Highly stereoselective addition of organozinc reagents to pentopyranose derived glycals: effect of protecting group and assignment of C-glycoside stereochemistry |
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Authors: | Matthew J Cook Diane Gray Timothy Gallagher |
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Institution: | a Department of Chemistry, School of Chemistry, University of Bristol, Cantocks Close, Bristol BS8 1TS, UK b GlaxoSmithKline, New Frontiers Science Park, Third Avenue, Harlow, Essex, CM19 5AW, UK |
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Abstract: | The nucleophilic addition of ethyl 3-propionylzinc iodide to a variety of differently protected pentopyranose derived d-glycals 6a-g proceeds with good to high levels of diastereoselectivity to provide the corresponding β-C-glycosides 7. The stereochemistry of the para-nitrobenzoate derivative 7d has been confirmed by X-ray crystallography, and the stereochemistry of the other β-C-glycoside products has been correlated to 7d. The stereochemical outcome observed supports the earlier suggestion by Isobe that through-space effects are important in stabilising and controlling the reactivity of the intermediate oxonium species represented by 11. |
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Keywords: | C-Glycosides Glycals Organozinc |
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