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Highly Acidic Conjugate‐Base‐Stabilized Carboxylic Acids Catalyze Enantioselective oxa‐Pictet–Spengler Reactions with Ketals
Author(s) -
Zhu Zhengbo,
Odagi Minami,
Zhao Chenfei,
Abboud Khalil A.,
Kirm Helmi Ulrika,
Saame Jaan,
Lõkov Märt,
Leito Ivo,
Seidel Daniel
Publication year - 2020
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201912677
Subject(s) - chemistry , enantioselective synthesis , oxocarbenium , ketone , stereocenter , organocatalysis , catalysis , carboxylic acid , acid catalysis , organic chemistry , intramolecular force , combinatorial chemistry , nucleophile
Acyclic ketone‐derived oxocarbenium ions are involved as intermediates in numerous reactions that provide valuable products, however, they have thus far eluded efforts aimed at asymmetric catalysis. We report that a readily accessible chiral carboxylic acid catalyst exerts control over asymmetric cyclizations of acyclic ketone‐derived trisubstituted oxocarbenium ions, thereby providing access to highly enantioenriched dihydropyran products containing a tetrasubstituted stereogenic center. The high acidity of the carboxylic acid catalyst, which exceeds that of the well‐known chiral phosphoric acid catalyst TRIP, is largely derived from stabilization of the carboxylate conjugate base through intramolecular anion‐binding to a thiourea site.