Diastereoselectivity in the Carroll rearrangement of b-keto esters of tertiary allylic alcohols

Carroll rearrangement of b-keto esters derived from tertiary allylic alcohols, for example, 7, under basic conditions followed by decarboxylation of the resulting b-keto acids yielded the expected c,d-unsaturated methyl ketones 8 with a range of olefin geometries from 100:0 to 1:1.8 E=Z, depending on the relative steric requirements of the two groups at the allylic center. 2003 Elsevier Ltd. All rights reserved. For a proposed synthesis of several biologically active polycyclic triterpene natural products, we investigated the use of the Carroll rearrangement in order to achieve the desired olefin geometry in the 7-substituted 6-methyl-5-hepten-7-one subunit (Scheme 1). In particular, we hoped that the steric difference between a silyloxymethyl and a methyl group in an intermediate such as 4 would afford predominantly the E-olefin geometry in the Claisen rearrangement product 3a. Likewise, we