Enol esters can be obtained in one step by direct addition of carboxylic acids to terminal alkynes in the presence of a ruthenium-phosphine catalyst of type RuCl2(PR3)(arene). The presence of a nucleophilic phosphine allows the addition of the carboxylate group to the substituted alkyne carbon with high regioselectivity. From hex-1-yne or propyne, enol esters can be obtained with a variety of carboxylic acids including N-protected alpha-amino acids. Alkenylacetylene derivatives are thus precursors of 2-acyloxy-1,3-dienes. Ruthenium-catalysed addition of carboxylic acids and N-protected alpha-amino acids to propargyl alcohol derivatives gives rise to the synthesis of beta-oxopropyl esters. These enol esters and beta-oxopropyl esters are shown to be efficient acylating reagents under mild conditions to produce optically active amides or dipeptides. Especially stable enol formates allow access at 25-degrees-C to a variety of formamides and alpha-formylamino esters and in the presence of imidazole as a catalyst, they react with functionalised alcohols to give formates. Enol oxalates are shown to give access to alpha-dioxo derivatives via acylation of ammonia, amines, and unsaturated alcohols.