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A 50 mL round-bottom flask, equipped with a magnetic stir bar, was charged with tert-butyl-1-piperazine carboxylate (445 mg, 2.39 mmol) under nitrogen. The solid was dissolved in 10 mL dichloromethane (anhydrous) and stirred at room temperature. 2-Fluoro-4-morpholinobenzaldehyde (500 mg, 2.39 mmol) was added followed by molecular sieves (440 mg, 8-12 mesh beads). The reaction was allowed to continue to stir at room temperature for 1 h. At that point, sodium triacetoxyborohydride (557 mg, 2.63 mmol, 1.10 equiv) was added. The reaction was monitored for disappearance of aldehyde by thin layer chromatography. After 15 h, the reaction was quenched with saturated sodium bicarbonate (15 mL). After the addition of dichloromethane (15 mL), the mixture was partitioned into two phases. The aqueous phase was extracted twice with dichloromethane (15 mL). The combined organic layers were dried over anhydrous sodium sulfate, filtered and concentrated. The crude mixture was applied to a chromatography column containing 24 g silica and dichloromethane. A gradient solvent was used from 100% dichloromethane to 10% methanol in dichloromethane to provide 833 mg (92%) of tert-butyl 4-(2-fluoro-4-morpholinobenzyl)piperazine-1-carboxylate as a pale yellow solid. 1H NMR 400 MHz (CDCl3) δ 7.22 (t, J=8.4 Hz, 1H), 6.66 (d, J=8.4 Hz, 1H), 6.57 (d, J=13.0 Hz, 1H), 3.90-3.85 (m, 4H), 3.53 (s, 2H), 3.43 (bs, 4H), 3.20-3.15 (m, 4H), 2.41 (bs, 4H), 1.46 (s, 9H).

1. customA 50 mL round-bottom flask, equipped with a magnetic stir bar
2. stirringto stir at room temperature for 1 h
3. customthe reaction was quenched with saturated sodium bicarbonate (15 mL)
4. additionAfter the addition of dichloromethane (15 mL)
5. customthe mixture was partitioned into two phases
6. extractionThe aqueous phase was extracted twice with dichloromethane (15 mL)
7. dry with materialThe combined organic layers were dried over anhydrous sodium sulfate
8. filtrationfiltered
9. concentrationconcentrated
10. additioncontaining 24 g silica and dichloromethane