Hui-Lan Yue et al.
COMMUNICATIONS
an alcohol could not be excluded at the present Acknowledgements
stage.[18] Furthermore, the formation of compounds 6a
We are grateful for the financial support from the National
Natural Science Foundation of China (20802072).
and 7a indicated that alkyl cation 5 (Scheme 5) might
be involved in this reaction system.
Based on the above results and previous studies,[18]
we propose possible mechanisms for this coupling re-
action as shown in Scheme 5. One pathway could be a
direct alkylation of alkene 2 with alcohol 1 to gener-
ate alkyl cation 5. Then, the deprotonation of 5 leads
to the formation of the desired product 3. Another
probable pathway is that the starting alcohol 1 is rap-
idly converted to corresponding dimeric ether 4 in the
presence of TfOH. Then, the alkylation of alkene 2
by dimeric ether 4 occurs, affording the desired prod-
uct 3 and releasing the starting alcohol.
References
[1] For reviews, see: a) Metal-Catalyzed Cross-Coupling
Reactions, (Eds.: A. D. Meijere, F. Diederich), Wiley-
VCH, New York, 2004; b) Acid Catalysis in Modern
Organic Synthesis, (Eds.: H. Yamamoto, K. Ishihara),
Wiley-VCH, New York, 2008.
[2] a) H. Tang, K. Menzel, G. C. Fu, Angew. Chem. 2003,
115, 5233–5236; Angew. Chem. Int. Ed. 2003, 42, 5079–
5082; b) J. Zhou, G. C. Fu, J. Am. Chem. Soc. 2003,
125, 12527–12530; c) S. R. Dubbaka, P. Vogel, J. Am.
Chem. Soc. 2003, 125, 15292–15293; d) S. L. Wiskur, A.
Korte, G. C. Fu, J. Am. Chem. Soc. 2004, 126, 82–83;
e) D. A. Powell, T. Maki, G. C. Fu, J. Am. Chem. Soc.
2005, 127, 510–511; f) X. Dai, N. A. Strotman, G. C. Fu,
J. Am. Chem. Soc. 2008, 130, 3302–3303; g) Y. Kobaya-
shi, Y. Tokoro, K. Watatani, Eur. J. Org. Chem. 2000,
3825–3834; h) N. Tsukada, T. Sato, Y. Inoue, Chem.
Commun. 2001, 237–238; i) L. Firmansjah, G. C. Fu, J.
Am. Chem. Soc. 2007, 129, 11340–11341.
In summary, we have successfully developed a con-
3
2
À
venient and efficient method for sp -sp C C bond
formation through the direct coupling of various ben-
zylic alcohols with alkenes by employing a simple
Brønsted acid, TfOH, as catalyst under mild condi-
tions. The present protocol provides an attractive ap-
proach to a diverse range of polysubstituted olefins in
good to excellent yields with high stereo- and regiose-
lectivities. Studies on the detailed mechanism and its
application are ongoing.
[3] Some reports for the coupling of alcohols with metallic
alkenyl nucleophiles, see: a) Y. Nishimoto, M. Kajioka,
T. Saito, M. Yasuda, A. Baba, Chem. Commun. 2008,
6396–6398; b) G. W. Kabalka, M. L. Yao, S. Borella,
Z. Z. Wu, Org. Lett. 2005, 7, 2865–2867.
Experimental Section
General Remarks
[4] For some examples of the Lewis and Brønsted acid-cat-
alyzed direct substitution reaction of alcohols, see:
a) M. Noji, T. Ohno, K. Fuji, N. Futaba, H. Tajima, K.
Ishii, J. Org. Chem. 2003, 68, 9340–9347; b) K. Mertins,
I. Iovel, J. Kischel, A. Zapf, M. Beller, Angew. Chem.
2005, 117, 242–246; Angew. Chem. Int. Ed. 2005, 44,
238–242; c) I. Iovel, K. Mertins, J. Kischel, A. Zapf, M.
Beller, Angew. Chem. 2005, 117, 3981–3985; Angew.
Chem. Int. Ed. 2005, 44, 3913–3917; d) K. Mertins, I.
Iovel, J. Kischel, A. Zapf, M. Beller, Adv. Synth. Catal.
2006, 348, 691–695; e) M. Rueping, B. J. Nachtsheim,
W. Ieawsuwan, Adv. Synth. Catal. 2006, 348, 1033–1037;
f) J. Liu, E. Muth, U. Flçrke, G. Henkel, K. Merz, J.
Sauvageau, E. Schwake, G. Dyker, Adv. Synth. Catal.
2006, 348, 456–462; g) M. Rueping, B. J. Nachtsheim,
A. Kuenkel, Org. Lett. 2007, 9, 825–828; h) R. Sanz, D.
Miguel, A. Martꢂnez, J. M. ꢃlvarez-Gutiꢄrrez, F. Rodrꢂ-
guez, Org. Lett. 2007, 9, 727–730; i) S. Shirakawa, S. Ko-
bayashi, Org. Lett. 2007, 9, 311–314; j) U. Jana, S.
Biswas, S. Maiti, Tetrahedron Lett. 2007, 48, 4065–4069;
k) W. Huang, J. Wang, Q. Shen, X. Zhou, Tetrahedron
Lett. 2007, 48, 3969–3973; l) S. Y. Zhang, Y. Q. Tu, C.
A. Fan, F. M. Zhang, L. Shi, Angew. Chem. 2009, 121,
8917–8921; Angew. Chem. Int. Ed. 2009, 48, 8761–8765;
m) E. Emer, R. Sinisi, M. G. Capdevila, D. Petruzziello,
F. De Vincentiis, P. G. Cozzi, Eur. J. Org. Chem. 2011,
647–666.
All commercially available reagent grade chemicals were
purchased from Aldrich, Acros and Alfa Aesar Chemical
Company. All reagents and solvents were used as received
without further purification unless otherwise stated. NMR
spectra were recorded in CDCl3 on a Bruker Avance 600
1
spectrometer with TMS as internal standard (600 MHz H,
150 MHz 13C) at room temperature, and the chemical shifts
(d) are expressed in ppm and J values are given in Hz. The
following abbreviations are used to indicate the multiplicity:
s (singlet), d (doublet), t (triplet), m (multiplet), br (broad).
Mass analyses and HR-MS were obtained on an Agilent
5973N MSD mass spectrometer and a Waters Micromass
GCT Premier mass spectrometer by the EI method, respec-
tively.
General Procedure for the Direct Coupling of an
Alcohol with an Alkene
To a stirred mixture of alcohol (0.5 mmol) and alkene
(0.6 mmol) in DBE (1 mL) under air, was added the TfOH
(7.5 mol%). The mixture was heated at 608C and stirred for
4–24 h. Upon completion of the reaction, the mixture was
filtered through silica gel and washed with ethyl acetate
(10 mL) to give a brown solution. After filtration, the sol-
vent was removed by vacuum evaporation. The residue was
purified by silica-gel flash column chromatography by using
hexane/ethyl acetate as the eluent. The desired product was
isolated as a white solid, which was suitable for analytical
purposes.
[5] a) N. Tsukada, T. Sato, Y. Inoue, Chem. Commun.
2003, 2404–2405; b) K. Komeyama, Y. Kouya, Y.
Ohama, K. Takaki, Chem. Commun. 2011, 5031–5033.
3144
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2011, 353, 3139 – 3145