The base catalyzed addition of sterically hindered 1,3-diketones to th
e activated multiple bond of ethyl acrylate and 4-methyl-4-methoxy-1-p
henylpent-2-yne-1-one has been studied. The addition of methyl(2-prope
nyl)ketone is partially accompanied by intramolecular cyclization of t
he resulting adduct.