Substituent effects in the stereoconvergent synthesis of β-hydroxyphenylalanine derivatives
摘要:
The degree of stereoconvergence in the synthesis of beta-hydroxyarylalanine derivatives from the corresponding beta-bromoarylalanine derivatives is governed by the electronic nature of the aryl substituents, and controlled by facially selective stabilisation of the benzylic cation through the neighbouring ester moiety. introduction of electron donating aryl substituents results in a decrease in selectivity, whereas electron withdrawing substituents induce an increase in selectivity for the threo-beta-hydroxyarylalanine diastereomer. (C) 1997 Elsevier Science Ltd.
Anchimeric Assistance in Hydrogen-Atom Transfer to Bromine
作者:Anna K. Croft、Christopher J. Easton
DOI:10.1071/ch04058
日期:——
N-bromosuccinimide exhibit anchimeric assistance by neighbouring ester and amido groups. Rate enhancement occurs through electron donation to the electropositive carbon centre that develops in the transition state of the hydrogen-atom transfer to bromine. The extent of the effect depends on the electron demand at the benzylic position and the electron-donating ability of the neighbouring group.
Dual Ligand-Enabled Nondirected C−H Olefination of Arenes
作者:Hao Chen、Philipp Wedi、Tim Meyer、Ghazal Tavakoli、Manuel van Gemmeren
DOI:10.1002/anie.201712235
日期:2018.2.23
The application of the Pd‐catalyzed oxidative C−H olefination of arenes, also known as the Fujiwara–Moritani reaction, has traditionally been limited by the requirement for directing groups on the substrate or the need to use the arene in large excess, typically as a (co)solvent. Herein the development of a catalytic system is described that, through the combined action of two complementary ligands
Ligand-Promoted Non-Directed C−H Cyanation of Arenes
作者:Luo-Yan Liu、Kap-Sun Yeung、Jin-Quan Yu
DOI:10.1002/chem.201805772
日期:2019.2.11
article reports the first example of a 2-pyridone accelerated non-directed C-H cyanation with an arene as the limiting reagent. This protocol is compatible with a broad scope of arenes, including advanced intermediates, drug molecules, and natural products. A kinetic isotope experiment (kH /kD =4.40) indicates that the C-H bond cleavage is the rate-limiting step. Also, the reaction is readily scalable