M. Guo et al. / Tetrahedron Letters 46 (2005) 9017–9020
9019
Table 2 (continued)
Entry
12
ArBr
Ar0B(OH)2
B(OH)2
Producta
Timeb
15
Yieldc(%)
96
H3CO
H3CO
H3CO
H3C
Br
H3CO
13
14
15
9
8
98
Br
F
B(OH)2
B(OH)2
B(OH)2
H3CO
H3CO
H3C
F
96
Br
Cl
H3C
H3C
CH3
12.5
21d
CH3
F
F
F
16
17
5
96
C3H7
Br
Br
C3H7
C3H7
F
F
(HO)2B
(HO)2B
5
95
C3H7
F
a Reaction conditions: 1.0 mmol of aryl bromide, 1.5 mmol of aryl boronic acid, 3.0 mmol of K3PO4Æ3H2O (dissolved in 2.0 mL H2O), 2 (0.01 mmol),
THF (2.0 mL).
b Reaction time not optimized.
c Isolated yield.
d The reaction was performed in DMF at 100 ꢁC.
such as 4-bromoanisole, also gave good yield at the
same temperature for 8–15 h14 (Table 2, entries 12–14).
The bromide containing ortho substituent also reacted
effectively to prepare the desired sterically demanding
biaryl products at room temperature for 5–9 h in moder-
ate to good yields (Table 2, entries 9–11). The incon-
spicuousness difference was observed in yield and the
reaction time, while the varying aryl boronic acids were
used in the Suzuki cross-coupling reactions. In addi-
tion, liquid crystal compounds with the construction
of C2SP–CS2P bonds, for example, 4-fluoro-(40-propyl-
cyclohexyl) biphenyl and 3,4-difluoro-(40-propyl-
cyclohexyl) biphenyl, can be synthesized by this
reaction to give excellent yield at room temperature
for 5 h (Table 2, entries 16–17). However, if these proce-
dures were catalyzed by triarylphosphane-based sys-
tems, it will require elevated reaction temperatures
(usually 50–100 ꢁC).5c Only with reactions involving aryl
chloride are low conversions achieved even at higher
reaction temperature, giving biaryls in 21% yield after
12.5 h in DMF at 100 ꢁC (Table 2, entry 15).
Acknowledgement
We gratefully acknowledge financial support of this
work by the National Natural Science Foundation of
China (Grants 20333060).
References and notes
1. Szmant, H. H. Organic Building Blocks for the Chemical
Industry; John Wiley & Sons: New York, 1989.
2. (a) Nicolaou, K. C.; Boddy, C. N. C.; Brase, S.;
Winssinger, N. Angew. Chem., Int. Ed. 1999, 38, 2096;
(b) Wang, X.; Snieckus, V. Tetrahedron Lett. 1991, 32,
1879; (c) Siddiqui, M. A.; Snieckus, V. Tetrahedron Lett.
1990, 31, 1523; (d) Kelly, T. R.; Garcia, A.; Lang, F.;
Walsh, J. J.; Bhaskar, K. V.; Boyd, M. R.; Go¨tz, R.;
Keller, P. A.; Walter, R.; Bringmann, G. Tetrahedron Lett.
1994, 35, 7621.
3. (a) Hird, M.; Gray, G. W.; Toyne, K. J. Mol. Cryst. Liq.
Cryst. 1991, 206, 187; (b) Kim, Y. H.; Webster, O. W. J.
Am. Chem. Soc. 1990, 112, 4592; (c) Wallow, T. I.; Novak,
B. M. J. Am. Chem. Soc. 1991, 113, 7411; (d) Lamba, J. J.
S.; Tour, J. M. J. Am. Chem. Soc. 1994, 116, 11723.
4. Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun.
1981, 11, 513.
In conclusion, we demonstrated that alkoxo-palla-
dium(II) complexes, [Pd(Ph2PCH2CH2O)2]
1
and
[Pd(Ph2PCH2CH(CH3)O)2] 2, are excellent air-stable
catalysts for general Suzuki cross-coupling reactions of
arylboronic acids and aryl bromides. All reactions
process in short times and at mild temperatures. These
complexes are ideal catalysts for the coupling of deacti-
vated and sterically hindered aryl bromides as they are
comparatively inexpensive, very easily synthesized and
can be used to give high conversions at low temperature.
To our knowledge, there have been only a few reports
on efficient Suzuki cross-coupling reactions of aryl bro-
mides at room temperature.5c,b,6b,15 Further investiga-
tions focusing on mechanistic aspects in related cross-
coupling reactions are ongoing in our laboratories.
5. (a) Littke, A. F.; Dai, C.; Fu, G. C. J. Am. Chem. Soc.
2000, 122, 4020; (b) Wolfe, J. P.; Singer, R. A.; Yang, B.
H.; Buchwald, S. L. J. Am. Chem. Soc. 1999, 121, 9550; (c)
Wolfe, J. P.; Buchwald, S. L. Angew. Chem., Int. Ed. 1999,
38, 2413; (d) Bei, X.; Turner, H. W.; Weinberg, W. H.;
Guram, A. S.; Petersen, J. L. J. Org. Chem. 1999, 64,
6797.
6. (a) Griffiths, C.; Leadbeater, N. E. Tetrahedron Lett. 2000,
41, 2487; (b) Albisson, D. A.; Bedford, R. B.; Lawrence, S.
E.; Scully, P. N. Chem. Commun. 1998, 2095; (c) Zapf, A.;
Beller, M. Chem. Eur. J. 2000, 6, 1830.
7. (a) Grasa, G. A.; Viciu, M. S.; Huang, J.; Zhang, C.;
Trudell, M. L.; Nolan, S. P. Organometallics 2002, 21,
2866; (b) Bo¨hm, V. P. W.; Gsto¨ttmayr, C. W. K.;