[en] A method for the production of two new carbon-11 labelled difunctional radiolabelling precursors, [¹¹C]diethyl oxalate,2, and [¹¹C]oxalic acid, 3 is described. Methyl chloroformate was reacted with no-carrier-added [¹¹C]cyanide to generate the intermediate nitrile, methyl [¹¹C]cyanoformate. Alcoholysis with HC1 in ethanol generated 2, which could subsequently be converted to 3 with aqueous acid. The total time of preparation from end-or-trapping of [¹¹C]cyanide was 6-7 min using combined microwave and thermal treatment or, by exclusively thermal treatment, 15 and 20 min for 2 and 3, respectively. The radiochemical conversion of [¹¹C]cyanide to 2 and 3 was ∼ 80% and ∼ 70%, respectively. Both 2 and 3 were used in a model reaction with 1,2-phenylenediamine to synthesize the heterocyclic compound, 2,3-dihydroxyquinoxaline, a basic structural unit in antagonists for the excitatory amino acid receptor system. (Author)