Azo Bridges from Azines, XIX. Intramolecular \documentclass{article}\pagestyle{empty}\begin{document}$ \left[ {\sigma _{\rm s}^2 + \pi _{\rm s}^2 } \right] $\end{document} Photocycloaddition Reaction of Parallel Three‐Membered Rings with Azo Groups

[3 + 2] Photocycloaddition reaction of three-membered rings with azo groups were accomplished for the first time by photochemically induced π,π* excitation of several systems of the general type CE exemplified by 1, 3, 5, 7, 10, 13, and 17. Intramolecular reaction of the parallel arranged functional groups yields cage compounds FH (2, 4, 6, 8, 11, 14, and 18) in a [σs2 + πs2] process, Systems CE are inert on n,π* excitation in aprotic solvents. In methanol or better 2-propanol, however, the azo groups are reduced from their triplet states. The resulting hydrazino groups, also available by catalytic hydrogenation, open the aziridine rings of 7, 10, and 13 as well as the oxirane ring of 17 by nucleophilic attack, producing the half cages 9, 12, and 19.