Polymer-supported Oxone and tert-butyl hydroperoxide: new reagents for the epoxidation of α,β-unsaturated aldehydes and ketones

Article abstract of DOI:10.1016/j.mencom.2010.03.017

Efficient, mild and selective epoxidation of α,β-unsaturated aldehydes and ketones was performed using polyvinylpyrrolidonesupported Oxone (Oxone/PVP) and Bu^tOOH/PVP.

Full text of DOI:10.1016/j.mencom.2010.03.017

Mendeleev
Communications
Mendeleev Commun., 2010, 20, 113–115
Polymer-supported Oxone and tert-butyl hydroperoxide: new reagents
for the epoxidation of α,β-unsaturated aldehydes and ketones
Ali Reza Pourali
School of Chemistry, Damghan University of Basic Sciences, Damghan 36715/364, Iran.
Fax: +98 232 523 5431; e-mail: pourali@dubs.ac.ir
DOI: 10.1016/j.mencom.2010.03.017
Efficient, mild and selective epoxidation of α,β-unsaturated aldehydes and ketones was performed using polyvinylpyrrolidone-
supported Oxone (Oxone/PVP) and ButOOH/PVP.
Epoxidation of alkenes, especially electron-deficient carbon–
carbon double bonds in α,β-enals and α,β-enones, is of great
interest.1 α,β-Unsaturated ketones are used in the production
of perfumes and flavouring substances.1(c) These compounds
could be functionalized by nucleophilic ring-opening of the
oxirane ring of the corresponding epoxide.2 One recent example
is reported for the synthesis of a novel class of C-10 halo-
genated and C-12 oxygenated prostaglandin-A2 derivatives.2(b)
Peroxides are frequently used as oxidants in organic synthesis
for the epoxidation of α,β-unsaturated carbonyl compounds.3,4
In the epoxidation of α,β-enones, peroxides are superior reagents
to organic peracids with respect to their mildness, good yields
and absence of by-products. Epoxidation of electron-deficient
alkenes is normally sluggish with electrophilic oxidizing agents
such as m-CPBA. Hydrolysis of produced oxirane ring and
oxidation of aldehyde functional group are disadvantages of
using organic peracids. Potassium peroxomonosulfate triple salt
(Oxone) is an efficient reagent for this purpose, but it requires
an aqueous reaction medium that can lead to extensive hydrolysis.
The epoxidation of α,β-unsaturated ketones with hydrogen
peroxide under basic conditions was discovered by Weitz and
Scheffer, and it is one of the oldest applications of hydrogen
peroxide as an oxidant in synthetic organic chemistry.5 It is
generally known that hydrogen peroxide decomposes on pro-
longed storage, and a large number of stabilizers has been
used for slowing down the decomposition.6 Other epoxidation
methods have been developed for α,β-unsaturated carbonyl com-
pounds, which involve sodium peroxide,7 Keggin heteropoly
compounds with aqueous H2O2 in acetonitrile,8 hydrogen peroxide
in the ionic liquid/water biphasic system,9 urea–hydrogen
peroxide,10 dioxirane,11 alkaline hydrogen peroxide in nonionic
microemulsions in the presence or absence of a phase-transfer
agent12 and many asymmetric methods are well known.13
On the other hand, the development of new clean oxidation
methods, which can supply the needs for improvements in
epoxide synthesis, is of general interest. Selective epoxidation
methods are implemented under heterogeneous conditions and
with safe, clean, cheap and regenerable oxidants.14 Polymer-
supported reagents are of considerable interest due to their
selectivity, stability and easy handling.15–18 They could serve as
heterogeneous, clean and regenerable reagents in epoxidation
reactions. Recently, the epoxidation of α,β-enones and other
double bonds with cross-linked polystyrene-supported tert-butyl
