Tritium labeling of simple 7-membered ring compounds

Seven‐membered ring compounds, from cylcoheptane to complex ring structures containing heteroatoms, substituents and fused phenyl rings, were labeled with tritium, using activated and adsorbed tritium. The 7‐membered ring structures are generally stable towards reactions with tritium, which allows compounds like 1‐benzosuberone, 1‐aza‐2‐methoxy‐1‐cycloheptene, iminostilbene and clozapine to be labeled to reasonably high specific activities. The best method varies greatly from compound to compound. By optimizing the labeling conditions and use of efficient support exceptionally good results can be obtained. The Pd‐on‐alumina support gives consistently higher specific activity and less radioimpurity than other supports. Even molecules containing carbon‐halogen bond and hydrogen bound to nitrogen can usually be labeled with tritium at stable positions and without dehalogenation.