Scandium(III) triflate as an efficient and reusable catalyst for synthesis of 3,4-dihydropyrimidin-2(1H)-ones

Article abstract of DOI:10.1080/00397910500213781

Sc(III) triflate efficiently catalyzes the three-component condensation reaction of an aldehyde, a β-ketoester, and urea in refluxing acetonitrile to afford the corresponding 3,4-dihydropyrimidin-2(1H)-ones in excellent yields. The catalyst can be recover

Full text of DOI:10.1080/00397910500213781

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Scandium(III) Triflate as
an Efficient and Reusable
Catalyst for Synthesis of
3,4‐Dihydropyrimidin‐2(1H)‐ones
Surya K. De a & Richard A. Gibbs a
a Department of Medicinal Chemistry and Molecular
Pharmacology, Purdue Cancer Center , Purdue
University , West Lafayette, Indiana, USA
Published online: 22 Aug 2006.
To cite this article: Surya K. De & Richard A. Gibbs (2005) Scandium(III) Triflate as
an Efficient and Reusable Catalyst for Synthesis of 3,4‐Dihydropyrimidin‐2(1H)‐ones,
Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 35:20, 2645-2651
To link to this article: http://dx.doi.org/10.1080/00397910500213781
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Synthetic Communicationsw, 35: 2645–2651, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500213781
Scandium(III) Triflate as an Efficient and
Reusable Catalyst for Synthesis of
3,4-Dihydropyrimidin-2(1H)-ones
Surya K. De and Richard A. Gibbs
Department of Medicinal Chemistry and Molecular Pharmacology,
Purdue Cancer Center, Purdue University, West Lafayette, Indiana, USA
Abstract: Sc(III) triflate efficiently catalyzes the three-component condensation
reaction of an aldehyde, a b-ketoester, and urea in refluxing acetonitrile to afford the
corresponding 3,4-dihydropyrimidin-2(1H)-ones in excellent yields. The catalyst can
be recovered and reused, making this method friendly and environmentally acceptable.
Keywords: Aldehydes, Biginelli reaction, dihydropyrimidinone, b-ketoester,
scandium triflate
3,4-Dihydropyrimidin-2(1H)-ones and their sulfur analogs (DHMPs) have
been reported to possess diverse pharmacological activities such as
antiviral, antibacterial, and antihypertensive activity as well as efficacy as
calcium channel blockers and a-antagonists.[1,2] Some marine alkaloids
recently isolated have been attributed to the presence of a dihyhropyrimidi-
none moiety and also exhibit interesting biological activities.[3] Thus, the
synthesis of dihydropyrimidinones is an ongoing active program in recent
years. In the literature, there are many reported methods[4] for the preparation
.
of dihydropyrimidinones employing Lewis acids such as BF3 OEt2, FeCl3,
InCl3, ZrCl4, BiCl3, Mn(OAc)3, LiClO4, and LiBr. However, many of these
methods have some drawbacks such as low yields of the products, long
reaction times, high temperature, harsh reaction conditions, difficulties in
Received in the USA May 18, 2005
Address correspondence to Surya K. De, Department of Medicinal Chemistry and
Molecular Pharmacology, Purdue Cancer Center, Purdue University, West Lafayette,
IN 47906, USA. Fax: 765-4941414; E-mail: skd125@pharmacy.purdue.edu
2645

