Importance of Singlet Oxygen in Photocatalytic Reactionsof 2‑Aryl-1,2,3,4-tetrahydroisoquinolines Using ChalcogenorosaminePhotocatalysts

Aerobic oxidation of 2-aryl-1,2,3,4-tetrahydroisoquinolines was achieved photocatalytically using chalcogenorosamine photocatalysts and LED irradiation. The photocatalytic aza-Henry reaction between these substrates and nitromethane was more efficient with selenorosamine and tellurorosamine photocatalysts than with thiorosamine and rosamine photocatalysts, corresponding to the propensity of the photocatalysts to generate singlet oxygen (1O2). Appropriately, yields for the photocatalytic aza-Henry reaction were greatly reduced when the reactions were conducted under a nitrogen atmosphere. The 2-aryl-1,2,3,4-tetrahydroisoquinolines were oxidized to the corresponding 2-aryl-3,4-dihydroisoquinolones 13a–13c with selenorosamine and tellurorosamine photocatalysts in 2% aqueous acetonitrile. Di-2-aryl-1,2,3,4-tetrahydroisoquinolin-1-yl peroxides 14a and 14b were shown to be intermediates in this reaction. Thiorosamine photocatalysts, which do generate 1O2 upon irradiation, did not give 2-aryl-3,4-dihydroisoquino...