N.C.A.¹¹C-Labelling of Benzenoid Compounds in Ring Positions: [¹¹C]Anisole Derivatives

The synthesis route to n.c.a. 3-nitro-[3-C-11]anisole (3) by use of the principle of synchronous six-electron cyclization of hexatriene systems into aromatics is described and discussed. Nitro-[C-11]-methane (1) reacts with the prepared precursor 5-dimethylamino-2-methoxy-penta-2,4-dienylidene-1-dimethylammonium tetrafluoroborate (2b) in the presence of BuLi to form 1-dimethylamino-4-methoxy-6-nitro-[6-C-11]hexatriene (IA, IB), followed by cyclization/ aromatization into 3. Starting from 1, 3-nitro-[3-C-11]anisole of a radiochemical purity of about 65 % and a mean specific radioactivity of 1 Ci/mu mol was obtained within 10 min. Related to [C-11]CH3NO2, the reproducible radiochemical yield of 3 (decay-corrected) was 60+/-5 %. Reduction of 3 by heating the above reaction mixture with aqueous Na2S gave 3-amino-[3-C-11]anisole (4) of a radiochemical purity of about 50 %. The reproducible radiochemical yield of 4 (decay-corrected) in relation to 1 was 45+/-5 %, the synthesis time from 1 was 16 min.