Xanthan sulfuric acid: A new and efficient biosupported solid acid catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones

Article abstract of DOI:10.1080/00397911.2010.538483

Xanthan sulfuric acid (XSA) is employed as a recyclable catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones. These syntheses were performed via a one-pot, threecomponent condensation of aldehydes, amines, and urea/thiourea under solvent-free con

Full text of DOI:10.1080/00397911.2010.538483

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Xanthan Sulfuric Acid: A New and
Efficient Biosupported Solid Acid
Catalyst for the Synthesis of 3,4-
Dihydropyrimidin-2(1H)-Ones
B. Suresh Kuarm a , J. Venu Madhav a , S. Vijaya Laxmi a & Dr. B.
Rajitha a
a Department of Chemistry , National Institute of Technology ,
Warangal , India
Accepted author version posted online: 07 Oct 2011.Published
online: 22 Dec 2011.
To cite this article: B. Suresh Kuarm , J. Venu Madhav , S. Vijaya Laxmi & Dr. B. Rajitha (2012)
Xanthan Sulfuric Acid: A New and Efficient Biosupported Solid Acid Catalyst for the Synthesis of
3,4-Dihydropyrimidin-2(1H)-Ones, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 42:8, 1211-1217, DOI: 10.1080/00397911.2010.538483
To link to this article: http://dx.doi.org/10.1080/00397911.2010.538483
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Synthetic Communications1, 42: 1211–1217, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.538483
XANTHAN SULFURIC ACID: A NEW AND EFFICIENT
BIOSUPPORTED SOLID ACID CATALYST FOR THE
SYNTHESIS OF 3,4-DIHYDROPYRIMIDIN-2(1H)-ONES
B. Suresh Kuarm, J. Venu Madhav, S. Vijaya Laxmi,
and B. Rajitha
Department of Chemistry, National Institute of Technology,
Warangal, India
GRAPHICAL ABSTRACT
Abstract Xanthan sulfuric acid (XSA) is employed as a recyclable catalyst for the synthesis
of 3,4-dihydropyrimidin-2(1H)-ones. These syntheses were performed via a one-pot, three-
component condensation of aldehydes, amines, and urea/thiourea under solvent-free
conditions.
Keywords Biginelli reaction; 3,4-dihydropyrimidin-2(1H)-ones; one-pot synthesis;
solvent-free conditions
INTRODUCTION
Evolution of organic synthesis involving environmentally clean protocols
under solvent-free conditions has emerged as an area of great interest from both
environmental and economical points of view.[1] 3,4-Dihydropyrimidin-2(1H)-ones
attract increasing interest because of their diverse therapeutic and pharmacological
properties.[2,3] They are also reported to serve as calcium channel blockers, antihy-
pertensive agents, a1a antagonists, and anti-HIV agents.[4] The biological activities
of some marine alkaloids isolated recently have been attributed to the presence of
a dihydropyrimidinone moiety.[5] To prepare the compounds, the first protocol
was presented by Biginelli[6] more than a century ago, a one-pot condensation of
Received June 17, 2010.
Address correspondence to Dr. Bavanthula Rajitha, Department of Chemistry, National Institute
of Technology, Warangal 506004, India. E-mail: rajithabhargavi@ymail.com
1211

