Preparation of o-Fluorophenols from Nonaromatic Precursors: Mechanistic Considerations for Adaptation to Fluorine-18 Radiolabeling
摘要:
The preparation of fluorine-18 labeled o-fluorophenols at high specific activity is challenging and requires use of [F-18]fluoride ion as the radioisotope source. As a novel, alternative approach, we found that treatment of alpha-diazocyclohexenones with Selectfluor and Et3N center dot 3HF followed by HF elimination and tautomerization afforded o-fluorophenols regioselectively and rapidly. To adapt this chemistry to F-18 radiolabeling, using bromine electrophiles in place of Selectfluor gave the o-fluorophenol via an alpha-bromo-alpha-fluoroketone intermediate in lower but still reasonable yields.