An environmentally benign protocol: Catalyst-free Michael addition of aromatic amines to α,β-unsaturated ketones in glycerol

Article abstract of DOI:10.1007/s11164-012-0575-0

Glycerol was used as a reaction medium as well as promoter for aza-Michael addition of aromatic amines to electronic deficient α,β-unsaturated ketones. Various aromatic amines can react smoothly with chalcone, 2-cyclohexen-1-one, 2-cyclopenten-1-one, and

Full text of DOI:10.1007/s11164-012-0575-0

Res Chem Intermed (2013) 39:517–525
DOI 10.1007/s11164-012-0575-0
An environmentally benign protocol: catalyst-free
Michael addition of aromatic amines to a,b-unsaturated
ketones in glycerol
•
Anguo Ying Qunhui Zhang Hongmin Li
•
•
•
Gangfeng Shen Weizhong Gong Mingju He
•
Received: 16 April 2012 / Accepted: 24 April 2012 / Published online: 13 May 2012
Ó Springer Science+Business Media B.V. 2012
Abstract Glycerol was used as a reaction medium as well as promoter for aza-
Michael addition of aromatic amines to electronic deficient a,b-unsaturated ketones.
Various aromatic amines can react smoothly with chalcone, 2-cyclohexen-1-one,
2-cyclopenten-1-one, and ethyl vinyl ketone to achieve good to excellent yields in
the absence of any catalyst.
Keywords Glycerol Á Aza-Michael addition Á Catalyst free Á Recyclability
Introduction
Crude glycerol, generated by the biodiesel industry as a by-product, has attracted
much attention due to its good solubility, low cost, non-volatility and high boiling
point, non-toxicity, and that it is readily available. Thus, synthesis of new
compounds using glycerol as starting material has been studied by many chemists
[1, 2]. However, the direct utilization of glycerol as a reaction solvent in organic
synthesis was developed slowly. Wolfson et al. [3, 4] reported that Pd-catalyzed
Heck C–C coupling and Suzuki reaction could proceed smoothly in glycerol with
´ ˆ
the advantage of readily product isolation. Jerome’s group [5] observed that glycerol
can be used as a promising medium for ring opening of epoxide with amine under
catalyst-free conditions. He et al. [6] depicted that some condensation reactions of
aldehydes that are conventionally carried out using acid catalysts could be
A. Ying (&) Á G. Shen
School of Pharmaceutical and Chemical Engineering, Taizhou University,
Taizhou 318000, People’s Republic of China
e-mail: agying@tzc.edu.cn
A. Ying Á Q. Zhang Á H. Li Á W. Gong Á M. He
Zhejiang Hisoar Pharmaceutical Co. Ltd., Taizhou 318000, People’s Republic of China
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performed in catalyst-free conditions in glycerol, which is beneficial for promoting
the electrophilic activity of aldehydes.
Aza-Michael addition has been regarded as one of the widely used reactions for
carbon–nitrogen bond formation in modern organic chemistry. Conjugate addition
of various amines to a,b-unsaturated carbonyl compounds can readily afford
b-amino carbonyl products, which represent a particularly attractive approach,
providing rapid access to anticancer agents, antibiotics, and other drugs [7–9].
Recently, some efficient and green methodologies for aza-Michael addition of
aliphatic amines to electron-deficient olefins have been developed, which include
silica gel in acetonitrile [10], b-cyclodextrin in water [11], PEG (MW 400) and
2-hydroxyethylammonium formate using as reaction medium as well as reaction
catalyst [12, 13], boric acid in water [14], and even using water as solvent without a
catalyst [15]. The reports with regard to aza-Michael reaction of aromatic amines
were relatively scarce for their inertness compared to aliphatic amines [16, 17].
With our continuous efforts for the development of green and highly efficient
protocols for Michael addition [18–21] and encouraged by the successful
applications of glycerol in organic reactions, we herein report glycerol as a solvent
for aza-Michael addition of aromatic amines to electronic deficient a,b-unsaturated
ketones in the absence of a catalyst.
Results and discussion
Firstly, the reaction of aniline and chalcone was selected as a model. In an initial
screening of solvents, while traditional organic solvents such as dichloromethane,
toluene, acetonitrile, and methanol showed not to be effective for the reaction
(Table 1, entries 1–4), glycerol provided the final product with a promising value of
yield (Table 1, entry 8). Moreover, some green reaction medium such as water,
ionic liquids were attempted in the model reaction as solvents and some moderate
yields were obtained (Table 1, entries 5–7). Finally, glycerol was the optimal one
furnishing the best product yield, and was selected for subsequent experiments.
