New Methods for the Synthesis of 3(2H)-Furanones and 2(5H)-Furanones

New procedures for the synthesis of 3(2H)-furanones and 4-alkoxy-2(5H)-furanones are reported. Reaction of ketones with the lithium salt of propynal diethyl acetal, followed by treatment of the resulting 4-hydroxy-2-alkynal diethyl acetals with sulfuric acid–methanol, gave 2,2-disubstituted 3(2H)-furanones. The action of a polymer reagent Hg/Nafion-H upon 4–hydroxy-2-alkynones produced 2,2,5-trisubstituted 3(2H)-furanones. Reaction of 1,1,1-triethoxy-2-alkyn-4-ols (4) with trifluoroacetic acid and mercury(II) acetate provided 5-ethoxy-2,2-disubstituted 3(2H)-furanones. In contrast, the adducts 4 were converted into 4-alkoxy-5,5-disubstituted 2(5H)-furanones upon reaction with Hg/Nafion-H.