Facile epoxidation of α, β-unsaturated ketones with urea-2,2-dihydroperoxypropane as a new oxidant

Article abstract of DOI:10.1007/s13738-016-0980-1

Abstract: Various aromatic α, β-unsaturated ketones were successfully transformed into their corresponding epoxides using urea-2,2-dihydroperoxypropane as the oxygen source for the first time. The reactions were carried out under mild alkaline conditions at room temperature in high yields and short reaction times. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s13738-016-0980-1

J IRAN CHEM SOC
DOI 10.1007/s13738-016-0980-1
ORIGINAL PAPER
Facile epoxidation of α, β‑unsaturated ketones
with urea‑2,2‑dihydroperoxypropane as a new oxidant
Kaveh Khosravi1 · Shirin Naserifar1
Received: 13 April 2016 / Accepted: 12 September 2016
© Iranian Chemical Society 2016
Abstract Various aromatic α, β-unsaturated ketones were
successfully transformed into their corresponding epoxides
using urea-2,2-dihydroperoxypropane as the oxygen source
for the first time. The reactions were carried out under mild
alkaline conditions at room temperature in high yields and
short reaction times.
precursors in flavonoid chemistry [11–13] and in the synthesis
of pharmaceuticals and natural compounds [14, 15]. Moreo-
ver, epoxides play an important role in industrial production
and serve as reactants to produce surfactants or detergents
(tensides), antistatic or corrosion protection agents, additives
to laundry detergents, lubricating oils, textiles, and cosmetics
[9, 16]. Therefore, the synthesis of epoxides remains a central
topic of interest in organic synthesis and numerous investiga-
tions have been made in order to develop useful methodolo-
gies for efficient preparations of epoxides.
Graphical Abstract
In recent years due to the critical role of epoxides in per-
fume formulations and also in the production of flavoring
substances, there has been an increasing interest in epoxi-
dation of α, β-unsaturated ketones [5, 16–19] and various
methodologies have been applied using different reagents
and catalysts. Hydrogen peroxide has been the most com-
monly used oxidant in numerous oxidation procedures.
This oxidant is favored since it is environmentally benign,
inexpensive and produces water as the only by-product [9,
20]. However, its low oxidation power in organic solvents
requires activation by various catalysts. Other oxidants
such as sodium hypochlorite [21], sodium peroxide [22],
m-chloroperbenzoic acid [23], sodium perborate tetrahy-
drate [24], oxone [25], trichloroisocyanuric acid, [26] and
dimethyldioxirane [27] have been used to carry out the
oxidation but all of them suffer from several drawbacks
including environmental damages caused by toxic solvents,
long reaction times, complexity of procedures, and the high
cost of catalysts [1, 11].
Keywords Epoxidation · Gem-dihydroperoxide · Urea-
2,2-dihydroperoxypropane · α, β-unsaturated ketones ·
Epoxide
Introduction
Epoxides are an important class of chemicals which pos-
sess various utility in organic synthetic chemistry [1–4].
