To a stirred solution of 4-amino-benzoic acid methyl ester (1 g, 6 mmol) and 2-ethyl-benzaldehyde (1.2 g, 8.9 mmol) in acetonitrile (40 mL) were added isobutene (1.7 mL, 24 mmol) and ytterbium(III) trifluoromethanesulfonate (Yb(OTf)3) (0.55 g, 0.9 mmol). The resulting mixture was stirred at 85° C. for 16 h in sealed tube. The mixture was diluted with ethyl acetate (100 mL) and washed with water (50 mL×2) and brine (50 mL×2) and then dried over anhydrous sodium sulfate. The solvent was removed in vacuo and the residue was purified by ISCO combi-flash chromatography (gradient elution, 10-50% ethyl acetate in petroleum ether) to afford 2-(2-ethyl-phenyl)-4,4-dimethyl-1,2,3,4-tetrahydro-quinoline-6-carboxylic acid methyl ester (1 g, 49%) as a light yellow solid: MS (ESI) M+1=337.0.
