Isoamyl Nitrite → 2-Fluoro-3-methyl-1,1'-biphenyl

A stirred solution of 3-methyl-[1,1'-biphenyl]-2-amine (7.5 g, 0.041 mole, as prepared in method K) in 20 ml of tetrahydrofuran was cooled to 5°. A solution of 40 ml tetrafluoroboric acid (48-50% solution) in 20 ml of water was added to the cooled reaction mixture, followed by dropwise addition of isoamyl nitrite (6.2 g, 0.053 mole). After complete addition, the reaction mixture was stirred for 15 minutes and filtered. The filter cake was rinsed successively with 50 ml each of 5% aqueous tetrafluoroboric acid, cold methanol, and cold diethyl ether. The filter cake was added to 100 ml of toluene and the mixture stirred and heated at 60° until the solid dissolved and bubbling subsided. The mixture was heated at reflux for 30 minutes, then held at room temperature for two days, causing separation of an oil. The toluene was decanted from the oil and evaporated under reduced pressure to give a second oil, which was purified by column chromatography on silica gel, elution by toluene:n-heptane (6:94), to give 2-fluoro-3-methyl-[1,1'biphenyl].