Chiral Lewis acid catalysis in a visible light-triggered cycloaddition/rearrangement cascade |
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Authors: | Simone Stegbauer Christian Jandl Thorsten Bach |
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Affiliation: | Technische Universität München, School of Natural Sciences, Department of Chemistry and Catalysis Research Center, Lichtenbergstrasse 4, Garching 85747 Germany, , Fax: +49 (0)89 289 13315 |
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Abstract: | Cascade (domino) reactions facilitate the formation of complex molecules from simple starting materials in a single operation. It was found that 1-naphthaldehyde derivatives can be converted to enantioenriched (82–96% ee) polycyclic benzoisochromenes via a cascade of ortho photocycloaddition and ensuing acid-catalysed rearrangement reactions. The cascade was initiated by irradiation with visible light (λ = 457 nm) and catalysed by a chiral AlBr3-activated 1,3,2-oxazaborolidine (14 examples, 65–93% yield). The absolute configuration of the products was elucidated by single crystal X-ray crystallography. Mechanistic experiments suggest that the ortho photocycloaddition occurs on the triplet hypersurface and that the chiral catalyst induces in this step the observed enantioselectivity.Chiral Lewis acid catalysis enables the formation of enantioenriched polycyclic benzoisochromenes 2 from simple 1-naphthaldehydes 1 in an efficient cascade process triggered by a visible light-initiated ortho photocycloaddition. |
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