Cyclo SiFA: The Next Generation of Silicon‐Based Fluoride Acceptors for Positron Emission Tomography (PET)

The ring‐opening Si‐fluorination of a variety of azasilole derivatives cyclo ‐1‐( i Pr 2 Si)−4‐X−C 6 H 3 −2‐CH 2 NR ( 4 : R=2,6‐ i Pr 2 C 6 H 3 , X=H; 4 a : R=2,4,6‐Me 3 C 6 H 2 , X=H; 9 : R=2,6‐ i Pr 2 C 6 H 3 , X= t BuMe 2 SiO; 10 : R=2,6‐ i Pr 2 C 6 H 3 , X=OH; 13 : R=2,6‐ i Pr 2 C 6 H 3 , X=HCCCH 2 O; 22 : R=2,6‐ i Pr 2 C 6 H 3 , X= t BuMe 2 SiCH 2 O) with different 19 F‐fluoride sources was studied, optimized and the experience gained was used in a translational approach to create a straightforward 18 F‐labelling protocol for the azasilole derivatives [ 18 F] 6 and [ 18 F] 14 . The latter constitutes a potential clickable Cyclo SiFA prosthetic group which might be used in PET tracer development using Cu‐catalysed triazole formation. Based on our findings, Cyclo SiFA has the potential to become a new entry into non‐canonical labelling methodologies for radioactive PET tracer development.