Photoinduced transformations. Part 60. Photoinduced rearrangements of cholesteryl nitrites with monochromatic light

Abstract

Photolysis of cholesteryl nitrite in benzene with monochromatic light (λ 389 nm) gave (E)-4′-azodi-(3,4-secocholest-5-en-3-one)NN′-dioxide (9) which was transformed into N-hydroxy-4-aza-4a-homocholest-5-en 3-one (10) and 3,3-bisisopropoxy-3,4-secocholest-5-en-4-one oxime (20) in isopropyl alcohol under reflux. Photolysis of the dimer (9) with Pyrex-filtered light gave 3,4-secocholest-5-ene-3,4-dione 4-oxime(25). In contrast, irradiation of 4,4-dimethylcholesteryl nitrite (2) in benzene with monochromatic light gave a good yield of 4a,4a-dimethyl-4-aza-4a-homocholest-5-en-3-one (11) without any accompanying nitroso-dimers. These results as evidence that hydroxamic acids [e.g.(10)] obtained from the photolysis of nitrites are formed by thermal cyclization of nitrosointermediates [e.g., (7)].

Although irradiation of the nitrite (2) with Pyrex-filtered light gave a result similar to that with monochromatic light, low yields of the Z-isomer (26) of the nitroso-dimer (9) and 3β(4-oxa-4a-homocholest-5-en-3α-yloxy)cholest-5-ene (27) were isolated from a mixture obtained from the photolysis of cholesteryl nitrite (1) with Pyrexfiltered light. Some notable features in the present results are discussed.