Chem-grafted Zn-SSA as an Efficient Heterogeneous Catalyst to Synthesize 2-Pyridinones

Article abstract of DOI:10.1007/s10562-016-1806-6

Abstract: Chemo-selectivity is always a hard problem in preparing 2-pyridinones. Silica sulfuric acid (SSA) modified with zinc chloride (Zn–SSA) was found to be a high efficient heterogeneous catalyst to solve this problem. Under Zn–SSA and solvent-free conditions, the one-pot cyclocondensation of 1,3-dicarbonyl compounds, malononitrile and arylaldehydes to afford 2-pyridinones was conveniently implemented. The heterogeneous reaction was much efficient and promising in pharmaceutical study and industrial production. Graphical Abstract: Improving chemo-selectivity is always a hard problem in preparing 2-pyridinones. Silica sulfuric acid (SSA) modified with zinc chloride (Zn–SSA) was found to be efficient heterogeneous catalyst to solve this problem. Under Zn-SSA and solvent-free conditions, the one-pot cyclocondensation of 1,3-dicarbonyl compounds, malononitrile and arylaldehydes to afford 2-pyridinones was conveniently implemented. The heterogeneous reaction was much efficient and promising in pharmaceutical study and industrial production.[Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-016-1806-6

Catal Lett
DOI 10.1007/s10562-016-1806-6
Chem-grafted Zn-SSA as an Efficient Heterogeneous Catalyst
to Synthesize 2-Pyridinones
Li Jun Zhang1 Xiang Zhang1 Zhen Sheng You1 Heng Li1 Tian Feng1
Wei Li Wang2
•
•
•
•
•
Received: 9 March 2016 / Accepted: 7 July 2016
Ó Springer Science+Business Media New York 2016
Abstract Chemo-selectivity is always a hard problem in
preparing 2-pyridinones. Silica sulfuric acid (SSA) modi-
fied with zinc chloride (Zn–SSA) was found to be a high
efficient heterogeneous catalyst to solve this problem.
Under Zn–SSA and solvent-free conditions, the one-pot
cyclocondensation of 1,3-dicarbonyl compounds, malononi-
trile and arylaldehydes to afford 2-pyridinones was conve-
Keywords 2-pyridinones Á Silica sulfuric acid Á Lewis
acid Á Heterogeneous catalyst
niently implemented. The heterogeneous reaction was much
efficient and promising in pharmaceutical study and industrial
production.
Graphical Abstract Improving chemo-selectivity is
always a hard problem in preparing 2-pyridinones. Silica
sulfuric acid (SSA) modified with zinc chloride (Zn–SSA)
was found to be efficient heterogeneous catalyst to solve
this problem. Under Zn-SSA and solvent-free conditions,
the one-pot cyclocondensation of 1,3-dicarbonyl com-
pounds, malononitrile and arylaldehydes to afford
2-pyridinones was conveniently implemented. The
heterogeneous reaction was much efficient and promising
in pharmaceutical study and industrial production.
1 Introduction
Nowadays, cancer has become a major health problem to
human beings. According to the world cancer report 2014,
new cases diagnosed will sharply increase 57 % than that
of 2012 in the next two decades [1]. Finding a safe and
reliable chemical drug is still a hard task. Pyridinone
derivatives have been demonstrated exhibiting important
role in regulating cell cycle, apoptosis, DNA repair,
senescence and angiogenesis [2]. Thus more and more
synthetic methods for these compounds are presented
[3–8].
Multi-substituted pyridinones, especially with cyano,
carbonyl and alkyl groups (Scheme 1, compound 5), are
important intermediates or building blocks for functional
chemicals. The common method to synthesize these
pyridinones is through the cyclocondensation reaction of
carbonyls and nitrogen-containing compounds. Krauze
et al. [9] reported a condensation reaction of 2-benzyli-
dene-3-oxobutanoate with cyanoacetamide in EtOH and
Et3N to afford 3,4-dihydropyridin-2-one in 37 % yield.
Another important synthetic routes to compound 5 is
through the cleavage-recyclization reaction of pyrans
(Scheme 1, from 4 to 5), which sometimes gives
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-016-1806-6) contains supplementary
material, which is available to authorized users.