1212
B. S. KUARM ET AL.
Scheme 1. Synthesis of 3,4-dihydropyrimidine-2(1H)-ones using xanthan sulfuric acid.
b-ketoester, aldehyde, and urea under strongly acidic conditions. This method has its
own merits and drawbacks. A major drawback of the classical Biginelli reaction is
poor to moderate yields, particularly when the reaction is performed with an ali-
phatic aldehyde.[7] To improve the efficiency of the Biginelli reaction, a number of
Lewis acids as well as protic acids as promoters such as BF3 etherate = copper (II)
acetate,[8] polyphosphonate ester (PPE),[9] montmorillonite,[10] InCl3,[11] lanthanide
triflate,[12] H2SO4,[13] ion-exchange resin,[14] 1-n-butyl- 3-methyl imidazolium tetra
fluoroborate (BMImBF4),[15] BiCl3,[16] LiClO4,[17] InBr3,[18] FeCl3,[19] ZrCl4,[20]
Cu(OTf)2,[21] Bi(OTf)3,[22] ytterbium triflate,[23] NH4Cl[24] have been used. However,
many of these protocols have some drawbacks, such as use of expensive, highly
acidic catalysts and prolonged reaction times. In addition, the yields of the corre-
sponding 3,4-dihydropyrimidin-2(1H)-ones are not always satisfactory. Because of
the importance of the Biginelli reaction, milder, faster, and more ecofriendly meth-
ods accompanied by higher yields are need to be introduced. Therefore, the search
continues for a better catalyst for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones
in terms of operational simplicity, reusability of catalyst, low cost, and greater
selectivity.
Xanthan and its derivatives[25–27] have some unique properties, which make
them attractive alternatives for conventional organic or inorganic supports for cata-
lytic applications. Xanthan is the most abundant bacterial exopolysaccharide in the
world and is produced through fermentation. It has been widely studied during the
past decades, as it is a biodegradable material and a renewable resource. Unlike
other gums, it is very stable under a wide range of temperatures and pH values.
Xanthan sulfuric acid can be easily prepared by the reaction of xanthan with chlor-
osulfonic acid; the number of acidic (Hþ) sites in xanthan sulfuric acid is determined
by acid–base titration to be 0.6 meq=g.
In continuation of our efforts to improve the Biginelli reaction,[28] and as part
of our ongoing interest, we here report a straightforward and versatile method
to afford 3,4-dihydropyrimidin-2(1H)-ones in good yield by employing xanthan
sulfuric acid, as a mild acid catalyst.
RESULTS AND DISCUSSION
Preparations of biologically important compounds are in high demand in
organic chemistry. Therefore here we describe a mild and efficient synthesis of
3,4-dihydropyrimidin-2(1H)-ones using xanthan sulfuric acid[29] as a catalyst under

3,4-DIHYDROPYRIMIDIN-2(1H)-ONES
1213
Table 1. Effect of various solventsa
Entry
Solvent
Yieldsb (%)
1
2
3
4
5
6
Neat
Acetonitrile
Ethanol
95c
75
92
50
82
86
Dichloroethane
Toluene
Methanol
aReaction conditions: benzaldehyde (1 mmol), EAA (1 mmol), urea (1.5 mmol),
and xanthan sulfuric acid (0.1 g) stirred at 40 ꢀC under solvent-free conditions.
bIsolated yields.
cThe same catalyst was used for four runs.
Table 2. Results of recyclability of the xanthan sulfuric acida
Run
Cycle
Time (min)
Yield (%)
1
2
3
4
0
1
2
3
20
20
20
20
95
94
91
84
aReaction conditions: benzaldehyde (1 mmol), EAA (1 mmol), urea (1.5 mmol),
and xanthan sulfuric acid (0.1 g) stirred at 40 ꢀC under solvent-free conditions.
solvent-free conditions. We explore catalytic properties of xanthan sulfuric acid
under solvent-free conditions for the Biginelli reaction. The reaction proceeded
smoothly without any solvent at 40 ꢀC with a catalytic amount of xanthan sulfuric
acid. Yields are excellent with high purity.
The model reaction was also examined in various solvents as well as under
solvent-free conditions in the presence of 0.1 g of xanthan sulfuric acid (Table 1).
The results showed that the efficiency and the yield of the reaction under solvent-free
conditions were better than those obtained in other solvents.
We can easily separate xanthan sulfuric acid from the reaction medium by
washing it with CHCl3 and drying in an oven (50 mm Hg pressure) at 60 ꢀC for
3 h prior to use in the other reaction. The recovered catalyst can be reused at least
three additional times in subsequent reactions without significant loss in product
yield (Table 2).
EXPERIMENTAL
All the melting points are uncorrected. The progress of the reaction was mon-
itored by thin-layer chromatography (TLC). Infrared (IR) spectra (KBr) were
recorded on a Shimadzu Fourier transofrm (FTIR)–model 8010 spectrometer, and
1
the H NMR spectra were recorded on a Varian Gemini 200-MHz spectrometer
using tetramethylsilane (TMS) as internal standard. Mass spectra were recorded
on a Jeol JMS D-300 spectrometer. All solvents and reagents were purchased from
Aldrich and Fluka.

