A solution of piperazine-1-carboxylic acid tert-butyl ester (19.6 g, 105 mmol) and 3-(4-chloro-phenoxy)-benzaldehyde (24.4 g, 105 mmol) in THF (90 mL) was treated with NaB(OAc)3H (33.4 g, 158 mmol). After 3 h, the resulting mixture was treated with 10% aq. KOH (500 mL). The aqueous phase was extracted with EtOAc (2×500 mL) then saturated aqueous NaCl (200 mL). The organic extracts were combined, dried (MgSO4) and purified (FCC) to give 4-[3-(4-chloro-phenoxy)-benzyl]-piperazine-1-carboxylic acid tert-butyl ester (29.6 g, 75%). MS (ESI+): calcd for C22H27ClN2O3 m/z 402.17. found 403.2 (M+H)+.