& Li Jun Zhang
cdlijun2002@tjut.edu.cn
1
Tianjin Key Laboratory of Organic Solar Cells and
Photochemical Conversion, School of Chemistry and
Chemical Engineering, Tianjin University of Technology,
Tianjin 300384, People’s Republic of China
2
General Section, Shuishanggongyuan Hospital,
Tianjin 300191, People’s Republic of China
123

L. J. Zhang et al.
R2
the shortcomings of PEG–SO3H and ZnO, which is diffi-
cult to be recovered, this step by step reaction is humble in
total yield and economy. To make the cyclocondensation
of 1,3-dicarbonyl compound, malononitrile and benzalde-
hyde more simple and effective, we attempted to use SSA
and M-SSA as heterogeneous catalysts, and thus a one-pot
and solvent-free method was obtained.
O
CN
R1
O
NH2
O
CHO
4
CN
cat.
R1
+
+
R2
CN
O
R2
2
3
1
2 Experimental
O
CN
O
R1
Typical procedure for the preparation of catalysts: Silica
sulfuric acid (SSA, 2.5 mmol H?/g) was prepared according
to ref. [31]. In a250 ml suction flask equipped with agas inlet
tube for conducting of HCl gas over an adsorbing solution
(i.e. water), 0.05 mol metal chloride was dissolved in 50 mL
anhydrous methanol. SSA (40 g, 0.1 mol sulfur content) was
slowly added with constantly stirring. The mixture was
refluxed for 2 h, and then filtered. The obtained solid was
washed repeatedly with methanol until chlorine could not be
detected from its eluate, and calcined for 2 h at 300 °C to
give the desired catalyst M-SSA.
N
H
5
Scheme 1 Reaction route of 3,4-dihydropyridin-2-ones
pyridinone with high yield [10]. In 2012, Pradhan et al.
[11] reported two highly efficient and green protocols to
synthesize 3,4-dihydropyridin-2-one derivatives. Combin-
ing with aldehyde and ethyl acetoacetate, malononitrile or
cyanoacetamide were utilized as different starting materials
and vitamin B1 and PEG-SO3H as catalysts. Dehghan et al.
[12] demonstrated a four-component reaction of cyanoac-
etamide, aryl aldehydes, acetoacetate, and ammonium
carbonate as an efficient way to synthesize 3,4-dihydro-1H-
pyridin-2-ones and 2-pyridones.
Typical procedure for the preparation of 2-pyridinone 5:
Ethyl acetoacetate or acetylacetone (40 mmol), malononi-
trile (42 mmol), and benzaldehyde (40 mmol), and catalyst
(0.1 eq) were added in flask, the mixture was heated to
reflux with stirring for about 5 h. After completion of the
reaction (indicated by TLC), the catalyst was filtered and
recovered, and the mixture was kept overnight in ice-box.
Then the obtained residue was filtered and recrystallized
with ethanol to give the pure products 5.
Nevertheless, the major problem still exists. These cat-
alysts such as PEG–SO3H is difficult to prepare and not
stable in reaction, and their solubility makes them hard be
isolated from reaction mixture. In addition, the cyclocon-
densation reaction of carbonyls and methylene compounds
always gives the mixture of two skeletons of products for
its bad chemo-selectivity, as illustrated in Scheme 1. The
tedious workup process increases the cost of production
and leads to many defects in economical and technical
aspects, hence more efforts to improve the reaction effi-
ciency are still demanded.
