Facile epoxidation of α,β-unsaturated ketones with trans -3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane as an efficient oxidant

Article abstract of DOI:10.1055/s-0030-1258996

Application of trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane as an efficient oxygen source has been explored in the epoxidation of trans-chalcones. The reactions proceed under mild conditions at room temperature in alkaline solution to afford the corresponding epoxides in excellent yields.

Full text of DOI:10.1055/s-0030-1258996

LETTER
2755
Facile Epoxidation of a,b-Unsaturated Ketones with trans-3,5-Dihydroperoxy-
3,5-dimethyl-1,2-dioxolane as an Efficient Oxidant
Epoxidation of
a,
b
a
-Unsaturate
v
dKetones ood Azarifar,* Kaveh Khosravi
Faculty of Chemistry, Buali Sina University, Hamedan 65178, Iran
Fax +98(811)8257407; E-mail: azarifar@basu.ac.ir
Received 17 August 2010
hydrogen peroxide,35–40 peroxide–ammonium fluoride,41
sodium perborate,42,43 tetra-n-butyl ammonium peroxy-
disulfate,44 and H2O2/[bmim]BF4.45 In addition, several
hydroperoxides have been reported in epoxidation reac-
tions including tert-butylhydroperoxide,46–50 PEG-sup-
Abstract: Application of trans-3,5-dihydroperoxy-3,5-dimethyl-
1,2-dioxolane as an efficient oxygen source has been explored in the
epoxidation of trans-chalcones. The reactions proceed under mild
conditions at room temperature in alkaline solution to afford the
corresponding epoxides in excellent yields.
ported
cinchona
ammonium
salt
catalyzed
Key words: a,b-unsaturated ketone, epoxide, dihydroperoxide,
trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane, epoxidation
hydroperoxides,51 and diketopiperazine-derived hydro-
peroxides.52 As known from literature survey, very few
reports have been recorded on application of organic dihy-
droperoxides in epoxidation of a,b-unsaturated ketones.44
Hydrogen peroxide (H2O2) is a well-known, versatile, and
environmentally benign (only generates water as byprod-
uct) oxygen source in various oxidative transformations.1–
3 However, the oxidation power of H2O2 is low for many
purposes and requires to be activated by systems based on
various acids such as AcOH,4 TBHP/PTSA,5 or transi-
tion-metal catalysts.6,7 Many of these reagents and cata-
lysts are subject to certain drawbacks such as toxicity of
the transition metals present in these catalysts, long reac-
tion times, and low yields.8 One way to overcome these
limitations is to convert H2O2 into dihydroperoxides.9 In
this respect, gem-dihydroperoxides have received consid-
erable interest in recent years due to their relevance to per-
oxidic antimalarial agents,10,11 which are structurally
similar to hydroperoxides. In contrast to H2O2, gem-dihy-
droperoxides act more efficiently as high-oxygen-content
oxidants for transferring oxygen to sulfides, a,b-unsatur-
ated ketones, amines, and other substrates.12–19 Anomeric
