Photochemische Reaktionen von Pyrazolidon-(3)-betainen. VI. Substituenteneinfluß auf die Photochemische Diaziridinbildung aus Pyrazolidon-(3)-azomethiniminen

Photochemical Reactions of 3-Pyrazolidone Betains. VI. Influence of Substituents on Photochemical Diaziridine Formation from 3-Pyrazolidone Azomethinimines UV-irradiation of 3-pyrazolidone azomethinimines 1a–g in methanol as a solvent produces 40–92% yields of the corresponding 1-(methoxycarbonylethyl)-3-aryl-diaziridines 3a–g . The formation of these products occurs by ring opening of the bicyclic diaziridines 2a–g primarily formed. Although the bicyclic diaziridines 2h and 2i are formed on UV-irradiation in methanol, the betains 1h and 1i do not yield the corresponding diaziridine esters 3 . Kinetical investigations of the acid catalyzed re-formation of the betaines 1a, c, h , and i from the corresponding bicyclic diaziridines show that the basicity of the diaziridine ring in 2 , influenced by substituents in the phenyl ring, is responsible for the re-formation to 1 and the reaction to 3 , respectively. In contrast to the behaviour of the other betains 1 , compound 1j does not react photochemically to yield the bicyclic diaziridine 2j . This shows that an extension of the 4-electron system of the dipolaric azomethinimine group in 1 is necessary for the photochemical cyclization to diaziridines 2 .