Formaldehyde → 1-Methyl-4-(2,3,4,5,6-pentafluorophenoxy)-4-phenylpiperidine

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To 50 ml of methanol, was added 4.0 g of 4-(2,3,4,5,6-pentafluorophenoxy)-4-phenylpiperidine and 15 ml of a 37% aqueous formaldehyde solution. After stirring at 70° C. for two hours, the mixture was cooled, and treated (portionwise) with 2.5 g of sodium borohydride over a period of five minutes. After stirring at ambient temperature for two hours, the reaction mixture was evaporated to a semi-solid. The semi-solid was stirred with 50 ml water, then extracted with ethyl acetate. The organic layer was washed with water, followed by a saturated sodium chloride solution, and dried over anhydrous magnesium sulfate. After filtering, evaporation of the solvent yielded a residue which was purified by means of a high pressure liquid chromatography (silica gel, elution with 5% methanol/dichloromethane). The desired fractions were combined, then evaporated to afford 1-methyl-4-(2,3,4,5,6-pentafluorophenoxy)-4-phenylpiperidine as an oil. The oil was dissolved in isopropanol, and acidified to pH 1 with etheral-oxalic acid. The resultant precipitate was collected and dried to give 2.5 g (47%), of 1-methyl-4-(2,3,4,5,6-pentaflurophenoxy)-4-phenylpiperidine oxalate, m.p. 152°-154° C. (dec).

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