Diethyl [2,3‐13C2] succinate was prepared by the oxidative dimerization of ethyl lithio [2‐13C] acetate in the presence of CuBr2. Its dienolate was generated with lithium diisopropylamide (LDA) and methylated with CH3I to afford diethyl 2‐methyl [2,3‐13C2] succinate which by acid hydrolysis gave the corresponding labelled acid. Treatment of the latter with SOCl2 provided 2‐methyl [2,3‐13C2] succinic anhydride. This anhydride upon treatment with Et3N, ZnCl2 and trimethylchlorosilane in acetonitrile afforded 2,5‐bis (trimethylsilyloxy)‐3‐methyl [3,4 13C2] furan which was subjected to a Diels Alder reaction with trichloroethylene giving rise to 2,3‐dichloro‐5‐methyl [5,6‐13C2] 1,4‐benzoquinone which, in turn, was transformed by a known procedure to [2,3‐13C2‐2,5‐cyclohexadienyl] ubiquinone 3. © 1998 John Wiley & Sons, Ltd.