Thermal stability of cis-oxidiaziridines. An example of anchimerically assisted ring opening.

Squillacote, Michael E.; Bergman, Adelle; Felippis, James De

doi:10.1016/s0040-4039(00)95705-8

Cited by 4 publications

References 11 publications

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Proximate,syn-Periplanar, Rigid Imine(Nitrone)/Ene-, and Diazene(Diazeneoxy)/Ene Systems: Syntheses, Homoconjugate Reactivity and Photochemistry

Fischer¹,

Fritz

Rihs

et al. 2000

Eur. J. Org. Chem.

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The chances for intramolecular imine/ene (→ azetidines), diazene/ene (→ 1,2‐diazetidines), diazeneoxy/ene (→ 1,2‐diazetidine oxides) and diazenedioxiene (→ 1,2‐diazetidine dioxides) [2+2]photocycloadditions and for the isolation of the respective photoproducts, have been probed with specifically designed substrates. Upon direct or sensitized excitation, [2+2]cycloaddition was found to be the exclusive or at least dominant chemical process for the CN/CC, NN/CC and ONN(O)/CC systems featuring very small π,π‐distances of 2.8‐3.0 Å and large π,π‐interorbital angles of 160‐170° (7 → 51, 17 → 55, 33 → 58 (competing N2 elimination), 22 → 62). This is not the case, however, in ONNO/CC (23, where electron transfer is a possibility), or in the more flexible, less “proximate” CN/CN (57) and CNO/CN (63) systems (π,π‐distances of >3.8 Å). While the corseted 1,2‐diazetidine photoadducts (55, 58) proved to be thermally stable, their N‐oxides (62, 65) were thermally too labile to be directly observable above ‐65 °C. For the latter's only fleeting existence, electronic rather than strain effects are held responsible (B3LYP/6‐31G* calculations). Very facile CNO/CC (12 → 13) and NNO/CC (22 → 24) [3+2]cycloadditions, homoconjugate addition of H2 and of dienophiles ([2+2+2]) to the diazene/ene 17 (→ 39, 41, 45) are manifestations of “proximity” in these bichromophoric skeletons.

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