Rapid and Efficient Synthesis of 11 C‐Labeled Benzimidazolones Using [ 11 C]Carbon Dioxide

[ 11 C]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, [ 11 C]CO 2 was used for direct 11 C‐labeling of a set of cyclic aromatic ureas starting from their corresponding ortho ‐phenylenediamines, BEMP (2‐ tert ‐butylimino‐2‐diethylamino‐1,3‐dimethylperhydro‐1,3,2‐diazaphosphorine) as fixation base, and Mitsunobu reagents (DBAD, n Bu 3 P) for the intramolecular cyclization. The procedure is rapid (6 minutes total synthesis time), mild (proceeds at room temperature) and provided a set of 11 C‐benzimidazolones in good to excellent radiochemical yields. As a final testament to the utility of this method, the beta‐adrenoceptor PET ligand [ 11 C]CGP12177, was successfully prepared using the optimized conditions.