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 NâO 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 13â15 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.
|Titolo:||On the Photochemistry of 1,2-Benzisoxazole: Capture of Elusive Spiro-2H-azirine and Ketenimine Intermediates|
|Data di pubblicazione:||2016|
|Parole Chiave:||Ab initio calculations; Benzisoxazole; Matrix isolation; Photochemistry; Reactive intermediates; Physical and Theoretical Chemistry; Organic Chemistry|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1002/ejoc.201600668|
|Appare nelle tipologie:||1.1 Articolo in rivista|