General procedure for the synthesis of 2-methyl-N-phenyl-1,2,3,4-tetrahydroquinolin-4-amine from 2-phenylaminopropionic acid: 2-phenylaminopropionic acid (66 mg, 0.4 mmol) and 4?molecular sieves (100 mg) were added to a 10 mL reaction vial, dried with an air pump, and then 200 μL of a reaction vial containing an organic photocatalyst, DPZ (0.28 mg 0.0008 mmol) in toluene solution. Subsequently, 4 mL of purified water was added, the reaction mixture was dried with chloroform, and the mouth of the flask was sealed with a rubber stopper and a balloon filled with dry air was inserted. The reaction flask was placed in a 25°C incubator and the reaction was stirred for 15 h under the illumination of two 1 W blue LEDs. Upon completion of the reaction, about 2/3 of the solvent was removed by distillation using a rotary evaporator. Purification by column chromatography (eluent: hexane/ethyl acetate, 60:30:1) afforded 2-methyl-N-phenyl-1,2,3,4-tetrahydroquinolin-4-amine (39.1 mg, 82% yield) as a colorless oily liquid.