With the most appropriate reaction conditions in hand, the substrate scope was
next explored with different aromatic amines as well as various a,b-unsaturated
ketones. The results are summarized in Table 2. Aromatic amines bearing with
electron-donating substituents such as MeO and Me can react smoothly with
chalcone, affording excellent product yields within 2 days at 150 °C in glycerol
(Table 2, entries 1–3) while amine bearing with electron withdrawn group such as
NO2 almost gave no adduct (Table 2, entry 4). Cyclic ketones 2-cyclopenten-1-one,
2-cyclohexen-1-one were tested as Michael acceptors to react with various
arylamines. 2-Cyclohexen-1-one can proceed readily to afford the desired products
in excellent yields at 100 °C (Table 2, entries 7–10). However, lower reactivity was
observed when 2-cyclopenten-1-one was used as acceptor, probably due to low
reactivity of the five-membered ring (Table 2, entries 5–6). 4-Methyl substituted
aromatic amine provided a higher yield than that with 2-methyl substitution
(Table 2, entries 7–8), demonstrating the negative effect of steric hindrance on
the reaction processes. Moreover, acyclic ethyl vinyl ketone (EVK) was also
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Table 1 Results of the reaction between aniline (1 mmol) and chalcone (1 mmol) in various solvents
(1 mL) without any catalyst within 48 h
O
NH
O
NH2
+
Entry
Solvents
Reaction temperature (°C)
Yieldsa (%)
1
2
3
4
5
6
7
8
a
Toluene
CH2Cl2
Reflux
Reflux
Reflux
Reflux
Reflux
150
44
6
CH3OH
CH3CN
38
35
41
58
53
95
Water
[Bmim]BF4
[Bmim]PF6
Glycerol
150
150
Isolated yields
investigated. Gratifying, glycerol was very suitable for the reaction of EVK with
aromatic amines and 93–98 % product yields were achieved within 12 h of reaction
times (Table 2, entries 11–14). Finally, the reactions when other deficient carbonyl
compounds were employed as acceptors were tested to react with aniline in glycerol
at 150 °C. To our disappointment, almost no corresponding products were detected
(Table 2, entries 15–16).
The recyclability of glycerol was then studied using the reaction of aniline and
chalcone as a model. The results are shown in Table 3. Upon the completion of the
reaction, the reaction solution was extracted with ethyl acetate and purified by flash
1
chromatography. The addition product was identified by H NMR, 13C NMR, and
mass spectra. The residual liquid was directly reused for subsequent reactions. As
shown in Table 3, the recovered glycerol could be reused five times without an
obvious loss of reactivity.
As reported by other authors [6], glycerol may play a role as a promoter as well
as a reaction medium for the aza-Michael addition of aromatic amines to electron-
deficient a,b-unsaturated ketones. We speculated that strong solubility of glycerol
can make the Michael reaction a homogenous process, which increases the
reactivity. Secondly, glycerol as a hydrogen donor can form stabilized hydrogen
bonds with the carbonyl of the ketone.
Conclusions
In conclusion, glycerol was proven to be an effective medium for promoting an aza-
Michael reaction between substituted aromatic amines and a,b-unsaturated ketones.
In glycerol, various aromatic amines can react smoothly with electron-deficient
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A. Ying et al.
Table 2 Results of aza-Michael reaction between various substituted aromatic amines and a,b-unsatu-
rated ketones
Entry Michael donors
Acceptors
Reaction Reaction Isolated
time (h) temperature yields
(°C)
1
48
150
150
150
150
95
92
O
O
O
O
NH2
2
36
36
96
NH2
3
97
MeO
NH2
4
NR
O2N
NH2
5
6
7
48
48
24
100
100
100
68
75
83
O
O
O
NH2
Br
NH2
NH2
8
24
24
100
100
92
85
O
O
NH2
9
Cl
NH2
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Table 2 continued
Entry Michael donors
Acceptors
Reaction Reaction Isolated
time (h) temperature yields
(°C)
10
24
100
90
O
NH2
11
12
12
12
100
100
100
98
95
96
O
O
O
MeO
NH2
12
13
NH2
NH2
14
15
16
12
96
96
100
150
150
93
NR
NR
O
O
Cl
NH2
CN
NH2
NH2
NH2
Reaction conditions: aromatic amines (1 mmol), a,b-unsaturated ketones (1 mmol), glycerol (1 mL), catalyst-free
conditions
Table 3 Recyclability of
glycerol for reaction of aniline
and chalcone
Cycle
Reaction time (h)
Isolated yield (%)
1
2
3
4
5
48
48
48
60
60
96
94
92
98
95
Reaction conditions: aniline
(1 mmol), chalcone (1 mmol),
glycerol (1 mL), catalyst-free
conditions and 150 °C
olefins to afford desired products in the absence of any catalyst. Considering the
high environmental compatibility and sustainability and catalytic activity of
glycerol, the extension of its application to organic reactions are underway in our
laboratory.
