To a suspension of (E)-methyl 4-(4-fluoro-3-nitrobenzylideneamino)benzoate (3.62 g, 12.0 mmol) in tetrahydrofuran (24 mL), yttrium(III) trifluoromethanesulfonate (75 mg, 0.12 mmol) and isobutyraldehyde (0.87 g, 12.0 mmol) were added under nitrogen at room temperature The resultant mixture was stirred at room temperature for 20 hours (turned into clear in 10 min). Water was added to the reaction mixture and extracted with Ethyl acetate. The combined organic layers were washed with brine, dried over anhydrous sodium sulfate. Solvent was removed and the residue was purified by column (petroleum ether/ethyl acetate=3:1, silica gel) to afford methyl 2-(4-fluoro-3-nitrophenyl)-4-hydroxy-3,3-dimethyl-1,2,3,4-tetrahydroquinoline-6-carboxylate 3.15 g (70%) as a yellow solid.
