Photo-oxidative cyclisation of 2'-hydroxychalcones leading to flavones induced by heterocycle -oxides : high efficiency of pybimido[54-]pteridine -oxide for the photochemical dehydrogenation
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 (1) 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
A novel example of thermal oxygenation of aromatic hydrocarbons with a heterocyclic N-oxide: unusual reactivity of pyrimido(5,4-g)pteridinetetrone 10-oxide.
Aromatic hydrocarbons, i.e., benzene, naphthalene (4), phenanthrene (6), toluene (19), p-xylene (14), mesitylene (18), and durene (21), were oxygenated by a member of a novel class of heterocyclic N-oxides, 1, 3, 6, 8-tetrabutyl-pyrimido[5, 4-g]pteridine-2, 4, 5, 7(1H, 3H, 6H, 8H)-tetrone 10-oxide (1), under certain thermal conditions to give the corresponding products oxygenated in either the benzene ring or the methyl group, presumably via a single-electron transfer process.
Distinct Solvent-Dependence in the Photoreactions of Purine Nucleosides with Pyrimido[5,4-g]pteridinetetrone N-Oxide: Possible Generatiion of Hydroxyl Radical from the Excited N-Oxide in Alcohols
Photoreaction of 2',3',5'-tri-O-acetyladenosine (5) with pyrimido[5,4-g]pteridinetetrone N-oxide (1) in acetonitrile gave N6-cyanomethyl-2',3',5'-tri-O-acetyladenosine (6) as a major detectable product via coupling of adenosyl radical with cyanomethyl radical generated by the mediation of 1. Under the analogous conditions, N2-benzoyl-2',3',5'-tri-O-acetylguanosine (8) underwent oxidative degradation of the guanine skeleton by 1. In sharp contrast, photoreactions of 5 and 8 with 1 in tert-butanol resulted in the formation of the corresponding 8-hydroxypurine nucleosides (7) and (9), respectively. These facts and other observations suggest that 1 could generate hydroxyl radical upon irradiation in alcohols.
Efficient oxygen-atom transfer agent: photochemical hydroxylation of benzene derivatives by pyrimido[5,4- ]pteridine -oxide