Multifunctional Crown-5-calix[4]arene-based Phase-Transfer Catalysts for Aromatic F-Fluorination.

Methylated bis-triethylene glycolic crown-5-calix[4]arene (M-BTC5A) as a phase-transfer catalyst showed the best performance among other analogues and even conventional Kryptofix 222 in the nucleophilic aromatic F-fluorination of diaryliodonium tosylate precursors owing to (i) the efficient release of reactive "naked" [F]fluoride, (ii) the high stabilization of the precursor in the reaction, and, presumably, (iii) the ease of access between the precursor and the KF/M-BTC5A complex facilitated by π-π interactions. [F]Flumazenil was produced in high radiochemical yield using M-BTC5A.