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Experimental
All chemicals were purchased from Aldrich or Fluka. 1H and 13C NMR were
recorded on a Bruker Avance DPX 400 spectrometer at 400 and 100 MHz in CDCl3
and DMSO-d6, respectively. Chemical shifts were reported in parts per million (d),
relative to the internal standard of tetramethylsilane (TMS). Melting points were
determined using a YRT-3 apparatus and were not corrected. Mass spectrometry
data were obtained on Brucker Esquire-LC for electro-spay (MS-ES) measurements.
Elemental analysis was carried out on a Carlo Erba 1160. All reactions were
monitored by thin-layer chromatography (TLC). Flash chromatography was
performed on silica gel (100–200 mesh). All Michael adducts were purified
through column chromatography and were characterized by NMR analysis, melting
points, and MS.
General procedure for catalyst-free aza-Michael reaction of aliphatic amines
with a,b-unsaturated compounds in glycerol
To a mixture of the aromatic amine (1 mmol) and Michael acceptor (1 mmol) in a
10-mL flask equipped with a magnetic stirrer was added glycerol (1 mL). The
reaction mixture was stirred at rational temperature for the desired time until the
disappearance of the starting material, monitored by TLC. Upon completion of the
reaction, the mixture was extracted with ethyl acetate several times. The combined
organic phase was concentrated through vacuum evaporation and the resulting crude
product was purified by silica-column chromatography to give the desired product.
These products are in good agreement with spectra data of the literature. The
recovered glycerol was then reused in subsequent reactions.
N-(3-oxo-1,3-diphenylpropyl)aniline (Table 2, entry 1)
1
White solid, mp 173–175 °C (lit. [23], 172–174 °C); H NMR (400 MHz, CDCl3):
d = 7.92 (d, 2H, J = 8.0 Hz, ArH), 7.56 (t, 1H, J = 7.2 Hz, ArH), 7.46–7.43 (m,
4H, ArH), 7.33 (t, 2H, J = 7.6 Hz, ArH), 7.24 (t, 1H, J = 7.6 Hz, ArH), 7.10 (t,
2H, J = 8.0 Hz, ArH), 6.67 (t, 1H, J = 7.2 Hz, ArH), 6.57 (d, 2H, J = 8.0 Hz,
ArH), 5.02 (brs, 1H, NH), 4.58–4.57 (m, 1H, CH), 3.55–3.40 (m, 2H, CH2); 13C
NMR (100 MHz, CDCl3): d = 198.2, 146.9, 142.9, 136.5, 133.4, 129.0, 128.8,
128.7, 128.2, 127.3, 126.3, 117.7, 113.7, 54.6, 46.3; ESI–MS (m/z): 302 (M?1).
N-(3-oxo-1,3-diphenylpropyl)-4-methylaniline (Table 2, entry 2)
1
White solid, mp 170–172 °C (lit. [23], 170–171 °C); H NMR (400 MHz, CDCl3):
d = 7.94–7.89 (m, 2H, ArH), 7.55 (t, 1H, J = 7.2 Hz, ArH), 7.43–7.42 (m, 4H,
ArH), 7.32–7.22 (m, 4H, ArH), 6.89 (d, 2H, J = 7.2 Hz, ArH), 6.47 (d, 2H,
J = 7.2 Hz, ArH), 4.96 (brs, 1H, NH), 4.43–4.41 (m, 1H, CH), 3.52–3.37 (m, 2H,
CH2), 2.17 (s, 3H, CH3); 13C NMR (100 MHz, CDCl3): d = 198.3, 144.7, 143.1,
136.7, 133.4, 129.6, 129.0, 128.8, 128.7, 128.2, 127.3, 126.4, 114.0, 55.0, 46.3,
20.3; ESI–MS (m/z): 316 (M?1).
