C-(4-[18F]fluorophenyl)-N-phenyl nitrone: A novel 18F-labeled building block for metal free [3+2]cycloaddition

Radiofluorination via [3+2]-nitrone-alkene cycloaddition was studied using the model reaction between 18F-labeled C-(4-fluorophenyl)-N-phenyl nitrone ([18F]1) and substituted maleimides 2a–c. [18F]1 was prepared in RCY of 73.6±5.8% and radiochemical purity of >95%. Cycloaddition of [18F]1 to 2a in toluene at 80 °C and in EtOH at 110 °C gave the respective isoxazolidine [18F]5a in >80% RCY at 10 min reaction time. Reaction between [18F]1 and 2b, c also went smoothly to afford the respective cycloaddition products in high radiochemical yields.

► [2+3]-Nitrone-alkene metal-free cycloaddition for radiolabelling.
► Optimized radiosynthesis of C-(4-[18F]fluorophenyl)-N-phenyl nitrone ([18F]1).
► Fast and high-yielding cycloaddition of [18F]1 to model maleimides.