They serve as versatile building blocks and intermediates in
organic synthesis [5–10]. They are also utilized as important
In recent years, gem-dihydroperoxides have attracted
considerable attention because of their relevance to their
peroxidic antimalarial drugs [28–30]. In addition, they
are valuable intermediates in the synthesis of versa-
tile peroxides such as tetraoxanes [31], silatetraoxanes
[32], spirobisperoxyketals [33], bisperoxyketals [34] and
* Kaveh Khosravi
khosravi.kaveh@gmail.com; k-khosravi@araku.ac.ir
1
Department of Chemistry, Faculty of Science, Arak
University, Arak 38156-8-8349, Iran
1 3

J IRAN CHEM SOC
Table 1 Screening of reaction parameters for formation of phenyl(3-
phenyloxiran-2-yl)methanone
Scheme 1. Synthesis of UDHPP catalyzed by sulfamic acid
Entrya
Base
Solvent
UDHPP
(mmol)
Time (h) Yield
(%)b
1
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
NaOH
HMTA
DABCO
MeCN
1
2
90
2
DME
1
2.5
5
50
3
H2O
1
Trace
97
4
1,4-dioxane
EtOH
1
1.4
1.8
5
Scheme 2. Epoxidation of α, β-unsaturated ketones with UDHPP
5
1
91
6
CH2Cl2
1
10
7
n-Hexane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1
8
Trace
65
1,2,4,5-tetraoxacycloalkanes [35]. Also, gem-dihydroper-
oxides have been used as oxidants in several oxidation pro-
cesses, as well as epoxidation of α, β-unsaturated ketones
[11, 30]. In continuation of our studies on the synthesis and
application of gem-dihydroperoxides [36–44], we decided
to evaluate and validate the application of urea-2,2-dihy-
droperoxypropane (UDHPP) as a new, efficient, and stable
oxidation reagent for the epoxidation of α, β-unsaturated
ketones. We herein wish to report a new, facile, convenient,
and efficient method for epoxidation of α, β-unsaturated
ketones under mild alkaline conditions at room temperature
to afford the corresponding epoxides (Schemes 1 and 2).
8
0.5
1.5
2
2.5
1.5
1.2
3
9
90
10
11
12
13
80
1
30
1
5
–
1
5
–
a
Reaction conditions: (E)-Chalcone (1 mmol, 0.224 g), solvent
(3 mL), base (1 M. 1 mL), UDHPP, room temperature
completion of the reaction as monitored by TLC, the mix-
ture was diluted with water (5 mL), extracted using ethyl
acetate (3 × 5 mL) and dried over MgSO4, and then urea
was added (1 mmol). After evaporation of the solvent under
reduced pressure, pure crystalline product was gained. The
product was characterized on the basis of its melting point,
Experimental
Solvents, reagents, and chemical materials were obtained
from Aldrich and Merck chemical companies and puri-
fied prior to use. Nuclear magnetic resonance spectra were
recorded on Bruker (300 MHz) spectrometer using tetra-
methylsilane (TMS) as an internal standard. Infrared spec-
tra were recorded on a PerkinElmer GX FT IR spectrom-
eter (KBr pellets).
Caution: Although we did not encounter any problems
with gem-dihydroperoxides, peroxides are potentially
explosive and should be handled with precautions; all reac-
tions should be carried out behind a safety shield inside a
fume hood and heating should be avoided.
elemental analysis and IR, H NMR, and 13C NMR spec-
tral analysis, and amount of peroxide in products has been
determined by iodometric titration (Table 1).
1
Physical and spectral data of UDHPP
White crystal, m.p: 114–116 C. IR νmax/cm−1 (KBr pel-
let): 3456, 3337, 3265, 2928, 2852, 1680, 1624, 1464, 1384,
1155, 1003, 787, 715, 715, 574, 503; H NMR (300 MHz,
DMSO-d6) δH: 1.26 (S, 6H, (CH3)), 5.49 (s, 4H, (NH2)),
10.23 (s, br, 2 H, (OOH)). 13C NMR: (75 MHz, DMSO-d6)
δC: 21.2, 108.2, 160.6; Anal. Calcd (%) for C4H12N2O5: C,
28.57; H, 7.19; N, 16.66; Found: C: 28.10; H: 7.52; N, 17.10.
1
General procedure for synthesis
of urea‑2,2‑dihydroxypropane
General procedure for synthesis of chalcones
Acetone (1 mmol, 0.074 mL) was added to acetonitrile
(5 mL), followed by the addition of NH2SO3H (0.1 mmol,
0.01 g)) which serves as the catalyst of this reaction. To
this stirred solution, H2O2 30 % (1 mL) was added and the
mixture was stirred for 2 h at room temperature. After the
Chalcones were synthesized by base catalyzed Claisen‐
Schmidt condensation reaction of appropriately substituted
acetophenones and aldehydes according to the literature
procedure [47].
