Lewis base activation of Lewis acids. Vinylogous aldol reactions |
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Authors: | Denmark Scott E Beutner Gregory L |
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Institution: | Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, IL 61801, USA. denmark@scs.uiuc.edu |
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Abstract: | A highly regioselective vinylogous aldol reaction catalyzed by SiCl4 and a chiral phosphoramide (R,R)-5, providing delta-hydroxy enones for a variety of aldehyde and dienol ether structures, has been developed. Low catalyst loadings (1 mol %) can be employed, giving the products in good yields, excellent enantioselectivities, and in some cases excellent anti diastereoselectivities. Both simple ester-derived dienol ethers as well as dioxanone-derived dienol ethers are employed. The observed regioselectivity is rationalized in terms of the sensitivity of the catalyst to the steric demands of the nucleophile. |
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