1H-cyclopenta[c]furan-4-carboxylic acid, 3,3a,6,6a-tetrahydro-1-oxo-, methyl ester InChI=1/C9H10O4/c1-12-8(10)5-2-3-6-7(5)4-13-9(6)11/h2,6-7H,3-4H2,1H methyl 1-oxo-3,3a,6,6a-tetrahydro-1H-cyclopenta[c]furan-4-carboxylate