2,3,4,9-Tetrahydro-1H-β-carboline (345 mg) and 4-dimethylamino-4-phenylcyclohexanone (435 mg) were dissolved in a mixture of THF (10 ml) and 1,2-dichloroethane (15 ml) under argon, and acetic acid (120 mg, 2 mmol.) was added thereto. After 15 minutes, NaBH(OAc)3 (600 mg) was added, stirring was carried out for 68 hours, the reaction mixture was concentrated and the residue was taken up in 1N hydrochloric acid (20 ml) and washed with ether (2×20 ml). The aqueous solution was rendered alkaline with 1M NaOH (30 ml) and extracted with ether (3×30 ml). After drying and concentration of the combined extracts, a semi-solid crude product was obtained which, after separation by column chromatography with methanol/NH3 (500:3), yielded the nonpolar diastereomer (334 mg, m.p. 147-150° C.) which, dissolved with heating in 2-butanone (20 ml) and ethanol (10 ml), was converted with 3.3M ethanolic hydrochloric acid (0.8 ml) into the corresponding dihydrochloride (335 mg; 264-269° C.).
