[3,3]-Sigmatropic rearrangements of propargyl alkynyl ethers. Synthesis of complex dienoates and unsaturated lactones.

In an extension of our studies on low-temperature rearrangements of 1-alkynyl ethers, we describe herein the [3,3]-sigmatropic rearrangement of formed propargyl alkynyl ethers to allenyl ketenes, which furnish complex -butyl-(2,4)-dienoates 2 in good yields upon -butanol addition. Similarly, sigmatropic rearrangements of formed propargyl lithioalkynyl ethers yield methyl-(2,4)-dienoates 4 upon methanol addition or unsaturated lactones 6 upon aldehyde or ketone addition to the allenyl ynolate intermediate.