PHOTO-OXIDATIVE CYCLISATION OF 2'-HYDROXYCHALCONES LEADING TO FLAVONES INDUCED BY HETEROCYCLE N-OXIDES: HIGH EFFICIENCY OF PYRIMIDOPTERIDINE N-OXIDE FOR THE PHOTOCHEMICAL DEHYDROGENATION

Article abstract of DOI:10.1016/S0040-4020(01)85950-0

Irradiation of 2'-hydroxychalcones (3) with UV-visible light in the presence of heterocycle N-oxides such as pyrimido<5,4-g>pteridine N-oxide (I) results in the formation of the corresponding flavones (4) and flavanones (5).The photooxidative cyclisation of (3) induced by (1) to give (4) most efficiently occurred among the heterocycle N-oxides examined and could be reasonably explained by considering an initial single-electron oxidation of (3) by (1) under the photochemical conditions and subsequent intramolecular cyclisation.