No-caririeir-added 11C-labelling of benzenoid compounds in ring positions by condensation of nitro-[11C]methane with pyrylium salts

Article abstract of DOI:10.1002/(SICI)1099-1344(200005)43:6<565::AID-JLCR342>3.0.CO;2-Q

A new synthesis is described for three no-carrier-added nitro-[1-¹¹C] benzenes 3a-c by condensation of nitro-[¹¹C]methane (1) with the appropriate pyrylium salts 2a-c in the presence of a base such as t-BuOK in t-BuOH. For synthesizing 4-nitro-[4-¹¹C]anisole (3a), tetrabutylammonium fluoride was successfully used as an auxiliary base. The best results were obtained in the synthesis of 3a. The conversion of 1 with 4-methoxypyrylium perchlorate (2a) yielded 3a of a radiochemical purity of up to 82% and a mean specific radioactivity of 30 GBq/μmol (0.8 Ci/μmol) within 20 min. Related to 1, the reproducible radiochemical yields of 3a are in the range of 77 ± 5% (decay-corrected). 2,6-Dimethyl-4-methoxy-nitro[1-¹¹C]benzene (3b) was prepared by reaction of 1 with 2,6-dimethyl-4-methoxypyrylium perchlorate (2b) in radiochemical yields of about 37% (decay-corrected) within 10 min. 2-Nitro-[2-¹¹C]mesitylene (3c) was obtained by condensation of 1 with 2,4,6-trimethylpyrylium tetrafluoroborate (2c) in radiochemical yields of about 29% (decay-corrected) within 20 min. ¹³C/¹¹C Co-labelling experiments were carried out in order to confirm the identity of 3a-c and the position of the label.