Aryl Nitrene Rearrangements: Spectroscopic Observation of a Benzazirine and Its Ring Expansion to a Ketenimine by Heavy-Atom Tunneling

In the photodecompositions of 4-methoxyphenyl azide (1) and 4-methylthiophenyl azide (5) in argon matrixes at cryogenic temperatures, benzazirine intermediates were identified on the basis of IR spectra. As expected, the benzazirines photochemically rearranged to the corresponding ketenimines and tr...

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Bibliographic Details
Published in:Journal of the American Chemical Society 2013-07, Vol.135 (28), p.10246-10249
Main Authors: Inui, Hiroshi, Sawada, Kazuhiro, Oishi, Shigero, Ushida, Kiminori, McMahon, Robert J
Format: Article
Language:English
Subjects:
Aziridines - chemistry
Ketones - chemistry
Molecular Structure
Quantum Theory
Spectrophotometry, Infrared
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Summary:In the photodecompositions of 4-methoxyphenyl azide (1) and 4-methylthiophenyl azide (5) in argon matrixes at cryogenic temperatures, benzazirine intermediates were identified on the basis of IR spectra. As expected, the benzazirines photochemically rearranged to the corresponding ketenimines and triplet nitrenes. Interestingly, with the methylthio substituent, the rearrangement of benzazirine 8 to ketenimine 7 occurred at 1.49 × 10–5 s–1 even in the dark at 10 K, despite a computed activation barrier of 3.4 kcal mol–1. Because this rate is 1057 times higher than that calculated for passing over the barrier and because it shows no temperature dependence, the rearrangement mechanism is interpreted in terms of heavy-atom tunneling.
ISSN:0002-7863
1520-5126
DOI:10.1021/ja404172s