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- Title
Concurrent Radical Addition and [3+2] Cycloaddition between Nitrones and Maleimide‐Based Acyclic Enediynes.
- Authors
Li, Jing; Zhang, Mengsi; Huang, Shuai; Ding, Yun; Hu, Aiguo
- Abstract
Enediyne compounds undergo Bergman cyclization while being activated with thermal or UV‐light triggers, and generate benzyne diradical intermediates, endowing their great potential as antitumor agents. The radical nature of the Bergman cyclization is generally confirmed through radical trapping experiments. While using phenyl tert‐butyl nitrone (PBN) as a radical trapping agent to study the Bergman cyclization of maleimide‐based enediyne compounds, we uncovered concurrent radical addition and [3+2] cycloaddition reactions between nitrones and enediyne compounds. The radical addition between the diradical intermediates and PBN was revealed through EPR analysis, while the [3+2] cycloaddition products were separated out and their structures were confirmed by NMR, HRMS and single crystal XRD analysis. Computational investigations showed that the energy barrier of the [3+2] cycloaddition was much lower than that of the Bergman reaction, corroborating the dominance of [3+2] cycloaddition between nitrone and enediyne compounds. Running around in cycles: When treated a series of enediyne compounds with excess PBN in different solvents, the results turned out to be very surprising! An unexpected [3+2] cycloaddition reaction between maleimide‐based acyclic enediyne compounds and PBN concurrent with Bergman cyclization. According to theoretical calculations, the [3+2] cycloaddition is kinetically more favored over Bergman cyclization.
- Subjects
NITRONES; MALEIMIDES; ENEDIYNES
- Publication
Asian Journal of Organic Chemistry, 2018, Vol 7, Issue 10, p2076
- ISSN
2193-5807
- Publication type
Article
- DOI
10.1002/ajoc.201800408