hydroperoxide has been investigated, but it suffers from low yields,
low selectivity and long reaction times.18 Asensio and co-workers
have found that anhydrous potassium peroxomonosulfate supported
on silica (SiO2·KHSO5) efficiently oxidizes a variety of acyclic
and cyclic ketones to the corresponding esters or lactones
(Baeyer–Villiger oxidation) without hydrolysis of products.19
Recently, we reported the use of polyvinylpyrrolidone-sup-
ported hydrogen peroxide (H2O2/PVP)20 as a stable solid oxi-
dizing reagent in the presence of KI or I2 for iodination of
activated aromatic compounds21 and epoxidation of α,β-unsatu-
rated carbonyl compounds.22 Now, we report the simple pre-
paration of PVP-supported Oxone (Oxone/PVP) and tert-butyl
hydroperoxide (ButOOH/PVP) as new stable, safe and recyclable
reagents. The peroxide contents of the supported reagents (as
determined by iodometric titration) were 1.7 and 6.4 mmol g–1
for Oxone and ButOOH, respectively. The reagents could be
stored in a refrigerator for several months without noticeable
loss of activity. In this work, we investigated an efficient method
for the epoxidation of α,β-enones by using these reagents under
heterogeneous conditions.†
†
Preparation of Oxone/PVP. To 6 g of polyvinylpyrrolidone K-30
(Mw 40000; from Fluka) a solution of Oxone® (from Fluka; 6.14 g) in
35 ml of distilled water was added with gently stirring in an ice bath.
After 1 h, the solvent was vacuum evaporated at room temperature, and
the resulting powder was dried in a vacuum to constant weight. The
peroxide content of the supported reagent (as determined by iodometric
titration) was 1.7 mmol peroxide g–1. The reagent could be stored at 0 °C
for several months without noticeable loss of activity.
Preparation of ButOOH/PVP. An aqueous 70% solution of ButOOH
(6 ml) was added to 3 g of polyvinylpyrrolidone at 0 °C with gently
stirring. After 2 h, the solvent was vacuum evaporated at room tempera-
ture, and the resulting solid was powdered and then dried in a vacuum to
constant weight. The peroxide content of the supported reagent (as deter-
mined by iodometric titration) was 6.4 mmol ButOOH g–1. The reagent could
be stored at 0 °C for several months without noticeable loss of activity.
Epoxidation of 3-phenyl-2-propenal with Oxone/PVP. Oxone/PVP
(0.588 g, 1 mmol) was added to a solution of 3-phenyl-2-propenal (0.132 g,
1 mmol) in acetone (5 ml). The mixture was stirred at room temperature,
and the progress of the reaction was monitored by TLC. After 4 h, the
reaction mixture was filtered. Evaporation of the solvent followed by
column chromatography on silica gel by using light petroleum–EtOAc
(5:1) as an eluent gave 2,3-epoxy-3-phenylpropanal (0.124 g, 84% yield).
Epoxidation of 2-cyclohexen-1-one with ButOOH/PVP. To a solution
of 2-cyclohexen-1-one (0.096 g, 1 mmol) in dioxane (5 ml), ButOOH/PVP
(0.155 g, 1 mmol) and four drops of an aqueous solution of NaOH
(0.1 M) were added. The mixture was refluxed, and the progress of the
reaction was monitored by TLC. After 6.5 h, the reaction mixture was
cooled and filtered. Then, dichloromethane (10 ml) was added to the filtrate,
and the mixture was washed with distilled water (3×10 ml). The filtrate
was dried over anhydrous magnesium sulfate. Evaporation of the solvent
followed by column chromatography on silica gel using light petroleum–
EtOAc (5:1) as an eluent gave 2,3-epoxycyclohexanone (0.110 g, 98%
yield).
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© 2010 Mendeleev Communications. All rights reserved.

