Table 2 Hydrolysis of dodecyl thioacetate in water
as deprotection of an aromatic ketal and an acetonide, trans-
thioacetalization of an acetal, and hydration of an epoxide
Scheme 1). It should be noted again that only 1 mol% of the
(
catalyst is sufficient to complete all reactions shown in Table 3
and Scheme 1. Interestingly, the analytically pure product was
obtained quantitatively after the reaction mixture was filtered,
washed with water, and concentrated in the case of the hydra-
tion of the epoxide. This procedure will be extended to a flow
system without the use of any organic solvent.
Ϫ1
Entry
Catalyst
Loading (mmol g
)
Yield (%)
1
2
3
1
2
2
0.46
0.41
0.17
44
82
a
94(96)
a
2
nd use.
Table 3 Deprotection of the ketal derived from 2-octanone
Ϫ1
Entry
Catalyst
Loading (mmol g
)
Yield (%)
a
1
1
1
1
2
2
5
6
4.41
1.55
0.12
1.40
0.17
0.19
0.11
3
17
78
80
96
6
2
3
4
5
6
7
24
a
Commercially available DOWEX 50W-X2 was used as a catalyst.
Scheme 1 LL–ALPS–SO H-catalyzed organic reactions in water.
3
Finally, it was found that LL–ALPS–SO H can also be used
for the hydration of an alkyne as shown in [eqn. (1)]. To the best
has a spacer, was not so effective for the hydrolysis (entry 8). It
is noteworthy that the amphiphilic polymer-supported catalyst
3
5
, which was prepared by sulfonation of a commercially avail-
able TentaGel resin (entry 9), did not catalyze the reaction at
all. Activity of macroporous PS–SO H 6, prepared from a
3
commercially available ArgoPore resin, was also low for this
reaction even if the catalyst was prepared at a low-loading level
(
entry 10). Based on these results, we conclude that the hydro-
(1)
phobic nature of the long alkyl chain is a significant key for the
catalyst to exhibit high activity in water.
We further investigated the effect of the loading of 2, which
was an effective catalyst according to the study of the structural
effects (entries 6, 11–14). It is interesting to note that, although
the reaction proceeded in good yield even using high loading
of our knowledge, this is the first example of the hydration of
an alkyne using a catalytic amount of a Brꢀnsted acid without
a metal salt in pure water.
In conclusion, we have investigated loading levels and struc-
tures of hydrophobic polymer-supported sulfonic acids, and
12
catalysts, 2 showed the same tendency as PS–SO H 1; the lower
found LL–ALPS–SO H to be one of the best catalysts for
3
3
the loading, the higher the catalytic activity. These studies on
both the effects of the loading levels and the structures revealed
several acid-catalyzed organic reactions in pure water. Hydro-
phobicity of the catalyst was suggested to be a key for efficient
catalysis. This concept will be applicable to various types of
catalysts for organic reactions in water.
that a low-loading and alkylated polystylene-supported sulfonic
Ϫ1
acid (LL–ALPS–SO H) such as 2 (0.17 mmol g ) is one of the
3
best catalysts for the hydrolysis in pure water as shown in entry
1
4.
We carried out the hydrolysis of another thioester using LL–
ALPS–SO H to demonstrate the effectiveness of the catalyst
Acknowledgements
This work was partially supported by CREST and SORST,
Japan Science and Technology Corporation (JST), and a
Grant-in-Aid for Scientific Research from Japan Society of the
Promotion of Science.
3
(
Table 2). This also showed remarkable effects of the structures
Ϫ1
and loading levels. To be precise, 2 (0.17 mmol g ) was the
most effective for the hydrolysis of this thioester, and it should
be noted that only 1 mol% of the catalyst is enough to complete
the reaction (entry 3). In addition, the catalyst was easily
recovered after the reactions by simple filtration and washing
with water and ether, and could be reused for the next reaction
without any loss of the catalytic activity.
Notes and references
1
(a) S. V. Ley, I. R. Baxendale, R. N. Bream, P. S. Jackson, A. G.
Laech, D. A. Longbottom, M. Nesi, J. S. Scott, R. I. Storer and S. J.
Taylor, J. Chem. Soc., Perkin Trans. 1, 2000, 3815; (b) S. Kobayashi,
Curr. Opin. Chem. Biol., 2000, 4, 338; (c) C. A. McNamara, M. J.
Dixon and M. Bradley, Chem. Rev., 2002, 102, 3275; (d ) D. E.
Bergbreiter, Chem. Rev., 2002, 102, 3345.
(a) Organic Synthesis in Water, ed. P. A. Grieco, Blackie Academic
and Professional, London, 1998; (b) C.-J. Li and T.-H. Chan,
Organic Reactions in Aqueous Media, John Wiley & Sons, New York,
LL–ALPS–SO H 2 was effective for other organic reactions
3
in water. In the case of the deprotection of the ketal derived
from 2-octanone, 2 (0.17 mmol g ) also showed excellent
catalytic activity compared with various types of catalysts
in water (Table 3). It is noteworthy that the catalytic activity was
much higher than that of commercially available DOWEX
Ϫ1
2
1
997; (c) Aqueous-Phase Organometallic Catalysis. Concepts and
Ϫ1
5
0W-X2 (4.41 mmol g ). Moreover, it was revealed that
Applications, eds. B. Cornils and W. A. Herrmann, Wiley-VCH,
Weinheim, 1998; (d ) U. M. Lindström, Chem. Rev., 2002, 102, 2751;
LL–ALPS–SO H was effective for several other reactions such
3
O r g . B i o m o l . C h e m . , 2 0 0 3 , 1, 2 4 1 6 – 2 4 1 8
2417