LiClO4-catalyzed one-pot synthesis of dihydropyrimidinones: An improved protocol for Biginelli reaction

Article abstract of DOI:10.1055/s-2001-15229

Lithium perchlorate efficiently catalyzes the three-component condensation reaction of aldehyde, β-keto ester and urea in refluxing acetonitrile to afford the corresponding dihydropyrimidinones in high yields under neutral conditions. LiOTf is also found

Full text of DOI:10.1055/s-2001-15229

PAPER
1341
LiClO4-Catalyzed One-Pot Synthesis of Dihydropyrimidinones: An Improved
Protocol for Biginelli Reaction1
LiClO4-
C
h
atalyzed On
i
e-Pot
S
l
ynthesi
l
s
of
D
i
u
hydropyrimidinone
S
s
. Yadav,* Basi V. Subba Reddy, R. Srinivas, C. Venugopal, T. Ramalingam
Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad-500 007, India
Fax +91(40)7170512; E-mail: yadav@iict.ap.nic.in
Received 4 January 2001; revised 11 April 2001
In recent years lithium perchlorate has received consider-
Abstract: Lithium perchlorate efficiently catalyzes the three-com-
ponent condensation reaction of aldehyde, -keto ester and urea in
refluxing acetonitrile to afford the corresponding dihydropyrimidi-
nones in high yields under neutral conditions. LiOTf is also found
able attention as a powerful reaction medium for effecting
various transformations11 such as cycloaddition reactions,
sigmatropic rearrangements, ring opening reactions of ep-
to be an efficient catalyst for the synthesis of dihydropyrimidinones oxides, glycosidation reactions, selective carbonyl protec-
from aldehyde, -keto ester and urea.
tion as dithioacetals, Michael reactions and aldol
reactions. Lithium perchlorate provides a convenient pro-
cedure to carry out the reactions under essentially neutral
and workup conditions. In addition, lithium perchlorate is
found to retain its activity even in the presence of nitrogen
containing compounds. These special properties inherent
to lithium perchlorate prompted us to explore this catalyst
for the synthesis of dihydropyrimidinones.
Keywords: Biginelli reaction, lithium perchlorate, lithium triflate,
dihydropyrimidinones
Dihydropyrimidinones are an important class of com-
pounds which are becoming increasingly interesting due
to their therapteutic and pharmacological activities.2 Sev-
eral functionalized dihydropyrimidines have been found
to exhibit a wide spectrum of biological effects3 including
antiviral, antitumor, antibacterial and anti-inflammatory
activities. In addition, 4-aryldihydropyrimidines have
emerged4 as potent calcium channel blockers, antihyper-
tensive, 1a-adrenergic antagonists and neuropeptide an-
tagonists. Further, dihydropyrimidinone-5-carboxylate
core unit is found in many marine natural products5 in-
cluding batzelladine alkaloids, which are found to be po-
tent-HIV gp-120-CD4 inhibitors. The simple and direct
method originally reported by Biginelli6 for the synthesis
of dihydropyrimidinones involves three component con-
densation reactions (i.e., aldehyde, -keto ester and urea)
often suffer from low yields practically in case of substi-
tuted aromatic and aliphatic aldehydes.7 Even though,
high yields could be achieved by following complex
multi-step procedures,8 these methods lack the simplicity
of original one-pot Biginelli protocol. Therefore, Biginelli
reaction continues to attract the attention of researchers
for the discovery of a milder and efficient procedure for
the synthesis of dihydropyrimidinones. Recently,
BF3 OEt2, PPE, KSF clay, InCl3, FeCl3 and lanthanide tri-
flates are found to be effective9 for this transformation. In
addition, microwave irradiations are also found to
accelerate10 the reaction. However, many of these one-pot
procedures generally require strong protic or Lewis acids,
prolonged reaction times and high temperatures. Thus, the
use of neutral alternative would extend the scope of useful
one-pot Biginelli reaction for the synthesis of dihydropy-
rimidinones.
In this report, we describe a simple and practical method
for the Biginelli reaction using catalytic amount of lithium
perchlorate in acetonitrile. The reaction of benzaldehyde,
ethyl acetoacetate and urea in the presence of 20 mol%
lithium perchlorate in refluxing acetonitrile resulted in the
formation of dihydropyrimidinone in 90% yield. Similar-
ly, several aromatic, aliphatic and heterocyclic aldehydes
reacted well under the present reaction conditions to give
the corresponding dihydropyrimidinones in excellent
yields (Scheme 1).
Scheme 1
The three component condensation reaction proceeded
smoothly in refluxing acetonitrile and was also completed
with in 5–8 h of reaction time. Many of the pharmacolog-
ical relevant substitution patterns on the aromatic ring
could be introduced with high efficiency. Aromatic alde-
hydes carrying either electron-donating or -withdrawing
substituents afforded high yields of products in high puri-
ty. Acid sensitive aldehyde such as furfural worked well
without the formation of any side products, which are nor-
mally observed either in the presence of protic or Lewis
acids. In addition to its simplicity and milder reaction con-
ditions, this method is effective even with aliphatic and
, -unsaturated aldehydes which normally give poor
yields in the presence of either protic or Lewis acids due
to thier decomposition or polymerization under acidic
Synthesis 2001, No. 9, 29 06 2001. Article Identifier:
1437-210X,E;2001,0,09,1341,1345,ftx,en;Z00301SS.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0039-7881

