Synthesis of diethyl [ carbonyl ‐ 11 C]malonate from [ 11 C]carbon monoxide by rhodium‐promoted carbonylation and its application as a reaction intermediate

Rhodium‐mediated carbonylation reaction was applied to synthesize diethyl [ carbonyl ‐ 11 C]malonate using [ 11 C]carbon monoxide at low concentration. The synthesis was performed starting with ethyl diazoacetate, ethanol and the rhodium complex being made in situ by chloro(1,5‐cyclooctadiene)rhodium(I) dimer ([Rh(cod)Cl] 2 ) and 1,2‐ bis (diphenylphosphino)ethane (dppe), and the reaction is assumed to proceed via a ketene intermediate. The isolated radiochemical yield was 20% (75% analytical radiochemical yield) and the trapping efficiency of [ 11 C]carbon monoxide in the order of 85%. The specific radioactivity of this compound was measured at 127 GBq/µmol (7.28 nmol total mass) after 8 µAh bombardment and 35 min synthesis. The corresponding 13 C‐labelled compound was synthesized using ( 13 C)carbon monoxide to confirm the position of the carbonyl‐labelled atom by 13 C‐NMR. Diethyl [ carbonyl ‐ 11 C]malonate was further used in subsequent alkylation step using ethyl iodide and tetrabutylammonium fluoride to obtain diethyl diethyl [ carbonyl ‐ 11 C]malonate in 50% analytical radiochemical yield. Copyright © 2006 John Wiley & Sons, Ltd.