Trimethylsilyl chloride: A facile and efficient reagent for one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones

Article abstract of DOI:10.1081/SCC-200028607

Trimethylsilyl chloride (TMSCl) was used as a Lewis acid to efficiently perform one-pot, three-components, Biginelli condensation reactions of aldehydes, 1,3-dicarbonyl compounds, and urea or thiourea. This resulted in simple one-pot synthesis of the corr

Full text of DOI:10.1081/SCC-200028607

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Trimethylsilyl Chloride: A
Facile and Efficient Reagent
for One‐Pot Synthesis of
3,4‐Dihydropyrimidin‐2(1H)‐ones
Yulin Zhu a , Yuanjiang Pan a & Shenlin Huang a
a Department of Chemistry, Zhejiang University,
Hangzhou, 310027, China
Version of record first published: 10 Jan 2011.
To cite this article: Yulin Zhu, Yuanjiang Pan & Shenlin Huang (2004):
Trimethylsilyl Chloride: A Facile and Efficient Reagent for One‐Pot Synthesis of
3,4‐Dihydropyrimidin‐2(1H)‐ones, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 34:17, 3167-3174
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 17, pp. 3167–3174, 2004
Trimethylsilyl Chloride: A Facile and
Efficient Reagent for One-Pot Synthesis
of 3,4-Dihydropyrimidin-2(1H)-ones
*
Yulin Zhu, Yuanjiang Pan, and Shenlin Huang
Department of Chemistry, Zhejiang University, Hangzhou, China
ABSTRACT
Trimethylsilyl chloride (TMSCl) was used as a Lewis acid to efficiently
perform one-pot, three-components, Biginelli condensation reactions of
aldehydes, 1,3-dicarbonyl compounds, and urea or thiourea. This resulted
in simple one-pot synthesis of the corresponding 3,4-dihydropyrimidin-
2(1H)-ones at room temperature with excellent yield.
Key Words: Biginelli reaction; Trimethylsilyl chloride; Lewis acid;
3,4-Dihydropyrimidin- 2(1H)-ones.
3,4-Dihydropyrimidin-2(1H)-ones (DHPMs) and their derivatives have
attracted increasing interest due to their wide range of therapeutical and
pharmacological properties, such as antiviral, antitumor, antibacterial, and
*
Correspondence: Yuanjiang Pan, Department of Chemistry, Zhejiang University,
Hangzhou 310027, China; E-mail: panyuanjiang@css.zju.edu.cn.
3167
DOI: 10.1081/SCC-200028607
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

3168
Zhu, Pan, and Huang
antiinflammatory properties.[1] Some of them have been successfully used as
calcium channel blockers, antihypertensive agents, and a1a-antagonists.[2]
Moreover, several marine alkaloids whose molecular structures contain the
dihydropyrimidinone core also exhibit interesting biological activities.[3]
Therefore, synthesis of these compounds is still of great importance.
The earliest method for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones
reported by Biginelli in 1893 involved the one-pot condensation of an aldehyde,
a b-ketoester, and urea under strong acidic conditions with low yield (often
20%–50%).[4] Recently, many improved procedures have been reported using
[5]
Lewis acids as promoters: BF3 OEt2, polyphosphate ester,[6] acidic clay
.
montmorillonite KSF,[7] FeCl3,[8] NiCl,[9] LaCl3,[10] InCl3,[11] ZrCl4,[12]
BiCl3,[13] Mn(OAc)3,[14] LiClO4,[15] and amidosulfonic acid.[16] Others have
also been reported to use ionic liquids such as: 1-n-butyl-3-methylimidazolium
tetrafluoroborate (BMIM-BF4) or hexafluorophosphorate (BMIM-PF6).[17] In
addition, there are still other methods such as microwave-assisted synthesis,[18]
solid-phase synthesis,[19] etc. In 2003, Bi(OTf)3,[20] ammonium chloride
(NH4Cl),[21] lithium bromide (LiBr),[22] silica sulfuric acid,[23] Cu(OTf)2,[24]
and NH2SO3H[25] were also reported for Biginelli reaction.
Although numerous methods have been reported, all have shortcomings due
to difficulties in actual preparation, especially expensive reagents, long reaction
time, unsatisfactory yield, etc. Therefore, the discovery of an inexpensive, facile,
and effective reagent for the preparation of 3,4-dihydropyrimidin-2(1H)-ones
under mild conditions is an active ongoing research topic. Here we report a
new method for the synthesis of dihydropyrimidinones by employing the
TMSCl-CH3CN-DMF system as a very inexpensive and easily available reagent.
As shown in Sch. 1, the representative reaction of benzaldehyde (3a,
5.0 mmol), ethyl acetoacetate or acetylacetone (1a or 1b, 5.0 mmol), and
urea or thiourea (2a or 2b, 6.0 mmol) in the presence of TMSCl (3.5 mmol)
Scheme 1. TMSCl-catalyzed synthesis of dihydropyrimidinones.

