Hydrochloric Acid → 1-(2,3-Dihydro-benzo[1,4]dioxin-2-ylmethyl)-pyrrolidine-3-carboxylic acid methyl ester

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A solution containing 300 mg (1.03 mmol) of 1-(2,3-dihydro-benzo[1,4]dioxin-2-ylmethyl)-5-oxo-pyrrolidine-3-carboxylic acid methyl ester in dry tetrahydrofuran (4 mL) was cooled to 0° C. under nitrogen. After adding 4 mL of 1M BH3-tetrahydrofuran solution (4.12 mmol), the reaction mixture was allowed to warm to room temperature and it was stirred for 5 h. Decomposition of the boron complexes was effected by addition of 3 mL of methanol and 3 mL of 6 M HCl-solution followed by stirring the mixture at 40° C. for ½ h. Tetrahydrofuran was evaporated off under vacuum. The residue was dissolved in 50 mL of water and the pH of the solution was adjusted to 10 using 1M Na2CO3 solution. The water phase was extracted with ethyl acetate (3×25 mL), and the combined organic phases were dried over anhydrous sodium sulfate, filtered, and evaporated to dryness. The crude product was purified by column chromatography (silica gel, heptane/ethyl acetate, 7:3).

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