Asymmetric Kinugasa reaction involving six-membered cyclic nitrones |
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Authors: | Barbara Grzeszczyk Kamila Poławska Yasser M. Shaker Sebastian Stecko Adam Mames Magdalena Woźnica Marek Chmielewski Bartłomiej Furman |
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Affiliation: | 1. Institute of Organic Chemistry of Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland;2. Department of Chemistry of Natural and Microbal Products, National Research Center, Tahrir St., Dokki, Cairo 12622, Egypt |
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Abstract: | Kinugasa reactions between terminal acetylenes and six-membered ring nitrones when one or both components are chiral, proceed in a low to moderate yield and with a high diastereoselectivity affording mostly one, dominant β-lactam product. The first step of the reaction is controlled by the configuration of the nitrone, whereas the protonation of the C-7 center of the carbacepham skeleton in the second step depends on: a) the configuration of the bridgehead carbon atom formed in the first step, b) epimerization process in the presence of a base, and c) on the configuration of the stereogenic center in the acetylenic partner. In the case of the nitrone derived from dihydroisoquinoline, the reaction proceeds in a more complex way affording not only β-lactams, but also products derived from the alternative regio-1,3-cycloaddition, or nucleophilic addition of the acetylene to the double bond of the nitrone. |
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