Enantio‐ and Diastereoselective Access to Distant Stereocenters Embedded within Tetrahydroxanthenes: Utilizing ortho‐Quinone Methides as Reactive Intermediates in Asymmetric Brønsted Acid Catalysis |
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| Authors: | M?Sc Chien‐Chi Hsiao M?Sc Hsuan‐Hung Liao Prof?Dr Magnus Rueping |
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| Institution: | Institute of Organic Chemistry, RWTH Aachen University, Landoltweg 1, 52074 Aachen (Germany) |
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| Abstract: | A protocol for the highly enantioselective synthesis of 9‐substituted tetrahydroxanthenones by means of asymmetric Brønsted acid catalysis has been developed. A chiral binol‐based N‐triflyphosphoramide was found to promote the in situ generation of ortho‐quinone methides and their subsequent reaction with 1,3‐cyclohexanedione to provide the desired products with excellent enantioselectivities. In addition, a highly enantio‐ and diastereoselective Brønsted acid catalyzed desymmetrization of 5‐monosubstituted 1,3‐dicarbonyl substrates with ortho‐quinone methides gives rise to valuable tetrahydroxanthenes containing two distant stereocenters. |
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| Keywords: | cyclization enantioselectivity heterocycles organocatalysis synthetic methods |
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