1,3-Dipolarcycloaddition of nitrones on several allyl silanes, allyl ethers, and allyl alcohol was investigated. The silicon atom in dipolarophiles controlled the regioselectivity in favor for 5-(silylmethyl)isoxazolidines, while the oxygen atom for 4-(alkoxymethyl)isoxazolidines.
Facile catalytic methods for intermolecular generation of allylic oxonium ylides and their stereoselective [2,3]- sigmatropic rearrangement
作者:Michael P. Doyle、Vahid Bagheri、Nancy K. Harn
DOI:10.1016/s0040-4039(00)80695-4
日期:1988.1
Allylic oxonium ylides, generated by rhodium(II) acetate-catalyzed decomposition of diazo carbonyl compounds in the presence of allyl methylethers, undergo the [2,3]-sigmatropic rearrangement with a high degree of diastereoselectivity.
Photolysis of diazomethane in (S)-2-methyloxetane gives 2- and 3-methyltetrahydrofuran (1:3.2), the latter being formed with 21 % net retention of configuration. In contrast, rhodium acetate catalysis yields racemic 3-methyltetrahydrofuran exclusively.
Selecting Double Bond Positions with a Single Cation-Responsive Iridium Olefin Isomerization Catalyst
作者:Andrew M. Camp、Matthew R. Kita、P. Thomas Blackburn、Henry M. Dodge、Chun-Hsing Chen、Alexander J. M. Miller
DOI:10.1021/jacs.0c11601
日期:2021.2.24
stereoselectivity. The same catalyst, in the presence of Na+, mediates two positional isomerizations to produce 3-alkenes. The synthesis of new iridium pincer-crown ether catalysts based on an aza-18-crown-6 ether proved instrumental in achieving cation-controlled selectivity. Experimental and computational studies guided the development of a mechanistic model that explains the observed selectivity for various functionalized
Gas phase nucleophilicsubstitution on oxygen-protonated but-1-en-3-ol and trans-but-2-en-1-ol by methanol proceeds via the concertedSN2′ mechanism in competition with the classical SN2mechanism.
甲醇对氧质子化的1--1-en-3-ol和反式-2- but-1-en-1-ol进行气相亲核取代是通过协同的S N 2'机制进行的,与经典的S N 2机制竞争。