To a 0° C. solution of 1H-indole-5-carbaldehyde (0.43 g, 2.96 mmol) in DMF (10 mL) was added NaH (60% in mineral oil; 0.14 mg, 3.55 mmol). After 45 min at 0° C., a solution of 4-(4-methanesulfonyloxy-butyl)-piperidine-1-carboxylic acid tert-butyl ester (1.00 g, 3.15 mmol) in DMF (5 mL) was added dropwise. The mixture was warmed to rt and stirred for 18 h. The mixture was diluted with CHCl3 (20 mL) and washed with water (15 mL). The organic layer was dried and concentrated to obtain the crude residue, which was used purified by FCC to give 0.96 g (88%). MS: mass calcd. for C22H30N2O3, 370.23; m/z found, 371.4 [M+H]+.