1 3

J IRAN CHEM SOC
Table 2 Epoxidation of E-chalcones by UDHPP under optimized
Physical and spectroscopic data for some selected
and new products are given
conditionsa
Product
Ar1
Ar2
Time (h) Yield (%)b
Compound 2c: White solid, m.p: 66–68 C. IR νmax/cm−1
(KBr pellet): 3055, 3005, 2976, 2935, 1655, 1602, 1572,
1444, 1334, 1257, 1224, 1184, 1016, 972, 829, 761, 694;
1H NMR (300 MHz, Acetone-d6) δH: 3.89 (s, 3 H, (OMe)),
4.09 (s, 1H, (epoxy ring)), 4.50 (s, 1 H, (epoxy ring)), 7.04–
7.06 (d, 2 H, (Ar–H)), 7-40-7.45 (m, 5 H, (Ar–H)), 8.05–
8.08, (d, 2 H, (Ar–H)). 13C NMR: (75 MHz, Acetone-d6)
δC: 55.16, 58.49, 60.21, 114.0, 126.0, 128.5, 128.7, 128.9,
130.6, 136.3, 163.6, 190.8. Anal. Calcd (%) for C16H14O3:
C, 75.58; H, 5.55; Found: C: 76.20; H: 5.41.
2a
2b
2c
2d
2e
2f
C6H5
C6H5
C6H5
C6H5
1.4
97
95
92
88
91
94
98
95
96
97
89
90
91
90
89
87
94
91
96
4-Cl-C6H4
4-MeO-C6H4
1.7
2
4-MeO-C6H4 C6H5
2.5
4-Me-C6H4
4-Cl-C6H4
C6H5
C6H5
1.9
1.3
2g
2h
2i
4-NO2-C6H4 C6H5
3-NO2- C6H4 C6H5
1
1.3
1.2
4-Cl-C6H4
4-Cl-C6H4
4-Cl-C6H4
4-Cl-C6H4
4-Cl-C6H4
4-Cl-C6H4
2j
4-Me-C6H4 1.3
Compound 2i: White solid, m.p: 117-119 C. IR νmax
/
cm−1 (KBr pellet): 3090, 3043, 2958, 2926, 2852, 1678,
1589, 1429, 1402, 1234, 1087, 1091, 1010, 883, 823, 734;
1H NMR (300 MHz, Acetone-d6) δH: 4.175–4.179 (d, 1H,
(j = 1.2 Hz), (epoxy ring)), 4.612–4.616 (d, 1 H, (j = 1.2),
(epoxy ring)), 7.46–7.60 (m, 6 H, Ar–H), 8.02–8.11 (m, 2H
(Ar–H)). 13C NMR: (75 MHz, Acetone-d6) δC: 58.2, 60.2,
127.8, 128.6, 129.0, 130.0, 131.2, 133.0, 134.1, 135.0,
139.5, 191.5. Anal. Calcd (%) for C15H10Cl2O2: C, 61.46;
H, 3.44; Found: C: 62.15; H: 3.30.
2k
2l
2-thionyl
2-furyl
1.4
1.2
1.9
1
2m
2n
2o
2p
2q
2r
2-naphthyl
2,6-diCl-C6H3 4-Cl-C6H4
2,6-diCl-C6H3 2-thionyl
1.1
2
4-Br-C6H4
2-naphthyl
4-Me-C6H4
4-Cl-C6H4
1.4
1.2
2.5
4-NO2-C6H4 2-naphthyl
C15H11O2 C6H4
2s:c
Compound 2j: White solid, m.p: 73–75 C. IR νmax/cm−1
(KBr pellet): 3088, 3026, 2924, 2856, 1658, 1602, 1493,
1
2t:
–
–
0.4
93
1440, 1311, 1292, 1186, 1089, 1014, 891, 731; H NMR
(300 MHz, Acetone-d6) δH: 2.41 (s, 3 H, (CH3)), 4.13 (s, 1 H,
(epoxy ring)), 4.60 (s, 1 H, (epoxy ring)), 7.35–7.48 (m, 6 H,
(Ar–H)), 7.97–7.99 (d, 2 H, (Ar–H)). 13C NMR: (75 MHz,
Acetone-d6) δC: 20.7, 57.9, 60.1, 127.8, 128.3, 128.6, 129.4,
133.3, 134.0, 135.3, 144.8, 191.8. Anal. Calcd (%) for
C16H13ClO2: C, 70.46; H, 4.80; Found: C: 71.35; H: 5.16.