2.1 5-Cyano-4-(4-methoxyphenyl)-2-methyl-6-oxo-
1,4,5,6-tetrahydropyridine-3-carboxylic ethyl
ester (5a)
White solid, IR(KBr, cm-1): 3230.14, 2977.83, 2863.52,
1
2840.91, 2260.79, 1703.88, 1633.85. H NMR (400 MHz,
Nowadays, the development of sustainable chemical pro-
cesses has posed a great demand for heterogeneous catalysts
to promote organic reactions. To obtain better selectivity,
cost-effectiveness and operational simplicity, many Bronsted
acids or Lewis acids have been loaded on solid materials, and
lots of achievements have been presented [13]. Silica sulfuric
acid (SSA), an easily prepared catalyst, has been widely
investigated as a versatile promoter that makes a lot of reac-
tion processes more convenient, economical, and environ-
mentally benign [14–26]. The further modification of SSA
with metal salts (M-SSA) was also reported recently and the
further research is under way [27, 28].
d6-CDCl3) d(ppm): 1.19–1.23(t, 3H, –CH3), 2.44(s, 3H,
–CH3), 3.79(s, 3H, –OCH3), 4.10–4.16(q, 2H, –OCH2–),
4.12–4.14(d, 1H, pyridine-H), 4.38–4.40(d, 1H, pyridine-
H), 6.77–6.80(d, 2H, Ar–H), 7.09–7.11(d, 2H, Ar–H),
7.48(brs, 1H, –NH). 13C NMR (100 MHz, d6-DMSO)
d(ppm): 14.47, 18.48, 41.35, 41.97, 55.47, 60.24, 106.42,
114.48(2C), 116.29, 129.25(2C), 130.13, 147.67, 159.25,
163.53, 165.92.
2.2 5-Cyano-4-(4-methoxyphenyl)-2-methyl-6-oxo-
1,4,5,6-tetrahydropyridine-3-carboxylic methyl
ester (5b)
In the heterogeneous synthetic method of 2-pyridinones,
ZnO and PEG-SO3H has been successfully used by Prad-
han [11] and Bhattacharyya [29]. However, in addition to
White solid, IR(KBr, cm-1): 3236.87, 2954.84, 2851.15,
2258.06, 1704.07, 1639.66. H NMR (400 MHz, d6-CDCl3)
123

Chem-grafted Zn-SSA as an efficient heterogeneous catalyst to synthesize 2-pyridinones
100
d(ppm): 2.47(s, 3H, pyridine-H), 3.70(s, 3H, Ar–OCH3),
Product 4
Product 5
90
80
70
60
50
40
30
20
10
0
3.81(s, 3H, acyl–OCH3), 4.13–4.14(d, 1H, J = 6.8 Hz,
pyridine-H), 4.47–4.49(d, 1H, J = 6.4 Hz, pyridine-H),
6.97–6.90(d, 2H, J = 8.8 Hz, Ar–H), 7.18-7.21(d, 2H,
J = 8.4 Hz, Ar–H), 7.98(brs, 1H, –NH). HRMS of [C16
H16N2O4 ? H?]: calcd: 300.1144, found: 300.1157.
2.3 5-Cyano-2-methyl-6-oxo-4-phenyl-1,4,5,6-
tetrahydro-pyridine-3-carboxylic acid methyl
ester (5d)
HHPy
SSA Zn-SSA Al-SSA Fe-SSA Sr-SSA
H2SO4
IR(KBr, cm-1): 3237.79, 2983.87, 2884.33, 2258.06,
1696.79, 1641.04. 1H NMR (400 MHz, d6-CDCl3) d(ppm):
2.43(s, 3H, –CH3), 3.67(s, 3H, –OCH3), 4.15–4.16(d, 1H,
J = 6.8 Hz, pyridine-H), 4.48–4.50(d, 1H, J = 7.2 Hz,
pyridine-H), 7.24–7.26(d, 2H, J = 7.2 Hz, Ar–H),
7.32–7.33(d, 2H, J = 6.8 Hz, Ar–H), 7.35–7.37(t, 1H, Ar–
H), 8.48(brs, 1H, –NH). HRMS of [C15H14N2O3 ? H?]:
calcd: 270.1038, found: 270.1049.
Catalyst
Fig. 1 Result of one-pot reaction of ethyl acetoacetate, malononitrile,
and benzaldehyde under different catalysts
presented, and its performance was evidently improved
when modified with Lewis acids, among which zinc
dichloride modified SSA (Zn–SSA) displayed the best
activity and selectivity.
