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A Thioxanthone Sensitizer with a Chiral Phosphoric Acid Binding Site: Properties and Applications in Visible Light-Mediated Cycloadditions |
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| Authors: | Franziska Pecho Dr You-Quan Zou Johannes Gramüller Prof?Dr Tadashi Mori Prof?Dr Stefan M Huber Dr Andreas Bauer Prof?Dr Ruth M Gschwind Prof?Dr Thorsten Bach |
| Institution: | 1. Department of Chemistry and Catalysis Research Center (CRC), Technical University Munich, Lichtenbergstr. 4, 85747 Garching, Germany;2. Faculty of Chemistry and Pharmacy, Institute of Organic Chemistry, University of Regensburg, Universitätsstraße 31, 93040 Regensburg, Germany;3. Department of Applied Chemistry, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka, 565-871 Japan;4. Faculty for Chemistry and Biochemistry, Organic Chemistry I, Ruhr-Universität Bochum, Universitätsstraße 150, 44801 Bochum, Germany |
| Abstract: | A chiral phosphoric acid with a 2,2’-binaphthol core was prepared that displays two thioxanthone moieties at the 3,3’-position as light-harvesting antennas. Despite its relatively low triplet energy, the phosphoric acid was found to be an efficient catalyst for the enantioselective intermolecular 2+2] photocycloaddition of β-carboxyl-substituted cyclic enones (e.r. up to 93:7). Binding of the carboxylic acid to the sensitizer is suggested by NMR studies and by DFT calculations to occur by means of two hydrogen bonds. The binding event not only enables an enantioface differentiation but also modulates the triplet energy of the substrates. |
| Keywords: | enantioselectivity hydrogen bonds organocatalysis photochemistry sensitizers |