RUTHENIUM-CATALYZED ADDITIONS TO ALKYNES - SYNTHESIS OF ACTIVATED ESTERS AND THEIR USE IN ACYLATION REACTIONS

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.