Methyl 2,4-dihydroxybenzoate (5.1 g, 30.33 mmol) and triphenylphosphine (9.52 g, 36.3 mmol) were stirred in THF (200 ml) under nitrogen. The mixture was cooled in an ice bath and treated with a solution of 1-Boc-4-hydroxypiperidine (6.8 g, 33.8 mmol) and diethyl azodicarboxylate (5.73 ml, 6.34 g, 36.4 mmol) in THF (100 ml) added dropwise over 30 min. The mixture was stirred at ambient temperature for 18 hours, then diluted with ethyl acetate and washed with 1M NaOH, saturated aqueous sodium bicarbonate, and brine. The organic layer was dried over sodium sulfate, filtered, and evaporated to dryness in vacuo. The residue was chromatographed on silica gel eluted with 10% ethyl acetate in hexane, and the product fractions were evaporated to dryness in vacuo to give methyl 2-hydroxy-4-(1-Boc-4-piperidyloxy)benzoate.
