通过表面拓扑化学实现非对映选择性乌尔曼偶联生成双螺旋烯
Diastereoselective Ullmann Coupling to Bishelicenes by Surface Topochemistry.
作者信息
Mairena Anaïs, Wäckerlin Christian, Wienke Martin, Grenader Konstantin, Terfort Andreas, Ernst Karl-Heinz
机构信息
Empa, Swiss Federal Laboratories for Materials Science and Technology , 8600 Dübendorf , Switzerland.
Department of Chemistry , University of Hamburg , 20146 Hamburg , Germany.
出版信息
J Am Chem Soc. 2018 Nov 14;140(45):15186-15189. doi: 10.1021/jacs.8b10059. Epub 2018 Nov 5.
The comparison of the self-assembly 9,9'-bisheptahelicene on the Au(111) surface, studied with scanning tunneling microscopy, with the self-assembly of the same species obtained by on-surface synthesis via Ullmann coupling from 9-bromoheptahelicene reveals a diastereomeric excess for the ( M, P)- meso-form of 50%. The stereoselectivity is explained by a topochemical effect, in which the surface-alignment of the starting material and the organometallic intermediate sterically favor the ( M, P)-transition state over the homochiral transition states.
通过扫描隧道显微镜研究了9,9'-双七螺旋烯在Au(111)表面的自组装，并将其与通过乌尔曼偶联从9-溴七螺旋烯进行表面合成得到的同一物种的自组装进行比较，结果表明( M, P)-内消旋体的非对映体过量为50%。这种立体选择性是由一种拓扑化学效应解释的，在该效应中，起始原料和有机金属中间体的表面排列在空间上有利于( M, P)-过渡态而非同手性过渡态。
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