A Facile and Efficient Reagent for Biginelli Dihydropyrimidine Synthesis 3169
in DMF/CH3CN (2.5 mL/5.0 mL) at room temperature for 1–3 hr resulted
in the corresponding dihydropyrimidinone (the compounds 1, 10, 19, 28) in
good yield (respectively: 94%, 91%, 87%, 95%). Subsequently, the three-
component reaction proceeded smoothly with different aldehydes (3b–3i),
such as 4-methyl-benzaldehyde (3b), 4-chlorobenzaldehyde (3c), anisaldehyde
(3d), cinnamaldehyde (3e), 4-fluoraldehyde (3f), 4-nitrobenzaldehyde (3g),
furfural (3h), and n-butyraldehyde (3i), to give the corresponding dihydro-
pyrimidinones. Results of these observations are summarized in Table 1.
Table 1. TMSCl-catalyzed synthesis of dihydropyrimidinones.a
R1
X
R2
Products
Yield (%)
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
OC2H5
CH3
O
O
O
O
O
O
O
O
O
S
C6H5
1
2
94
93
95
92
79
89
92
81
86
91
90
89
92
83
91
93
76
88
87
97
96
90
84
87
91
79
91
95
4-CH322C6H4
4-Cl22C6H4
4-OCH322C6H4
C6H5CH55CH
4-F22C6H4
4-NO222C6H4
C4H3O
3
4
5
6
7
8
n-C3H7
C6H5
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
S
4-CH322C6H4
4-Cl22C6H4
4-OCH322C6H4
C6H5CH55CH
4-F22C6H4
4-NO222C6H4
C4H3O
S
S
S
S
S
S
S
n-C3H7
C6H5
O
O
O
O
O
O
O
O
O
S
CH3
CH3
4-CH322C6H4
4-Cl22C6H4
4-OCH322C6H4
C6H5CH55CH
4-F22C6H4
4-NO222C6H4
C4H3O
CH3
CH3
CH3
CH3
CH3
CH3
n-C3H7
C6H5
CH3
(continued)

3170
Zhu, Pan, and Huang
Table 1. Continued.
R1
X
R2
Products
Yield (%)
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
S
S
S
S
S
S
S
S
4-CH322C6H4
4-Cl22C6H4
4-OCH322C6H4
C6H5CH55CH
4-F22C6H4
4-NO222C6H4
C4H3O
29
30
31
32
33
34
35
36
93
96
89
86
87
91
79
83
n-C3H7
aGeneral procedure for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs).
1,3-cyclohexandion (10 mmol), aromatic aldehydes (10 mmol), urea or thiourea
(12 mmol), and DMF/CH3CN (12 mL) were mixed in a 25-mL flask and TMSCl
(10 mmol) was added drop-wise at room temperature. The resulting reaction mixture
was stirred at room temperature for 2 to 3 hr and precipitation was observed. The
products were isolated by filtering through a Buechner funnel and washed with
water followed by ethanol, and then dried to give the crystalline powder products.
1
Spectral data for selected compounds: Product 6: H NMR (DMSO-d6, 500 Mz) d
9.22 (s, 1H), 7.75 (s, 1H), 7.28–7.13 (m, 4H), 5.15 (s, 1H), 4.00–3.96 (m, 2H), 2.25
(s, 3H), 1.10 (t, J ¼ 7.1, 3H). 13C NMR (DMSO-d6, 125 Mz) d 166.3, 163.3, and
161.4 (split), 153.0, 149.5, 142.1, 129.3, 129.2, 116.2, 116.0, 100.2, 60.2, 54.3, 18.8,
15.1. MS (ESI) (m/z) [M þ H]þ279. Product 9: 1H NMR (DMSO-d6, 500 Mz) d
8.91 (s, 1H), 7.31 (s, 1H), 4.07–4.04 (m, 3H), 2.16 (s, 3H), 1.39–1.32 (m, 4H), 1.19
(t, J ¼ 7.0, 3H), 0.86 (t, J ¼ 7.1, 3H). 13C NMR (DMSO-d6, 125 Mz) d 166.6,
153.9, 149.3, 100.6, 60.2, 50.9, 18.8, 18.1, 15.3, 14.8. MS (ESI) (m/z)
[M þ H]þ227. Product 15: 1H NMR (DMSO-d6, 500 Mz) d 10.34 (s, 1H), 9.64
(s, 1H), 7.27–7.15 (m, 4H), 5.19 (d, J ¼ 3.4, 1H), 4.01–3.99 (m, 2H), 2.30 (s, 3H),
1.10 (t, J ¼ 7.0, 3H). 13C NMR (DMSO-d6, 125 Mz) d 175.3, 166.2, 163.6, and
161.7 (split), 146.3, 140.9, 129.6, 129.5, 116.5, 116.3, 101.7, 60.7, 54.5, 18.3, 15.1.
MS (ESI) (m/z) [M þ H]þ295. Product 20: 1H NMR (DMSO-d6, 500 Mz) d 9.13
(s, 1H), 7.75 (s, 1H), 7.12 (s, 4H), 5.22 (s, 1H), 2.27 (s, 3H), 2.25 (s, 3H), 2.08
(s, 3H). 13C NMR (DMSO-d6, 125 Mz) d 195.4, 153.2, 149.0, 142.3, 137.6, 130.1,
1
127.4, 110.6, 54.6, 31.2, 21.6, 19.9. MS (ESI) (m/z) [M þ H]þ245. Product 24: H
NMR (DMSO-d6, 500 Mz) d 9.21 (s, 1H), 7.84 (s, 1H), 7.38 (d, J ¼ 8.0, 2H), 7.25
(d, J ¼ 7.9, 2H), 5.24 (s, 1H), 2.27 (s, 3H), 2.11 (s, 3H). 13C NMR (DMSO-d6,
125 Mz) d 195.2, 153.1, 149.5, 144.2, 132.9, 129.5, 129.3, 110.5, 54.1, 31.4, 20.0.
MS (ESI) (m/z) [M þ H]þ265. Compound 31: 1H NMR (DMSO-d6, 500 Mz) d
10.22 (s, 1H), 9.68 (s, 1H), 7.15 (d, J ¼ 8.6, 2H), 6.90 (d, J ¼ 8.6, 3H), 5.23
(d, J ¼ 3.6, 1H), 3.72 (s, 3H), 2.31 (s, 3H), 2.11 (s, 3H). 13C NMR (DMSO-d6,
125 Mz) d 195.8, 174.7, 159.7, 145.1, 136.0, 128.8, 114.9, 111.4, 56.0, 54.3, 31.2,
19.1. MS (ESI) (m/z) [M þ H] þ 277.

