Photoinduced transformations. Part 32. Scrambling of unlabelled and [15N]nitrogen monoxide in the photo-induced rearrangement of (22S,25S)-5α-veratr-13(17)-enin-11β-yl nitrites to nitrones

Abstract

Cross-over experiments with unlabelled nitrite and ¹⁵N-labelled species in the photorearrangement of (22S,25S)-veratr-13(17)-enin-11β-yl nitrites to the corresponding six-membered ring nitrones indicate that nitrogen monoxide generated from the nitrites in toluene or methanol is randomly distributed in the nitrones. A study of the nitrones obtained by irradiation of each of the two nitrites recovered from the cross-over experiment shows that no scrambling of ¹⁴NO and ¹⁵NO in the nitrites had occurred in the original photolysis. The results imply that a discrete allyl radical intermediate is involved in the reaction, and the observed scrambling between ¹⁵NO and ¹⁴NO takes place after collapse of the 11β-oxyl radical.