N.C.A. 11C-labelling of benzenoid compounds in ring positions: Synthesis of nitro-[1-11C]benzene and [1-11C]aniline

Article abstract of DOI:10.1002/jlcr.2580360104

The paper describes the first method for n.c.a. ¹¹C-ring labelling of benzenoid compounds having a reactive group for further derivatization by use of the known principle of synchronous six-electron cyclization of hexatriene systems into aromatics. Nitro-[¹¹C]methane (1) prepared from cyclotron-produced [¹¹C]carbon dioxide reacts in the presence of t-BuOK with 5-dimethylaminopenta-2,4-dienylidene-dimethylammonium perchlorate (2) to form 6-nitro-1-dimethylamino-[6-¹¹C]hexatriene (3) followed by cyclization/aromatization into nitro-[1-¹¹C]benzene (4) at increased temperatures. Starting from 1, nitro-[1-¹¹C]benzene of a radiochemical purity of about 92% and a mean specific radioactivity of 1 Ci/μmol was obtained within 7 min. Related to [¹¹C]CO₂, the reproducible radiochemical yield of 4 (decay-corrected) was 80 ± 5%. Reduction of 4 by heating the above reaction mixture with aqueous Na₂S gave [1-¹¹C]aniline (5) of a radiochemical purity of about 81%. The reproducible radiochemical yield of 5 (decay-corrected) in relation to [¹¹C]CO₂ was 65 ± 5%, the synthesis time from I was 18 min.