2646
S. K. De and R. A. Gibbs
workup, the use of stoichiometric amounts of catalysts, and the use of metal
halides as catalysts. Moreover, the main disadvantage of almost all existing
methods is that the catalysts are destroyed in the workup procedure and
cannot be recovered or reused. Therefore, the search continues for a better
catalyst in terms of operational simplicity, reusability, economic viability,
and greater selectivity. As part of our continuing interest in the development
of new synthetic methodologies,[5] herein we report a simple and efficient
procedure for the synthesis of dihydropyrimidinones using Sc(OTf)3 as a
reusable catalyst.
Recently, scandium triflate has been introduced as promising mild and
selective reagent in organic synthesis.[6] Although most conventional Lewis
acids are decomposed in the presence of water or under reaction conditions,
Sc(OTf)3 is stable in water and does not decompose under aqueous workup
conditions. Thus, recycling is often possible. A catalytic amount of Sc(OTf)3
is sufficient to obtain the desired compounds in excellent yields (Scheme 1).
As a representative example, the reaction of benzaldehyde, ethylacetoacetate,
and urea in the presence of 5 mol% Sc(OTf)3 in refluxing acetonitrile
afforded the corresponding dihydropyrimidinone in 93% yield. Thus, several
aromatic aldehydes carrying either electron-releasing or electron-withdrawing
substituents afforded high yields of products. The results shown in Table 1
clearly indicate the scope and generality of the reaction with respect to
different aromatic, aliphatic, heterocyclic, and unsaturated aldehydes. The
experimental procedure is mild and has the ability to tolerate a variety of func-
tional groups such as halide, ether, hydroxyl, and unsaturation. Thiourea was
used with similar success to provide the corresponding 3,4-dihydropyrimidin-
2(1H)-thiones, which are also of interest because of their biological activities.[7]
In conclusion, the present procedure provides an efficient and improved
modification of the Biginelli reaction. Excellent yields, recycling of the
catalyst, mild reaction conditions, ease of workup, and short reaction times
are some of the important features of this new method.
EXPERIMENTAL
NMR spectra were recorded on a Bruker ARX 300 (300-MHz) instrument.
Low-resolution mass spectra (CI, EI) were recorded on a Finnigan 4000
Scheme 1.

Scandium(III) Triflate
2647
Table 1. Sc(OTf)3-catalyzed synthesis of dihydropyrimidinones and thio-derivatives
Time
(h)
Yielda
(%)
Entry
R
X
1
2
C6H5
O
O
O
O
O
O
O
O
O
O
O
O
O
S
3
4
4
4
4
4
6
4
3
6
4
7
8
4
5
5
4
93
94
85
83
81
89
76
90
84
88
91
73
77
83
85
90
82
4-MeOC6H4
4-C1C6H4
4-NO2C6H4
3-HOC6H4
3-MeOC6H4
3
4
5
6
7
4-NMe2C6H4
3,4,5-(OMe)3C6H3
PhCH55CH
4-F-C6H4
8
9
10
11
12
13
14
15
16
17
2-Furfuryl
i-Pr
C9H19
C6H5
3-MeOC6H4
4-MeOC6H4
3,4-Methelenedioxyphenyl
S
S
S
aYields refer to isolated products and were characterized by comparison of their mp,
IR, and 1H NMR spectra with those of authentic samples.
mass spectrometer. High-resolution mass spectra (HRMS, EI, CI, ESI) were
recorded on Finnigan MAT XL95 mass spectrometer. The reactions were
monitored by TLC and visualized with UV light followed by development
using 15% phosphomolybdic acid in ethanol. All solvents and reagents
were purchased from Aldrich, high-grade quality, and were used without
any purification. All yields refer to isolated products. All of the products are
known compounds and were identified by comparing their spectral data
(1H NMR) and physical properties (mp or bp) with those of authentic
samples.[4,8]
Typical Procedure
A mixture of benzaldehyde (5 mmol), urea (5 mmol), ethyl acetoacetate
(5 mmol), and anhydrous Sc(OTf)3 (5 mol%) in acetonitrile (10 mL) was

