Synthesis of [1‐11C]propyl and [1‐11C]butyl iodide from [11C]carbon monoxide and their use in alkylation reactions

A method to prepare 1‐¹¹C]propyl iodide and 1‐¹¹C]butyl iodide from ¹¹C]carbon monoxide via a three step reaction sequence is presented. Palladium mediated formylation of ethene with ¹¹C]carbon monoxide and hydrogen gave 1‐¹¹C]propionaldehyde and 1‐¹¹C]propionic acid. The carbonylation products were reduced and subsequently converted to 1‐¹¹C]propyl iodide. Labelled propyl iodide was obtained in 58±4% decay corrected radiochemical yield and with a specific radioactivity of 270±33 GBq/µmol within 15 min from approximately 12 GBq of ¹¹C]carbon monoxide. The position of the label was confirmed by ¹³C‐labelling and ¹³C‐NMR analysis. 1‐¹¹C]Butyl iodide was obtained correspondingly from propene and approximately 8 GBq of ¹¹C]carbon monoxide, in 34±2% decay corrected radiochemical yield and with a specific radioactivity of 146±20 GBq/µmol. The alkyl iodides were used in model reactions to synthesize O‐propyl‐1‐¹¹C]propyl and O‐butyl‐1‐¹¹C]butyl benzoate. Propyl and butyl analogues of etomidate, a β‐11‐hydroxylase inhibitor, were also synthesized. Copyright © 2006 John Wiley & Sons, Ltd.