4258
G. Lu et al. / Tetrahedron Letters 46 (2005) 4255–4259
Pd0
nistic study, details about the isolation and determina-
Ar Ar' (yield 25%)
Ar Br
IIPd
tion of the two by-products, benzene and PhB(OH)2,
were also given. Supplementary data associated with
this article can be found, in the online version, at
Ar
Br
Ar
1
IIPd
Ar'
References and notes
Ar'3B
Ar'4BNa
1. For general reviews, see: (a) Miyaura, N.; Suzuki, A.
Chem. Rev. 1995, 95, 2457–2483; (b) Suzuki, A. In Metal-
catalyzed Cross-coupling Reactions; Diederich, F., Stang,
P. J., Eds.; Wiley-VCH: Weinheim, 1998; vol. 1, pp 49–97;
(c) Suzuki, A. J. Organomet. Chem. 1999, 576, 147–168;
(d) Chemler, S. R.; Trauner, D.; Danishefsky, S. J. Angew.
Chem., Int. Ed. 2001, 40, 4544–4568; (e) Hassan, J.;
0.25 equiv OH−
Ar Ar' (yield 25%)
Ar Ar' (yield 25%)
Ar Ar' (yield 25%)
2
Ar'2B(OH)
0.25 equiv OH−
3
Ar'B(OH)2
4
´
Sevignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M. Chem.
Rev. 2002, 102, 1359–1469; (f) Kotha, S.; Lahiri, K.;
Kashinath, D. Tetrahedron 2002, 58, 9633–9695.
0.25 equiv OH−
2. For ligandless palladium catalyst system for the Suzuki
reaction, see: (a) Reetz, M. T.; Westermann, E. Angew.
Chem., Int. Ed. 2000, 39, 165–168; (b) Kabalka, G. W.;
Namboodiri, V.; Wang, L. Chem. Commun. 2001, 775; (c)
Ma, D. W.; Wu, Q. Q. Tetrahedron Lett. 2001, 42, 5279–
5281; (d) Molander, G. A.; Biolatto, B. Org. Lett. 2002, 4,
1867–1870; (e) Leadbeater, N. E.; Marco, M. J. Org.
Chem. 2003, 68, 888–892; (f) Zhu, L.; Duquette, J.; Zhang,
M. B. J. Org. Chem. 2003, 68, 3729–3732; (g) Deveau, A.
M.; Macdonald, T. L. Tetrahedron Lett. 2004, 45, 803–
807; (h) Tao, X. C.; Zhao, Y. Y.; Shen, D. Synlett 2004,
359–361.
3. For Pd/C as a phosphine-free catalyst for the Suzuki
reaction, see: (a) Marck, G.; Villiger, A.; Buchecker, R.
Tetrahedron Lett. 1994, 35, 3277–3280; (b) Gala, D.;
Stamford, A.; Jenkins, J.; Kugelman, M. Org. Process Res.
Dev. 1997, 1, 163–164; (c) Ennis, D. S.; McManus, J.;
Wood-Kaczmar, W.; Richardson, J.; Smith, G. E.; Car-
stairs, A. Org. Process Res. Dev. 1999, 3, 248–252; (d)
McClure, M. S.; Roschangar, F.; Hodson, S. J.; Millar,
A.; Osterhout, M. H. Synthesis 2001, 11, 1681–1685; (e)
LeBlond, C. R.; Andrews, A. T.; Sun, Y.; Sowa, J. R., Jr.
Org. Lett. 2001, 3, 1555–1557; (f) Dyer, U. C.; Shapland,
P. D.; Tiffin, P. D. Tetrahedron Lett. 2001, 42, 1765–1767;
(g) Sakurai, H.; Tsukuda, T.; Hirao, T. J. Org. Chem.
2002, 67, 2721–2722; (h) Heidenreich, R. G.; Kohler, K.;
Krauter, J. G. E.; Pietsch, J. Synlett 2002, 1118–1122; (i)
Organ, M. G.; Mayer, S. J. Comb. Chem. 2003, 5, 118–
124; (j) Conlon, D. A.; Pipik, B.; Ferdinand, S.; LeBlond,
C. R.; Sowa, J. R., Jr.; Izzo, B.; Collins, P.; Ho, G. J.;
Williams, J. M.; Shi, Y. J.; Sun, Y. Adv. Synth. Catal.
2003, 345, 931–935; (k) Arcadi, A.; Cerichelli, G.; Chia-
rini, M.; Correa, M.; Zorzan, D. Eur. J. Org. Chem. 2003,
20, 4080–4086.
B(OH)3
0.75 equiv base, 100% yield theoretically
Scheme 1. Proposed mechanism of Pd/C-catalyzed cross-coupling of
aryl bromide with sodium tetraarylborate.
part in the next catalytic cycle in the presence of base.
Totally, 0.25 equiv Ar04BNa and 0.75 equiv base are
needed and nearly 100% product is formed after four cat-
alytic cycles. Unfortunately, we could not directly detect
Ph3B and Ph2B(OH) during the reaction due to their
instability when Ph4BNa was used. Barnes and co-work-
ers10 have, on the other hand, studied the kinetic decom-
position of Ph4BNa, Ph3B and Ph2B(OH) catalyzed by
copper in aqueous alkaline solutions. We also noticed
that when insufficient amount of base was used, benzene
and phenylboronic acid, generated by the decomposition
of phenylborate species in the mixture, could be detected.
In summary, we would like to report a novel Pd/C-cata-
lyzed, ligandless Suzuki reaction in water by using
tetraarylborates. The reaction proceeds in excellent yield
particularly in the presence of sodium hydroxide or car-
bonate, etc. Based upon the results found in the coupling
of 6-bromo-2-naphthoic acid and 4-bromophenol with
Ph4BNa in the presence of different amounts of base,
we would like to first report a concise mechanism consist-
ing of four catalytic cycles for the reaction. This mild and
environmental friendly reaction is suitable for the prepa-
ration of various biaryl carboxylic acids or phenols.
4. (a) Ciattini, P. G.; Morera, E.; Ortar, G. Tetrahedron Lett.
1992, 33, 4815–4818; (b) Villemin, D.; Go¨mez-Escalonilla,
M. J.; Saint-Clair, J. F. Tetrahedron Lett. 2001, 42, 635–
637; (c) Leadbeater, N. E.; Marco, M. J. Org. Chem. 2003,
68, 5660–5667; (d) Wang, J. X.; Yang, Y. H.; Wei, B. G.
Synth. Commun. 2004, 34, 2063–2069.
Acknowledgements
We are grateful to Liaoning Natural Science Found-
ation of China for the Talent Doctors Fund
(No. 20041037) and Magnus Ehrnrooths Foundation
of Finland for the financial support.
5. Bumagin, N. A.; Bykov, V. V. Tetrahedron 1997, 53,
14437–14450.
6. It was very difficult to get the isolated yields due to the
similar Rf values of all aryl bromides and the coupling
products on TLC plates. In order to obtain pure products
by recrystallization or flash chromatography as standards
for HPLC analyses, we should first carry out the reactions
to completion using a sufficient amount of catalyst. Typical
procedure: a 50 mL flask equipped with a stirring bar and a
Supplementary data
General experimental procedures and characterization
of all coupling products were depicted. For the mecha-