Iodotrimethylsilane-accelerated one-pot synthesis of 5-unsubstituted 3,4-dihydropyrimidin-2(1H)-ones: A novel procedure for the Biginelli-like cyclocondensation reaction at room temperature

Article abstract of DOI:10.1002/hlca.200590242

A novel Biginelli-like cyclocondensation reaction is efficiently catalyzed by iodotrimethylsilane (Me₃SiI) in MeCN. The reaction proceeds at room temperature by a three-component one-pot condensation of ketones with aldehydes and urea to afford

Full text of DOI:10.1002/hlca.200590242

2
996
HELVETICA CHIMICA ACTA – Vol. 88 (2005)
Iodotrimethylsilane-Accelerated One-Pot Synthesis of 5-Unsubstituted 3,4-
Dihydropyrimidin-2(1H)-ones: A Novel Procedure for the Biginelli-Like
1
Cyclocondensation Reaction at Room Temperature )
by Gowravaram Sabitha*, Kusuma B. Reddy, Rangavajjula Srinivas, and Jillu S. Yadav
Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad-500 007, India
(
fax: +91-40-27160512; e-mail: sabitha@iictnet.org)
3
A novel Biginelli-like cyclocondensation reaction is efficiently catalyzed by iodotrimethylsilane (Me SiI) in
MeCN. The reaction proceeds at room temperature by a three-component one-pot condensation of ketones with
aldehydes and urea to afford 5-unsubstituted 3,4-dihydropyrimidin-2(1H)-ones in good yields (Scheme 1 and
Table).
Introduction. – The Biginelli reaction [1], first described more than a century ago,
consists in a three-component, one-pot condensation of b-keto esters with aldehydes
and ureas under strongly acidic conditions to afford 3,4-dihydropyrimidinones.
Recently, the interest in the synthesis of these derivatives has increased tremendously
because they exhibit promising activities as calcium-channel modulators, antihyperten-
sive agents, a-1a receptor antagonists, and neuropeptide Y (NPY) antagonists [2], as an
anticancer drug capable of inhibiting Kinesinmotor protein [3], and as an anti-HIV
agent in some marine natural products containing the dihydropyrimidinone structure
[
4]. Thus, Biginelli’s reaction for the synthesis of dihydropyrimidinone has received
renewed interest, and several improved procedures have recently been reported [5],
although some of these methods involve strong Lewis acids such as BF ·OEt , protic
3
2
acids such as HCl, or AcOH, and additives. Generally these reagents require long reac-
tion times and reflux temperatures. In this regard, we recently reported a rapid, high-
yielding protocol for the synthesis of dihydropyrimidinones using iodotrimethylsilane
[
6] at room temperature. Eventhough several reagents are available for the synthesis
of Biginelli’s compounds, the reports on the synthesis of novel Biginelli-like structures
is very limited [7][8]. The reported methods result in low yields (<0.5%) with multiple
by-products, either proceed in a multistep fashion via the saponification of an ester
group at C(5) followed by thermal decarboxylation [9] or require harsh reaction con-
ditions. More recently, FeCl ·7H O [10] has been employed for this transformation
3
2
but the reaction requires long reaction times and reflux conditions.
As an extension to the Biginelli reaction [6], we herein disclose a novel, highly effi-
cient Biginelli-like cyclocondensation reaction for the preparation of 5-unsubstituted
3
,4-disubstituted pyrimidinones in the presence of iodotrimethylsilane (Me SiI) in
3
1)
IICT Communication No. 041020.
©
2005 Verlag Helvetica Chimica Acta AG, Zürich

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MeCN at room temperature (Scheme 1). To the best of our knowledge, there are no
earlier reports on one-pot syntheses of Biginelli-like structures at room temperature.
Scheme 1
Results and Discussions. – First, we studied the reaction of acetophenone (1), benzal-
dehyde (2), and urea (3) in the presence of Me SiI generated in situ from Me SiCl and
3
3
NaI in MeCN. The reaction was found to be very fast, and complete conversion was
observed in 1 h at room temperature to afford 5-unsubstituted 3,4-dihydro-4,6-diphe-
nylpyrimidin-2(1H)-one (4a) in 87% yield (Table, Entry 1). Encouraged by these
results, several substituted acetophenones 1 were examined under similar conditions
(Table, Entries 2–7). To explore the generality of the present protocol, cyclic ketones
such as a-tetralone (=3,4-dihydronaphthalen-1(2H)-one), indan-2-one (=1,3-dihy-
dro-2H-indan-2-one), and chromanone (=2,3-dihydro-1-benzopyran-4-one) were
also treated with aldehydes 2 and urea (3) to produce novel fused pyrimidinones in
good yields (see, e.g., Table, Entries 8–12; Scheme 2). Electron-rich as well as elec-
tron-deficient aldehydes proved to be excellent substrates for the cyclocondensation
reaction. In all cases, the three component one-pot reaction proceeded smoothly and
rapidly to afford the corresponding 5-unsubstituted 3,4-dihydropyrimidin-2(1H)-one
derivatives in excellent yields.
Scheme 2
In conclusion, we have developed a simple and general method for the synthesis of
5
-unsubstituted 3,4-disubstituted pyrimidin-2(1H)-ones using Me SiI as an efficient
3
Lewis acid catalyst. The method offers several advantages including short reaction

