A Structurally Robust Chiral Borate Ion: Molecular Design, Synthesis, and Asymmetric Catalysis

Catalysis by chiral weakly‐coordinating anions (WCAs) remains underdeveloped due to the lack of a molecular design strategy for exploiting their characteristics, such as the non‐nucleophilic nature. Here, we report the development of a chiral borate ion comprising an O,N,N,O‐tetradentate backbone, w...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2020-07, Vol.59 (28), p.11456-11461
Main Authors: Uraguchi, Daisuke, Ueoka, Fumito, Tanaka, Naoya, Kizu, Tomohito, Takahashi, Wakana, Ooi, Takashi
Format: Article
Language:English
Subjects:
Anions
asymmetric catalysis
Asymmetry
borates
Catalysis
Catalysts
Chemical synthesis
cyclization
Ethers
ion pairs
organocatalysis
Selectivity
Vinyl ethers
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Summary:Catalysis by chiral weakly‐coordinating anions (WCAs) remains underdeveloped due to the lack of a molecular design strategy for exploiting their characteristics, such as the non‐nucleophilic nature. Here, we report the development of a chiral borate ion comprising an O,N,N,O‐tetradentate backbone, which ensures hitherto unattainable structural robustness. Upon pairing with a proton, the hydrogen borate acts as an effective catalyst for the asymmetric Prins‐type cyclization of vinyl ethers, providing access to structurally and stereochemically defined dihydropyrans. The key to selectivity control is the distinct ability of the borate ion to discriminate the prochiral faces of the acyclic oxonium ion intermediate and dictate the regiochemical outcome. We anticipate that this study paves the way for exploring the untapped potential of WCA catalysis for selective chemical synthesis. A chiral borate ion comprising an O,N,N,O‐tetradentate backbone was developed. The corresponding hydrogen borate acted as a catalyst for the asymmetric protonative Prins‐type cyclization through precise control of the prochiral oxonium ion intermediate and the final deprotonation pathway.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.202001637