Acetic Acid → Ethyl 4-(4-cyclopropyl-1,4-diazepan-1-yl)benzoate

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A solution of ethyl 4-(1,4-diazepan-1-yl)benzoate (0.621 g, 2.5 mmol), (1-ethoxycyclopropoxy)trimethylsilane (2.51 mL, 12.50 mmol) and acetic acid (0.286 mL, 5.00 mmol) in tetrahydrofuran (50 mL), methanol (5 mL) was treated with sodium cyanoborohydride (0.393 g, 6.25 mmol) at 20° C. The resulting solution was stirred at 60° C. for 18 h. The reaction mixture was cooled, filtered and evaporated to dryness. 1N HCl (40 ml) and water (60 ml) were added and the solution extracted with ethyl acetate (3×50 ml). The aqueous layer was basified to pH 10 with solid potassium carbonate and extracted with ethyl acetate (4×50 ml). The organic extracts washed with saturated NaCl (50 ml) and dried over MgSO4, filtered and evaporated to dryness. The crude product was purified by silica column chromatography, eluting with a gradient of 0 to 5% MeOH in DCM. Pure fractions were evaporated to dryness to afford ethyl 4-(4-cyclopropyl-1,4-diazepan-1-yl)benzoate (0.849 g, 118%) as a colourless oil.

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