T. Xu et al. / Journal of Organometallic Chemistry 696 (2011) 46e49
49
Pd(OAc)2 (5 mol%)
References
Bathocuproine (5.5 mol%)
Ph
n
NHTs
N
BuOH (3 equiv)
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Ts
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Scheme 3. Pd-catalyzed intramolecular hydroamination of styrenes.
In contrast to our previous study on Pd-catalyzed intramolecular
hydroamination of allene coupled with aerobic alcohol oxidation [10],
neither the intramolecular nor intermolecualr hydroamination of
styrene can proceed under aerobic reaction condition (Scheme 3).
These results suggest that the CeN bond formation may undergo
a nucelophilic attack of nitrogen nucleophile to the carbon center of
CePd(IV) intermediate, which is generated from the oxidation of Pd(II)
intermedaite by NFSI (the PdII/IV pathway) [19].
In conclusion, we have developed a novel strategy for the
palladium-catalyzed inter- and intramolecular hydroamination of
styrenes that are coupled to alcohol oxidation under oxidative
condition. This reaction employs a nitrogen-based ligand and NFSI
as the oxidant. Further study on the asymmetric hydroamination of
styrene is in progress.
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In a dried glass tube, Pd(OAc)2 (2.3 mg, 0.01 mmol, 5 mol%),
bathocuproine (0.011 mmol, 5.5 mol%), N-fluorobenzenesulfonimide
(157 mg, 0.5 mmol, 2.5 equivalents) were dissolved in 1,4-dioxane
(2.0 mL), and then styrene 4a (0.2 mmol, 1.0 equivalent) and butanol
(0.6 mmol, 3 equivalents) were added. After the mixture was stirred
at 50 ꢀC for 15 h, the solvent was removed under vacuum. The residue
was purified by column chromatography on silica gel with a gradient
eluant of petroleum ether and ethyl acetate to afford the hydro-
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amination product 5a in 74% yield. 1H NMR (400 MHz, CDCl3)
d 7.71
(bs, 4H), 7.56 (t, J ¼ 7.6 Hz, 2H), 7.46e7.40 (m, 6H), 7.30e7.27 (m, 3H),
5.63 (q, J ¼ 7.6 Hz, 1H), 1.65 (d, J ¼ 7.6 Hz, 3H); 13C NMR (100 MHz,
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Acknowledgement
This work was supported by the Chinese Academy of Science,
the National Natural Science Foundation of China (20821002,
20872155, 20972175 and 20923005), the National Basic Research
Program of China (973-2009CB825300) and STCSM (08PJ1411600
and 08dj1400100) for funding support.
Appendix. Supplementary material
[18]
A
byproduct was obtained, but its structure cannot be characterized
currently.
Supplementary data associated with this article can be found, in
[19] For the oxidation of Pd(II) to Pd(IV) by NFSI, see: P.A. Sibbald, C.F. Rosewall,
R.D. Swartz, F.E. Michael, J. Am. Chem. Soc. 131 (2009) 15945.