Mesoporous aluminosilicate promoted alcoholysis of epoxides

Article abstract of DOI:10.1016/j.tetlet.2007.05.010

Mesoporous aluminosilicates efficiently catalyze the ring-opening of epoxides with a range of alcohols to give the corresponding β-alkoxyalcohols in high yields under extremely mild conditions and in short reaction times.

Full text of DOI:10.1016/j.tetlet.2007.05.010

Tetrahedron Letters 48 (2007) 4723–4725
Mesoporous aluminosilicate promoted alcoholysis of epoxides
Mathew W. C. Robinson, Richard Buckle, Ian Mabbett,
Gemma M. Grant and Andrew E. Graham*
Department of Chemistry, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK
Received 13 March 2007; revised 23 April 2007; accepted 2 May 2007
Available online 10 May 2007
Abstract—Mesoporous aluminosilicates efficiently catalyze the ring-opening of epoxides with a range of alcohols to give the corre-
sponding b-alkoxyalcohols in high yields under extremely mild conditions and in short reaction times.
ꢀ
2007 Elsevier Ltd. All rights reserved.
Epoxides are highly versatile synthetic intermediates in
organic synthesis and undergo ring-opening reactions
to give b-substituted alcohols with a variety of nucleo-
b-alkoxyalcohols (Scheme 1) utilizing a mesoporous
aluminosilicate catalyst.
1
philic species with high regio- and stereoselectivity.
A small range of mesoporous aluminosilicate materials
7
The addition of alcohols to epoxides to produce b-
alkoxyalcohols is a widely studied reaction, however,
its application is limited due to the poor nucleophilicity
of alcohols which requires the use of strongly acidic or
were synthesized using the literature procedures, and
their ability to catalyze the nucleophilic ring-opening
of styrene oxide with methanol was studied. It was
found that the reaction was successfully catalyzed to
varying degrees by all of the aluminosilicate materials.
However, under the conditions studied to date, materi-
als with Si/Al ratios = 14, as measured by EDX analy-
sis, were found to be the most efficient. Interestingly,
the plain silicate material displayed little catalytic activ-
ity and starting material was recovered unchanged from
2
basic conditions or Lewis acid promoters. These proto-
cols are often far from ideal, and suffer from disadvan-
tages such as high toxicity and corrosiveness of the
acids employed, the requirement to use stoichiometric
quantities, long reaction times or inconvenient handling
3
procedures. Therefore, the introduction of new meth-
8
ods for the nucleophilic ring-opening of epoxides that
work under mild conditions is of great importance.
The use of heterogeneous catalysts provides an ideal
solution to these limitations and the use of solid acid
catalysts such as Amberlyst-15, pillared clays, function-
alized alumina or silica and polymer supported ferric
chloride or copper sulfate has shown great promise in
these reactions, suggesting that the transformation is
dependent on the Lewis acid nature of the catalyst
9
rather than simple Br o¨ nsted acid activity. The few
reports that utilize Br o¨ nsted acid catalysis typically
require forcing conditions, microwave irradiation or
1
0
report low yields.
4
this area. The recent advent of the mesoporous alumi-
Reactions utilizing catalytic quantities of this mesopor-
ous aluminosilicate catalyst in methanol at room tem-
perature readily transformed styrene oxide into 2-
methoxy-2-phenyl-ethanol in a highly efficient manner
(Table 1). This protocol was also found to be effective
when higher molecular weight alcohols were used,
nosilicate materials has had a substantial impact in the
area of heterogeneous catalysis, and they have been
shown to promote a range of synthetic transforma-
5
tions. However, there is no precedent in the literature
for the use of mesoporous aluminosilicates as catalysts
6
for ring-opening reactions of epoxides. In this study,
we wish to report the facile conversion of epoxides into
OR
O
ROH, rt, 1-4.5 h
Catalyst (50 mg)
OH
Keywords: Aluminosilicates; Epoxides; b-Alkoxyalcohols; Hetero-
geneous catalysis.
*
Corresponding author. Fax: +44
A.E.Graham@swan.ac.uk
0
1792 295747; e-mail:
Scheme 1.
0040-4039/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2007.05.010

