To a solution of (E)-methyl 4-(4-nitrobenzylideneamino)benzoate (284 mg 1 mmol) and yttrium(III) trifluoromethanesulfonate (62 mg, 0.1 mmol) in tetrahydrofuran (5 mL) was added isobutyraldehyde (72 mg, 1.5 mmol). The resultant mixture was stirred at room temperature for 16 h. Thin layer chromatography showed the starting material was completely consumed. The reaction mixture was quenched with water and separated. The aqueous solution was extracted with dichloromethane and the combined organic layers were dried over anhydrous sodium sulfate. Solvent was removed in vacuo to give the crude product, which was purified by column chromatography (petroleum ether/ethyl acetate=3:1) to afford 70 mg of methyl 4-hydroxy-3,3-dimethyl-2-(4-nitrophenyl)-1,2,3,4-tetrahydroquinoline-6-carboxylate as a yellow solid. Yield: 20%.
