One-pot synthesis of chalcone epoxides - A green chemistry strategy

Article abstract of DOI:10.1016/j.tetlet.2014.06.057

Waste minimization is a very important aspect of an environmentally benign protocol. A one-pot consecutive process has been developed for chalcone epoxide synthesis that allows compounds to be prepared without having to isolate and purify the intermediates. The strategy utilizes consecutive Claisen Schmidt condensation and epoxidation reactions to prepare chalcone epoxides from substituted benzaldehydes and acetophenones in good yields.

Full text of DOI:10.1016/j.tetlet.2014.06.057

Accepted Manuscript
One-pot synthesis of chalcone epoxides – A green chemistry strategy
Dalyna Ngo, Mbelu Kalala, Victoria Hogan, Renuka Manchanayakage
PII:
S0040-4039(14)01048-X
DOI:
http://dx.doi.org/10.1016/j.tetlet.2014.06.057
TETL 44781
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
30 May 2014
12 June 2014
13 June 2014
Please cite this article as: Ngo, D., Kalala, M., Hogan, V., Manchanayakage, R., One-pot synthesis of chalcone
epoxides – A green chemistry strategy, Tetrahedron Letters (2014), doi: http://dx.doi.org/10.1016/j.tetlet.
2014.06.057
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1
Tetrahedron Letters
journal homepage: www.els evier.com
One-pot synthesis of chalcone epoxides – A green chemistry strategy
Dalyna Ngoa, Mbelu Kalalaa, Victoria Hogana, and Renuka Manchanayakagea*
a Department of Chemistry, Susquehanna University, 514 University Avenue, Selinsgrove, PA 17870
ARTICLE INFO
ABSTRACT
Article history:
Received
Waste minimization is a very important aspect of an environmentally benign
protocol. A one-pot consecutive process has been developed for chalcone epoxide
synthesis that allows compounds to be prepared without having to isolate and
purify the intermediates. The strategy utilizes consecutive Claisen Schmidt
condensation and epoxidation reactions to prepare chalcone epoxides from
substituted benzaldehydes and acetophenones in good yields.
Received in revised form
Accepted
Available online
Keywords:
One-pot synthesis
Chalcone epoxides
Epoxidation
2009 Elsevier Ltd. All rights reserved
.
Claisen Schmidt condensation
∗ Corresponding author. Tel.: +1-570-372-4608; fax: +1-570-372-2752; e-mail: manchanayakage@susqu.edu

2
Tetrahedron Letters
At an era of new development and technology, a shift in
chemistry principles, aqueous hydrogen peroxide is one of the
oxidants of choice because of its ease of handling, high active
oxygen content and the formation of water as the only
byproduct.9 Armed with this information, we investigated the
application of one-pot consecutive reactions of Claisen
Schmidt condensation and epoxidation to prepare chalcone
epoxides.
emphasis towards more environmental friendly chemical
approaches has become of great importance. Green chemistry,
also widely-known as sustainable chemistry, is the “design of
chemical products and processes that reduce or eliminate the
use or generation of hazardous substances”.1 This form of
environmentally safe chemistry can be applied across the life
cycle of different chemical products ranging from research,
industry, manufacture, and design.2 Recent literature shows
that green chemistry has the significant potential for not only
reducing byproducts, waste pollutants, and energy costs, but
also the potential to develop new methodologies towards
previously unobtainable chemical products.3
One-pot syntheses have been previously introduced as a green
chemistry approach.4 This simple, yet efficient method allows
compounds to be prepared without having to isolate and
purify the intermediates thereby reducing waste and
increasing reaction efficiency. Reacting three or more
components in a single operation can avoid the use of large
amounts of solvents and expensive purification techniques.
There are two forms of one-pot syntheses. In a one-pot
multicomponent process, desired reactants are added into one
reactor in a single step whereas a one-pot consecutive process
occurs when the reactants are added in a series of different
stages under different experimental conditions.5 In this paper,
we introduce a simple and efficient one-pot synthesis for
chalcone epoxides (Figure 1).
