A mixture of 1.5 g of 1,3-dihydro-1-(4-oxocyclohexyl)-2H-benzimidazol-2-one, 1.21 g of tert-butyl 1-piperazinecarboxylate, 20 mL of 1,2-dichloroethane, 0.40 mL of glacial acetic acid and 1.79 g of sodium triacetoxyborohydride was stirred at room temperature for 48 h. The reaction mixture was poured into 50 mL chloroform and 50 mL saturated aqueous Na2CO3 and the layers separated. The aqueous layer was extracted with 2×25 mL of chloroform and the combined organic layers dried over MgSO4 and concentrated under reduced pressure. Chromatography of the crude product on silica gel, eluting with 10% methanol in chloroform gave, firstly, 0.63 g of 1,3-dihydro-1-{cis-4-[4-(tert-butylcarbonyl)piperazin-1-yl]-1-cyclohexyl}-2H-benzimidazol-2-one: 1H NMR (400 MHz, CDCl3) 7.47 (m, 1H), 7.25 (m, 1H), 7.05 (m, 2H), 4.55 (m, 1H), 3.54 (m, 4H), 2.49 (m, 6H), 2.27 (s, 0.8H), 2.15 (d, 2H), 1.97 (m, 0.2H), 1.57 (m, 4H), 1.49 (s, 9H). Later fractions gave 1,3-dihydro-1-{trans-4-[4-(tert-butylcarbonyl)piperazin-1-yl]-1-cyclohexyl}-2H-benzimidazol-2-one: 1H NMR (400 MHz, CDCl3) 7.15 (m, 2H), 7.06 (m, 2H), 4.28 (m, 1H), 3.46 (m, 4H), 2.56 (m, 4H), 2.5 (m, 1H), 2.26 (m, 2H), 2.03 (m, 6H), 1.47 (s, 9H).
