Synthesis of 11C-labelled N,N′-diphenylurea and ethyl phenylcarbamate by a rhodium-promoted carbonylation via [11C]isocyanatobenzene using phenyl azide and [11C]carbon monoxide

The reaction with phenyl azide and [C-11] carbon monoxide to give N,N'-diphenyl[C-11] urea and ethyl phenyl[C-11] carbamate has been studied with the aim of development of a new methodology for carbonylation using [C-11] carbon monoxide with high specific radioactivity. The synthesis of C-11-labelled N,N'-diphenylurea from phenyl azide and [C-11] carbon monoxide, with 1,2-bis(diphenylphosphino) ethane-bound Rh(I) complex at 120degreesC at a pressure of 35 MPa in the presence of aniline was accomplished in 82% trapping efficiency and 82% conversion yield. This approach was also useful for the synthesis of ethyl phenyl[C-11] carbamate with lithium ethoxide as a nucleophilic reagent giving 90% trapping efficiency and 76% conversion yield. These reactions can be considered to proceed via a [C-11] isocyanate or a [C-11] isocyanate-coordinated Rh complex to give the corresponding C-11-products. This protocol provides the chemical basis for the synthesis of [C-11] urea and [C-11] carbamate derived from [C-11] isocyanates.