Catalytic enantioselective 1,3-dipolar cycloaddition reactions of cyclic nitrones: a simple approach for the formation of optically active isoquinoline derivatives |
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Authors: | Jensen K B Roberson M Jorgensen K A |
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Institution: | Center for Metal Catalyzed Reactions, Department of Chemistry, Aarhus University, DK-8000 Aarhus C, Denmark. |
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Abstract: | The first highly diastereo- and enantioselective catalytic 1, 3-dipolar cycloaddition reaction of cyclic nitrones activated by chiral Lewis acids with electron-rich alkenes has been developed. The nitrones, mainly 3,4-dihydroisoquinoline N-oxides, are activated by chiral 3,3'-aryl BINOL-AlMe complexes and undergo a regio-, diastereo-, and enantioselective 1,3-dipolar cycloaddition reaction with especially alkyl vinyl ethers, giving the exo diastereomer of the cycloaddition products in high yield, >90% de and up to 85% ee. The reaction has been investigated under various conditions, and it is demonstrated that the reaction is an attractive synthetic procedure for the introduction of a chiral center in the 1-position of the isoquinoline skeleton. The mechanism of the reaction is discussed on the basis of the assignment of the absolute configuration of the cycloaddition product and theoretical calculations. |
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