Table 1: Reaction conditions and results for one-pot syntheses
of chalcone epoxides
Entry Solvent
NaOH/
H2O2/
molar eq. molar eq.
Time/
Yieldb
%
19
43
43
45
72
86
86
h
3
3
3
5
3
3
3
5
1
2
3
4
5
6
7
Ethanol
Ethanol
Ethanol
Ethanol
Methanol
Methanol
Methanol
Methanol
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
2.5
3.0
2.5
1.5
2.5
3.0
2.5
8
a
87
4-chlorobenzaldehyde (5 mmol), acetophenone (5 mmol)
and 30% aq. NaOH (7.5 mmol) at r.t. followed by 30% H2O2
at 0 oC. b Isolated yields.
The reaction conditions for one-pot synthesis was developed
using 4-chlorobenzaldehyde and acetophenone (Figure 2).
First 4-chlorobenzaldehyde and acetophenone were stirred at
room tempearature in the presence of 1.5 molar equivelant of
30% aqueous NaOH in ethanol for 1.5 h to complete the step
1; Claisen Schmidt condensation. The formation of a solid
product of chalcone was observed. To the reaction mixture, a
o
solution of 30% H2O2 was then dropwise added at 0 C and
stirred another 1.5 h to complete the epoxidation step. After
vacuume filtration, the solid product was recovered and
analyzed using spectroscopic methods. The highest yield of
43% was obtained in ethanol when 2.5 molar equivelant of
H2O2 was used (Table 1, entry 2). In addition, the synthesis
was performed by increasing the molar equivelant of H2O2
and extending the overall reaction time from 3 to 5 hours by
increasing the reaction time of each step in an hour (Table 1,
entries 3 and 4). However, the reaction yield was not
significantly changed with the change of these parameters.
When the same reaction conditions were used to carry out the
reaction in methanol, the percent yield of chalcone epoxide
was increased up to 86% (Table 1, entry 6). It is possible that
the greater solubility of intermediate chalcone in methanol
over ethanol improves the overall reaction yield.10 Again,
increasing the molar equivalency of H2O2 or extending the
overall reaction time in methanol did not significantly
improve the yields (Table 1, entris 7 and 8). Having
established the optimum conditions for the reaction (Table 1,
entry 6), we then proceeded to investigate its generality and
scope. A series of one-pot syntheses of various substituted
benzaldehydes and substituted acetophenones were performed
in methanol and these results are provided in Tables 2 and 3.
Figure 1: Synthetic design for the one-pot synthesis of
chalcone epoxides.
Chalcone epoxides (α,β-epoxyketones) are an important class
of organic compounds and used as constituents in perfume
formulations, and as intermediates in the production of
flavoring substances.6 They have distinct structural features
and high synthetic utility as they not only undergo the usual
reactions of epoxides, but are also susceptible to several
useful reactions owing to the presence of carbonyl groups.7
Epoxidation has been widely studied using various reagents,
catalysts and reaction conditions.8 Taking into account green
Figure 2: One-pot synthesis of substituted benzaldehydes with
acetophenone.

3
Table 2: Results of the one-pot syntheses of chalcone
epoxides from substituted benzaldehydes and acetophenonea
Table 3: Results of one-pot syntheses of chalcone epoxides
from substituted acetophenones and 4-chlorobenzaldehydea
Entry Substituted
benzaldehyde
Chalcone epoxide
Yieldb
%
Entry Substituted
acetophenone
Chalcone epoxide
Yieldb
%
1
2
Benzaldehyde
84
1
4-bromo
acetophenone
84
4-chloro
benzaldehyde
86
2
3
4-methyl
acetophenone
74
68
4-methoxy
acetophenone
3
4
4-methyl
benzaldehyde
61
43
4
4-nitro
acetophenone
62
4-methoxy
benzaldehyde
a
4-chlorobenzaldehyde (5 mmol), substituted acetophenone
(5 mmol) and 30% aq. NaOH (7.5 mmol) at r.t. followed by
30% H2O2 (12.5 mmol) at 0 oC. b Isolated yields.
