title: Lewis base activation of Lewis acids. Vinylogous aldol reactions.
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.
authors.affiliation: Roger Adams Laboratory, Department of Chemistry, University of Illinois, Urbana, IL 61801, USA. denmark@scs.uiuc.edu
authors.forename: Scott E
authors.initials: SE
authors.lastname: Denmark
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Beutner