Broadband irradiation (λ > 320 nm) of hemicarceplex H1 between −74 °C and −84 °C, produces encapsulated didehydroazepine (2), triplet phenylnitrene (3PN), 2-azabicyclo[3.2.0]hepta-1,3,6-triene (6), and 4-azaspiro[2.4]hepta-1,4,6-triene (7). The highly strained anti-Bredt imine 6 is formed from 2 via a photochemical four-electron electrocyclization. Under the irradiation conditions, 6 rearranges further to azaspirene 7. In addition, 6 thermally rearranges to 7 via a 1,5-sigmatropic shift (ΔG267K = 20.0 ± 0.5 kcal/mol), yielding a final equilibrium composed of [7]/[6] = 5 at room temperature. The observation of a photochemical rearrangement of 2 to 6 contrasts earlier results of narrow band irradiations (λ = 334 nm) of matrix-isolated 2, which gave 3PN (Hayes, J. C.; Sheridan, R. S. J. Am. Chem. Soc. 1990, 112, 5879−5881). Encapsulated 3PN is remarkably stable due to the prevention of its dimerization by the surrounding hemicarcerand. Above 255 K, it slowly decays with a rate constant k = 107.7±0.4 s-1 × exp {(13300 ± 500 cal/mol)/RT}. The isolation of substantial amounts of a hemicarcerand lacking one acetal spanner suggests that 3PN decays preferentially by inserting into an inward-pointing acetal C−H bond of H.
Authors
- dr hab. Sławomir Makowiec link open in new tab ,
- Ralf Warmuth
Additional information
- Category
- Publikacja w czasopiśmie
- Type
- artykuł w czasopiśmie wyróżnionym w JCR
- Language
- angielski
- Publication year
- 2007