2648
S. K. De and R. A. Gibbs
refluxed for 3 h. After completion of reaction (TLC), the reaction mixture was
cooled to room temperature and filtered through a sintered funnel. The crude
product was further purified by recrystallization (EtOH) to afford the pure
product. The filtrate containing the Sc(OTf)3 was further treated with the
reactants. Only a slight decrease in the yield of 3,4-dihydropyrimidin-
2(1H)-one was observed (from 93 to 80% after the fifth time).
Product Characterization Data
Compound 4a (entry 1): mp 203–2048C, lit.[8] 202–2048C; 1H NMR
(300 MHz, DMSO-d6) d 1.15 (t, J ¼ 7.2 Hz, 3H), 2.33 (s, 3H), 4.05
(q, J ¼ 7.2 Hz, 2H), 5.41 (d, J ¼ 2.4 Hz, 1H), 5.62 (br.s., 1H), 7.30–7.34
(m, 5H), 7.78 (br.s., 1H). Anal. calcd. for C14H16N2O3: C, 64.60; H, 6.20;
N, 10.76. Found: C, 64.57; H, 6.24; N, 10.77.
1
Compound 4b: mp 198–1998C, lit.[8] 200–2018C; H NMR (300 MHz,
DMSO-d6) d 1.12 (t, J ¼ 7 Hz, 3H), 2.25 (s, 3H), 3.72 (s, 3H), 3.98
(q, J ¼ 7 Hz, 2H), 5.10 (s, 1H), 6.88 (d, J ¼ 8.5 Hz, 2H), 7.15 (d,
J ¼ 8.5 Hz, 2H), 7.16 (s, 1H, NH), 9.14 (s, 1H, NH). Anal. calcd. for
C15H18N2O4: C, 62.06; H, 6.25; N, 9.65. Found: C, 62.08; H, 6.26;
N, 9.68.
1
Compound 4c: mp 210–2118C, lit.[8] 211–2128C; H NMR (300 MHz,
DMSO-d6) d 1.08 (t, J ¼ 7 Hz, 3H), 2.24 (s, 3H), 4.01 (q, J ¼ 7 Hz, 2H),
5.14 (d, J ¼ 3 Hz, 1H), 7.26 (d, J ¼ 8 Hz, 2H), 7.41 (d, J ¼ 8 Hz, 2H), 7.80
(d, J ¼ 3 Hz, 1H, NH), 9.25 (s, 1H, NH).
l
Compound 4d: mp 212–2138C, lit.[8] 210–2118C; H NMR (300 MHz,
DMSO-d6) d 1.10 (t, J ¼ 7 Hz, 3H), 2.27 (s, 3H), 4.01 (q, J ¼ 7 Hz, 2H),
5.29 (d, J ¼ 3.2 Hz, 1H), 7.51 (d, J ¼ 8.5 Hz, 2H), 7.92 (s, 1H, NH), 8.21
(d, J ¼ 8.5 Hz, 2H), 9.36 (s, 1H, NH). Anal. calcd. for C14H15N3O5:
C, 55.08; H, 4.95; N, 13.76. Found: C, 55.05; H, 4.99; N, 13.80.
1
Compound 4e: mp 188–1898C, lit.[4] 189–1908C; H NMR (300 MHz,
DMSO-d6) d 1.12 (t, J ¼ 7 Hz, 3H), 2.24 (s, 3H), 5.10 (d, J ¼ 3.1 Hz, 1H),
6.60–6.69 (m, 3H), 7.08 (t, J ¼ 7.8 Hz, 1H), 7.67 (s, 1H, NH), 9.12 (s, 1H,
NH).
1
Compound 4f: mp 208–2098C, lit.[4] 206–2078C; H NMR (300 MHz,
DMSO-d6) d 1.09 (t, J ¼ 7 Hz, 3H), 2.23 (s, 3H), 3.71 (s, 3H), 3.98
(q, J ¼ 7 Hz, 2H), 5.09 (d, J ¼ 2.8 Hz, 1H), 6.79 (m, 3H), 7.22
(t, J ¼ 7.8 Hz, 1H), 7.71 (s, 1H), 9.15 (s, 1H); 13C NMR (75 MHz, DMSO-
d6) d 14.4, 18.2, 54.6, 55.6, 59.4, 99.4, 102.6, 112.6, 118.5, 129.9, 146.5,
148.9, 152.3, 159.5, 165.8.
1
Compound 4g: mp 252–2548C, lit.[8] 253–2548C; H NMR (300 MHz,
DMSO-d6) d 1.10 (t, J ¼ 7 Hz, 3H), 2.22 (s, 3H), 2.84 (s, 6H), 3.95
(q, J ¼ 7 Hz, 2H), 5.01 (d, J ¼ 2.4 Hz, 1H), 6.64 (d, J ¼ 8.5 Hz, 2H), 7.02
(d, J ¼ 8.5 Hz, 2H), 7.56 (s, 1H), 9.05 (s, 1H); 13C NMR (75 MHz, DMSO-

