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Anion‐Binding Catalysis by Electron‐Deficient Pyridinium Cations
Author(s) -
Berkessel Albrecht,
Das Somnath,
Pekel Daniel,
Neudörfl JörgM.
Publication year - 2014
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201403778
Subject(s) - pyridinium , chemistry , electrophile , catalysis , bromide , substituent , ketene , moiety , medicinal chemistry , photochemistry , inorganic chemistry , organic chemistry
A new activation principle in organocatalysis is presented: halide binding through Coulombic interactions. This mode of catalysis was realized by using 3,5‐di(carbomethoxy)pyridinium ions that carry an additional electron‐withdrawing substituent on the nitrogen atom, for example, pentafluorobenzyl or cyanomethyl. For the N ‐pentafluorobenzyl derivative, Coulombic interaction with the pyridinium moiety is complemented in the solid state by anion–π interactions with the perfluorophenyl ring. Bromide and chloride are bound by these cations in a 1:1 stoichiometry. Catalysis of the CC coupling between 1‐chloroisochroman (and related electrophiles) with silyl ketene acetals occurs at −78 °C and at low catalyst loading (2 mol %).