Rapid and efficient synthesis of ¹¹C-labeled benzimidazolones using [¹¹C]carbon dioxide

[11C]Carbon dioxide is an attractive synthon for the labeling of positron emission tomography (PET) tracers for subsequent use in biomedical research and drug development. In this study, [11C]CO2was used for direct11C‐labeling of a set of cyclic aromatic ureas starting from their correspondingortho‐phenylenediamines, BEMP (2‐tert‐butylimino‐2‐diethylamino‐1,3‐dimethylperhydro‐1,3,2‐diazaphosphorine) as fixation base, and Mitsunobu reagents (DBAD,nBu3P) for the intramolecular cyclization. The procedure is rapid (6 minutes total synthesis time), mild (proceeds at room temperature) and provided a set of11C‐benzimidazolones in good to excellent radiochemical yields. As a final testament to the utility of this method, the beta‐adrenoceptor PET ligand [11C]CGP12177, was successfully prepared using the optimized conditions.