Synthesis of 13 C and 2 H‐labelled 2‐phenylcyclododecanones

13 C labelled (1,2 and 1,12) and perdeuterated derivatives of 2‐phenyl cyclododecanones, as precursors for labelled triplet flexible biradicals to probe magnetic isotope effects at the radical centers on the triplet decay dynamics, were synthesized. Isotopomers of 2‐phenylcyclododecanone‐ 13 C 2 ‐(1,2 and 1,12) were synthesized from cyclododecanone‐ 13 C 2 ‐(1,2) by dibromination, followed by phenylation with lithiumdiphenylcuprate. Cyclododecanone‐ 13 C 2 ‐(1,2) was obtained from 1, 10‐dibromodecane via the following sequence: (1) K 13 CN; (2) hydrolysis; (3) esterification; (4) acyloin condensation. Perdeuterio‐2‐phenyl cyclododecanone (95% isotopic purity) was prepared from unlabelled 2‐phenyl cyclododecanone by a substitution of deuterium for hydrogen by treatment with excess D 2 O, catalyzed with D 2 ‐reduced PtO 2 in the presence of D 2 O 2 .