reacted in the presence of benzoic acid, so as to simulate the
acidity of the catalytic solutions. In this case (Table 3, entry 5),
28% of the recovered phenol was d3 and 9% was d4, showing that
acid conditions can affect the incorporation of D into phenol.
However, this incoproration is still much less than in the presence
of the Pd/BDTBPMB, which gives 37% d3, 46% d4 and small
amounts of d5 and d6 phenol.
Although an increase in D2O increased the amount of deuter-
ation in the product, it also significantly lowered the yield of the
decarboxylation (Table 3, entries 1 and 2). This can be explained
by the instability of the catalyst in the presence of water.13
lower than that required in other catalytic systems such as the
Cu/quinoline system.2 Different phosphines and conditions were
tested, and it can be concluded that highly electron donating
phosphines such as BDTBPMB or PtBu3 are ideal for this reaction.
[Pd(MeCN)4][BF4]2 has also been proven to be an interesting
alternative as the palladium precursor.
Different metal catalysts were tested for the decarboxylation,
and it was found that palladium complexes are significantly more
active that the other metals which were tested.
The addition of D2O to the medium resulted in deuteration of
the aromatic ring. This deuteration has been proven to be mainly
in the position ortho to the hydroxyl group.
Desulfonation
Palladium catalysts have been proven to be active in the
desulfonation reaction by significantly lowering the reaction
temperature and giving high conversion in this reaction.
Desulfonation of aromatic sulfonic acids is a difficult process,
which usually requires sulfuric acid under harsh conditions,14 or
stoichiometric reductive agents such as RANEYꢀ Nickel15 to give
R
good conversion. Hence, the possibility of palladium-catalysed
desulfonation is considered to be a highly attractive route.
Acknowledgements
We thank Lucite International for a studentship (A. A. N. M) and
P. Pogorzelec for his assistance.
Comparing benzoic acid and benzenesulfonic acid, some simi-
larities can be found. Both compounds possess an acidic proton,
and the distance between the ipso carbon and this proton is
two bonds. Thus, it is possible that the results obtained in
the decarboxylation can be extrapolated to desulfonation by
synthesising phenol from 4-hydroxybenzenesulfonic acid (Fig. 5).
Notes and references
1 (a) For example of Murai reaction, see: M. Sonoda, F. Kakiuchi, A.
Kamatani, N. Chatani and S. Murai, Chem. Lett., 1996, 25, 109; (b) S.
Murai, N. Chatani and F. Kakiuchi, 1995, JP07082205; (c) M. Grellier,
L. Vendier, B. Chaudret, A. Albinati, S. Rizzato, S. Mason and S.
Sabo-Etienne, J. Am. Chem. Soc., 2005, 127, 17592; (d) M. Miura, T.
Tsuda, T. Satoh, S. Pivsa-Art and M. Nomura, J. Org. Chem., 1998, 63,
5211; (e) R. H. Crabtree, J. Organomet. Chem., 2004, 689, 4083; (f) Y.
Guari, A. Castellanos, S. Sabo-Etienne and B. Chaudret, J. Mol. Cat.
A. Chem., 2004, 212, 77.
2 (a) T. Cohen and R. A. Schambach, J. Am. Chem. Soc., 1970, 92,
3189; (b) T. Cohen, R. W. Berninger and J. T. Wood, J. Org. Chem.,
1978, 43, 837; (c) A. Cairncross, J. R. Roland, R. M. Henderson and
W. A. Sheppard, J. Am. Chem. Soc., 1970, 92, 3187; (d) L. J. Goosen,
N. Rodriguez, B. Melzer, C. Linder, G. Deng and L. M. Levy, J. Am.
Chem. Soc., 2007, 129, 4824.
3 (a) H. Gilman and G. F. Wright, J. Am. Chem. Soc., 1933, 55, 3302;
(b) G. B. Deacon, M. F. O’Donoghue and G. N. Stretton, J. Organomet.
Chem., 1982, 233, C1.
