Indium-catalyzed 2-alkenylation of 1,3-dicarbonyl compounds with unactivated alkynes.

1,3-Dicarbonyl compounds add to unactivated alkynes in the presence of a catalytic amount of indium(III) trifluoromethanesulfonate in high to excellent yield to give 2-alkenylated 1,3-dicarbonyl compounds with exclusive regioselectivity as to the position of C-C bond formation on the acetylene moiety. In most of the cases, the reaction requires less than 1-mol % loading of the catalyst and does not require solvent. The reaction tolerates a wide variety of functional groups including ester, ether, allylic halide, furan, thiophene, and protected amine. Experimental and theoretical studies suggested that the reaction proceeds via a concerted carbometalation reaction of an indium(III) enolate with the acetylene, where indium-acetylene interaction is important.