N‐ Alkyl 3‐aminobut‐2‐enenitrile as a Non‐radioactive Side Product in Nucleophilic 18 F‐Fluorination

We found that acetonitrile acted as a reactant under the conventional reaction conditions for aliphatic nucleophilic 18 F‐fluorination in acetonitrile to provide the N ‐alkyl 3‐aminobut‐2‐enenitrile as one of the side products. Dimerization of acetonitrile promoted by a complex of K 2 CO 3 and K222 provided 3‐aminobut‐2‐enenitrile, which acted as nucleophile to provide N ‐alkyl amino derivatives. Based on the finding, avoiding acetonitrile in the drying of [ 18 F]fluoride as well as 18 F‐labeling enabled the preparation of 18 F‐labeled compounds containing only a small amount of the corresponding alcohol. Finally, we used an automated synthesizer to achieve an efficient phase‐tag‐assisted synthesis of 18 F‐labeled stilbene derivative as a 18 F‐labeled amyloid‐β ligand.