Compound 2o: White solid, m.p: 100–102 C. IR
νmax/cm−1 (KBr pellet): 3086, 2922, 2852, 1656, 1606,
a
All of the reactions were carried out using α,β-unsaturated ketones
(0.5 mmol), UDHPP (1 mmol), aq KOH (1 M, 1 mL), and 1,4-diox-
ane (3 mL)
b
Isolated yields
c
Amount of oxidant, KOH, and solvent is doubled
1
1413, 1303, 1219, 1176, 1062, 972, 860, 773, 721; H
General procedure for epoxidation of α, β‑unsaturated
ketones
NMR (300 MHz, Acetone-d6) δH: 4.342–4.347 (d, 1H,
j = 1.5 Hz), (epoxy ring)), 4.545–4.551 (d, 1H, j = 1.8 Hz,
(epoxy ring)), 7.32-7.50 (m, 4 H, (Ar–H)), 8.05-8.07
(d, 1 H, (Ar–H)), 8.31–8.32 (d, 1 H, (Ar–H)). 13C NMR:
(75 MHz, Acetone-d6) δC: 56.6, 57.7, 128.6, 128.8, 130.8,
131.7, 134.3, 135.4, 135.7, 142.2, 186.1. Anal. Calcd (%)
for C13H8Cl2O2S: C, 52.19; H, 2.70; S, 10.72; Found: C:
52.56; H: 3.11; S, 11.02.
To a stirred solution of chalcones (1 mmol) in 1,4-dioxane
(3 mL) and UDHPP (1 mmol, 0.136 g), KOH (1 M, 1 mL)
was added and the mixture was stirred at room tempera-
ture for an appropriate time (Table 2). After the comple-
tion of the reaction as monitored by thin-layer chroma-
tography (TLC), the mixture was quenched with Na2SO3
solution (2 M, 1 mL), diluted by water (5 mL) and
extracted with EtOAc (3 × 5 mL). Then, aqueous layer
and organic layer were separated, dried over anhydrous
Mg2SO4 and evaporated under reduced pressure. The resi-
due was purified by silica-packed column chromatogra-
phy (hexane–EtOAc) to afford pure epoxides (Table 2).
Products were characterized on the basis of their melt-
Compound 2p: White solid, m.p: 117–119 C. IR νmax
/
cm−1 (KBr pellet): 3026, 2918, 2856, 1658, 1604, 1487,
1440, 1294, 1186, 1107, 1062, 952, 891, 842, 802, 727,
1
669; H NMR (300 MHz, Acetone-d6) δH: 2.41 (s, 3 H,
(CH3)), 4.12 (s, 1 H, (epoxy ring)), 4.54 (s, 1 H, (epoxy
ring)), 7.34–7.43 (m, 4 H, (Ar–H)), 7.58–7.61 (d, 2 H, (Ar–
H)), 7.96–7.98 (d, 2 H, (Ar–H)). 13C NMR: (75 MHz, Ace-
tone-d6) δC: 20.7, 57.9, 60.1, 122.2, 128.3, 128.3, 129.4,
131.6, 133.4, 135.7, 144.7, 191.8. Anal. Calcd (%) for
C16H13BrO2: C, 60.59; H, 4.13; Found: C: 61.23; H: 4.45.
