The ortho-nitro effect was discovered in sulfa-Staudinger cycloadditions of ethoxycarbonylsulfene with linear imines. When an ortho-nitro group is present at the C-aryl substituents of linear imines, the sulfa-Staudinger cycloadditions deliver cis-β-sultams in considerable amounts, together with the predominant trans-β-sultams. In other cases, the above sulfa-Staudinger cycloadditions give rise to trans-β-sultams
Direct access to vicinally functionalized and <i>N</i>-trifluoroacetylated (bicyclic)ketopiperazines using a readily affordable N-heterocyclic anhydride
作者:Antonio Moreno、Timothy K. Beng
DOI:10.1039/d0ob00049c
日期:——
stereoselective, modular, and chemoselective annulation protocol between a novel N-trifluoroacetyl anhydride and several reactive partners, including lactimethers, imidoyl chlorides, aryl aldimines, and 1,3-azadienes, leading to vicinally functionalized (bicyclic) 2-piperazinones.
Steric and Electronic Effects in Capsule-Confined Green Fluorescent Protein Chromophores
作者:Anthony Baldridge、Shampa R. Samanta、Nithyanandhan Jayaraj、V. Ramamurthy、Laren M. Tolbert
DOI:10.1021/ja1094606
日期:2011.2.2
The turn-on of emission in fluorescent protein chromophores sequestered in an "octaacid" capsule is controlled by stereoelectronic effects described by a linear free energy relationship. The stereochemical effects are governed by both the positions and volumes of the aryl substituents, while the electronic effects, including ortho effects, can be treated with Hammett sigma parameters. The use of substituent volumes rather than A values reflects packing of the molecule within the confines of the capsule.