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N-(3-oxo-1,3-diphenylpropyl)-4-methoxyaniline (Table 2, entry 3)
1
White solid, mp 142–143 °C (lit. [24], 140–144 °C); H NMR (400 MHz, CDCl3):
d = 7.90 (d, 2H, J = 7.6 Hz, ArH), 7.55 (t, 1H, J = 7.2 Hz, ArH), 7.43–7.42 (m,
4H, ArH), 7.31 (t, 2H, J = 7.2 Hz, ArH), 7.22 (t, 1H, J = 7.2 Hz, ArH), 6.67 (d,
2H, J = 8.4 Hz, ArH), 6.52 (d, 2H, J = 8.4 Hz, ArH), 4.92 (brs, 1H, NH), 4.23 (m,
1H, CH), 3.68 (s, 3H, CH3), 3.50–3.36 (m, 2H, CH2); 13C NMR (100 MHz, CDCl3):
d = 198.3, 152.3, 143.2, 141.2, 136.7, 133.4, 128.8, 128.7, 128.2, 127.3, 126.4,
115.3, 114.7, 55.6, 46.4, 39.9; ESI–MS (m/z): 332 (M?1).
3-(o-Toluidinyl)-cyclopentan-1-one (Table 2, entry 5)
Pale yellow oil; 1H NMR (400 MHz, CDCl3): d = 7.16–7.02 (m, 2H, ArH),
6.73–6.65 (m, 2H, ArH), 4.19–4.10 (m, 1H, CH), 3.57 (brs, 1H, NH), 2.77–2.68 (m,
2H, CH2), 2.51–1.97 (m, 4H, 2 9 CH2), 2.44–2.19 (m, 2H, CH2); 13C NMR
(100 MHz, CDCl3): d = 217.1, 144.7, 134.5, 130.3, 127.0, 117.6, 110.4; ESI–MS
(m/z): 190 (M?1).
3-(2-Bromoanilinyl)-cyclopentan-1-one (Table 2, entry 6)
Pale yellow oil; 1H NMR (400 MHz, CDCl3): d = 7.45–7.39 (m, 1H, ArH),
7.22–7.17 (m, 1H, ArH), 6.67–6.60 (m, 2H, ArH), 4.37 (brs, 1H, NH), 4.14 (m, 1H,
CH), 2.77–2.69 (m, 2H, CH2), 2.53–2.45 (m, 2H, CH2), 2.44–2.19 (m, 2H, CH2);
13C NMR (100 MHz, CDCl3): d = 216.4, 143.7, 132.6, 128.5, 118.5, 111.8, 110.1,
51.1, 45.8, 36.6, 29.7; ESI–MS (m/z): 255 (M?1).
3-(o-Toluidinyl)-cyclohexan-1-one (Table 2, entry 7)
Pale yellow oil; 1H NMR (400 MHz, CDCl3): d = 7.14–7.06 (m, 2H, ArH), 6.70–6.66
(m, 2H, ArH), 6.62–6.60 (m, 1H, ArH), 3.44 (brs, 1H, NH), 2.89–2.85 (m, 1H, CH),
2.42–2.28 (m, 4H, 2 9 CH2), 2.12 (s, 3H, CH3), 2.08–2.01 (m, 2H, CH2), 1.82–1.70
(m, 2H, CH2); 13C NMR (100 MHz, CDCl3): d = 209.7, 144.1, 130.4, 127.1, 122.0,
117.3, 110.2, 52.0, 48.6, 41.1, 38.0, 31.0, 22.1, 17.5; ESI–MS (m/z): 204 (M?1).
3-(p-Toluidinyl)-cyclohexan-1-one (Table 2, entry 8)
1
Pale yellow oil; H NMR (400 MHz, CDCl3): d = 6.98 (d, 2H, J = 8 Hz, ArH),
6.51 (d, 2H, J = 8 Hz, ArH), 3.73 (brs, 1H, NH), 2.82–2.78 (m, 1H, CH), 2.43–2.24
(m, 4H, 2 9 CH2), 2.16–2.03 (m, 2H, CH2), 1.72–1.67 (m, 2H, CH2); 13C NMR
(100 MHz, CDCl3): d = 210.1, 144.2, 130.1, 127.4, 113.8, 52.9, 48.9, 41.4, 31.3,
22.4, 20.6; ESI–MS (m/z): 204 (M?1).
3-(4-Chloroanilinyl)-cyclohexan-1-one (Table 2, entry 9)
1
Pale yellow oil; H NMR (400 MHz, CDCl3): d = 7.11 (d, 2H, J = 8 Hz, ArH),
6.50 (d, 2H, J = 8 Hz, ArH), 3.74 (brs, 1H, NH), 2.83–2.81 (m, 1H, CH), 2.43–2.23
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(m, 4H, 2 9 CH2), 2.20–2.00 (m, 2H, CH2), 1.77–1.62 (m, 2H, CH2); 13C NMR
(100 MHz, CDCl3): d = 209.6, 145.1, 129.5, 122.6, 114.6, 52.6, 48.5, 41.3, 31.1,
22.3; ESI–MS (m/z): 224 (M?1).