4724
M. W. C. Robinson et al. / Tetrahedron Letters 48 (2007) 4723–4725
Table 1. Mesoporous aluminosilicate promoted alcoholysis of epoxides
a
b,c
d
Entry
Epoxide
Time (h)
Product
Yield (%)
O
OMe
OH
1
1.5
95
OEt
O
O
OH
OH
2
3
2.5
3.5
86
52
i
O Pr
OMe
4
5
O
1
1
69
96
97
OH
OEt
O
OH
O
O
OMe
OH
6
7
3
OMe
O
OH
e,f
4.5
90
OMe
OH
8
1
99
a
b
c
d
e
f
14
All epoxides were used as supplied or synthesized according to the literature procedures.
i
Reactions at room temperature in 10 mL of the alcohol (MeOH, EtOH, PrOH) utilizing 50 mg of catalyst.
1
Regioselectivity was determined from crude H NMR spectra.
All compounds gave satisfactory spectroscopic data.
Isolated yield after column chromatography.
Reaction at 50 ꢁC.
however, sterically hindered alcohols, such as 2-propa-
nol, gave low isolated yields of addition products due
Typical procedure for the formation of b-alkoxyalcohols:
Styrene oxide (120 mg, 1 mmol) was dissolved in metha-
nol (10 mL) at room temperature. The catalyst (50 mg)
was added and the reaction mixture stirred at room tem-
perature and monitored by TLC. Upon completion of
the reaction the catalyst was removed by filtration
through a Celite plug which was washed with dichloro-
methane (2 · 5 mL) and the combined solvents were
removed under reduced pressure to give the product
1
1
to a competing Meinwald rearrangement. Gratify-
ingly, the alcoholysis of a range of both cyclic and acy-
clic epoxides with methanol proceeded readily at room
temperature to produce the expected b-alkoxyalcohols
3
d,12
in high yields and with high regioselectivity.
Fur-
thermore, in a number of cases the crude products did
not require chromatographic purification, further dem-
onstrating the synthetic utility of this protocol. Reac-
tions of cyclohexene oxide with higher molecular
weight alcohols resulted in low isolated yields even
though NMR analysis of the crude reaction mixtures
indicated complete conversion of the starting material
to the desired b-alkoxyalcohol. This may be attributed
to the organophilicity of these materials where the prod-
uct remains adsorbed on the aluminosilicate.13 Attempts
to remove the product from the catalyst by washing did
not lead to improved isolated yields.
2-methoxy-2-phenyl-ethanol (114 mg, 95%) as a colour-
1
less oil; H NMR (400 MHz; CDCl ) d = 7.44–7.29
3
(5H, m), 4.34 (1H, dd, J = 4 and 5 Hz), 3.74–3.59 (2H,
1
3
m), 3.34 (3H, s), 2.45 (1H, br s); C NMR (100 MHz;
CDCl ) d = 138.7, 129.4, 129.3, 128.9, 127.4, 127.3,
3
þ
85.1, 67.8, 57.3; MS (CI+NH ) m/z 170 ðMþNH Þ;
3
4
HRMS
(CI+NH )
calculated
for
C H NO
3
9
16
2
þ
þ
ðMþNH4 Þ 170.1176, found ðMþNH4 Þ 170.1176.
Acknowledgements
In conclusion, it has been shown that mesoporous
aluminosilicates efficiently catalyze the regioselective
addition of alcohols to epoxides to produce b-alkoxyal-
cohols in high yields and in short reaction times. The
facile synthesis of these catalysts, their benign nature,
the ease of handling and the simplified reaction and iso-
lation procedures make them a highly attractive alterna-
tive to current methodologies.
The authors thank the Engineering and Physical Sci-
ences Research Council (EPSRC) for financial support
(MWCR), the EPSRC National Mass Spectrometry ser-
vice, the University of Wales, Swansea, UK and the
EPSRC Solid-State NMR Service, the University of
Durham, UK. We also wish to thank Mr. Peter Davies
(School of Engineering, the University of Wales Swan-

M. W. C. Robinson et al. / Tetrahedron Letters 48 (2007) 4723–4725
4725
sea) for his assistance in obtaining EDX data and Dr.
S.H. Taylor (Cardiff University) for his continued inter-
est in this work.
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