1H-2-benzopyran-3,4-dicarboxylic acid, 1-oxo-, dimethyl ester InChI=1/C13H10O6/c1-17-12(15)9-7-5-3-4-6-8(7)11(14)19-10(9)13(16)18-2/h3-6H,1-2H dimethyl 1-oxo-1H-isochromene-3,4-dicarboxylate