5
6
4-nitro
benzaldehyde
72
85
The one-pot syntheses of substituted benzaldehydes with
acetophenone resulted the corresponding chalcone epoxides in
moderate to good yields under these conditions (Table 2).11,12
The electronic effect of the substituents on benzaldehyde
showed slight influence on the reactions. The benzaldehyde
derivatives with electron withdrawing groups gave higher
yields when comparing to those with electron donating
groups. While the yields of 4- and 2-substituted
benzaldehydes were comparable, 3-substituted benzaldehydes
showed somewhat lower yields (Table 2, entries 8 and 9).
One-pot syntheses performed using substituted acetophenone
with 4-chlorobenzaldehyde also afforded corresponding
chalcone epoxides in good yields (Figure 3, Table 3).11.13 4-
chlorobenzaldehyde was used in these reactions as it afforded
the best yield with acetophenone (Table 2, entry 2). The
electronic effect of the substituents on acetophenone showed
no significant influence on these syntheses.
2-chloro
benzaldehyde
7
8
2-methyl
benzaldehyde
60
64
3-chloro
benzaldehyde
The synthesis was also completed via conventional two-step
method using 4-chlorobenzaldehyde and acetophenone (5
molar equiv. of each). After completing the step 1 using 30%
NaOH (3 molar equiv.) in methanol, intermediate chalcone
was isolated in 92% yield. Epoxidation of chalcone in the
second step using 30% NaOH (3 molar equiv.) and 30% H2O2
(5 molar equiv.) afforded the final epoxide in 90% yield. The
overall yield of chalcone epoxide obtained from the two-step
method was calculated to be 83%. When comparing with the
conventional method, the developed one-pot synthesis
eliminates the isolation time for the intermediate and reaction-
set up time for the second step. In addition, one-pot synthesis
uses less solvents and reagents which minimizes the waste
formation. Methanol was used only once in this method and
NaOH added in step 1 to initiate the Claisen Schmidt
condensation, also activates the H2O2 used in step 2 for the
epoxidation of intermediate chalcone (Figure 4).14
9
3-methyl
benzaldehyde
48
a Substituted benzaldehyde (5 mmol), acetophenone (5 mmol)
and 30% aq. NaOH (7.5 mmol) at r.t. followed by 30% H2O2
(12.5 mmol) at 0 oC. b Isolated yields.
Figure 3: One-pot synthesis of substituted acetophenones with
4-chlorobenzaldehyde.

4
Tetrahedron Letters
8. (a) Aminia, M. Haghdoostb, M. M.; Bagherzadeh, M.
Coordination Chem. Rev. 2014, 268, 83-100. (b) Bernini, R.;
Mincione, E.; Coratti, A.; Fabrizib, G.; Battistuzzib, G.
Tetrahedron 2004, 60, 967-971. (c) Jia, R.; Yub, K.; Loua, L.;
Liu S. Journal of Molecular Catalysis A: Chemical 2013, 378,
7-16. (d) Erdem, O.; Guzel, B. Inorganica Chimica Acta
2014, 418, 153-156.
Figure 4: Mechanism for the epoxidation step
9. (a) Yamaguchi, K.; Mori, K.; Mizugaki, T.; Ebitani K.;
Kaneda, K. J. Org. Chem., 2000, 65, 6897-6903. (b) Hanma,
T.; Nakajo, M.; Mizugaki, T.; Ebitani K.; Kaneda, K.;
Tetrahedron Lett. 2002, 43, 6229-6232. (c) Lakouraj, M. M.;
Movassagh, B.; Bahrami, K. Synth. Commun. 2001, 31, 1237-
1242.
10. Cativiela, C.; Figueras, F.; Fraile, J. M.; Garcia, J. I.;
Mayoral, J. A. Tetrahedron Lett. 1995, 36, 4125-4128.
