On the Photochemistry of 1,2‐Benzisoxazole: Capture of Elusive Spiro‐2H‐azirine and Ketenimine Intermediates
On the Photochemistry of 1,2‐Benzisoxazole: Capture of Elusive Spiro‐2H‐azirine and Ketenimine Intermediates
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1,2-苯并异恶唑的光化学：捕获难以捉摸的螺环-2H-氮丙啶和乙烯亚胺中间体
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发表时间：
2016
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通讯作者：
R. Fausto
中科院分区：
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作者：
Cláudio M. Nunes;S. Pinto;I. Reva;R. Fausto
用低温基质隔离结合红外光谱和量子化学计算研究了1，2-苯并异恶唑(1)的光化学。我们首次确定了螺环-2H-氮杂环丙烷2和酮亚胺3为1-氰基苯酚(4)光异构化反应的中间体。这些结果间接证明了1，2-苯并异恶唑的光化学中存在乙烯基硝基中间体。将1的N-O键断裂所产生的势能面与母体异恶唑的势能面进行了比较。在CBS-QB3水平上的计算表明，当引入一个与异恶唑稠合的苯环时，三重态乙烯基硝烯没有得到稳定。然而，2和3的能量比异恶唑生成的2H-氮杂环和酮亚胺类似物高13-15千卡/摩尔，这解释了以前没有观察到它们的原因。我们的一般机理模型也很好地预测了2和3到4的光致异构化。
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.