Broensted Acid Catalyzed, Conjugate Addition of [beta]-Dicarbonyls to In Situ Generated ortho-Quinone Methides-Enantioselective Synthesis of 4-Aryl-4H-Chromenes

We describe herein a catalytic, enantioselective process for the synthesis of 4H-chromenes which are important structural elements of many natural products and biologically active compounds. A sequence comprising a conjugate addition of [beta]-diketones to in situ generated ortho-quinone methides fo...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2014-07, Vol.53 (30), p.7923-7927
Main Authors: El-Sepelgy, Osama, Haseloff, Stefan, Alamsetti, Santosh Kumar, Schneider, Christoph
Format: Article
Language:English
Subjects:
Bonding
Carbon-carbon composites
Catalysis
Catalysts
Conjugates
Esters
Phosphoric acid
Structural members
Synthesis
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Summary:We describe herein a catalytic, enantioselective process for the synthesis of 4H-chromenes which are important structural elements of many natural products and biologically active compounds. A sequence comprising a conjugate addition of [beta]-diketones to in situ generated ortho-quinone methides followed by a cyclodehydration reaction furnished 4-aryl-4H-chromenes in generally excellent yields and high optical purity. A BINOL-based chiral phosphoric acid was employed as a Broensted acid catalyst which converted ortho-hydroxy benzhydryl alcohols into hydrogen-bonded ortho-quinone methides and effected the carbon-carbon bond-forming event with high enantioselectivity. Chiral phosphoric acids permit the in situ generation of hydrogen-bonded ortho-quinone methides which react with [beta]-diketones and [beta]-keto esters with excellent enantioselectivity and furnish valuable 4-aryl-4H-chromenes and related heterocycles upon subsequent cyclodehydration. These observations extend the substrate scope of enantioselective phosphoric acid catalysis towards an important additional class of compounds.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201403573