Hydrochloric Acid → 2,3,4-Trichlorophenol

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Ethyl 5'-(4-formyl-3,5-dimethoxyphenoxy)valerate (13.2 g, 42.5 mmol) was dissolved in 1 n NaOH-MeOH (1:1) (100 mL) and after 10 minutes of stirring sodium borohydride (2.2 g, 60 mmol) was added portionwise over 45 minutes. After stirring two additional hours at 25° C., the solutions was chilled to 4° C., acidified with 1 N HCl to pH 5, and extracted with ethyl acetate (4×25 mL). The combined organic phases were washed with saturated aqueous NaCl (2×25 mL) and dried over MgSO4. 2,4,5-trichlorophenol (6.9 g, 35 mmol) and N,N'-dicyclohexylcarbodiimide (7.2 g, 35 mmol) were added to the ethyl acetate solution. The mixture was stirred overnight at 25° C. and then N,N-dicyclohexylurea was removed by filtration. The filtrate was washed with carbonate buffer, pH 9.5 (3.50 mL), and with saturated aqueous NaCl (2.25 mL), dried (MgSO4) and rotary evaporated. The residue was recrystallized from ethyl acetate with pentane added at 25° C. and was further chilled to -5° C. to provide a slightly orange solid (11.6 g, 25 mmol, 59% yield with respect to formyl derivative or 72% yield to trichlorophenol).

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