11. Representative procedure: A 30 wt% aq. NaOH solution
(1 mL) was added to a mixture of substituted benzaldehyde (5
mmol), substituted acetophenone (5mmol) and methanol (10
mL), and stirred at room temperature for 1.5 h. The reaction
mixture was heated to dissolve the solid and a 30% hydrogen
peroxide solution (1 mL) was added. Then, the reaction was
stirred between 0-2 oC for 1.5 h. The final chalcone epoxides
were recovered by vacuum filtration.
In conclusion, we have developed a one-pot greener synthesis
for chalcone epoxides using consecutive reactions of Claisen
Schmidt condensation and epoxidation with low concentration
of hydrogen peroxide. The epoxides were synthesized from
substituted benzaldehydes and acetophenones and obtained in
good yields. The developed strategy allows chalcone epoxides
to be prepared without having to isolate and purify chalcone
intermediates. Selective ring opening of these chalcone
epoxides in ionic liquids are currently being investigated in
this laboratory.
Acknowledgement
The authors thank Susquehanna University Summer Partners
Program for the financial support of this research.
References and notes
12. All products exhibited spectral properties consistent with
1
the assigned structures. H, 13C and IR data are as follows.
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1
Table 2, entry 1: H NMR (400 MHz, CDCl3) δ 8.01 (d, J =
8.0 Hz, 2H), 7.61 (t, J = 6.4 Hz, 1H), 7.49 (t, J = 7.6 Hz, 2H),
7.38 (m, 5H), 4.27 (d, J = 2 Hz, 1H), 4.08 (d, J = 2 Hz, 1H);
13C NMR (100 MHz, CDCl3) δ 192.5, 135.6, 134.1, 129.2,
129.0, 128.9, 128.5, 125.9, 61.1, 59.5; IR (ν/cm-1) 3074, 1687,
1450, 1280. Entry 2: 7.98 (d, J = 7.6 Hz, 2H), 7.62 (t, J = 7.2
Hz, 1H), 7.48 (t, J = 7.6 Hz, 2H), 7.36 (d, J = 8.0 Hz, 2H),
7.29 (d, J = 8.0 Hz, 2H), 4.24 (d, J = 2 Hz, 1H), 4.05 (d, J = 2
Hz,
1H);
13C
NMR
(100
MHz,
CDCl3)
δ 192.8, 135.5, 135.0, 134.2, 134.1, 129.1, 129.0, 128.5, 127.2
1
, 61.0, 58.8; IR (ν/cm-1) 3008, 1680, 1350, 1200. Entry 3: H
NMR (400 MHz, CDCl3) δ 8.00 (d, J = 8.0 Hz, 2H), 7.61 (t, J
= 6.8 Hz, 1H), 7.48 (t, J = 8.0 Hz, 2H), 7.26 (d, J = 8.0 Hz,
2H), 7.20 (d, J = 8.0 Hz, 2H), 4.29 (d, J = 2 Hz, 1H), 4.05 (d,
J = 2 Hz, 1H), 2.38 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ 193.3, 139.2, 135.6, 134.1, 132.6, 129.6, 128.9, 128.4,
125.9, 61.2, 59.6, 21.4; IR (ν/cm-1) 3050, 1655, 1400, 1350.
1
Entry 4: H NMR (400 MHz, CDCl3) δ 7.99 (d, J = 7.6 Hz,
2H), 7.60 (t, J = 7.6 Hz, 1H), 7.47 (t, J = 7.6 Hz, 2H), 7.28 (d,
J = 8.4 Hz, 2H), 6.91 (d, J = 8.4 Hz, 2H), 4.29 (d, J = 2 Hz,
1H), 4.01 (d, J = 2 Hz, 1H), 3.83 (s, 3H); 13C NMR (100
MHz, CDCl3) δ 193.3, 160.4, 135.6, 134.0, 130.3, 128.9,
128.5, 127.3, 114.3, 61.2, 59.5, 55.5; IR (ν/cm-1) 3065, 1690,
1420, 1280. Entry 5: 1H NMR (400 MHz, CDCl3) δ 7.98 (d, J
= 7.6 Hz, 2H), 7.61 (t, J = 7.2 Hz, 1H), 7.48 (t, J = 7.6 Hz,
2H), 7.36 (d, J = 8.0 Hz, 2H), 7.29 (d, J = 8.4 Hz, 2H), 4.24
(d, J = 2 Hz, 1H), 4.04 (d, J = 2 Hz, 1H); 13C NMR (100 MHz,
CDCl3) δ 192.2, 148.4, 142.9, 135.3, 134.4, 129.1, 128.5,
126.7, 124.2, 60.9, 58.1; IR (ν/cm-1) 3025, 1695, 1420, 695.
