Designing Fluorinated Cinchona Alkaloids for Enantioselective Catalysis: Controlling Internal Rotation by a Fluorine‐Ammonium Ion gauche Effect (φNCCF) |
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Authors: | Eva‐Maria Tanzer Dr W Bernd Schweizer Dr Marc‐Olivier Ebert Prof Dr Ryan Gilmour |
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Institution: | Laboratory for Organic Chemistry, Swiss Federal Institute of Technology (ETH) Zürich, 8093 Zürich (Switzerland), Fax: (+41)?44‐632‐79‐34 |
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Abstract: | The C9 position of cinchona alkaloids functions as a molecular hinge, with internal rotations around the C8? C9 (τ1) and C9? C4′ (τ2) bonds giving rise to four low energy conformers ( 1 ; anti‐closed, anti‐open, syn‐closed, and syn‐open). By substituting the C9 carbinol centre by a configurationally defined fluorine substituent, a fluorine‐ammonium ion gauche effect (σC?H→σC?F*; Fδ????N+) encodes for two out of the four possible conformers ( 2 ). This constitutes a partial solution to the long‐standing problem of governing internal rotations in cinchonium‐based catalysts relying solely on a fluorine conformational effect. |
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Keywords: | alkaloids conformation analysis fluorine gauche effect |
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