Non-sensitized photooxygenation of some steroidal isoxazolidines
摘要:
UV irradiation of the steroidal isoxazolidines 2a, 2b, and 2c in various solvents in the presence of molecular oxygen, results in oxidative cleavage of the epoxyimino bridge to give several products; the N--unsubstituted isoxazolidine 2a afforded the nitro products 3, 4, and 5 and the azoxy compounds 6 and 7, while the N-methyl and N-acetyl derivatives 2b and 2c produced only the nitro compounds 3 and 5 as sole identifiable material. An explanation of the observed photooxygenation processes involving exciplex formation followed by proton transfer from isoxazolidine to molecular oxygen is presented.