Scandium(III) Triflate
2649
d6) d 14.8, 18.5, 40.9, 53.9, 59.8, 100.6, 112.9, 127.6, 133.4, 148.3, 150.4,
152.9, 166.2.
1
Compound 4h: mp 215–2168C, lit.[8] 212–2148C; H NMR (300 MHz,
DMSO-d6) d 1.12 (t, J ¼ 7 Hz, 3H), 2.24 (s, 3H), 3.62 (s, 3H), 3.72 (s, 6H),
4.01 (q, J ¼ 7 Hz, 2H), 5.08 (s, 1H), 6.52 (s, 2H), 7.68 (s, 1H), 9.12 (s, 1H);
13C NMR (75 MHz, DMSO-d6) d 14.2, 17.8, 53.8, 55.7, 59.2, 59.9, 98.9,
103.3, 136.6, 140.3, 148.3, 152.5, 165.2.
1
Compound 4i: mp 233–2348C, lit.[4]234–2358C; H NMR (300 MHz,
DMSO-d6) d 1.20 (t, J ¼ 7 Hz, 3H), 2.22 (s, 3H), 4.08 (m, 2H), 4.74
(d, J ¼ 5.80 Hz, 1H), 6.20 (dd, J ¼ 15.8, 6 Hz, 1H), 6.38 (d, J ¼ 15.8 Hz,
1H), 7.21–7.47 (m, 5H), 7.53 (d, J ¼ 1.9 Hz, 1H, NH), 9.12 (s, 1H, NH);
13C NMR (75 MHz, DMSO-d6) d 14.2, 17.7, 51.9, 59.3, 97.9, 126.3, 127.4,
128.2, 128.5, 130.1, 136.2, 148.4, 152.6, 165.2.
1
Compound 4j: mp 174–1758C, lit.[8] 173–1758C; H NMR (300 MHz,
DMSO-d6) d 1.08 (t, J ¼ 7.2 Hz, 3H), 2.25 (s, 3H), 3.98 (q, J ¼ 7.1 Hz,
2H), 5.15 (s, 1H), 7.22 (m, 4H), 7.76 (s, 1H, NH), 9.23 (s, 1H, NH);
13C NMR (75 MHz, DMSO-d6) d 14.2, 17.8, 53.3, 59.3, 99.2, 115.1, 128.2,
141.2, 148.4, 152.1, 159.8, 162.7, 165.3; EIMS m/z 278 (Mþ).
1
Compound 4k: mp 208–2098C, lit.[4] 207–2088C; H NMR (300 MHz,
DMSO-d6) d 1.12 (t, J ¼ 7.2 Hz, 3H), 2.21 (s, 3H), 4.01 (m, 2H), 5.17
(d, J ¼ 2.4 Hz, 1H), 6.04 (d, J ¼ 2.5 Hz, 1H), 6.34 (dd, J ¼ 1.6, 3.2 Hz,
1H), 7.53 (s, 1H), 7.74 (s, 1H), 9.23 (s, 1H); 13C NMR (75 MHz, DMSO-
d6) d 14.7, 18.4, 48.3, 59.9, 97.4, 105.9, 111.2, 142.8, 150.2, 153.1, 156.5,
165.6.
1
Compound 4l: mp 194–1958C, lit.[8] 194–1958C; H NMR (300 MHz,
DMSO-d6) d 0.74 (d, J ¼ 7 Hz, 3H), 0.81 (d, J ¼ 7 Hz, 3H), 1.18
(t, J ¼ 7 Hz, 3H), 1.68 (m, 1H), 2.17 (s, 3H), 3.96 (t, J ¼ 7 Hz, 1H), 4.04
