A. Yu et al. / Tetrahedron Letters 49 (2008) 5405–5407
5407
product) under mild conditions. Benzaldehyde derivatives with
electron-withdrawing groups gave good to excellent yields of
benzhydrol derivatives (Table 2, entries 4–11). The efficiency of
the protocol proved to have a noteworthy tolerance to functional
groups. Incorporation of an ortho-methyl substituents on the
aldehydes had no effect on the reaction yield. Interestingly, in
contrast to other reaction conditions, electron-donating group at
the ortho position of the aryl aldehyde gave nearly quantitative
yield, using KFꢀ2H2O as the additive (Table 2, entry 2). Pentanal
and several other aliphatic aldehydes were also tested but gave
no conversion (Table 2, entry 12). The lower electrophilicity of
the aliphatic aldehydes likely accounted for the results.12 A con-
trasting electronic effect was also observed when substituted aryl-
boronic acids were used. Electron-rich phenylboronic acids gave
excellent yields of coupling product, even though in the presence
of steric hindrance (Table 2, entries 13–17). Incorporation of other
catalytic systems, electron-deficient arylboronic acids, could also
give moderate to good yields (Table 2, entries 18–20). In contrast
cat. 2, the methodology proved to have less efficiency for cat. 3,
and most yields obtained were not satisfactory. These results imply
that the ligand 2-20-bipyridine plays a more crucial role in this
reaction.
Zhengzhou University (No. 000000533011) for financial support.
We thank Dr. Weiguo Zhu and Mr. Jianxun Kang for their excellent
analytical support.
References and notes
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In summary, we have developed a highly efficient and environ-
mentally friendly procedure for aryl transfer reactions to arylalde-
hyde by cyclopalladated ferrocenylimine bipyridine complex 2.
Significantly most of the products were obtained with good to
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substituents in the molecules of the substrates.
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Acknowledgments
We thank the National Science Foundation of China (Nos.
20472074 and 20772114), the Innovation Fund for Outstanding
Scholar of Henan Province (No. 0621001100) and Fund of