Dimethylformamide → 3-Cyclopentyloxy-6-fluoro-4-methoxybenzaldehyde

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A mixture of 6-fluoro-3-hydroxy-4-methoxybenzaldehyde (2 g), potassium carbonate (1.66 g) and anhydrous dimethylformamide (20 mL) is treated with cyclopentyl bromide (1.62 mL) and heated on a steam bath for 43 hours. The mixture is cooled, poured into water (200 mL) and extracted with diethyl ether (3×100 mL). The combined ethereal extracts are washed with sodium hydroxide solution (2×50 mL; 2 N), and brine (2×50 mL), dried over magnesium sulphate and concentrated. The residual brown oil is subjected to flash chromatography [a solvent gradient of 9:1 to 4:1 v/v petroleum ether (b.p. 60–80° C.) and ethyl acetate is used as eluent on a silica gel column] to give 3-cyclopentyloxy-6-fluoro-4-methoxybenzaldehyde (1.42 g) in the form of a yellow oil. [NMR (CDCl3):—10.22(s,1H),7.27(d,1H,J=8 Hz),6.63(d,1H,J=16 Hz), 4.81–4.76(m,1H),3.91(s,3H),2.01–1.57(m,8H)].

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