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