Abstract
The synthesis from carbon‐14C dioxide of 1, 3‐dihydro‐1‐methyl‐7‐nitro‐5‐phenyl‐2H‐1, 4‐benzodiazepin‐2‐one‐5‐14C (I) for use in metabolic studies has been described. The synthesis was achieved by the sequence shown in figure 1. The overall yield of labelled nimetazepam (I) was nearly 36%.