.DELTA..alpha.,.beta.-Butenolide .DELTA..alpha.,.beta.-Butolide .gamma.-Crotonolactone .gamma.-Hydroxycrotonic acid lactone 2(5H)-Furanone 2-Buten-4-olide 2-Butenoic acid, 4-hydroxy-, .gamma.-lactone 2-Butenoic acid-.gamma.-lactone 2-Butenolide 4-Hydroxy-2-butenoic acid .gamma.-lactone 4-Hydroxy-2-butenoic acid lactone 497-23-4 Butenolide Crotonolactone Isocrotonolactone NSC51296