Petrone、Erick M. Carreira
DOI:10.1021/jacs.1c00609
日期:2021.3.10
Enantioselective bond formation between stericallyhinderedfragments to furnish acyclic products with vicinal quaternary centers is a formidable challenge. We report a solution that involves cocatalysis between a chiral Ir–(phosphoramidite,olefin) complex and La(OTf)3. This robust catalytic system effects highly enantioconvergent and regioselective alkylation of racemic tertiary α-allenyl alcohols
在空间位阻片段之间形成对映选择性键以提供具有邻位四元中心的无环产物是一项艰巨的挑战。我们报告了一种解决方案,该解决方案涉及手性 Ir–(亚磷酰胺、烯烃)配合物和 La (OTf) 3之间的共催化. 这种强大的催化系统可实现外消旋叔 α-烯醇与四取代甲硅烷基乙烯酮缩醛的高度对映收敛和区域选择性烷基化。该转化对两种反应组分均显示出广泛的官能团耐受性,并允许以良好的收率和出色的对映选择性有效生成 β-烯丙酯产物。此外,通过一系列立体选择性金属催化的官能化反应,利用丙二烯和酯官能度来提升产品的结构复杂性。
Alkylation of Ketene Silyl Acetals with Nitroolefins Mediated by Sterically Encumbered Lewis Acids
作者:John A. Tucker、Terrance L. Clayton、Donald M. Mordas
DOI:10.1021/jo9624004
日期:1997.6.1
procedures for the corresponding reaction of esters suffer from important limitations such as modest yields, lack of demonstrated generality, inconveniently low reaction temperatures, and/or the use of a large excess of one of the two reactants. In the present work, we examined the efficacy of a series of Lewisacid catalysts for the alkylation of ketenesilylacetals with nitroolefins. Previously reported
Harnessing Energy-Transfer in N-Centered Radical-Mediated Synthesis of Pyrrolidines
作者:Peter Fodran、Carl-Johan Wallentin
DOI:10.1002/ejoc.202000537
日期:2020.6.16
Photo‐initiated energy‐transfer provides a route to nitrogen centered radicals, which can be harnessed in a formal [3+2] cycloaddition. The reaction is scalable, proceeds at very mild conditions tolerates various functional groups, and provides the corresponding trisubstituted pyrrolidines in good to excellent yields.
The first observation of the stereospecificity in the benzyne-olefin [2 + 2] cycloaddition is described. The key points reside in (1) the efficient method for generating benzyne species by the halogen-lithium exchange reaction of ortho-halo aryl triflates, and (2) the choice of ketene silyl acetal as the partner olefin.
Stereoselection in the condensation between ethyl propionate and aldehydes
作者:T.H. Chan、T. Aida、P.W.K. Lau、V. Gorys、David N. Harpp
DOI:10.1016/s0040-4039(01)86495-9
日期:——
Ethyl propionate can be converted stereoselectively into geometrical isomers of O-ethyl-O-trimethylsilylmethylketene acetal (). The E-isomer of condenses with aldehydes by titanium tetrachloride to give stereoselectively the threo isomers of ethyl 2-methyl-3-hydroxy carboxylates.