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Chemistry Letters Vol.36, No.5 (2007)
Efficient Preparation of vic-Diacetates from Epoxides and Acetic Anhydride
in the Presence of Iron(III)-substituted Polyoxometalate as Catalyst
Bahram Yadollahià and Farhad Kabiri Esfahani
Institute for Advanced Studies in Basic Sciences (IASBS), Gava Zang, Zanjan 45138-79368, Iran
(Received February 20, 2007; CL-070191; E-mail: yadollahi@iasbs.ac.ir)
.
Iron(III)-substituted polyoxometalate (TBA)4PFeW11O39
At first, we examined the reaction of phenyl glycidyl ether
3H2O, has been demonstrated as an efficient catalyst in the ring
opening of 1,2-epoxides with acetic anhydride for the one-pot
synthesis of 1,2-diol esters in high to excellent yields under
solvent-free condition.
(1 mmol) with acetic anhydride (net solvent) using catalytic
amounts of various polyoxometalate complexes at 100 ꢀC
temperature to give the corresponding 1,2-diol esters. Although
the reaction without a catalyst gave no product (below 3%), it
proceeded catalytically upon addition of transition metal-substi-
tuted polyoxometalates. Among the catalysts tested, FeIII-
.
Because of their ease of formation and wide reactivity with
nucleophiles, Lewis acids, radicals, reducing agents, oxidizing
agents, acids, and bases, epoxides are often used as starting
material and intermediates in organic synthesis.1 The opening
of epoxides to the corresponding alcohols is one of the most
useful reactions in organic synthesis,2 and O-acetylation of
hydroxy group is one of the most important and widely used
transformations in organic chemistry,3 especially in the con-
straction of polyfunctional molecules such as nucleosides,
carbohydrates, steroids, and natural products as a protection
strategy.4 Thus, it is very important if we have epoxide which
opens to yield corresponding 1,2-diol diacetate selectively, and
for example if we need to 1,2-diol, this 1,2-diol diacetate can
be hydrolyzed and used in other synthesis procedures.
As a part of our continued effort to explore unique reactivity
of polyoxometalates,5 we try to use from transition metal-substi-
tuted polyoxometalates as catalyst in the ring-opening reaction
of 1,2-epoxides with acetic anhydride. Transition metal-substi-
tuted polyoxometalates as oxidatively stable inorganic porphy-
rins have received much attention in the preceding two decades.6
The versatility of these catalysts has also been demonstrated by
applications in various oxidation reactions. The possibility of
working with these polyoxometalates in both polar and nonpolar
solvents can lead to valuable applications in catalysis. However,
there has been very little exploitation of their catalytic reactivity
in nucleophilic ring-opening of epoxides.7
substituted polyoxometalate, (TBA)4PFeW11O39 3H2O was
found to be highly active for the reaction (99%). The
catalytic activity for other transition metal-substituted polyoxo-
metalates, after 3 h reaction appears to be in the following order:
.
.
(TBA)5PW11MnO39 3H2O
(93%) > (TBA)5PW11CoO39
.
3H2O (78%) ꢁ (TBA)4PW11VO40 3H2O (78%) > (TBA)5-
.
PW11ZnO39 3H2O (57%) > (TBA)4PW11CrO39 3H2O (50%)
> (TBA)5PW11CuO39 3H2O
.
.
.
(30%) > (TBA)5PW11NiO39
.
3H2O (20%) > (TBA)5H2PW11O39 3H2O (5%).
After studied the various amount of the catalyst, we found
that the 0.05 equiv. from (TBA)4PFeW11O39 3H2O is the best,
and the synthesis of 1,2-diol diacetate was efficiently achieved
under this condition. To show the scope of the reaction, we
extended it to a variety of epoxides, and in all cases a very clean
reaction was observed. Thus 1,2-epoxides (1 mmol) were treated
with acetic anhydride (2 mL) in the presence of (TBA)4PFeW11-
.
ꢀ
.
O39 3H2O (5 mol %) at 100 C temperature (Scheme 1), and
after appropriate time gave the corresponding 1,2-diol diacetate
in high to excellent yields (Table 1).
As shown in Table 1, the reaction of various epoxides such
as cyclohexene and cyclopenten oxides, styrene oxide, allyl
2,3-epoxypropyl ether, 2,3-epoxypropyl isopropyl ether, and
2,3-epoxypropylphenyl ether as examples of aliphatic, alicyclic,
activated and deactivated epoxides, affording the corresponding
1,2-diol diacetates in high to excellet yields and good reaction
times. Moreover, the reactions are clean and chemoselective
while no side products or decomposition of the products is
observed. For example, with ꢀ,ꢁ-unsaturated 2,3-epoxypropyl
metacrylate and allyl 2,3-epoxypropyl ether, we have only
diacetylated product and any of other side products have not
obtained. Thus, in comparison with some of the reported results
The tetrabutylammonium (TBA) salts of transition metal-
.
substituted polyoxometalates, (TBA)n[PMW11O39] xH2O,
M = VIII, CrIII, MnII, FeIII, CoII, NiII, CuII, and ZnII, used in this
work have been prepared previously.8 In our work, the required
catalysts were made by starting from an aqueous solution of
the required anion prepared in situ, to which was added a solu-
tion of TBA bromide, and determined by spectroscopy methods
like elemental and thermogravimetric analysis, IR and UV–vis
spectroscopy, and powder X–ray diffraction method. The results
indicated that the hydration numbers for all of these compounds
are about 3.
for other catalytic systems,9 the use of (TBA)4PFeW11O39
3H2O is more suitable and give better results.
One could imagine a mechanism for this reaction in which
.
.
Fe in (TBA)4PFeW11O39 3H2O (POM) undergoes addition to
one of the carbonyl groups of acetic anhydride, the resulting
intermediate reacts with epoxide and then reacts with
CH3COOÀ, that is produced in this step, gives the final 1,2-diol
The reactions involving one-pot transformations of sub-
strates to products are currently of interest because of potential
applications in organic synthesis. As mentioned above, we used
from tetrabutylammonium salts of transition metal-substituted
keggin-type polyoxometlates as a suitable and efficient catalyst
in one-pot synthesis of 1,2-diol diacetates from 1,2-epoxides
and acetic anhydride under solvent free condition.
O
AcO
R
.
(TBA)4[PFeW11O39] 3H2O
R
Ac2O, 100 oC
OAc
Scheme 1.
Copyright Ó 2007 The Chemical Society of Japan