Efficient Preparation of TMSCCl2 Br and Its Use in Dichlorocyclopropanation of Electron-Deficient Alkenes.
Efficient Preparation of TMSCCl2 Br and Its Use in Dichlorocyclopropanation of Electron-Deficient Alkenes.
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DOI：
10.1002/chem.201600607
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发表时间：
2016-05
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影响因子：
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通讯作者：
Darren S. Lee;M. Durán-Peña;Laurence Burroughs;S. Woodward
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文献类型：
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作者：
Darren S. Lee;M. Durán-Peña;Laurence Burroughs;S. Woodward
过量TMSCl与LiCCl_2Br在低温下反应是一条技术简单、产率高的TMSCCl_2Br合成路线。后者是二氯溴甲基碳负离子的稳定来源，其与环状硝基烯烃和（E）-取代物进行1，4-加成，在溴化物排出后产生二氯环丙烷。对于硝基苯乙烯，反应在1，4-加成产物处停止。低温NMR光谱研究和DFT计算表明形成了“酸盐”物质[（硝膦酸盐）SiFMe 3]（-），其在TMSF在10-20 °C下蒸发时产生环丙烷。DFT计算也支持氟化物和乙酸盐作为促进剂之间的实验差异。
The reaction of excess TMSCl and LiCCl2 Br at low temperature is a technically simple high yield route to TMSCCl2 Br. The latter is a stable source of the dichlorobromomethide carbanion, which undergoes 1,4-addition with cyclic nitroalkenes and (E)-fumarates leading to dichlorocyclopropanes after bromide expulsion. For nitrostyrenes the reaction arrests at the 1,4-addition product. Low temperature NMR spectroscopy studies and DFT calculations suggest the formation of an "ate" species [(nitronate)SiFMe3 ](-) which, upon boil-off of TMSF at 10-20 °C, yields the cyclopropane. DFT calculations also support the experimental differences between fluoride and acetate as promotors.