Unexpected stereoselectivity in the anionic oxy-Cope rearrangement of acyclic enol ethers

The anionic oxy-Cope rearrangement of alkoxides derived from (1E,SZ)-4-methyl-5-alkoxy-1-pheny-1,5-heptadien-3-ols proceeds via a chair-like transition state with the oxyanion axial, even when there is a 3,4-relationship between the methyl group and the oxyanion so that both groups are axial in the transition state of the [3,3]-sigmatropic rearrangement. We believe that this is the first example of chelation control in the AOC rearrangement. The reaction forms the basis of a stereoselective synthesis of beta-hydroxycyclohexanones containing four chiral centres. (C) 2000 Elsevier Science Ltd. All rights reserved.