A mixture of ethyl 2-methyl-2-(4-oxo-1-piperidinyl)propanoate (Int. A4) (25.6 g, 1.2 equiv), {[4′-(trifluoromethyl)-4-biphenylyl]methyl}amine (Int. A1) (31.1 g, 1.0 equiv), DCE (400 ml) and acetic acid (6.3 ml, 1.1 equiv) was stirred at room temperature under nitrogen. Sodium triacetoxyborohydride (33.5 g, 1.5 equiv) was added and stirring continued for 19 hours. Aqueous sodium carbonate (2M solution, excess) was added and stirred for 1.5 h, then the mixture was extracted with a mixture of diethyl ether and THF. The organic extracts were backwashed with water and brine, filtered through a pad of silica gel, dried over sodium sulfate and evaporated in vacuo. The desired product was obtained as a white solid (44.2 g) which was used without further purification.
