DBU-mediated Ireland–Claisen rearrangement of allyl alk-3-enoates: an efficient synthesis of 2-ethylidene-γ,δ-unsaturated carboxylic acids

Ireland–Claisen rearrangement, triggered by silyl enolization of allylic but-3-enoates 2, has been developed using DBU as the base in the presence of an excess amount of TMSCl under reflux in acetonitrile for a couple of hours. The procedure allows the synthesis of a range of 2-ethylidene-γ,δ-unsaturated carboxylic acids 5 in moderate to high yields. It is further revealed that the rearrangement proceeds equally well with allylic (E)-hexa-3,5-dienoates 10 derived from sorbic acid under similar conditions to provide 2-allyl substituted hexa-2,4-dienoic acids 13.