To a mixture of 4-[(5-bromo-pyridin-3-ylmethylene)-amino]-benzoic acid ethyl ester (33.8 g, 100 mmol) and Ytterbium(III) triflate hydrate (6.2 g, 10 mmol) in dry tetrahydrofuran (100 mL) at 25° C. was added isobutyraldehyde (9.2 mL, 100 mmol) and water (1.8 mL, 100 mmol) dropwise. The reaction mixture was stirred at 25° C. for 16 h. Then the reaction mixture was concentrated in vacuo and the residue was extracted with ethyl acetate (2×200 mL), washed with brine, dried over anhydrous sodium sulfate and concentrated in vacuo to afford 2-(5-bromo-pyridin-3-yl)-4-hydroxy-3,3-dimethyl-1,2,3,4-tetrahydro-quinoline-6-carboxylic acid ethyl ester (42.2 g, quant.) as a light yellow oil which was used for next step without further purification: LC/MS m/e calcd for C19H21BrN2O3 (M+H)+: 406.29, observed: 405.0 & 406.9.