4. (a) Parsons, P. J.; Penkett, C. S.; Shell, A. J. Chem. Rev.
1996, 96, 195-206. (b) Domling, A. Chem. Rev. 2006, 106,
17-89.
5. (a) Jeon, H. J.; Choi, J. H.; Kang, J. K. Tetrahedron Lett.
2010, 51, 6243-6245. (b) Keyume, A.; Esmayil, Z.; Wang, L.;
Jun, F. Tetrahedron, 2014, 70, 3976-3980. (c) Suzuki, Y.;
Murofushi, M.; Manabe, K. Tetrahedron, 2013, 69, 470-473.
(d) Lu, B. Z.; Zhao, W.; Wei, H.; Dufour, M.; Farina, V.;
Senanayake, C. H. Organic Lett. 2006, 8, 3271-3274. (e)
Chung, W.; Lindovska, P.; Camp, J. E. Tetrahedron Lett.
2011, 52, 6785-6787. (f) Mattia, E.; Porta, A.; Merlini, V.;
Zanoni, G.; Vidari, G. Chemistry, 2012, 18, 11894-11898.
6. (a) Ho, T. L.; Liu, S. H. Synth. Commun. 1983, 13, 685-
690. (b) Huo, C.; Xu, X.; Jia, X.; Wang, X.; An, J.; Sun, C.
Tetrahedron 2012, 68, 190-196.
7. (a) Hasegawa, E.; Ishiyama, K.; Fujita, T.;Kato, T.; Abe, T.
J. Org. Chem. 1997, 62, 2396-2400. (b) Joy, B.; Ghosh, S.;
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573-577. (c) Chang, C.; Kumar, M. P.; Liu, R. J. Org. Chem.
2004, 69, 2793-2796. (d) Suda, K.; Baba, K.; Nakajima, S.;
Takanami, T. Chem. Commun. 2002, 2570-2571.
1
Entry 6: H NMR (400 MHz, CDCl3) δ 8.09 (d, J = 7.3 Hz,
2H), 7.15-7.61 (m, 9H), 4.34 (d, J = 2 Hz, 1H), 4.11 (d, J = 2
Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 192.8, 134.9, 134.1,
133.9, 133.7, 129.8, 129.5, 128.9, 128.5, 126.2, 124.8, 60.1,
1
57.2; IR (ν/cm-1) 3020, 1688, 1600, 1350. Entry 7: H NMR
(400 MHz, CDCl3) δ 8.00 (d, J = 7.4 Hz, 2H), 7.74 (t, J = 7.2
Hz, 1H), 7.58 (t, J = 7.3 Hz, 2H), 7.25-7.15 (m, 4H), 4.21 (d, J
= 2 Hz, 1H), 4.02 (d, J = 2 Hz, 1H), 2.35 (s, 3H); 13C NMR
(100
MHz,
CDCl3)
δ 192.2, 139.5, 135.9, 135.7, 134.6, 129.9, 129.1, 128.9, 128.2
, 126.8, 123.5, 61.5, 59.2, 21.4; IR (ν/cm-1) 3021, 1675, 1580,

5
1
950. Entry 8: H NMR (400 MHz, CDCl3) δ 7.97 (d, J = 7.1
Hz, 2H), 7.60 (t, J = 7.0 Hz, 1H), 7.47 (t, J = 7.4 Hz, 2H),
7.23-7.31 (m, 4H), 4.22 (d, J = 2 Hz, 1H), 4.02 (d, J = 2 Hz,
1H); 13C NMR (100 MHz, CDCl3) δ 192.6, 137.9, 134.8,
134.6, 134.2, 130.5, 129.3, 129.0, 128.5, 125.8, 60.9, 58.6; IR
(ν/cm-1) 3010, 1669, 1200, 750. Entry 9: 1H NMR (400 MHz,
CDCl3) δ 7.99 (d, J = 7.4 Hz, 2H), 7.77 (t, J = 7.2 Hz, 1H),
7.60 (t, J = 7.3 Hz, 2H), 7.27-7.16 (m, 4H), 4.28 (d, J = 2 Hz,
1H), 4.02 (d, J = 2 Hz, 1H), 2.36 (s, 3H); 13C NMR (100
MHz,
CDCl3)
δ 193.2, 139.1, 135.9, 135.8, 134.1, 130.0, 129.0, 128.8, 128.4
, 126.4, 123.1, 61.1, 59.6, 21.5; IR (ν/cm-1) 3009, 1688, 1230,
980.
