protoanemonin 4-Methylenebut-2-en-4-olide 5-methylene-2(5H)-furanone 5-methylenefuran-2(5H)-one 96.08406 A butenolide that has formula C5H4O2. Beilstein:105670 C5H4O2 C=C1OC(=O)C=C1 CAS:108-28-1 CHEBI:20447 CHEBI:28906 CHEBI:8585 InChI=1S/C5H4O2/c1-4-2-3-5(6)7-4/h2-3H,1H2 KEGG:C07090 KNApSAcK:C00000301 Protoanemonin RNYZJZKPGHQTJR-UHFFFAOYSA-N UM-BBD_compID:c0298 chebi_ontology cis-4-Methylenebut-2-en-4-olide butenolide