Terminal alkynes and allyl alcohol are coupled, with carbon-carbon bond formation, in the presence of a Ru-IV(C(5)Me(5)) catalyst, to give gamma,delta-unsaturated acetals and with [{RuCl(CMe(5))}(4)] Or [RuCl(cod)(C(5)Me(5))] preferentially to produce the branched gamma,delta-unsaturated aldehydes.