hydroperoxides derived from 3,4,6-tri-O-benzyl-galac-
tose and glucose were used for enantioselective epoxida-
tion of naphthoquinone, chalcones, (E)-1,2-dibenzoyl
ethylene, and (E)-iso-butyrylphenyl ethylene.20 Most re-
cently, we reported a novel use of trans-3,5-dihydroper-
oxy-3,5-dimethyl-1,2-dioxolane in selective sulfoxidation
of sulfides.21 In the last few years, great attention has been
paid to epoxidation of a,b-unsaturated ketones due to the
important role of epoxides,22,23 especially chiral epoxides,
as useful building blocks in organic synthesis, for exam-
ple, in the synthesis of pharmaceutical and natural prod-
ucts.24–29 Also, these compounds have been used as
intermediates in flavonoid chemistry,30–32 in the synthesis
of natural products and drug molecules.33
In our ongoing research in the synthesis of gem-dihydro-
peroxides,53,54 and their applications as oxidants for vari-
ous organic transformations,21 we became interested in
using these dihydroperoxides as potential oxidants for ep-
oxidation of trans-chalcones. Herein, we wish to report
for the first time the application of trans-3,5-dihydroper-
oxy-3,5-dimethyl-1,2-dioxolane (1) in the epoxidation of
a,b-unsaturated ketones. trans-3,5-Dihydroperoxy-3,5-
dimethyl-1,2-dioxolane has been prepared in this labora-
tory following the reported procedure as a white crystal-
line compound in high yield (Scheme 1).21
aq H2O2 (30%)
SnCl2⋅2H2O (cat.)
H
OOH
O
O
O
O
HOO
MeCN, r.t.
H
1
Scheme 1
We preliminary studied the Weitz–Scheffer epoxidation
reaction of trans-chalcone 2a as the test compound using
trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane (1)
and 1.0 M aqueous KOH as the base at room temperature.
To study the effect of the solvent on the reaction, various
solvents including n-hexane, toluene, dichloromethane,
ethanol N,N-dimethyl formamide (DMF), acetonitrile,
1,2-dimethoxyethane (DME), and 1,4-dioxane were ex-
amined and the results are summarized in Table 1. As
could be seen in Table 1, the polarity of the solvent plays
a crucial role in the reaction yield. So that, nonpolar n-
hexane and toluene were found not suitable for this reac-
tion, since no epoxide was obtained in these two solvents
after a long reaction time (entries 1 and 2). Nevertheless,
the reaction did happen in polar solvents, CH2Cl2 (entry
3), EtOH (entry 4), and DMF (entry 5) to give the desired
epoxide 3a in 35%, 60%, and 85% yields, respectively.
Water-soluble polar solvents MeCN (entry 6), DME (en-
try 7), and 1,4-dioxane (entry 10) produced the epoxide
Several approaches to epoxides have been investigated
using various systems such as, m-chloroperbenzoic acid,34
SYNLETT 2010, No. 18, pp 2755–2758
x
x
.x
x
.2
0
1
0
Advanced online publication: 08.10.2010
DOI: 10.1055/s-0030-1258996; Art ID: G23910ST
© Georg Thieme Verlag Stuttgart · New York