1214
B. S. KUARM ET AL.
Typical Procedure for Synthesis of Dihydropyrimidinones (4a–r)
Xanthan sulfuric acid (0.1 g) was added to the mixture of aldehyde (1 mmol),
1,3-dicarbonyl compound (1 mmol), and urea or thiourea (1.5 mmol). The reaction
mass was stirred at 40 ꢀC for an appropriate time (Table 3). The reaction progress
was checked by TLC. After completion of the reaction, the reaction mixture was
cooled to room temperature, and CHCl3 (15 ml) was added. The catalyst was filtered
off, the solid was washed with CHCl3 (5 ml), and the combined CHCl3 solution was
concentrated in a vacuum to afford the crude product. The pure product was
obtained by further recrystallization from ethanol.
We examined the amount of catalyst loading in reaction. The best results
were obtained by using 0.1 g of catalyst (yield 95%). If the catalyst is less than
0.1 g, poor yields are obtained. In the absence of catalyst, yields are in traces
(Table 4).
Product Characterization Data
5-(Ethoxycarbonyl)-6-methyl-4-phenyl-3,4-dihydropyrimidin-2(1H)-one
1
(Table 1, Entry 4a). Mp 201–203 ꢀC. H NMR: d 9.21 (s, 1H, NH), 7.73 (s, 1H,
NH), 7.27 (m, 5H, Ar-H), 5.14 (s, 1H,CH), 3.99 (q, 2H, OCH2), 2.23 (s, 3H,
CH3), 1.08 (t, 3H, CH3); IR (KBr): 3243, 1722, 1639 cmꢁ1. EIMS, 70 ev, m=z: 260
(Mþ). Calcd. for C14H16N2O3: C, 64.60; H, 6.20; N, 10.76. Found: C, 64.72; H,
6.29; N, 10.66.
Table 3. Xanthan sulfuric acid–catalyzed synthesis of 3,4-dihydropyrimidin-2(1H)-ones under solvent-
free conditions
Product
Aldehyde
R1
X
Time (min)
Yieldb (%)
4a
4b
4c
4d
4e
4f
Benzaldehyde
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OEt
OMe
OMe
OMe
OMe
OMe
OEt
OEt
OEt
OEt
O
O
O
O
O
O
O
S
20
30
25
20
25
30
30
20
40
25
20
20
20
30
20
25
40
30
95
94
91
92
90
89
92
90
93
90
89
88
81
83
74
78
72
76
4-Methoxybenzaldehyde
4-Nitrobenzaldehyde
4-Chlorobenzaldehyde
4-Fluorobenzaldehyde
2,4-Dichlorobenzaldehyde
2-Bromobenzaldehyde
4g
4h
4i
4-Hydroxybenzaldehyde
4-Methyoxybenzaldehyde
Benzaldehyde
S
4j
O
O
O
O
O
O
S
4k
4l
4-Methoxybenzaldehyde
4-Nitrobenzaldehyde
4m
4n
4o
4p
4q
4r
2,4-Dichlorobenzaldehyde
4-Flourobenzaldehyde
6-Nitro-4-oxo-4H-chromene-3-carbaldehyde
2-Naphthaldehyde
4-Hydroxy-2-oxo-2H-chromene-8-carbaldehyde
4-Oxo-4H-chromene-3-carbaldehyde
O
O
aAll the compounds are known; characterized by IR, 1H NMR, and mass spectral analysis; and
compared with the authentic samples.
bIsolated yields.

