1-cyclopropene-1,2-dicarboxylic acid, 3-oxo-, diethyl ester InChI=1/C9H10O5/c1-3-13-8(11)5-6(7(5)10)9(12)14-4-2/h3-4H2,1-2H diethyl 3-oxocycloprop-1-ene-1,2-dicarboxylate