To a mixture of 4-{[1-(3-bromo-5-methyl-phenyl)-methylidene]-amino}-benzoic acid ethyl ester (2.5 g, 7.3 mmol) and ytterbium(III) triflate hydrate (0.45 g, 0.73 mmol) in dry tetrahydrofuran (15 mL) at 25° C. was added isobutyraldehyde (0.53 g, 7.3 mmol) and water (0.13 mL, 7.3 mmol) dropwise. The reaction mixture was stirred at 25° C. for 5 h. Then the reaction mixture was concentrated in vacuo and the residue was extracted with ethyl acetate (2×100 mL), washed with brine, dried over anhydrous sodium sulfate and concentrated in vacuo to afford 2-(3-bromo-5-methyl-phenyl)-4-hydroxy-3,3-dimethyl-1,2,3,4-tetrahydro-quinoline-6-carboxylic acid ethyl ester (3.1 g, 100%) as a light yellow oil: LC/MS m/e calcd for C21H24BrNO3 M+: 418.3, observed: 400.1.
