On the Photochemistry of 1,2-Benzisoxazole: Capture of Elusive Spiro-2H-azirine and Ketenimine Intermediates

Nunes C. M., Pinto S. M. V., Reva I., Fausto R.

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, vol.2016, no.24, pp.4152-4158, 2016 (SCI-Expanded) identifier identifier

  • Publication Type: Article / Article
  • Volume: 2016 Issue: 24
  • Publication Date: 2016
  • Doi Number: 10.1002/ejoc.201600668
  • Journal Name: EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.4152-4158
  • Istanbul Kültür University Affiliated: Yes

Abstract

The photochemistry of 1,2-benzisoxazole (1) was studied using low-temperature matrix isolation coupled with infrared spectroscopy and quantum chemistry calculations. We identified, for the first time, spiro-2H-azirine 2 and ketenimine 3 as intermediates in the photoisomerization of 1 to 2-cyanophenol (4). These results constitute indirect evidence for the existence of vinylnitrene intermediates in the photochemistry of 1,2-benzisoxazoles. The potential energy surface (PES) resulting from the N-O bond cleavage of 1 was compared with the respective PES of the parent isoxazole. Calculations at the CBS-QB3 level show that no stabilization is gained for the triplet vinylnitrene upon introduction of a benzene ring fused with isoxazole. However, the energies of 2 and 3 are higher by 13-15 kcal/mol comparing with the 2H-azirine and ketenimine analogs resulting from isoxazole, which explains why they had not been observed before. Our general mechanistic proposal also predicts well the photoisomerizations of 2 and 3 to 4.