Enantioselective protonation of α-hetero carboxylic acid-derived ketene disilyl acetals under chiral ionic Brønsted acid catalysis

Abstract

Highly enantioselective protonation of α-halo and alkoxy carboxylic acid-derived ketene disilyl acetals is achieved by using P-spiro chiral diaminodioxaphosphonium barfate as a Brønsted acid catalyst, where the enantiofacial discrimination by the catalyst mainly stems from the recognition of the electronic difference between two substituents on the ketene disilyl acetal.

Catalytic Enantioselective Synthesis of Heterocyclic Vicinal Fluoroamines by Using Asymmetric Protonation: Method Development and Mechanistic Study

“…An alternative strategy for C(sp 3 )ÀFb ond formation that avoids S N 2i sb y asymmetricprotonation of prochiral C(sp 2 )ÀFcentres; however, there are limited examples of this and none for benzylic C(sp 3 )ÀF. [10] Herein, we presentamethodf or the enantioselective synthesiso fb enzylic C(sp 3 )ÀFv icinal fluoroamines by asymmetric protonation of in situ-generated prochiral fluoroenamines (Scheme 1c). [10][11][12] This method allowst he formation of an ew CÀNb ond and ab enzylic stereogenic CÀFb ond in as ingle catalytic reaction, thereby providing direct modular access to chiral heterocyclic vicinal fluoroamines from readily accessible vinyl fluoride precursors.…”

“…[10] Herein, we presentamethodf or the enantioselective synthesiso fb enzylic C(sp 3 )ÀFv icinal fluoroamines by asymmetric protonation of in situ-generated prochiral fluoroenamines (Scheme 1c). [10][11][12] This method allowst he formation of an ew CÀNb ond and ab enzylic stereogenic CÀFb ond in as ingle catalytic reaction, thereby providing direct modular access to chiral heterocyclic vicinal fluoroamines from readily accessible vinyl fluoride precursors. [13] As the process does not rely upon the use of af luorinating reagent, the issue of stereochemical erosioni sa voided.…”

Deracemizing α‐Branched Carboxylic Acids by Catalytic Asymmetric Protonation of Bis‐Silyl Ketene Acetals with Water or Methanol

“…reported the use of p ‐spiro diaminodioxaphosphonium barfates as chiral catalysts, expanding the scope of the transformation to α‐halo and α‐alkoxy alkyl bis‐SKAs [Eq. (2) in Figure ] . This method also requires 2,6‐dimethylphenol as PS, strict inert conditions, extremely low temperatures, and electronically biased substrates.…”

Deracemisierung von α‐verzweigten Carbonsäuren durch katalytische asymmetrische Protonierung von Bis‐Silylketenacetalen mit Wasser oder Methanol

“…Zwei Jahrzehnte später haben Ooi et al. die Anwendung von p ‐Spiro‐diaminodioxaphosphoniumbarfaten als chirale Katalysatoren berichtet, wodurch der Umfang der Transformation auf α‐Halo‐ und α‐Alkoxyalkyl‐bis‐SKA erweitert wurde . Diese Methode benötigt ebenfalls 2,6‐Dimethylphenol als PQ, strikt inerte Bedingungen, extrem niedrige Temperaturen und elektronisch voreingenommene Substrate.…”