3,4-DIHYDROPYRIMIDIN-2(1H)-ONES
1215
Table 4. Influence of xanthan sulfuric acid on reaction rates and yieldsa
Entry
Catalyst (g)
Time (min)
Yield (%)b
1
2
3
4
5
6
None
0.01
0.04
0.08
0.1
120
20
20
20
20
40
Trace
25
51
81
95
0.1
95
aReaction conditions: Mixture of benzaldehyde (1 mmol), EAA (1 mmol),
urea (1.5 mmol), and xanthan sulfuric acid (0.1 g) stirred at 40 ꢀC under
solvent-free conditions.
bIsolated yield.
Ethyl 1,2,3,4-tetrahydro-6-methyl-4-(6-nitro-4-oxo-4H-chromen-3-yl)-2-
oxopyrimidine-5-carboxylate (Table 3, Entry 4o). Mp 90 ꢀC. 1H NMR
(DMSO-d6): d 9.13 (bs, 1H, NH), 7.92 (bs, 1H, NH), 7.12–7.25 (m, 3H, Ar-H),
7.02 (s, 1H, CH), 5.18 (s, 1H, C4-H), 4.09 (q, 2H, OCH2), 2.40 (s,3H, CH3), 1.75
(t, 3H, CH3); IR (KBr): 3250, 3196, 1734, 1716, 1652 cmꢁ1. EIMS, 70 ev, m=z: 373
(Mþ). Calcd. for C17H15N3O7: C, 54.69; H, 4.05; N, 11.26. Found: C, 54.62; H,
4.16; N, 11.06.
Ethyl 1,2,3,4-tetrahydro-6-methyl-4-(naphthalen-6-yl)-2-thioxopyrimi-
1
dine-5-carboxylate (Table 3, Entry 4p). Mp 149–150 ꢀC. H NMR (DMSO-d6):
d 9.27 (bs, 1H, NH), 7.52 (bs, 1H, NH), 7.20–7.81 (m, 7H, CH), 5.19 (s, 1H, C4-
H), 3.97 (q, 2H, OCH2), 2.25 (s,3H, CH3), 1.10 (t, 3H, CH3); IR (KBr) : 3245,
3170, 1723, 1639 cmꢁ1. EIMS, 70 ev, m=z: 326 (Mþ). Calcd. for C17H15N3O7: C,
66.23; H, 5.56; N, 8.58. Found: C, 66.31; H, 5.44; N, 8.62.
Ethyl 1,2,3,4-tetrahydro-4-(7-hydroxy-2-oxo-2H-chromen-8-yl)-6-methyl-
1
2-oxopyrimidine-5-carboxylate (Table 3, Entry 4q). Mp 121–122 ꢀC. H NMR
(DMSO-d6): d 9.23 (bs, 1H, NH), 8.01 (d, 1H, C4-H), 7.90 (bs,1H, NH), 7.57 (d,
1H, Ar-H), 7.14 (d, 1H, Ar-H), 6.35 (d, 1H), 5.12 (d, 1H, C4-H), 3.97 (q, 2H,
OCH2), 2.20 (s,3H, CH3), 1.17 (t, 3H, CH3); IR (KBr): 3415, 3,315, 1728, 1710,
1690 cmꢁ1. EIMS, 70 ev, m=z: 344 (Mþ). Calcd. for C17H16N2O6: C, 59.30; H,
4.68; N, 8.14. Found: C, 59.37; H, 4.54; N, 8.09.
Ethyl
1,2,3,4-tetrahydro-6-methyl-2-oxo-4-(4-oxo-4H-chromen-3-yl)
1
pyrimidine-5-carboxylate (Table 3, Entry 4r). Mp 110 ꢀC. H NMR (DMSO-
d6): d 9.40 (bs, 1H, NH), 8.20 (d, 1H, Ar-H), 7.90 (bs, 1H, NH), 7.45-7.60 (m,
3H, Ar-H), 6.95 (1H, CH), 5.10 (s, 1H, C4-H), 4.12 (q, 2H, OCH2), 2.20 (s, 3H,
CH3), 1.25 (t, 3H, CH3); IR (KBr): 3310, 3170, 1734, 1710, 1695 cmꢁ1. EIMS,
70 ev, m=z: 328 (Mþ). Calcd. for C17H16N2O5: C, 62.19; H, 4.91; N, 8.53. Found:
C, 62.27; H, 4.83; N, 8.59.
CONCLUSION
In conclusion, we have developed a mild, simple, cost-effective procedure
for the synthesis of 3,4-dihydropyrimidinones=thiones using a reusable solid acid

1216
B. S. KUARM ET AL.
catalyst. Moreover, the mild reaction conditions, good yield of products, easy work-
up, ready availability of the catalyst, and the ecologically clean procedure make the
present method a useful and important addition to the present methodologies for the
Biginelli synthesis.
ACKNOWLEDGMENT
One of the authors, B. S. K., is grateful to the Council of Scientific and
Industrial Research (CSIR), New Delhi, India, for providing financial support in
the form of a CSIR Senior Research Fellowship.
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