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Preparation of o-Fluorophenols from Nonaromatic Precursors: Mechanistic Considerations for Adaptation to Fluorine-18 Radiolabeling
- Yasui, Norio, Mayne, Christopher
G., Katzenellenbogen, John A.
- Organic letters 2015 v.17 no.22 pp. 5540-5543
- Lewis acids, bromine, chemical structure, fluorides, radiolabeling, radionuclides, regioselectivity, tautomerization, trimethylamine
- The preparation of fluorine-18 labeled o-fluorophenols at high specific activity is challenging and requires use of [¹⁸F]fluoride ion as the radioisotope source. As a novel, alternative approach, we found that treatment of α-diazocyclohexenones with Selectfluor and Et₃N·3HF followed by HF elimination and tautomerization afforded o-fluorophenols regioselectively and rapidly. To adapt this chemistry to ¹⁸F radiolabeling, using bromine electrophiles in place of Selectfluor gave the o-fluorophenol via an α-bromo-α-fluoroketone intermediate in lower but still reasonable yields.