Communication
phenylmaleimide (PMI), and cyclohexene were unsuccessful,
probably due to the facile intramolecular processes in 5.
Conclusions
In conclusion, we synthesized and characterized 1,3-bis(trimeth-
ylsilyl)-2,3-dihydro-1H-naphtho[1,8-cd]borinines (3). Oxidation
of 3 with DDQ upon heating afforded acenaphthylene, which
indicates the generation of the desired B-heterocyclic singlet
biradical species (5). Because of the instability of 5, the harsh
oxidation step to remove the silyl groups should be replaced.
Another approach is introducing suitable substituents into the
naphthalene moiety. Further efforts to capture the B-hetero-
cyclic singlet biradicals and confirm the reaction mechanism
CCDC 1542485 (for 3a) contains the supplementary crystallographic
Figure 4. LUMO of the optimized structure for 3a at the M06-2X/6-31G(d)
level.
Acknowledgments
dianionic intermediate leading to the desired biradical was not
achieved. Thus, we examined one-electron processes that This work was supported in part by the Ministry of Education,
would remove dihydrogen from 3. Although chloranils gave Culture, Sports, Science and Technology, Japan though Grants-
complex mixtures, we found that heating of 3 with DDQ af- in-Aid for Scientific Research [Nos. JP25288033 and JP15H00923
forded acenaphthylene together with recovery of the starting (Stimuli-responsive Chemical Species for the Creation of Func-
materials (Scheme 4).
tional Molecules, No. 2408)], by the Collaborative Research Pro-
gram of Institute for Chemical Research, Kyoto University (grant
#
2015-23), and Nissan Chemicals Co. Ltd. The authors thank
Prof. Dr. Toshiro Takao of Tokyo Institute of Technology for sup-
ports of X-ray crystallographic analysis.
Keywords: Boron · Heterocycles · Conjugation · Radicals ·
Oxidation
[
[
[
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electron oxidation of bis[(trimethylsilyl)methyl]amine.
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–
·
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which may give acenaphthylene through thermolysis. In con-
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Eur. J. Inorg. Chem. 2017, 2936–2939
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