3-(Anilinyl)-cyclohexan-1-one (Table 2, entry 10)
Pale yellow oil; 1H NMR (400 MHz, CDCl3): d = 7.19–7.13 (m, 3H, ArH),
6.77–6.69 (m, 2H, ArH), 3.78 (brs, 1H, NH), 2.83 (m, 1H, CH), 2.43–2.15 (m, 4H,
2 9 CH2), 2.09–1.99 (m, 2H, CH2), 1.79–1.64 (m, 2H, CH2); 13C NMR (100 MHz,
CDCl3): d = 209.4, 146.0, 129.1, 117.6, 113.0, 52.0, 48.2, 40.8, 30.7, 21.8; ESI–MS
(m/z): 190 (M?1).
1-(4-Methoxylanilinyl)-3-pentanone (Table 2, entry 11)
1
White solid, mp 42–43 °C (lit. [22], 41–43 °C); H NMR (400 MHz, CDCl3):
d = 6.78 (d, 2H, J = 7.2 Hz, ArH), 6.66 (d, 2H, J = 7.2 Hz, ArH), 3.28 (s, 3H,
OCH3), 3.36 (t, 2H, J = 6 Hz, CH2), 2.71 (t, 2H, J = 6 Hz, CH2), 2.42 (q, 2H,
J = 7.2 Hz, CH2), 1.05 (t, 3H, J = 7.2 Hz, CH3); 13C NMR (100 MHz, CDCl3):
d = 211.1, 152.1, 141.8, 114.7, 114.5, 55.6, 41.2, 39.5, 36.2, 7.6; ESI–MS (m/z):
208 (M?1).
1-(p-Toluidinyl)-3-pentanone (Table 2, entry 12)
White solid, mp 64–65 °C; 1H NMR (400 MHz, CDCl3): d = 6.98 (d, 2H,
J = 8.0 Hz, ArH), 6.53 (d, 2H, J = 8.0 Hz, ArH), 3.88 (brs, 1H, NH), 3.39 (t, 2H,
J = 6 Hz, CH2), 2.70 (t, 2H, J = 6 Hz, CH2), 2.43 (q, 2H, J = 7.2 Hz, CH2), 2.23
(s, 3H, CH3), 1.04 (t, 3H, J = 7.2 Hz, CH3); 13C NMR (100 MHz, CDCl3):
d = 211.0, 145.3, 129.7, 126.8, 113.2, 41.2, 38.8, 36.2, 20.3, 7.6; ESI–MS (m/z):
192 (M?1).
1-(o-Toluidinyl)-3-pentanone (Table 2, entry 13)
1
Pale yellow oil; H NMR (400 MHz, CDCl3): d = 7.13 (t, 2H, J = 8.0 Hz, ArH),
7.05 (d, 2H, J = 7.2 Hz, ArH), 6.68–6.61 (m, 2H, ArH), 3.94 (brs, 1H, NH), 3.47 (t,
2H, J = 6 Hz, CH2), 2.75 (t, 2H, J = 6 Hz, CH2), 2.43 (q, 2H, J = 7.2 Hz, CH2),
2.11 (s, 3H, CH3), 1.03 (t, 3H, J = 7.2 Hz, CH3); 13C NMR (100 MHz, CDCl3):
d = 211.0, 145.6, 130.2, 127.0, 122.5, 117.0, 109.5, 41.1, 38.3, 36.3, 17.4, 7.6; ESI–
MS (m/z): 192 (M?1).
1-(4-Chloroanilinyl)-3-pentanone (Table 2, entry 14)
White solid, mp 74–76 °C; 1H NMR (400 MHz, CDCl3): d = 7.12 (d, 2H,
J = 8.8 Hz, ArH), 6.53 (d, 2H, J = 8.8 Hz, ArH), 4.07 (brs, 1H, NH), 3.39 (t, 2H,
J = 6 Hz, CH2), 2.72 (t, 2H, J = 6 Hz, CH2), 2.45 (q, 2H, J = 7.2 Hz, CH2), 1.06
(t, 3H, J = 7.2 Hz, CH3); 13C NMR (100 MHz, CDCl3): d = 210.8, 146.2, 129.0,
121.9, 114.0, 40.9, 38.4, 36.37.6; ESI–MS (m/z): 212 (M?1).
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Acknowledgments This work was supported by the Natural Science Foundation of China (No.
21106090).
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