Photochemical and thermal reaction of intermediates in the phenylnitrene rearangment inside a hemicarcerand

Sławomir Makowiec; Ralf Warmuth

Photochemical and thermal reaction of intermediates in the phenylnitrene rearangment inside a hemicarcerand

Abstract

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 (2)

Sławomir Makowiec dr hab.
Ralf Warmuth

Cite as

Full text

full text is not available in portal

full content of the article see on external site open in new tab

Keywords

Details

Category:: Articles
Type:: artykuł w czasopiśmie wyróżnionym w JCR
Published in:: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY no. 129, pages 1233 - 1241,
ISSN: 0002-7863
Language:: English
Publication year:: 2007
Bibliographic description:: Makowiec S., Warmuth R.: Photochemical and thermal reaction of intermediates in the phenylnitrene rearangment inside a hemicarcerand// JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. -Vol. 129, nr. iss. 5 (2007), s.1233-1241
Verified by:: Gdańsk University of Technology