Palladium-mediated oxidative carbonylation reactions for the synthesis of (11) C-radiolabelled ureas.

Palladium(II)-mediated oxidative carbonylation reactions have been used to synthesize (11) C-radiolabelled ureas via the coupling of amines with [(11) C]carbon monoxide, in a one-pot process. Following trapping of (11) CO in a solution of copper(I) tris(3,5-dimethylpyrazolyl)borate, homocoupling reactions of primary aliphatic amines proceed in the presence of Pd(PPh3 )2 Cl2 to give the corresponding N,N-disubstituted [(11) C]ureas. Secondary amines do not produce the corresponding N,N,N,N-tetrasubsituted [(11) C]ureas under these conditions. This difference in reactivity allows for the formation of unsymmetrical N,N',N'-trisubstituted [(11) C]ureas using a mixture of a primary amine and a reactive secondary amine. The potential use of this method in positron emission tomography (PET) was demonstrated by the synthesis of the M1 muscarinic acetylcholine receptor radiotracer, [(11) C-carbonyl]GSK1034702.