A solution of N-(l-benzylpiperidin-4-yl)benzenesulfonamide from Example 1 above, (18.7 g, 56.5 mmol) and 210 ml dimethoxyethane was chilled at 0° C. under N2, followed by a slow addition over 25 minutes of 2.3 equivalent of n-butyl lithium (52 ml, 2.5 N/hexanes, 130 mmol) keeping the temperature below 15° C. After mechanically stirring for 35 minutes longer, 4-fluorobenzaldehyde (7.4 g, 59 mmol) in 50 ml dimethoxyethane was added at 5° C., and the reaction was stirred for 2 hours. Ether (400 ml) was added, and the reaction was washed with water and brine, dried (MgSO4), and concentrated in vacuo. The residue was chromatographed on silica gel eluting with CHCl3 to CHCl3 :5% MeOH to afford 11.85 g (46% yield) of the intermediate as a foam.
