S. Yamada et al. / Tetrahedron Letters 51 (2010) 2533–2535
2535
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In conclusion, we have found that r-cct and r-ctc dimers 2 and 3
were directly produced by [2+2] photocycloaddition of (Z)-4-sty-
rylpyridine through a cation–p interaction. A catalytic amount of
3. For reviews, see: (a) Georgiev, I. G.; MacGillivray, L. R. Chem. Soc. Rev. 2007, 36,
1239–1248; (b) MacGillivray, L. R.; Papaefstathiou, G. S.; Frišcic, T.; Hamilton, T.
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Nagarathinam, M.; Peedikakkal, A. M. P.; Vittal, J. J. Chem. Commun. 2008,
5277–5288.
hydrochloric acid plays a key role in the formation of cation–
p
complexes between (Z)-1 and (E)-1, which enables the synthesis
of cis–cis–trans dimers that cannot be obtained by general photo-
cycloaddition reactions.
4. For selected examples, see: (a) Anet, F. A. L. Can. J. Chem. 1962, 40, 1249; (b)
Hammond, G. S.; Stout, C. A.; Lamola, A. A. J. Am. Chem. Soc. 1964, 86, 3103–
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812.
5. Recently, Sakamoto reported that photodimerization of chromone produced a
type C dimer, see: Sakamoto, M.; Kanehiro, M.; Mino, T.; Fujita, T. Chem.
Commun. 2009, 2379–2380.
Acknowledgement
This work was supported by a Grant-in-Aid for Scientific Re-
search (C) (No. 21550097) from the Japan Society for the Promo-
tion of Science.
6. Yamada, S.; Uematsu, N.; Yamashita, K. J. Am. Chem. Soc. 2007, 129, 12100–
12101.
Supplementary data
7. Ma, J. C.; Dougherty, D. A. Chem. Rev. 1997, 97, 1303–1324.
8. For reviews on synthetic applications, see: Yamada, S. J. Syn. Org. Chem. Jpn.
2005, 63, 339–350; Yamada, S. Org. Biomol. Chem. 2007, 5, 2903–2912.
9. (a) Hewlins, M. J. E.; Salter, R. Synthesis 2007, 2164–2174; (b) Lewis, F. D.;
Kalgutkar, R. S.; Yang, J.-S. J. Am. Chem. Soc. 2001, 123, 3878–3884; (c) Galiazzo,
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Cauzzo, G.; Galiazzo, G. Tetrhedron Lett. 1966, 239–242.
Supplementary data (experimental details, 1H NMR spectra of 2
and 3, and single crystal X-ray analysis of 3) associated with this
article can be found, in the online version, at doi:10.1016/
10. r-cct: r-1, c-3-di(4-pyridyl)-c-2, t-4-diphenylcyclobutane; r-ctc: r-1, t-3-di(4-
pyridyl)-c-2, c-4-diphenylcyclobutane.
References and notes
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