Mendeleev Commun., 2010, 20, 113–115
In our procedure, α,β-unsaturated carbonyl compounds reacted
Oxone/PVP, the hydroxyl and aldehyde groups were intact and
double bonds were selectively converted to oxirane (Table 1,
entries 8–11). Polyvinylpyrrolidone can be recycled by simple
filtration after completion of the reaction.
with Oxone/PVP in acetone at room temperature (Scheme 1).
We first optimized the epoxidation reaction with 2-cyclohexen-
1-one as a model (Table 1, entry 1) and then applied the con-
ditions for other enones. Under these conditions, 2-cyclohexen-
1-one was converted into 2,3-epoxycyclohexanone in 82%
isolated yield after 3 h.
α,β-Unsaturated carbonyl compounds reacted with ButOOH/
PVP in dioxane under reflux conditions (Scheme 2). In this case,
the best results were obtained when the reaction was performed
in the presence of NaOH in dioxane. Under these conditions,
2-cyclohexen-1-one was converted into 2,3-epoxycyclohexanone
in 98% isolated yield after 6.5 h. As shown in Table 1, various
α,β-unsaturated carbonyl compounds were efficiently converted
into the corresponding epoxides with ButOOH/PVP in dioxane
under reflux conditions in good to excellent yields. During epoxi-
dation of unsaturated aldehydes and alcohols with ButOOH/
O
O
R1
R2
R1
O
R2
R4
R4
Oxone/PVP
Acetone,
room temperature
R3
R3
Scheme 1
Table 1 shows that α,β-unsaturated carbonyl compounds,
including aldehydes and ketones, were efficiently converted
into the corresponding epoxides with Oxone/PVP in acetone
at room temperature in good to excellent yields. Under these
conditions, cyclohexene was epoxidized slowly, and the corre-
sponding epoxide was obtained in poor yield (Table 1, entry 12).
During epoxidation of unsaturated aldehydes and alcohols with
O
O
R1
R2
R1
O
R2
ButOOH/PVP
R4
R4
NaOH,
dioxane, reflux
R3
R3
Scheme 2
Table 1 Conversion of carbon–carbon double bonds to epoxides with Oxone/PVP and ButOOH/PVP.
Oxone/PVP
Yieldb (%)
ButOOH/PVP
Yieldb (%)
Entry
1
Substrate
O
Producta
O
Time/h
3
Time/h
82
93
6.5
7
98
94
O
O
O
2
3
4
O
Me
Me
O
O
6.2
96
6
90
O
O
O
O
C
O
C
O
C
O
C
O
C
O
C
O
4
5
6
12
8
88
90
60
24
85
95
70
PhCH CH
PhCH CH
Ph
PhHC CH
Ph
O
20
28
Me
PhHC CH
Me
O
24
PhCH CH
O
OMe
PhHC CH
OMe
O
O
Me
Me
7
4.5
95
7.5
98
MeHC
C
MeC
H
C
Me
Me
O
CHO
Me
CHO
Me
8
9
9.5
5.5
4
90
88
84
48
25
8
90
80
92
PhCH
C
PhC
H
C
O
MeHC CH CHO
PhHC CH CHO
Me2C CH CH2OH
MeC CH CHO
H
O
PhC CH CHO
H
10
O
5
85
50
14
48
88
30
Me2C CH CH2OH
11
12
48
O
aAll products are known compounds identified by comparison of their physical (mp or bp) and spectral data with those of authentic samples. bIsolated yield.
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Mendeleev Commun., 2010, 20, 113–115
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PVP, the aldehyde and hydroxyl groups were intact (Table 1,
entries 8–11), and cyclohexene oxide was obtained in poor yield
(Table 1, entry 12).
We also examined the selectivity of this method by using
ButOOH/PVP as a mild oxidizing reagent. We observed excellent
selectivity in the epoxidation of a mixture of 2-cyclohexen-1-one
and cyclohexene. 2,3-Epoxycyclohexanone was obtained with
95% yield in the presence of cyclohexene after 8 h in refluxing
dioxane, while cyclohexene remained intact (Scheme 3).
3
4
5
6
7
O
O
8
9
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100%
+
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NaOH, dioxane,
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Scheme 3
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In conclusion, Oxone/PVP and ButOOH/PVP are stable,
mild, recyclable and environmentally friendly reagents for the
selective, clean and safe epoxidation of α,β-unsaturated carbonyl
compounds. Unsaturated aldehydes and alcohols are epoxidized
without oxidation of their formyl or hydroxyl groups. Oxone/PVP
is more reactive than ButOOH/PVP, but the latter is more selec-
tive. Excellent selectivity was observed in the epoxidation of a
mixture of 2-cyclohexen-1-one and cyclohexene with ButOOH/
PVP in refluxing dioxane. High reaction yields, mild reaction
conditions, simple setup and workup procedure are additional
merits of our protocol.
14 H. Heaney, in Organic Peroxygen Chemistry, ed. W. A. Herrmann,
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This work was supported by the Research Council of
Damghan University of Basic Sciences (grant no. 1814).
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Received: 14th October 2009; Com. 09/3402
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