N[C:2]1[CH:11]=[CH:10][CH:9]=[C:8]2[C:3]=1[CH:4]=[CH:5][CH:6]=[C:7]2[O:12][CH3:13].C1COCC1.[H+].[B-](F)(F)(F)[F:21].N([O-])=O.[Na+]>O.F[B-](F)(F)F.C([N+]1C=CN(C)C=1)C.CCOCC>[F:21][C:2]1[CH:11]=[CH:10][CH:9]=[C:8]2[C:3]=1[CH:4]=[CH:5][CH:6]=[C:7]2[O:12][CH3:13]
A stirred mixture of 6.8 g of 5-amino-1-methoxynaphthalene, 57 ml THF and 74 ml of 48-50% HBF4 was cooled in an ice/salt bath. To the stirred suspension was added dropwise a solution of 3.00 g of sodium nitrite in 6 ml of water. The mixture was stirred at 0-5° C. for 30 minutes after which 300 ml of ether was added. The mixture was stirred at 0-5° C. for 45 minutes after which it was filtered and the residue washed three times with dry ether. The resulting dark red solid was air dried overnight to yield 12.2 g. The material was dissolved in 70 ml of 1-ethyl-3-methylimidazolium tetrafluoroborate and heated at 70-80° C. for 2 h (gas evolution was observed). The mixture was allowed to cool to room temperature, extracted twice with ether, washed with brine, dried (magnesium sulphate), filtered and concentrated to an oil. The material was dissolved in dichloromethane and flash chromatographed on silica gel, eluting with ethyl acetate/heptane to provide 2.08 g (30%) of 5-fluoro-1-methoxynaphthalene.
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