1
ing points, elemental analysis and IR, H NMR, and 13C
NMR spectral analysis.
1 3

J IRAN CHEM SOC
Scheme 3. Suggested mechanism for epoxidation of α, β-unsaturated ketones with UDHPP
Compound 2 s: White solid, m.p: 200–202 C. IR νmax
/
KOH was identified as the best base to afford the corre-
sponding epoxides in high yields.
cm−1 (KBr pellet): 3070, 3026, 2926, 2852, 1689, 1602,
1425, 1327, 1294, 1184, 1132, 1072, 1026, 935, 707,
Secondly, we extended our studies to investigate the
effect of various solvents on the epoxidation reaction.
Based on the collected results, 1,4-dioxane proved to be the
best solvent of choice due to the solubility of chalcones and
UDHPP, the obtained yields and reaction times.
To understand the scope of the reaction, we studied the
epoxidation of various α, β-unsaturated ketones. All of
the reactions were carried out under the optimized condi-
tions using α, β-unsaturated ketones (1 mmol), UDHPP
(1 mmol), aq KOH (1 M, 1 mL), and 1,4-dioxane (3 mL).
The results are summarized in Table 2.
1
669, 551; H NMR (300 MHz, DMSO-d6) δH: 4.18 (s, 2
H, (epoxy ring)), 4.82 (s, 2 H, (epoxy ring)), 7.35–8.03
(m, 14 H, (Ar–H)). 13C NMR: (75 MHz, DMSO-d6) δC:
58.6, 61.1, 119.1, 120.0, 122.0, 125.0, 127.1, 128.6, 129.4,
130.5, 134.5, 135.0, 136.1, 140.0, 192.0. Anal. Calcd (%)
for C24H18O4: C, 77.82; H, 4.90; Found: C: 78.41; H: 4.59.
Results and discussion
Regarding to the high oxidizing power of gem-dihydrop-
eroxides in various oxidation procedures, it was predicted
that these oxidants would have the potential to carry out
the epoxidation of chalcones. Although 1,1-dihydroperoxy-
cyclohexane has been used as a new oxidant for epoxida-
tion of different chalcones previously [20], it suffers from
some serious drawbacks such as explosive potential, sticky
oil state, and insufficient stability as it decomposes within
a few hours at room temperature. So, due to safety consid-
eration and in order to enhance the stability of peroxides,
we decided to convert acetone as a low cost, available and
low-toxic ketone to the corresponding gem-dihydroperox-
ide by H2O2 (aq, 30 %) in the presence of sulfamic acid as
an efficient catalyst (Scheme 1). In the work-up step, we
added urea to oily acetone peroxide to prepare UDHPP as
a stable white solid compound which can be stored for a
few months without any loss of its activity at room temper-
ature as evidenced by IR spectroscopy and manganometric
or iodometric titration. The stability of UDHPP as reported
for UHP [45] arises from hydrogen bonding between per-
oxidic hydrogens and N–H bonds of urea (Scheme 1).
UDHPP has been characterized by IR, 1H NMR, 13C NMR
spectroscopy, and elemental analysis. Also, the amount of
peroxide has been determined by manganometric and iodo-
metric titrations. All analysis data confirmed the peroxide
structure.
On the basis of the experimental evidences, the probable
mechanism introduced is depicted in Scheme 3. The reac-
tion begins with the in situ generation of peroxide anion by
means of adding KOH to UDHPP as shown in Scheme 3.
The reaction is followed by the nucleophilic addition of the
peroxide anion to β-carbon of chalcone, and the intermedi-
ate anion is generated. In the last step, an SN2 cyclization
takes place by pushing out the acetone and hydroperoxide
anion.
