The manganese (III)-based aerobic oxidation of arylacetylenes with 2, 4-pentanedione at ambient temperature unexpectedly gave the 1, 2-dioxolane derivatives in moderate yields together with a small amount of the oxiranes. The 1, 2-dioxolanes underwent silica gel- assisted contraction to quantitatively give the oxiranes. The reaction pathway for the formation of the 1, 2-dioxolanes and the by-product was discussed.
