AbstractTwo14C‐labelled leukotriene receptor antagonists were prepared from two aryl bromides and potassium [14C]cyanide. Potassium cyanide was converted to copper(I) [14C]cyanide and was subsequently used to displace the bromine atom from two aryl bromides, 2‐dodecylbromobenzene and 2‐(8‐phenyloctyl)bromobenzene. The resulting nitriles were reduced to aldehydes with diisobutylaluminum hydride and the aldehydes were reacted with 3‐mercaptopropionic acid to give 5‐(2‐dodecylphenyl)‐4,6‐dithianonanedioic acid (14C‐SK&F 102081) and 5‐[2‐(8‐phenyloctyl)phenyl]‐4,6‐dithianonanedioic acid (14C‐SK&F 102922), respectively. These products were snythesized in about 30% overall yield with radiochemical purity of greater than 95%. Their structures were assigned based on the analytical data of the corresponding nonradiolabelled compounds obtained from