To a solution of 1-(tert-butoxycarbonyl)-4-(formyl)piperidine (2.59 g) and 4-(4-pyridyl)piperidine (1.97 g) in methanol/acetic acid (99:1) (50 ml) was added sodium cyanoborohydride (2.29 g) portionwise over 30 minutes and the resultant suspension stirred at ambient temperature for 3 hours. The suspension was quenched by addition of saturated aqueous sodium bicarbonate and the resulting mixture extracted with ethyl acetate. The organic phase was dried (Na2SO4) and evaporated, The residue was purified by chromatography eluting with 5% methanol in dichloromethane to give 1-[1-tert-butoxycarbonyl(4-piperidinylmethyl)]-4-(4-pyridyl)piperidine (1.65 g) as a solid: NMR (CDCl3): 1.10 (m, 2H), 1.40 (s, 9H), 1.75 (m, 7H), 2.00 (dt, 2H), 2.20 (d, 2H), 2.45 (m, 1H), 2.70 (m, 2H), 3.00 (d, 2H), 4.10 (m, 2H), 7.20 (d, 2H), 8.50 (d, 2H); m/z 360 (M+1).
