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Communication | Special issue | Vol 69, No. 1, 2006, pp.83-89
Published online, 21st July, 2006
DOI: 10.3987/COM-06-S(O)22
Direct Observation of ESR Spectra of Bicyclic Nine-Membered Enediynes at Ambient Temperature

Masahiro Hirama,* Kimio Akiyama,* Parthasarathi Das, Takashi Mita, Martin J. Lear, Kyo-ichiro Iida, Itaru Sato, Fumihiko Yoshimura, Toyonobu Usuki, and Shozo Tero-Kubota

*Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan


The ESR spectra for synthetic bicyclo[7.3.0]epoxydodecadienediynes in solution at room temperature are steady. These spectra originate from the Masamune-Bergman cyclization of bicyclo[7.3.0]epoxydodecadienediynes to p-benzyne biradicals and the equilibrium between the two forms. Comparison of the ESR spectra of the unlabeled and 13C-labeled nine-membered enediynes indicated that the spectra are not directly due to the p-benzyne biradicals but rather to more stable secondary radical intermediates.