1342
J. S. Yadav et al.
PAPER
Table LiClO4-Catalyzed Formation of Dihydropyrimidinonesa
Substrate
R
R1
R2
Reaction Time Product
(h)
Yieldb (%)
Mp (° C)c
Reported
Found
1a
1b
1c
Me
Me
Me
OEt
OEt
OEt
6
7
8
2a
2b
2c
89
90
87
201–203
188–190
174–176
20210
18710
17710
1d
1e
1f
Me
Me
Me
OEt
OEt
OEt
8
10
8
2d
2e
2f
90
85
87
164–165
222–223
247–248
–
2239
24610
1g
1h
Me
Me
OEt
OEt
12
6
2g
2h
81
90
251 (dec.)
–
–
193–194
1i
Me
OEt
7
2i
83
229–231
2329
1j
1k
1l
Me
Me
Me
OEt
OEt
OEt
5
5
7
2j
2k
2l
90
85
81
207–208
206–208
182–184
20810
2059
1867
1m
1n
Me
Me
OEt
OEt
8
7
2m
2n
87
89
237–238
170–171
2377
1729
1o
Me
OEt
5
2o
90
206–207
2089
1p
1q
Me
Ph
OEt
OEt
7
2p
2q
82
75
161–162
16310
1599
10
158
1r
1s
Me
Me
OMe
Me
6
7
2r
2s
90
88
208–210
241–243
2099
–
a All products were characterized by 1H NMR, IR and mass spectra and also by comparison of physical characteristics with authentic samples.
b Isolated and unoptimized yields.
c Melting points were uncorrected.
conditions. Another important feature of this procedure is action lies in its simplicity. No additive or protic or Lewis
the survival of a variety of functional groups such as ole- acid is required in this procedure. This procedure not only
fins, ethers, esters, nitro and halides under the reaction preserves the simplicity of Biginelli reaction but also pro-
conditions. The advantage of the use of LiClO4 for this re- duces excellent yields of the dihydropyrimidinones. Thus
Synthesis 2001, No. 9, 1341–1345 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
LiClO4-Catalyzed One-Pot Synthesis of Dihydropyrimidinones
1343
1H NMR (DMSO-d6): = 1.15 (t, 3 H, J = 7.0 Hz), 2.30 (s, 3 H),
3.80 (s, 6 H), 4.05 (q, 2 H, J = 7.0 Hz), 5.25 (s, 1 H), 6.80 (m, 2 H),
6.85 (m, 1 H), 7.25 (br s, 1 H, NH), 8.95 (br s, 1 H, NH).
EIMS: m/z (%) = 320 (M+), 292, 276, 247, 232, 183, 155, 137, 97,
69.
this procedure offers an easy access to substituted dihy-
dropyrimidinones with a variety of substitution patterns.
Among various solvents like acetonitrile, methanol, dieth-
yl ether, THF and nitromethane used for this transforma-
tion, methanol and acetonitrile were the solvents of choice
as best results were obtained with them. Several examples
illustrating this novel and general method for the synthesis
of dihydropyrimidinones are summarized in the Table.
The reaction may proceed through the acylimine forma-
tion from aldehydes and urea, which is stabilized by lithi-
um ion. Subsequent addition of the -keto ester enolate to
the acylimine followed by cyclodehydration would afford
dihydropyrimidine (Scheme 2).
IR (KBr): = 3253, 3118, 2956, 1723, 1682, 1654, 1519, 1461,
1237, 1139, 1095, 790 cm–1.
2d
Solid; mp 164–165°C.
1H NMR (DMSO-d6): = 1.20 (t, 3 H, J = 6.9 Hz), 1.45 (t, 6 H,
J = 6.9 Hz), 2.30 (s, 3 H), 4.05 (m, 6 H), 5.20 (s, 1 H), 6.80 (m, 2 H),
6.85 (m, 1 H), 7.15 (br s, 1 H, NH), 8.85 (br s, 1 H, NH). EIMS: m/