2.4 5-Acetyl-6-methyl-2-oxo-4-phenyl-1,2,3,4-
tetrahydro-pyridine-3-carbonitrile (5 h)
The good performance of Zn-SSA may be due to proper
proportion of L/B acid sites. The FTIR spectrum of pyridine
absorption (Fig. 2) shows the change of Lewis acidity of Zn-
SSA along with the loading amount of ZnCl2. With the
increase of impregnated ZnCl2, the peak area around
1540 cm-1, which indicates the characteristic of pyridinium
ion revealing the Brønsted acidic character of the surface,
IR(KBr, cm-1): 3235.61, 2989.46, 2862.57, 2259.11,
1723.26, 1648.72. 1H NMR (400 MHz, d6-DMSO)
d(ppm): 2.04(s, 3H, pyridine–CH3), 2.28(s, 3H, –CH3),
4.14–4.16(d, 1H, J = 6.8 Hz, pyridine-H), 4.25–4.27(d,
1H, J = 7.2 Hz, pyridine-H), 7.18–7.36(m, 5H,
J = 7.2 Hz, Ar–H), 9.44 (brs, 1H, –NH). HRMS of [C15
H14N2O2 ? H?]: calcd: 255.1089, found: 255.1066.
decreases gradually, while the peak area around 1450 cm-1
,
which represents Lewis acid sites, increases evidently. The
acidity changes no more after ZnCl2 loading reaches
1.6 mmol on 1 g SSA. The figure shows that the nature of
solid catalyst SSA is clearly modified by Lewis acid.
3 Results and Discussion
Figure 3 shows typical isotherms and the corresponding
pore size distribution (PSD). The sharp peaks in the PSD
plots confirm the narrow size distributions of Zn–SSA, and
Homogeneous catalysts, piperidine (HHPy) and H2SO4,
were firstly used to the one-pot reaction of ethyl acetoac-
etate, malononitrile, and benzaldehyde (Scheme.1), no
additional solvent was added. After the completion of the
reaction which was monitored with TLC, the products were
isolated, and their yields were illustrated in Fig. 1. In order
to compare the catalyzation of different solid acids, SSA
and M-SSA were successively employed to promote this
one-pot reaction (Scheme 1), and the result was also pre-
sented in Fig. 1.
100
90
80
70
a
b
c
d
60
50
40
30
20
1544.01
e
f
10
Load of ZnCl2
It is shown in Fig. 1 that the structure of product is
mainly controlled by the acidity and alkalinity of catalysts.
It gave 2-aminopyran 4 as main product when alkali cat-
alyst such as piperidine was used, while 2-pyridinone 5 was
obtained in high yield when employing the catalyst with
suitable acidity. Using strong acid, such as sulfuric acid,
the mixture of product 4 and 5 was obtained. Solid acid
SSA showed better performance in selectivity than sulfuric
acid, although a certain amount of 2-aminopyran was also
0.0
-10
-20
1449.65
1450
1600
1550
1500
1400
1350
1300
-1
Wave (cm )
Fig. 2 FTIR spectrum of pyridine absorption indicating the change
of caid sites with the loading of ZnCl2. Amount of ZnCl2 adding to
1 g SSA: (a). 0.0 mmol, (b). 0.4 mmol, (c): 0.8 mmol, (d). 1.2 mmol,
(e). 1.6 mmol, (f). 2.0 mmol
123

L. J. Zhang et al.
Using the same reaction, we optimized temperature and
time, and the result is illustrated in Fig. 4. The figure shows
that the yield of 2-pyridinone increases with the elevation
of temperature and time till reaching their peaks. The
optimal temperature and time is 140 °C and 5 h,
respectively.
The recovery and reusability of Zn–SSA was also
investigated. The catalyst was separated by simple filtration
after reaction, washed three times with methanol, and then
evaporated and dried in a vacuum at 100 °C, and at last
reused for consecutive catalytic runs under similar exper-
imental conditions. Figure 5 shows the results of reused
five runs, and it reveals the high stability of the catalyst
under the experimental conditions.
Fig. 3 Nitrogen sorption isotherms for Zn–SSA. Inset diagram shows
the pore size distribution (PSD) of the corresponding sample
90
79%
78%
76%
80
70
60
50
40
30
20
10
0
75%
75%
all pores being in the mesoporous range. The BET specific
surface is around 151 m2/g which coincide with SSA, it
indicates that chemical modification did not influence the
catalyst surface area.
