Highly diastereoselective Lewis acid promoted Claisen–Ireland rearrangement

In the presence of catalytic amounts of Lewis acids silyl ketene acetals of trans allylic esters undergo a highly diastereoselective Claisen–Ireland rearrangement to the corresponding disubstituted γ-δ-unsaturated erythro carboxylic acids. Diastereoselectivities of up to 15:1 were achieved when using TiCl4 as catalyst. The uncatalyzed process proceeds slowly and with significantly lower selectivity. A wide range of aryl- and alkyl-substituents are tolerated.