N-(Trimethylsilyl)diethylamine-Promoted Intramolecular SNAr Reaction of Electron-Rich Aryl Fluorides

N-(Trimethylsilyl)diethylamine (TMSNEt2) significantly promotes intramolecular nucleophilic aromatic substitution (SNAr) reactions of electron-rich aryl fluorides with t-BuOK and crown ether. Although substrates bearing electron-donating groups are conventionally inert under SNAr conditions, the activation of substrates by TMSNEt2 enables the reactions to proceed even at room temperature. This method is applicable to the preparation of benzo-fused oxygen-containing heterocycles, such as 3,4-dihydro-2H-1,4-benzoxazines, 3,4-dihydro-2H-1,5-benzoxazepines, and 3,4-dihydro-2H-1-benzopyran, in good to excellent yields (56–93%).