Synthesis of [ 11 C]cyanoalkyltriphenylphosphoranes via [ 11 C]cyanide substitution on haloalkylphosphonium salts

The synthesis of the 11 C‐labelled bifunctional precursors 3‐[ 11 C]cyanoethyltriphenylphosphonium bromide ( 1 ′), 4‐[ 11 C]cyanopropyltriphenylphosphonium bromide ( 2 ′), 5‐[ 11 C]cyanobutyltriphenylphosphonium bromide ( 3 ′), 4‐[ 11 C]cyanobutyltriphenylphosphonium iodide ( 4 ′) and 5‐[ 11 C]cyanobutyltriphenylphosphonium iodide ( 5 ′) is presented. The label was introduced using [ 11 C]cyanide in a substitution reaction on the ω‐haloalkyltriphenylphosphonium salt (bromide or iodide salt). The phosphonium salts 1 ′ − 5 ′ were formed in 33–99% radiochemical yield in 5–10 min reaction time. After addition of epichlorohydrin as generator of base, the precursors 1–3 were formed. The potential of the intermediates 1 – 3 in Witting reactions was shown in model reactions with aromatic and aliphatic aldehydes. The aromatic olefins obtained from 1 ′– 5 ′ were formed in 85–96 % radiochemical yield, with Z/E ratios between 67/33–75/25. The aliphatic olefins were obtained in 60–78% radiochemical yield from 4 ′ and 5 ′. In the reaction with 1 ′ and an aliphatic aldehyde, the yield decreased to 5–10%. The Z/E ratios were 100/0 for the aliphatic olefins. In an experiment starting with 2,7 GBq (73 mCi) hydrogen [ 11 C]cyanide, 451 MBq (12.2 mCi) olefin from 3 ′ and 4‐nitrobenzaldehyde was obtained in 44 min from hydrogen [ 11 C]cyanide production, with a 55 % decay corrected radiochemical yield, the radiochemical purity was 96%.