Background The reaction of an allylic alcohol with a acetamide dialkyl acetal3 or a substituted acetamide dialkyl acetal4 has proved a popular alternative to the classical Claisen rearrangement as a method of obtaining y, b-unsaturated carbonyl compounds. While 3-methyl-4-penten-1-yn-3-01 (1) 5 undergoes the predicted ortho ester Claisen rearrangement, 6 treatment of this alcohol with dimethylacet-