Boron Trichloride → 5-(2-Formyl-3-hydroxyphenoxy)pentanoic acid

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5-(2-Formyl-3-methoxyphenoxy)pentanoic acid (504 mg., 0.002 M) was dissolved in anhydrous dichloromethane (20 ml.) and cooled to -70° C., with stirring. A solution of boron trichloride in anhydrous dichloromethane (0.25 g/ml., 3.76 ml., 0.94 g, 0.008 M) was added dropwise over 10 mins. and the mixture stirred at -70° C. (15 mins). The reaction mixture was allowed to reach ambient temperature and stirred at that temperature (1.25 hrs). After cooling to 10° C., 10% sodium acetate solution (15 ml.) was added dropwise with stirring so that the temperature did not rise above 15° C. The resulting mixture was diluted with ethyl acetate (50 ml.) and filtered. The filtrate was transferred to a separating funnel and the aqueous layer separated. The organic phase was extracted with 10% sodium carbonate solution (2×50 ml.), the combined extracts acidified with concentrated hydrochloric acid and extracted with ethyl acetate. The combined extracts were washed with water, dried (sodium sulphate) and evaporated to give a crystalline solid. This solid was dissolved in the minimum of chloroform-methanol (95:5) and passed through a pad of Kieselgel G. Evaporation of the filtrate and recrystallisation from benzene-petrol gave 5-(2-formyl-3-hydroxyphenoxy)pentanoic acid, m.p. 97°-99° C. (Found: C, 60.42; H, 6.15. C12H14O5 requires C, 60.50; H, 5.92%).

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