Anion-Binding Catalysis by Electron-Deficient Pyridinium Cations

• Published in: Angewandte Chemie (International ed.) Vol. 53; no. 43; pp. 11660 - 11664
• Main Authors: Berkessel, Albrecht, Das, Somnath, Pekel, Daniel, Neudörfl, Jörg-M.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 20.10.2014; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Acetals; Activation; anion-binding catalysis; anion-π interactions; Binding; Catalysis; Catalysts; Cations; Chemistry; Chemistry, Multidisciplinary; Chlorides; Ketenes; Nitrogen atoms; organocatalysis; organofluorine compounds; Physical Sciences; pyridinium cations; Science & Technology; organocatalysis; anion- interactions; anion-binding catalysis; pyridinium cations; PI INTERACTIONS; DONORS; HALOGEN; RECEPTORS; organofluorine compounds; anion-π interactions
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201403778

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 CC coupling between 1‐chloroisochroman (and related electrophiles) with silyl ketene acetals occurs at −78 °C and at low catalyst loading (2 mol %). A successful trio: Pyridinium cations carrying three electron‐withdrawing substituents catalyze the alkylation of α‐halo ethers with silyl ketene acetals through Coulombic anion binding. This CC bond formation proceeds efficiently at low temperatures and at low catalyst loading.