An efficient one-pot synthesis of [11C]ureas and [11C]isocyanates via dehydration of intermediately formed carbamate salts is described as a general alternative to their formation via [11C]phosgene. After optimization of the reaction parameters, in-target produced n.c.a. [11C]CO2 can be used for labelling in a one pot reaction within a very short reaction time of 10 minutes resulting in good radiochemical yields. The developed method has been applied to the 11C-carbonylation of aniline, benzyl- and phenethylamine and 1,2-diaminobenzene yielding the appropriate n.c.a. [11C]ureas in about 65, 85, 25 and 70% radiochemical yield (RCY), respectively. The presented reaction sequence can be handled easily and safely and lends itself to simple automation.
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Schirbel et al. (1999) studied this question.