13. All products exhibited spectral properties consistent with
1
the assigned structures. H, 13C and IR data are as follows.
1
Table 3, entry 1: H NMR (400 MHz, CDCl3) δ 7.85 (d, J =
7.8 Hz, 2H), 7.61 (d, J = 7.2 Hz, 2H), 7.54 (d, J = 7.2 Hz, 2H),
7.36 (d, J = 8.0 Hz, 2H), 4.16 (d, J = 1.6 Hz, 1H), 4.03 (d, J =
1.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 192.6, 144.0,
136.8, 132.2, 129.9, 129.8, 129.6, 128.1, 127.1, 61.0, 58.9; IR
1
(ν/cm-1) 3024, 1690, 1420, 690. Entry 2: H NMR (400 MHz,
CDCl3) δ 7.88 (d, J = 7.8 Hz, 2H), 7.35 (d, J = 7.2 Hz, 2H),
7.30-7.25 (m, 4H), 4.22 (d, J = 2 Hz, 1H), 4.04 (d, J = 2 Hz,
1H), 2.37 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ 192.3, 145.3, 134.2, 134.0, 133.1, 129.7, 129.5, 128.6, 127.2
, 60.9, 58.7, 21.9; IR (ν/cm-1) 3015, 1685, 1215, 750. Entry 3:
1H NMR (400 MHz, CDCl3) δ 8.01 (d, J = 7.8 Hz, 2H), 7.55
(d, J = 7.6 Hz, 2H), 7.36 (d, J = 7.6 Hz, 2H), 6.96 (d, J = 8.0
Hz, 2H), 4.19 (d, J = 2 Hz, 1H), 4.04 (d, J = 2 Hz, 1H), 3.87
(s,
3H);
13C
NMR
(100
MHz,
CDCl3)
δ 191.1, 164.4, 142.5, 136.2, 134.5, 130.9, 129.6, 129.2, 113.9
, 60.9, 58.5, 55.6; IR (ν/cm-1) 3000, 1655, 1100, 695. Entry 4:
1H NMR (400 MHz, CDCl3) δ 8.02 (d, J = 7.2 Hz, 2H), 7.47
(d, J = 7.2 Hz, 2H), 7.34 (d, J = 7.2 Hz, 2H), 7.29 (d, J = 8.0
Hz, 2H), 4.23 (d, J = 2.0 Hz, 1H), 4.03 (d, J = 2.0 Hz, 1H);
13C NMR (100 MHz, CDCl3) δ 192.8, 135.4, 135.1, 134.2,
134.1, 129.1, 129.0, 128.4, 127.2, 61.0, 58.8; IR (ν/cm-1)
3024, 1690, 1420, 690.
14. Fraile, J. M.; Garcia, J. I.; Mayoral, J. A.; Sebti, S.; Tahir,
R. Green Chem. 2001, 3, 271-274.