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Self‐Sensitized Photooxygenation of a C 60 –Cycloheptatriene Dyad to Form Norcaradiene‐Derived Endoperoxides
Author(s) -
Hanamura Masaaki,
Kamada Jun,
Amano Akiyo,
Takeuchi Ken'ichi,
Okazaki Takao,
Hirai Katsuyuki,
Kitagawa Toshikazu
Publication year - 2010
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200901453
Subject(s) - cycloheptatriene , chemistry , cycloaddition , singlet oxygen , photooxygenation , photochemistry , isomerization , dabco , octane , singlet state , tautomer , medicinal chemistry , stereochemistry , oxygen , organic chemistry , excited state , catalysis , physics , nuclear physics
The [60]fullerene–cycloheptatriene dyad 1 readily underwent [4+2] cycloaddition of molecular oxygen at the cycloheptatriene moiety to give endoperoxides 5 ‐ exo and 5 ‐ endo . The involvement of singlet oxygen was verified by the complete inhibition of oxygenation on addition of 1,4‐diazabicyclo[2.2.2]octane (DABCO), which is an efficient singlet‐oxygen quencher. The observed facile oxygenation was attributed to both the strong photosensitizing ability of the fullerene cage and to the valence isomerization of 1 to the norcaradiene form, which was facilitated by the bulky tert ‐butyl groups. Competitive oxygenation of 1 and a related cycloheptatriene lacking the fullerenyl group ( 2 ) resulted in the formation of endoperoxides of the two molecules in comparable yields. This result demonstrates that the cycloaddition is not an in‐cage reaction but occurs after the singlet oxygen has diffused from the solvent cage.