Trifluoroacetic acid → 6-Fluoro-3-methylquinoline

Participants

Reaction Conditions

Reaction Steps

(4-Fluoro-phenyl)-carbamic acid tert-butyl ester (2.11 g, 10.0 mmol, ABCR, Karlsruhe, Germany) was added to a round bottom and purged with nitrogen. Anhydrous tetrhydrofuran (200 mL) was added to dissolve the solids and the flask placed in a dry ice/acetone bath (internal temperature −74° C. uncorrected). tert-Butyl lithium (1.7 M in pentane, 14.2 mL, 24.0 mmol) was added over 5 min causing a yellow color to develop. After the addition was complete the reaction was stirred in a −20° C. bath for 1 h. At this point, 3-ethoxymethacrolein (1.43 mL, 12.0 mmol) was added dropwise over 5 min, keeping the temperature below −19° C. The reaction was stirred at −20° C. for 2 h before slowly adding trifluoroacetic acid (14 mL) over 5 min. The red solution was stirred at room temperature for 16 h before bring to pH 12 with 1 N NaOH. This was extracted twice with ethyl acetate and the combined organics dried over MgSO4. Purification by silica gel flash chromatography (ethyle acetate/heptanes) gave impure desired material. This was extracted into three portions of 1 N HCl, the combined aqueous layers were brought to pH 12 with 6 N NaOH, and then extracted into two portions of ethyl acetate. The combined organics were dried over MgSO4 and concentrated in vacuo to give 6-fluoro-3-methyl-quinoline (48.0 mg) as an orange oil. 1H NMR (400 MHz, CDCl3) δ 8.74 (s, 1 H) 8.07 (dd, J=9.1, 5.4 Hz, 1 H) 7.88 (s, 1 H) 7.33-7.46 (m, 2 H) 2.53 (s, 3 H); MS (M+1): 162.1.

Provenance & Evidence