2,3-dihydro-2-oxofuran-5-acetate 2-oxo-2,3-dihydrofuran-5-acetate 3-OXOADIPATE-ENOL-LACTONE 4,5-dihydro-5-oxofuran-2-acetate 5-oxo-4,5-dihydrofuran-2-acetate beta-ketoadipate-enol-lactone