Mechanisms of hydrolysis of phenyl- and benzyl 4-nitrophenyl-sulfamate esters
作者:William J. Spillane、Sergio Thea、Giorgio Cevasco、Michael J. Hynes、Cheryl J. A. McCaw、Neil P. Maguire
DOI:10.1039/c0ob00362j
日期:——
unimolecular expulsion of the leaving group from the ionized ester to give N-sulfonylamine [HNSO2] as an intermediate. In more alkaline solution further ionization of the conjugate base of the ester occurs to give a dianionic species which expels the aryloxide leaving group to yield the novel N-sulfonylamine anion [−NSO2]; in a final step, rapid attack of hydroxide ion or a water molecule on it leads again
研究了一系列苯氨基磺酸酯1在中等酸强度(pH区间2-5)下的水解动力学,发现它们通过缔合S N 2(S)机理与水 充当亲核试剂攻击硫,裂解S–O键,同时与a的氧形成新的S–O键 水 分子导致 氨基磺酸 和 苯酚作为产品。在中性至中度碱性溶液(pH≥〜6–9)中,遵循解离(E1cB)途径,其中包括:i)氨基电离,然后ii)从电离酯中单分子驱离离去基团,得到N-磺胺[HN SO 2 ]作为中间体。在更碱性溶液中的酯的共轭碱的进一步电离发生以得到排出的芳基氧化物的离去基团,得到新颖的双阴离子物种Ñ -sulfonylamine阴离子[ - Ñ SO 2 ]; 在最后一步中,氢氧根离子或氢氧根离子的快速侵蚀水 分子再次导致 氨基磺酸。在6.4–14的pH范围内水解了一系列取代的4-硝基苯基氨基磺酸苄酯4,形成了Hammett关系,该关系的反应常数与E1cB机理一致。
<i>Para</i>-Selective C–H Borylation of Common Arene Building Blocks Enabled by Ion-Pairing with a Bulky Countercation
作者:Madalina T. Mihai、Benjamin D. Williams、Robert J. Phipps
DOI:10.1021/jacs.9b07267
日期:2019.10.2
The selective functionalization of C–H bonds at the arene para position is highly challenging using transition metal catalysis. Iridium-catalyzed borylation has emerged as a leading technique for arene functionalization, but there are only a handful of strategies for para-selective borylation, which operate on specific substrate classes and use bespoke ligands or catalysts. We describe a remarkably