Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 61, Issue 19, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202201424
Keywords
Acridiniums; Atropisomers; Bronsted Acid Catalysis; Ion-Paring Catalysis; Ortho-Quinone Methide Iminiums
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Funding
- Swiss National Science Foundation [BSSGI0-155902/1, 175746]
- University of Basel
- NCCR Molecular Systems Engineering
- Marie Skodowska-Curie Actions [H2020-MSCA-IF-2019840456]
- Universitat Basel
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This paper describes the feasibility of an intramolecular Friedel-Crafts 6 pi electrocyclization, which is stereocontrolled by contact ion pairs. Through the use of a disulfonimide catalyst, enantioenriched acridinium tetrafluoroborate salts can be selectively synthesized.
Quinone methides are fundamental intermediates for a wide range of reactions in which catalyst stereocontrol is often achieved by hydrogen bonding. Herein, we describe the feasibility of an intramolecular Friedel-Crafts 6 pi electrocyclization through ortho-quinone methide iminiums stereocontrolled by a contact ion pair. A disulfonimide catalyst activates racemic trichloroacetimidate substrates and imparts stereocontrol in the cyclization step, providing a new avenue for selective ortho-quinone methide iminium functionalization. A highly stereospecific oxidation readily transforms the enantioenriched acridanes into rotationally restricted acridiniums. Upon ion exchange, the method selectively affords atropisomeric acridinium tetrafluoroborate salts in high yields and an enantioenrichment of up to 93 : 7 e.r. We envision that ion-pairing catalysis over ortho-quinone methide iminiums enables the selective synthesis of a diversity of heterocycles and aniline derivatives with distinct stereogenic units.
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