Unexpected ambidoselectivity in crossed-aldol reactions of α-oxy aldehyde trichlorosilyl enolates |
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Authors: | Scott E. Denmark Sunil K. Ghosh |
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Affiliation: | Roger Adams Laboratory, Department of Chemistry, University of Illinois, 600 South Mathews Avenue, Urbana, IL 61801, USA |
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Abstract: | The ambido-, stereo- and enantioselectivity of the phosphoramide-promoted aldol reactions of α-oxy aldehyde trichlorosilyl enolates with benzaldehyde has been investigated. Analysis of the products from α-tert-butyldimethylsilyloxy α-deuterioacetaldehyde trichlorosilyl enolate confirmed that this 1,2-bis-silyloxyethene derivative reacted as a tert-butyldimethylsilyl enolate rather than trichlorosilyl enolate in the aldol reaction with very high ambidoselectivity. The phosphoramide-coordinated trichlorosilyl group acted as an organizing center for the aldol reaction. From the aldol process, excellent anti-diastereoselectivity could be achieved. The enantioselectivity remained moderate to low for both anti- and syn-diastereomer with a wide range of phosphoramide catalysts. α-Triisopropylsilyloxy, phenoxy and benzyloxy acetaldehyde trichlorosilyl enolates also reacted in a similar fashion with benzaldehyde to give aldol products with varying degrees of selectivities. |
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Keywords: | Aldol Enolate Deuterium labeling Enantioselective Diastereoselective |
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