11 C‐Carbonylation through in Situ Generated 11 C‐Benzoyl Chlorides with Tetrabutylammonium Chloride as Chloride Source

Aromatic 11 C‐containing acids, amides, esters, and aldehydes were obtained through a novel 11 C‐carbonylative reaction. In the two‐step process, aryl iodides are first reacted with 11 CO and tetrabutylammonium chloride in a palladium‐mediated reaction to yield 11 C‐benzoyl chlorides in situ. The crude mixture is then further treated with either a hydroxide, amine, alcohol, or a hydride in a second vial to furnish the final 11 C‐carbonyl product. The monodentate ligand tri‐ tert ‐butylphosphonium tetrafluoroborate was proven to be crucial for obtaining high radiochemical yields (RCY). A wide range of 11 C‐containing carbonyl compounds were successfully radiolabeled in moderate to excellent RCYs, ranging from 41–93 %. The synthetic retinoic acid tamibarotene was obtained in a RCY of 89 %, whereas the Boc‐protected procainamide was labelled in 68 % RCY, which is a significantly increase (2–3 fold) in RCY compared to other published methods.