Abstract The addition of various carboxylic acids to (trans-2-ethoxycyclopropyl) ethyne (1) by catalysis with [Ru (O 2 CH)(CO) 2 (PPh 3)] 2 proceeds regioselectively in the Markovnikov sense with ring opening of the cyclopropyl group to furnish allenylacetaldehyde acyl ethyl acetals 3 in high yields (44-96%, 11 examples). The allenylacetaldehyde derivatives undergo palladium-catalyzed Heck-type cross coupling with iodobenzene and ...