Diastereoselectivity of Chiral Nitrone 1,3-Dipolar Cycloaddition to <Emphasis Type="Italic">Baylis-Hillman</Emphasis> Adducts |
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Authors: | Branislav?Dugovi? Email author" target="_blank">Lubor?Fi?eraEmail author Christian?Hametner Micha? K?Cyrański Nada?Prónayová |
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Institution: | (1) Department of Organic Chemistry, Slovak University of Technology, SK-812 37 Bratislava, Slovak Republic;(2) Institute of Applied Synthetic Chemistry, Vienna University of Technology, A-1060 Vienna, Austria;(3) Department of Chemistry, University of Warsaw, 02 093 Warsaw, Poland;(4) Central Laboratory of Chemical Techniques, Slovak University of Technology, SK-812 37 Bratislava, Slovak Republic |
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Abstract: | Summary. 1,3-Dipolar cycloadditions of chiral nitrones to Baylis-Hillman adducts ( -hydroxy- -methylene esters) proceed with complete regioselectivity in good yields to afford the corresponding diastereomeric 3,5,5-trisubstituted isoxazolidines. Attack of the dipole from the less sterically hindered side of the dipolarophiles affords C-3/C-5 cis isoxazolidines as the predominant isomers. The strong preference for the C-3/C-5 cis isoxazolidines provided more sterically demanding O-tert-butyldimethylsilylsubstituted nitrone 2. Addition of Lewis acids accelerates the reaction and increases the portion of C-3/C-5 trans isoxazolidines. Microwave irradiation accelerates the reaction, but it produces only a small effect on the diastereoisomeric product ratio. |
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Keywords: | , Dipolar cycloaddition, Stereoselectivity, Nitrones, Isoxazolidines, Microwave heating, |
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