A Facile and Efficient Reagent for Biginelli Dihydropyrimidine Synthesis 3171
In our case, the reaction was generally run at a molar ratio of
1.0 : 1.0 : 1.2 : 0.7 (aldehyde : ethyl acetoacetate or acetylacetone : urea or
thiourea : TMSCl), and all the reactions were exothermic. The product preci-
pitated directly from the reaction mixture at ambient room temperature. After
the reaction, the whole reaction mixture was placed in a refrigerator overnight.
In the above-mentioned syntheses, aromatic aldehydes carrying either elec-
tron-donating (-CH3, -OCH3) or electron-withdrawing (-F, -NO2) substituents
all reacted efficiently in excellent yield with high purity; while the reactions of
cinnamaldehyde (3e) and furfural (3h) were irritated with lower yields. With
the aid of TMSCl, the Biginelli reactions of aliphatic aldehydes (such as
n-butyraldehyde), ethyl acetoacetate, or acetylacetone and urea or thiourea
were also investigated (the compounds 9, 18, 27, 36). Reaction of thiourea
exhibited analogous behavior to that of urea and provided the corresponding
thio-derivatives of dihydropyrimidinones.
TMSCl exhibited remarkable reactivity and was used in Biginelli reaction
by Kulikova et al.[26] and et al. Sabitha [27] But the former needed longer reac-
tion times, troublesome work-up followed by column chromatography purifi-
cation using methanol as solvent, and lower yields for aliphatic aldehydes in
the reaction TMSCl-DMFA system. Gowravaram Sabitha reported that iodo-
trimethylsilane (TMSI) was used as Lewis acid for the Biginelli reactions in
excellent yields, but there are some deficiencies: (a) the troublesome isolation
must be needed as aresult of NaCl precipitated directly from the reaction
mixture; (b) the reaction would not yield the desired product without the aid
of NaI only under TMSCl.
The present procedure demonstrates that TMSCl-CH3CN-DMF acts as
a highly effective reaction system for the Biginelli reaction for one-pot syn-
theses of dihydropyrimidinones. Based on our studies, this method offers
several advantages including the cheapest materials, mild reaction conditions,
excellent yield, shorter reaction time, very facile purification, and very simple
experimental procedure.
ACKNOWLEDGMENTS
This research was funded by NSFC of China (20375036) and NSF of
Zhejiang Province (Rc0042)
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Received in Japan March 3, 2004