Using ethyl acetoacetate, malononitrile, and benzalde-
hyde as materials, we investigated the relationship of
selectivity for 2-pyridinone and Lewis acidity. Table 1
shows the changes of 2-pyridinone selectivity with Lewis
acidity of Zn-SSA, in which a, b, c, d and e represent
different catalysts as like as Fig. 2. It indicates that
2-pyridinone selectivity increase with the rising of Lewis
acidity, it reaches the peak at about 1.6 mmol ZnCl2
loading upon 1 g SSA.
1
2
3
4
5
Number of runs
Fig. 5 The reusability of Zn–SSA (five runs with the same exper-
imental conditions)
Table 1 The relationship of 2-pyridinone selectivity with Lewis
acidity of Zn–SSA. As like Fig. 2a–e represent SSA modified with
different amount of ZnCl2
Zn–SSA
A
B
C
D
E
Selectivity for 2-pyridinone (%) 96.2 97.6 98.4 99.0 99.8
t-Y
100
T-Y
80
60
40
20
0
1
2
3
4
5
6
7
Reaction time (h) / Temperature (×20 °C)
Fig. 4 Result of one-pot reaction of ethyl acetoacetate, malononitrile,
and benzaldehyde under different catalysts
Fig. 6 Proposed mechanism
123

Chem-grafted Zn-SSA as an efficient heterogeneous catalyst to synthesize 2-pyridinones
Table 2 One-pot cyclocondensation of 1,3-dicarbonyl compounds, arylaldehydes and malononitrile
R2
CHO
O
R1
CN
CN
Zn-SSA
reflux
CN
O
O
O
R1
+
+
N
H
R2
1
2
3
5
Entry
1
2
Yield of 5 (%)a
Mp (°C)
(Data of ref.)
a
b
c
d
e
f
R1 = OEt
R1 = OMe
R1 = OEt
R1 = OMe
R1 = OMe
R1 = OEt
R1 = OEt
R1 = Me
R1 = Me
R1 = Me
R1 = Me
R2 = 4-OMe
R2 = 4-OMe
R2 = H
79
78
86
85
86
91
89
75
90
92
86
185–187 (182) [11]
174–176
141–143 (143–145) [32]
177–179
R2 = H
R2 = 3-NO2
R2 = 3-NO2
R2 = 4-NO2
R2 = H
212–214 (211–213) [33]
174–176 (175–176) [34]
103–104 (103) [11]
122–124 (156) [29]
106–108 (106–107) [35]
106–107 (105–106) [35]
175–177 (173–174) [35]
g
h
i
R2 = 2-NO2
R2 = 4-NO2
R2 = 4-Cl
j
k
Using 0.1eq. Zn-SSA (based on molar content of zinc on silica gel) as catalyst, all reactants refluxed 5h under solvent-free conditions
a
Isolated yields
The mechanism of Zn–SSA promoted elimination is
proposed as Fig. 6. Zinc atom becomes a high active particle
with electrophilic power for the effect of silica vitriolic
groups, and results in its combination with the acyl oxygen of
ethyl acetoacetate to produce the conformation of enol spe-
cies (II). Then the attack of enol to ethylenic bond of com-
pound (I) leads to the intermediate (III), which becomes an
enol type again to occur the intramolecular nucleophilic
attack of oxygen to cyano to give dihydropyran (V). Under
the effect of Zn–SSA, the pyran becomes dihydropyridine
(VI) via Dimroth rearrangement [30, 31], and at last affords
pyridin-2-one product through the protonation of unsatu-
rated nitrogen and tautomerism of enol (VI).
toward the cyclocondensation of ethyl acetoacetate,
malononitrile, and benzaldehyde, thus provides a simple,
efficient and eco-friendly synthetic method for multi-sub-
stituted 2-pyridinones. The reaction which can be easily
realized in one-pot and solvent-free conditions, is much
promising in pharmaceutical study and industrial
production.
Acknowledgments The authors are grateful to Tianjin Municipal
Science and Technology Commission for its financial support.
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