2756
D. Azarifar, K. Khosravi
LETTER
even in better 87%, 96%, and 90% yields, respectively. chalcones 2b–q under the optimized conditions (r.t., 1.0
Among the solvents examined, 1,2-dimethoxyethane M aq KOH in DME) (Scheme 2), and the results are sum-
(DME) proved to be the solvent of choice for this reaction marized in Table 2.55 As shown in Table 2, the oxidant 1
in producing the epoxide in almost quantitative yield has conveniently accomplished the conversion of all
(96%, entry 7) within two hours without posing any tox- trans-chalcones 2a–q into their corresponding epoxides
icity.
3a–q in relatively short reaction times with excellent
yields (82–96%, Table 2). Also, it should be mentioned
that in all the reactions acetylacetone was recovered in
high yield after the reaction as evidenced by the spectral
analysis. The structures of the products 3a–q were fully
established by analysis of their spectral (1H NMR, 13C
NMR, IR) and physical data and compared with those re-
ported.45,56
Table 1 Solvent Screening in the Epoxidation of trans-Chalcone 2a
with trans-3,5-Dihydroperoxy-3,5-dimethyl-1,2-dioxolane (1)a
O
O
1, aq KOH
O
Ph
Ph
Ph
solvent, r.t.
Ph
2a
3a
Entry
1
Solvent
n-hexane
toluene
CH2Cl2
EtOH
Time (h) Yield (%)b Oxidant (mmol)
O
O
1, aq KOH (1.0 M)
O
26
26
24
12
4
0
0
1
Ar2
Ar1
Ar2
....Ar1
dioxane, r.t.
2
1
2a–q
3a–q
3
35
60
85
87
96
92
90
90
85
36
42
1
Scheme 2
4
1
Table 2 Epoxidation of a,b-Unsaturated Ketones 2a–q with trans-
3,5-Dihydroperoxy-3,5-dimethyl-1,2-dioxolane (1) under the Opti-
mized Conditionsa
5
DMF
1
6
MeCN
DME
7
1
Entry Ar1
Ar2
Product Time (h) Yield (%)b
7
2
1
1
2
Ph
Ph
3a
3b
2
96
92
90
93
95
92
94
94
94
90
91
90
90
82
95
94
92
8
DME
2
2
Ph
2-ClC6H4
3
9
DME
3
0.5
1
3
Ph
4-MeOC6H4 3c
4
10
11
12
13
1,4-dioxane
1,4-dioxane
DMEc
2
4
Ph
2-naphthyl
Ph
3d
3e
3f
3
2
0.5
1
5
4-ClC6H4
4-ClC6H4
4-ClC6H4
2-ClC6H4
4-ClC6H4
3-ClC6H4
4-ClC6H4
4-ClC6H4
2.5
3
2
6
4-ClC6H4
4-MeC6H4
4-MeC6H4
2-naphthyl
2-naphthyl
2-thionyl
2-furyl
DMEc
2
2
7
3g
3h
3i
2
a All reactions were carried out with trans-chalcone 2a (1.0 mmol), aq
KOH (1.0 M, 1.0 mL), and the solvent (5.0 mL) at r.t.
b Isolated yield.
8
3
c With 30% H2O2 as the oxidant.
9
3
10
11
12
13
14
15
16
17
3j
3
It was observed that, using lower or higher amounts of the
oxidant 1 did not show any improving effect on the yield
(entries 8 and 9). Also, the effect of the base on the reac-
tion was investigated using different bases such as aque-
ous NaOH, KOH, hexamethylenetetramine, and n-
Bu4NOH. Among these, KOH was found to be the most
convenient in terms of yield (96%) and reaction time (2
h), whereas no detectable amount of epoxide was formed
when hexamethylenetetramine and n-Bu4NOH were used
as the bases. The role of the base used in the reaction was
substantiated by conducting the reaction in the absence of
KOH that resulted in only trace amount of the expected
epoxide. In order to compare the oxidative power of the
oxidant 1 with that of H2O2, the reaction was carried out
by using 30% H2O2 in DME under similar reaction condi-
tions and lower yields of the epoxide were obtained (en-
tries 12 and 13).
3k
3l
2.5
2.2
3
4-MeC6H4 Ph
4-MeOC6H4 Ph
4-O2NC6H4 Ph
3-O2NC6H4 Ph
4-O2NC6H4 2-naphthyl
3m
3n
3o
3p
3q
5
2
2.5
2.5
a All reactions were carried out with a,b-unsaturated ketone (1.0
mmol), trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxolane (1, 1.0
mmol), aq KOH (1.0 M, 1.0 mL), and 1,4-dioxane (5.0 mL) at r.t.
b Isolated yield.
On the basis of the experimental evidences, a probable
mechanism to explain the stereoselective formation of
trans-epoxides 3 is depicted in Scheme 3. As shown in
To develop the scope of reaction, we were encouraged to
extend this reaction to a variety of other substituted trans-
Synlett 2010, No. 18, 2755–2758 © Thieme Stuttgart · New York

