gamma,delta-Unsaturated acetals and aldehydes have been obtained via a new ruthenium-catalysed coupling of allyl alcohol with alkynes. The branched isomer is regioselectively formed. Comparative studies of catalyst precursors have shown that (C(5)Me(5))Ru(IV) derivatives favours the formation of acetals and that, with (C(5)Me(5))Ru(II) moieties, the reaction can be carried out either in water or without solvent at room temperature. Copyright (C) 1996 Elsevier Science Ltd