13C–1H COLOC analyses of 3a–d showed a correlation between the methine proton resonances and three fullerene carbons. These observations, as well as the 1H NMR chemical shifts of the methine protons, suggest a remarkable diastereoselectivity, with the silyl groups located above a five-membered ring. Two transition states of the thermal nitrogen-extrusion of pyrazoline intermediate (2a) were theoretically
在室温下向富勒烯C 60中添加甲硅烷基重氮甲烷(1a – d)可得到中等收率的甲硅烷基富勒烯(3a – d)单加合物,双加合物和三加合物。通过质谱,1 H和13 C NMR表征甲硅烷基富勒酸的结构。3a - d的门控1 H NMR和13 C- 1 H COLOC分析表明,次甲基质子共振与三个富勒烯碳之间存在相关性。这些观察结果以及1次甲基质子的1 H NMR化学位移表明其非对映选择性,甲硅烷基位于五元环上方。理论上获得了吡唑啉中间体(2a)的热氮挤出的两个过渡态,其结构揭示了非对映选择性是使甲硅烷基与N 2部分之间的排斥相互作用最小化的结果。甲硅烷基富勒烯的桥头C C双键被POAV分析认为是反应性的。发现甲硅烷基富勒酸酯(3a,b)与单态氧反应,通过二酮(1,3-甲硅烷基)的迁移生成甲硅烷基烯醇醚(9a,b)。8a,b)。这是富勒酸的1 O 2氧合的第一个例子。
A Dinickel Catalyzed Cyclopropanation without the Formation of a Metal Carbene Intermediate
作者:Arnab K. Maity、Annah E. Kalb、Matthias Zeller、Christopher Uyeda
DOI:10.1002/anie.202011602
日期:2021.1.25
Mechanistic studies reveal that a metal carbene intermediate is not part of the catalytic cycle. The (NDI)Ni2(CHSiMe3) complex was independently synthesized and found to be unreactive toward dienes. Based on DFT models, we propose an alternative mechanism that begins with a Ni2‐mediated coupling of (Me3Si)CHN2 and the diene. N2 extrusion followed by radical C−C bond formation generates the cyclopropane product
ethylsilanes 12 by base-induced α-elimination. This is confirmed by [2+1] cycloadditions with alkenes to give the cyclopropanes 4a–d and 14. Product 4a is identical with the product obtained from carbanion 1c, phenyloxirane, and styrene, for which a carbene intermediate 5a had been invoked. On heating in the presence of copper triflate, cyclopropane 4a undergoes ringenlargement to the thiochroman
Mechanism of the Regio- and Diastereoselective Ring Expansion Reaction Using Trimethylsilyldiazomethane
作者:Takeo Sakai、Satoshi Ito、Hiroki Furuta、Yuki Kawahara、Yuji Mori
DOI:10.1021/ol302032w
日期:2012.9.7
attack of TMS-diazomethane was determined to be the first step of the BF3-promoted ringexpansionreaction of six-membered ketones using TMS-diazomethane. The migration reaction occurred in a conformation in which the carbonyl oxygen and the TMS group were antiperiplanar to predominantly afford trans-seven-membered ketones.
The intramolecular cooperative reactions of 1,2-bis(diazoketone)s initiated by the Wolff rearrangement of alpha-diazoketones have been investigated. Under thermal conditions, 1,2-bis(diazoketone)s are efficiently transformed into 2-cyclopenten-1-one derivatives with complete stereospecificity. Thus, a most extraordinary result is reported, that trans-hydro-2-inden-1-ones (1-3) were synthesized for the first time from trans-1,2-bis(diazoketone)s (5, 11, and 12), respectively. The unprecedented trans-hydroindenone structure was confirmed by X-ray analysis of 3 as well as H-1 NMR analysis and was supported by ab initio molecular orbital calculations. The same reactions were also carried out under photochemical conditions and were applied to 1,3-bis(diazoketone)s, giving 2-cyclohexen-1-one derivatives.