Photoinitiated carbonylation with [11C]carbon monoxide using amines and alkyl iodides

Photoinitiated radical carbonylation with [C-11]carbon monoxide at low concentration was employed in syntheses of carbonyl-C-11-labeled amides using alkyl iodides and amines as precursors. Eleven C-11-amides were synthesized in up to 74% decay-corrected radiochemical yields with reaction times of 400 s and with up to 95% conversion of carbon monoxide. Starting with 26.3 GBq of [C-11]carbon monoxide, 10.6 GBq of 1-cyclohexane [C-11]carbonyl-4-phenyl-piperazine (15) was obtained within 35 min from the end of bombardment (33 muA) and with a specific radioactivity of 192 GBq/mumol at the same time point. The influence of solvents was investigated. The described procedure extends the range of accessible labeling methods. The method may also be useful for preparation of C-13- and C-14-substituted compounds.