Methyl 4-amino-3-phenylbutanoate hydrochloride x11 (0.19 g, 0.83 mmol, 1.05 eq) is added to a solution of aldehyde x235 (0.17 g, 0.79 mmol) in dry dichloroethane (DCE) (7.8 ml). The mixture is kept at room temperature for 30 min, cooled to 10-12° C., and a solution of triethylamine (0.15 ml, 0.83 mmol, 1.05 eq) in dry DME (2.5 ml) is added dropwise. The mixture is additionally stirred at the same temperature for 1 h and cooled to 0-5° C. Then STAB (0.23 g, 1.10 mmol, 1.4 eq) is added in portions under vigorous stirring. The mixture is additionally stirred at 0-5° C. for 30 min and kept at room temperature overnight. Then the mixture is heated to 60° C. for 2 h and cooled to room temperature. An equal volume of dichloromethane is added, and the mixture is washed with 10% K2CO3 (2×10 ml). The mixture is dried over anhydrous Na2SO4 and evaporated. The oily residue is triturated with ether, and the formed crystals are separated by filtration, washed twice with ether, and vacuum-dried to give white fine-crystalline 4-phenyl-1-{[3-(trifluoromethyl)[1,2,4]triazolo[4,3-b]pyridazin-7-yl]methyl}pyrrolidin-2-one 255.
