N-Halogeno compounds. Part 18. 1-Alkyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane salts: user-friendly site-selective electrophilic fluorinating agents of the N-fluoroammonium class

Abstract

Methods of synthesis are described for a range of 1-alkyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane salts [R–N⁺(CH₂CH₂)₃N⁺–F(X^–)₂, where R = CH₃, CH₂Cl, C₂H₅, CF₃CH₂, C₈H₁₇ and (X^–)₂=(TfO^–)₂, (BF₄^–)₂, (PF₆^–)₂, (TfO^–, BF₄^–), (TfO^–, PF₆^–), (TfO^–, FSO₃^–)] by direct fluorination (with neat F₂ at ⩽20 mmHg or F₂–N₂ blends at 1 atm pressure) of monoquaternary salts of 1,4-diazabicyclo[2.2.2]octane [R–⁺N(CH₂CH₂)₃N X^–] or their 1:1 adducts with boron trifluoride, phosphorus pentafluoride, or sulfur trioxide in acetonitrile at ca– 35 °C. The results of site-selective electrophilic fluorination of diethyl sodio(phenyl)malonate [→PhCF(CO₂Et)₂], 1-morpholinocyclohexene (→2-fluoro-cyclohexanone), phenol(→2-and 4-FC₆H₄OH), 1-and 2-hydroxynaphthalene (→2-and 4-FC₁₀H₆OH, and 1-FC₁₀H₆OH and 1,1-difluoro-2-oxo-1,2-dihydronaphthalene, respectively), acetanilide (→2-and 4-FC₆H₄NHCOCH₃), anisole (→2-and 4-FC₆H₄OCH₃) and sodium benzenesulfinate (→ PhSO₂F) with these N-fluoroammonium salts are presented.