We could see that reactivity of this double bond is
decreased due to conjugation with the aryl ring, while
cyclohex-2-en-1-one as a cyclic aliphatic α, β-unsaturated
and unconjugated ketone were converted to corresponding
epoxy faster than conjugated aromatic analogues (Table 2,
entry 2t). So, investigation through the results has led to
this conclusion that electron-withdrawing substituents on
the rings cause accomplishment of the reactions in shorter
reaction times (Table 2, entries 2f-2r) and in contrast, elec-
tron-donating substituents lead to longer reaction times
(Table 2, entries 2c–e). The observed results and inves-
tigation through the mechanism in probable Scheme 3,
confirmed that the more positive c = c and c = o bonds in
chalcones would promote the addition of peroxide anion.
Moreover, (E)-3-(4-cinnamoylphenyl)-1-phenylprop-2-en-
1-one as a bi-symmetric chalcone has been converted to its
corresponding epoxide successfully. It is notable that both
double bonds have been converted to the corresponding bi-
epoxides effectively (Table 2, entry 2s). 1HNMR, 13CNMR,
IR, and physical data of the products were carefully ana-
lyzed to establish their structures, and they were also
compared with previously reported data. Also, for some
selected products (Table 2, entries 2c, 2i and 2 j) and new
compounds, (Table 2, entries 2o, 2p and 2s) all spectrum
In order to study the epoxidation reaction, (E)-chalcone
(Table 2, compound 2a) was selected as the model substrate
and some reaction parameters including solvent, type of
base, and amount of oxidant were studied (Table 1).
Firstly, the reaction was studied using different bases
such as aqueous NaOH, 1,4-diazabicyclo[2.2.2]octane
(DABCO) and hexamethylenetetramine. Among these,
1 3

J IRAN CHEM SOC
Table 3 Comparing efficiency of present work with some reported methods for synthesis of phenyl(3-phenyloxiran-2-yl)methanone
Entry
Oxidant
Conditions
Time (h)
Yields (%)
Ref
1
2
3
4
5
6
7
UDHPP
r.t
1.4
97
95
96
93
99
88
91
This work
1,1-dihydroperoxycyclohexane
r.t
2
20
11
46
48
49
1
DHPDMDO
t-BuOOH
H2O2
r.t
2
Diaryl-2-pyrrolidinemethanols
Phase transfer catalyst, 20 °C
Barium aluminate nano-powder
Ultrasonic
3
2
H2O2
17 (Ref)
0.25
UHP
5. M.A. Zolfigol, Gh Chehardoli, M. Shiri, React. Funct. Polym.
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(2010)
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and physical analysis are available in supporting informa-
tion file.
Finally, the results of this procedure for synthesis of
phenyl(3-phenyloxiran-2-yl)methanone (Table 2, product
2a) have been compared with some other reported meth-
odologies in Table 3. As revealed in this table, in contrast
with 1,1-dihydroperoxycyclohexane, H2O2 and t-BuOOH,
UDHPP is a more efficient and powerful solid oxidant
which has improved reaction times, yields and also the
reaction conditions clearly. All reactions were carried out
in mild reaction conditions at room temperature. Finally,
unlike some reported methods [1, 11, 20, 46–50], this
method does not need any catalysts or metal cations.
Conclusions
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In conclusion, UDHPP has been utilized in an eco-friendly
oxidation reaction in which α, β-unsaturated ketones were
transformed into their corresponding epoxides under mild
alkaline conditions. This reported procedure is new, sim-
ple, catalyst-free, efficient, and environmentally benign
which can be used in the oxidation of various substituted
α, β-unsaturated ketones. The considerable advantage of
UDHPP is its potential to be prepared and stored in large
scales for a few months. On the other hand, UDHPP is not
accompanied by water, so this procedure may be appropri-
ate for the oxidation of water-sensitive compounds.
27. A.L. Baumstark, D.B. Harden, J. Org. Chem. 58, 7615 (1993)
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Acknowledgments The authors thank Arak University for the scien-
tific and instrumental support.
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