LETTER
Epoxidation of a,b-Unsaturated Ketones
2757
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HOO–
OH–
OH–
HO
O
O
O
OH–
O
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H
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(A)
H
2
3
Scheme 3
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LETTER
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mL). The reaction mixture was stirred at r.t. for 2 h. After
completion of the reaction (TLC), the remaining peroxide
was neutralized with aq Na2SO3 solution. The resulting
mixture was diluted with Et2O (15 mL) and washed with
H2O (10 mL). The organic layer was dried over anhyd
MgSO4, and then the solvent was removed under reduced
pressure. The remaining crude product was purified by
column chromatography (eluent hexane–EtOAc, 90:10) to
provide pure epoxide3 (Table 2). Physical and spectroscopic
(IR, 1H NMR, and 13C NMR) data for some selected
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Compound 3g: white solid, mp 72–74 °C. 1H NMR (90
MHz, CDCl3–TMS): d = 7.10–8.00 (m, 8 H), 4.42 (d, 1 H),
4.03 (d, 1 H), 2.21 (s, 3 H). 13C NMR (22.5 MHz, CDCl3):
d = 195.1, 143.6, 136.0, 134.2, 129.0, 125.8, 70.3, 63.0,
25.5. IR (KBr): nmax = 3069, 1677, 1605, 1415, 1236, 1162,
1012, 899, 766, 674 cm–1. Anal. Calcd (%) for C16H13ClO2:
C, 70.59; H, 4.78. Found: C, 70.52.14; H, 4.74. MS (EI):
m/z = 272 [M+].
Compound 3m: white solid, mp 78–80 °C. 1H NMR (90
MHz, CDCl3–TMS): d = 7.20–8.00 (m, 9 H), 4.36 (d, 1 H),
4.04 (d, 1 H), 2.37 (s, 3 H). 13C NMR (22.5 MHz, CDCl3):
d = 193.5, 155.0, 150.8, 142.4, 136.0, 131.05, 129.7, 126.0,
114.4, 72.5, 62.1, 55.6. IR (KBr): nmax = 3020, 2983, 2867,
1667, 1583, 1502, 1455, 1305, 1279, 1165, 1140, 1054, 827,
731, 693 cm–1. Anal. Calcd (%) for C16H14O2: C, 80.67; H,
5.88. Found: C, 80.63; H, 5.82. MS (EI): m/z = 238 [M+].
Compound 3o: white solid, mp 146–148 °C. 1H NMR (90
MHz, CDCl3–TMS): d = 7.50–8.30 (m, 9 H), 4.30 (d, 1 H),
4.18 (d, 1 H). 13C NMR (22.5 MHz, CDCl3): d = 192.2,
153.8, 143.5, 140, 138.0, 130.7, 128.5, 125.0, 119.6, 70.1,
62.5. IR (KBr): nmax = 3063, 1659, 1594, 1493, 1395, 1333,
1128, 824, 742, 687 cm–1. Anal. Calcd (%) for C15H11NO4:
C, 66.91; H, 4.09; N, 5.20. Found: C, 66.82; H, 4.02; N, 5.15.
MS (EI): m/z = 269 [M+].
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(55) Caution
Although we did not encounter any problem with trans-3,5-
dihydroperoxy-3,5-dimethyl-1,2 dioxolane (1), it is
potentially explosive and should be handled with
precautions; all reactions should be carried out behind a
safety shield inside a fume hood and transition-metal salts or
heating should be avoided.
Preparation of trans-3,5-Dihydroperoxy-3,5-dimethyl-
1,2-dioxolane (1)21
To a stirred solution of acetylacetone (100 mg, 1 mmol) in
MeCN (5 mL) was added SnCl2⋅2H2O (45 mg, 0.2 mmol),
and stirring of the reaction mixture was continued for 5 min
at r.t. Then, aq 30% H2O2 (5 mmol) was added to the reaction
mixture and was allowed to stir for 12 h at r.t. After
completion of the reaction as monitored by TLC, H2O (15
mL) was added, and the product was extracted into EtOAc
(2 ´ 10 mL). The combined organic layer was dried over
anhyd MgSO4 and evaporated under reduced pressure to
give almost pure white crystalline product 1, in 85% yield
(140 mg); mp 98–100 °C.
Compound 3p: white solid, mp 117–119 °C. 1H NMR (90
MHz, CDCl3–TMS): d = 7.50–8.03 (m, 9 H), 4.32 (d, 1 H),
4.22 (d, 1 H). 13C NMR (22.5 MHz, CDCl3): d = 198.2,
153.8, 145.7, 137.4, 134.3, 133.0, 129.5, 126.8, 121.7, 71.1,
62.0. IR (KBr): nmax = 3061, 3025, 2923, 1797, 1595, 1495,
1395, 1337, 1139, 848, 747, 690 cm–1. Anal. Calcd (%) for
C15H11NO4: C, 66.91; H, 4.09; N, 5.20. Found: C, 66.85; H,
4.04; N, 5.17. MS (EI): m/z = 269 [M+].
General Experimental Procedure
To a mixture of trans-chalcone 2 (1.0 mmol) and trans-3,5-
dihydroperoxy-3,5-dimethyl-1,2-dioxolane (1, 166 mg, 1
mmol) in DME (5 mL) was added 1.0 M aq KOH solution (1
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Synlett 2010, No. 18, 2755–2758 © Thieme Stuttgart · New York

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