A novel synthetic route for the total syntheses of 1-benzoyl-3,4-dihydroisoquinoline alkaloids was developed. Nelumstemine was synthesized for the first time via 6 steps in 50% overall yield starting from 3,4-dimethoxybenzaldehyde, and longifolonine was also synthesized for the first time via 9 steps in 35% overall yield starting from vanillin. The key step of these total syntheses is photo-oxidation of 1-benzyl-3,4-dihydroisoquinolines to 1-benzoyl-3,4-dihydroisoquinolines by air under visible-light irradiation at room temperature. The unique mild photo-oxidation of 1-benzyl-3,4-dihydro-isoquinolines has been studied in detail.