1, 3-DIPOLAR CYCLOADDITIONS OF AZOMETHINE YLIDE WITH ELECTRON-RICH OR NORMAL OLEFINS

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1. Effects of the N-Substituent in Aziridine on the ReactionThe photochemical and thermal reactions of (α, β-unsaturated γ, δ-epimino esters 1 and 2 possessing respectively N-phenyl or N-benzoyl group and olefins were studied. The photoreaction of 1 with acrylonitrile gave the adduct in 45% yield. On the other hand, the thermal reactions of 1 and 2 and the photoreactions of 2 afforded no adduct, but enamines formed via C(γ), O-bong cleavage. The N-substituents conjugated with the aziridine ring tend to cleave the C(γ), O-bong in aziridine.2. Effects of the α-Substituent in the side chain on the ReactionThe reactions of α, β-unsaturated γ, δ-epimino system possessing two electron withdrawing groups in α-position and olefins were investigated. The photoreactions of the dinitrile 3 and the diester 4 and acrylonitrile gave the adducts as obtained before. Furthermore, the novel photocycloadditions of the dinitrile 3 proceeded with isoprene and vinyl acetate successfully.The yields of the acrylonitrile adducts decreased with increasing the electron deficiency in the side chain of aziridine.3. Reactions of Aziridines Possessing Substituent at 3-PositionIn order to clarify the reaction mechanism, the reactions of 3-methyl and 3-phenyl substituted aziridines 5 and 6 and olefins were performed. The photochemical and thermal reaction of 5 shows that the ring-opening of aziridine and cycloaddition with olefins did not proceed concertedly. On the other hand, on the photochemical and thermal reactions the aziridine 6 underwent ring-opening and cycloaddition concertedly leading to adducts. The 3-p-cyanophenyl (more electron deficient substituent) aziridine did not react with isoprene and vinyl acetate.The aziridines 5 and 6 react with molecular oxygen photochemically affording the dioxazolidine and its decomposed compounds. The results may suggest that the reaction intermediate possesses biradical character.