The synthesis of [ 3 H]cadralazine of high specific activity

The title compound has been prepared by two different approaches. The first involved a five‐stage “hot” synthesis where the tritiation step was selective debromination of a cyclic β‐bromo‐α‐β‐unsaturated ketone. The double bond was protected by formal aromatisation. The absolute structure of this intermediate was determined by 3 H‐FTNMR spectroscopy of its reduction product. Cadralazine was also labelled in its side chain by reduction of the appropriate ketone with high specific activity sodium borotritide. Both labelled products had specific activities of 18 Ci/mmol and radiochemical purities of 90–96%.