(m, 2H), 7.25 (s, 1H, NH), 8.85 (s, 1H, NH); 13C NMR (75 MHz, DMSO-
d6) d 14.2, 16.1, 17.6, 18.5, 34.5, 55.6, 59.2, 98.1, 148.4, 153.1, 165.7.
Compound 4m: mp 168–1698C, lit.[8] 167–1688C; 1H NMR (300 MHz,
DMSO-d6) d 0.89 (t, J ¼ 7 Hz, 3H), 1.26–1.31 (m, 19H), 2.28 (s, 3H), 4.16
(m, 2H), 4.30 (m, 1H), 5.61 (s, 1H), 7.75 (s, 1H).
1
Compound 4n: mp 207–2088C; H NMR (300 MHz, DMSO-d6) d 1.07
(t, J ¼ 7.2 Hz, 3H), 2.26 (s, 3H), 3.98 (q, J ¼ 7.2 Hz, 2H), 5.15 (d,
J ¼ 4 Hz, 1H), 7.17–7.35 (m, 5H), 9.63 (s, 1H); 13C NMR (75 MHz,
DMSO-d6) d 14.7, 17.8, 54.7, 60.3, 94.6, 101.3, 127.1, 128.3, 129.2, 144.2,
145.9, 165.8, 174.9.
1
Compound 4o: mp 150–1518C, lit.[4] 151–1528C; H NMR (300 MHz,
DMSO-d6) d 1.12 (t, J ¼ 6.5 Hz, 3H), 2.30 (s, 3H), 3.73 (s, 3H), 4.02
(q, J ¼ 6.5 Hz, 2H), 5.91 (s, 1H), 6.85 (m, 3H), 7.28 (t, J ¼ 9 Hz, 1H), 9.71
(s, 1H), 10.36 (s, 1H); 13C NMR (75 MHz, DMSO-d6) d 14.2, 17.5, 54.2,
55.4, 60.1, 101.2, 112.7, 118.6, 130.2, 145.2, 145.4, 159.6, 165.3, 174.4.
1
Compound 4p: mp 152–1538C, lit.[8] 152–1538C; H NMR (300 MHz,
DMSO-d6) d 1.18 (t, J ¼ 7.1 Hz, 3H), 2.34 (s, 3H), 3.78 (s, 3H), 4.10
(q, J ¼ 7.1 Hz, 2H), 5.35 (d, J ¼ 3 Hz, 1H), 6.85 (d, J ¼ 8.5 Hz, 2H), 7.23

2650
S. K. De and R. A. Gibbs
(d, J ¼ 8.5 Hz, 2H), 7.91 (s, 1H), 8.52 (s, 1H); 13C NMR (75 MHz, DMSO-d6)
d 14.1, 18.1, 55.2, 55.5, 60.3, 103.1, 114.1, 128.1, 134.8, 142.6, 159.5, 165.4,
174.1.
1
Compound 4q: mp 174–1758C, lit.[8] 174–1768C; H NMR (300 MHz,
DMSO-d6) d 1.12 (t, J ¼ 7 Hz, 3H), 2.26 (s, 3H), 4.02 (q, J ¼ 7 Hz, 2H),
5.10 (d, J ¼ 3.8 Hz, 1H), 5.99 (s, 2H), 6.65–6.72 (m, 2H), 6.85
(d, J ¼ 7.8 Hz, 1H), 9.56 (s, 1H), 10.27 (s, 1H); 13C NMR (75 MHz,
DMSO-d6) 14.1, 17.2, 53.7, 59.5, 100.7, 101.1, 106.6, 108.1, 119.6, 137.4,
144.9, 146.6, 147.3, 165.1, 174.1.
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