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998
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ELVETICA
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Table. Iodotrimethylsilane-Mediated Three-Component Biginelli-Like Cyclocondensation Reactiona)
Entry
Ketone 1
Aldehyde 2
Time [min]
Product 4
yield [%]b)
m.p. [8]
1
2
3
4
5
6
7
8
9
PhC(=O)Me
PhCHO
PhCHO
PhCHO
PhCHO
45
50
60
55
55
60
60
50
55
50
50
50
87 (4a)
84 (4b)
81 (4c)
85 (4d)
80 (4e)
82 (4f)
82 (4g)
88 (4h)
86 (4i)
75 (4j)
77 (4k)
88 (4l)
218–219
174–175
223–224
152–153
214–215
232–233
204–206
260–262
4-MeÀC
4-ClÀC
4-MeOÀC
4-MeÀC
4-MeOÀC
6
H
4
ÀC(=O)Me
ÀC(=O)Me
ÀC(=O)Me
ÀC(=O)Me
ÀC(=O)Me
ÀC(=O)Me
6
H
4
6
H
4
6
H
4
4-NO
4-NO
PhCHO
PhCHO
2
ÀC
6
H
H
4
ÀCHO
ÀCHO
6
H
4
2
ÀC
6
4
4-OHÀC
6
H
4
c
a-tetralone )
a-tetralone )
indan-2-one )
indan-2-one )
c
4-FÀC
PhCHO
4-FÀC
PhCHO
6
H
4
ÀCHO
220–222
d
1
1
1
0
1
2
gummy material
gummy material
272–274
d
6
H
4
ÀCHO
e
chromanone )
a) Reaction run at room temperature. b) Yields of isolated products.
c) d) e)
times, high yields, and simple product-isolation procedures, which makes it a useful
addition to existing methods.
K. B. R. thanks UGC and R. S. thanks CSIR, New Delhi, for financial support.
Experimental Part
One-pot Synthesis of 5-Unsubstituted 3,4-Dihydropyrimidin-2(1H)-ones. Procedure A: Me
3
SiCl (8 mmol)
was added to a stirred mixture of acetophenone (1; 10 mmol), benzaldehyde (2, R =H; 10 mmol), urea (3;
5 mmol), and NaI (8 mmol) in MeCN (5 ml) at r.t. After the reaction was complete (TLC monitoring), the mix-
2
1
ture was poured into crushed ice, and the separated solid product was filtered and recrystallized from EtOH to
afford pure, 4a in 87% yield.
Similarly, compounds 4b–i and 4l were prepared.
Procedure B: Me
one; 1j; 10 mmol), benzaldehyde (2, R =H) or 4-fluorobenzaldehyde (2, R =4-F; 10 mmol), urea (3;
5 mmol), and NaI (8 mmol) in MeCN (5 ml) at r.t. After the reaction was complete (TLC monitoring), the mixture
was poured into crushed ice, extracted with AcOEt, washed with sodium thiosulfate soln., dried (Na SO ), and
3
SiCl (8 mmol) was added to a stirred mixture of indan-2-one (=1,3-dihydro-2H-inden-2-
2
2
1
2
4
evaporated and the residue purified by column chromatography (hexane/AcOEt): 4j or 4k as gummy materials.
Data of 1,3,4,9-Tetrahydro-2H-indeno[1,2-d]pyrimidin-2-one (4j): Gummy material. IR (KBr): 3228, 3231,
1
2
940, 1667, 1455, 1254, 772. H-NMR (400 MHz, CDCl
3
): 3.39 (AB(‘q’), J=22.0, 2 H); 5.50 (s, 1 H); 6.19 (br. s,
NH); 6.50 (d, J=7.3, 1 H); 6.88 (t, J=8.1, 1 H); 6.96 (t, J=7.3, 1 H); 7.15–7.32 (m, 4 H); 7.39 (d, J=7.3, 2 H);
1
3
9
3
.56 (br. s, NH). C-NMR (75 MHz, CDCl ): 35.23; 56.86; 111.55; 117.51; 122.80; 123.41; 126.54; 127.44; 128.36;
1
28.88; 137.94; 139.91; 141.84; 141.94; 154.06. FAB-MS: 263 (M+H).
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Received July 25, 2005