4 J. S. Dickstein, C. A. Mulrooney, E. M. O’Brien, B. J. Morgan and
M. C. Kozlowski, Org. Lett., 2007, 9, 2441.
5 (a) For some examples of tandem decarboxylative Heck see: A. G.
Myers, D. Tanaka and M. R. Mannion, J. Am. Chem. Soc., 2002, 124,
11250; (b) D. Tanaka, S. P. Romeril and A. G. Myers, J. Am. Chem.
Soc., 2005, 125, 10323; (c) D. Tanaka and A. G. Myers, Org. Lett.,
2004, 6, 433.
Fig. 5 Generation of phenol by extrusion of SO3.
For the initial study, a blank assay was carried out. The substrate
showed certain thermal instability, and the reaction without any
catalyst gave moderate conversion (Table 4, entry 1). The optimum
conditions obtained from decarboxylation were examined. After
5 hours, high conversion was obtained (Table 4, entry 2). The
use of PtBu3 in place of BDTBPMB increased the conversion
(Table 4, entry 3). However, PBz3 did not provide significant
activity (Table 4, entry 4). High conversion was obtained when
[Pd(OAc)2] was replaced by [Pd(MeCN)4][BF4]2 (Table 4, entry 5)
for a reaction using BDTBPMB as the ligand.
In conclusion, systems formed from highly electron rich palla-
dium complexes have been proven to be active in the decarboxyla-
tion of 4-hydroxybenzoic acid. Although the reaction required
high temperatures (~140 ◦C), this temperature is significantly
6 (a) For example of tandem decarboxylative Suzuki see: J. Becht,
C. Catala, C. Le Drian and A. Wagner, Org. Lett., 2007, 9,
1781.
7 C. J. Mathews, P. J. Smith and T. Welton, J. Mol. Cat. A. Chem., 2003,
206, 77.
8 R. Ziessel, Tetrahedron Lett., 1989, 30, 463.
Table 4 Elimination of SO3 from 4-hydroxybenzenesulfonic acida
9 M. Kranenburg, Y. E. M. Van der Burgt, P. C. J. Kamer and P. W. N. M.
Van Leeuwen, Organometallics, 1995, 14, 3081.
10 (a) For BDTBPMB in catalysis, see: W. Clegg, G. R. Eastham, M. R. J.
Elsegood, R. P. Tooze, X. L. Wang and K. Whiston, Chem. Commun.,
1999, 1877; (b) G. R. Eastham, J. M. Thorpe and R. P. Tooze, 1999,
WO09909040; (c) G. R. Eastham, 2004, WO2004024322; (d) G. R.
Eastham, and N. Tindale, 2005, WO2005079981; (e) A. J. Rucklidge,
G. E. Morris and D. J. Cole-Hamilton, Chem. Commun, 2005, 1176;
(f) C. Rodriguez J´ımenez, D. F. Foster, G. R. Eastham and D. J. Cole-
Hamilton, Chem. Commun., 2004, 1720; (g) G. R. Eastham, B. T.
Heaton, J. A. Iggo, R. P. Tooze, R. Whyman and S. Zacchini, Chem.
Commun., 2000, 609; (h) G. R. Eastham, R. P. Tooze, M. Kilner, D. F.
Foster and D. J. Cole-Hamilton, J. Chem. Soc. Dalton Trans., 2002,
1613; (i) W. Clegg, G. R. Eatham, M. R. J. Elsegood, B. T. Heaton,
Entry
Palladium species
Ligand
Yield (%)
1
2
3
4
5
—
—
44
70
83
44
93
[Pd(OAc)2]
[Pd(OAc)2]
[Pd(OAc)2]
[Pd(MeCN)4][BF4]2
BDTBPMB (1 mol%)
PtBu3 (2 mol%)
PBz3 (2 mol%)
BDTBPMB (1 mol%)
a Conditions: 4-hydroxybenzenesulfonic acid (2.9 mL, 14.5 mmol), pal-
ladium precatalyst (0.7 mmol), ligand (as described), toluene (10 mL),
140 ◦C, 5 h.
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