To the solution of N-(t-butyloxycarbonyl)-N-(2-pyridinylmethyl)-N′-(5,6,7,8-tetrahydro-8-quinolinyl)-1,4-benzenedimethanamine (195 mg, 0.43 mmol) and N-Boc-3-pyrrolidone (91 mg, 0.49 mmol) in methanol (3 ml) was added trimethylorthoformate (2 ml) and three drops of acetic acid, at room temperature. This mixture was allowed to stir for 30 min. at room temperature and sodium cyanoborohydride (130 mg, 2.09 mmol) was added. Stirring was continued for a further 18 hours at room temperature and then the reaction mixture was concentrated. The residue was dissolved in ethylacetate (300 mL), and washed with saturated aqueous NaHCO3 and brine, then dried (Na2SO4) and evaporated. Purification of the residue by column chromatography on silica gel (1.5×20 cm, 50:50 EtOAc/CH2Cl2) gave the desired product (120 mg, 45%) as a mixture of diastereomers.
