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Published on: July 21, 2018
Diastereoselective Ullmann Coupling to Bishelicenes by Surface Topochemistry
Anaïs Mairena1, Christian Wäckerlin1, Martin Wienke2
1Empa, Swiss Federal Laboratories for Materials Science and Technology , 8600 Dübendorf , Switzerland.
Abstract:
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.
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