Tritium labelled compounds of high specific activity I. Tofizopam

The possibilities of tritium labelling of tofizopam (1) at high specific activity were investigated. Two methods, one by isotopic exchange, and one by catalysed halogen‐tritium replacement were developed. The latter was found to be more rational, and 1 specifically labelled with tritium at a specific activity of 12 Ci/mmole was prepared by applying this route. An attempted labelling by catalysed multiple bond reduction with tritium is also described.