Organic Letters
Letter
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Figure 3. Oxidative formation of BINOL-based chiral Brønsted acids
from H8-BINOL based Brønsted acids. Conditions: The reactions
were performed on a 0.026 mmol scale with DDQ (8 equiv) in
chlorobenzene (16) or dichlorobenzene (17) (0.05 M) at reflux for 15
h. The yields represent an average of two runs.
(10) Klussmann, M.; Ratjen, L.; Hoffmann, S.; Wakchaure, V.;
Goddard, R.; List, B. Synlett 2010, 14, 2189.
disulfonimides. The reverse transformation allowing the
oxidation of H8-BINOL-based catalysts into BINOL-based
catalysts has also been demonstrated using DDQ as the oxidant.
The outlined strategy would allow a rapid diversification of the
existing libraries of Brønsted acids and will expand the
availability of BINOL and H8-BINOL-based Brønsted acid
catalysts for asymmetric transformations.
(11) Bergman, J.; Pelcman, B. Tetrahedron 1988, 44, 5215.
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(13) Dehydrogenation with quinones: (a) Braude, E. A.; Brook, A.
G.; Linstead, R. P. J. Chem. Soc. 1954, 3569. Dehydrogenation of
BINAM derivatives: (b) Kano, T.; Tanaka, Y.; Osawa, K.; Yurino, T.;
Maruoka, K. J. Org. Chem. 2008, 73, 7387.
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental procedures, characterization data, and NMR
spectra. The Supporting Information is available free of charge
AUTHOR INFORMATION
Corresponding Author
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work has been supported by the National Science
Foundation CAREER Award (CHE-1350060). PN is a Sloan
Foundation Fellow.
REFERENCES
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