4956
J. Liu et al. / Tetrahedron Letters 46 (2005) 4953–4956
formed zwitterionic intermediates, which appear to be
controlled by fluorine substituents, ultimately deter-
mined the specific position of photoisomerization. We
believe that the current system involving the different
number of polar fluorine substituents further strength-
ens the fact that the polar character of the excited state
has a significant role in directing the position of photo-
isomerization. In addition, the same regioselectivity of
photoisomerization of 1–5 found in different solvents
states crucial substituent effect as compared to solvent
effect.
References and notes
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In summary, we have demonstrated that the selective
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J.L. thanks Kentucky NSF EPSCoR and Howard
Hughes Medical Institution for financial support.
Supplementary data
Spectroscopic data (1H NMR, 13C NMR, and UV) of
new compounds included in the Supplementary data
associated with this article can be found, in the online
21. Liu, J.; Boarman, K. J. Chem. Commun. 2005, 340–341.