z 348 (M+), 319, 303, 275, 252, 231, 183, 155, 137.
IR (KBr): = 3256, 3118, 2978, 2933, 1717, 1705, 1653, 1519,
1226, 1091, 775 cm–1.
2e
Solid; mp 222–223°C (Lit.9 mp 223°C).
1H NMR (DMSO-d6): = 1.10 (t, 3 H, J = 6.9 Hz), 2.25 (s, 3 H),
4.05 (q, 2 H, J = 6.9 Hz), 5.20 (s, 1 H), 7.15 (m, 1 H), 7.35 (m, 2 H),
7.40 (br s, 1 H, NH), 9.0 (br s, 1 H, NH).
EIMS: m/z (%) = 328 (M+), 300, 254, 183, 155, 137, 69.
Scheme 2
IR (KBr): = 3352, 3225, 3109, 2975, 1697, 1645, 1469, 1400,
1321, 1228, 1099, 1032, 790 cm–1.
In summary, the present method for the synthesis of
DHPMs by lithium perchlorate catalyzed three-compo-
nent condensation of -keto ester, aldehyde and urea pro-
vides a novel and improved protocol for Biginelli
reaction. In addition to its simplicity and neutral reaction
conditions, this method is effective for aromatic, aliphatic,
, -unsaturated and heterocyclic aldehydes.
2f
Solid; mp 247–248°C (Lit.10 mp 246°C).
1H NMR (DMSO-d6): = 0.90 (t, 3 H, J = 7.0 Hz), 2.40 (s, 3 H),
3.90 (q, 2 H, J = 7.0 Hz), 6.10 (s, 1 H), 7.40–7.55 (m, 5 H), 7.80 (t,
1 H, J = 8.2 Hz), 7.85 (d, 1 H, J = 8.2 Hz), 8.30 (d, 1 H, J = 8.2 Hz),
9.10 (br s, NH).
EIMS: m/z (%) = 310 (M+), 217, 176, 133, 119, 91, 69.
IR (KBr) : = 3245, 3118, 2977, 1698, 1647, 1431, 1231, 1088, 790
cm-1.
3,4-Dihydro-2(1H)-pyrimidinones 2; General Procedure
A mixture of aldehyde (5 mmol), -keto ester (5 mmol), urea (10
mmol) and LiClO4 or LiOTf (20% w/w of aldehyde) was stirred in
refluxing MeCN for an appropriate time (Table). After completion
of the reaction as indicated by TLC, the reaction mixture was
poured into crushed ice and the resulting solid was filtered under
suction and recrystallized from hot methanol to afford the pure
product.
2g
Solid; mp 251°C (dec.).
1H NMR (DMSO-d6): = 1.19 (t, 3 H, J = 7.0 Hz), 2.28 (s, 3 H),
4.18 (q, 2 H, J = 7.0 Hz), 5.30 (br s, 1 H), 7.15–7.75 (m, 9 H).
EIMS: m/z = 360 (M+), 332, 316, 288, 240, 212, 177.
IR (KBr): = 3247, 2978, 1716, 1696, 1497, 1261 cm–1.
2a
Solid; mp 201–203°C (Lit.7 mp 202°C).
2h
1H NMR (DMSO-d6): = 1.17 (t, 3 H, J = 6.8 Hz), 2.30 (s, 3 H),
4.05 (q, 2 H, J = 6.8 Hz), 5.25 (s, 1 H), 7.15–7.35 (m, 6 H), 8.95 (br
s, NH).
EIMS: m/z = 260 (M+), 232, 184, 156, 138, 43.
IR (KBr): = 3245, 3120, 2950, 2925, 1720, 1702, 1640, 1590 cm–1.
Solid; mp 193–194°C.
1H NMR (DMSO-d6): = 1.15 (t, 3 H, J = 6.8 Hz), 2.35 (s, 3 H),
4.10 (q, 2 H, J = 6.8 Hz), 5.35 (s, 1 H), 5.80 (br s, 1 H, NH), 6.85 (m,
1 H), 7.05 (m, 5 H), 7.45 (m, 3 H), 8.40 (br s, 1 H, NH).
EIMS: m/z = 352 (M+), 323, 279, 183, 155, 137, 91, 69.
2b
IR (KBr): = 3243, 3113, 2981, 1712, 1654, 1582, 1487, 1245,
1097, 785 cm–1.
Solid; mp 188–190°C (Lit.10 mp 187°C).
1H NMR (DMSO-d6): = 1.15 (t, 3 H, J = 7.0 Hz), 2.35 (s, 3 H),
4.10 (q, 2 H, J = 7.0 Hz), 5.25 (s, 1 H), 5.50 (br s, 1 H, NH), 5.95 (s,
2 H), 6.75 (m, 3 H), 7.95 (br s, 1 H, NH).
2i
Solid; mp 229–231°C (Lit.9 mp 232–235°C).
1H NMR (DMSO-d6): = 1.05 (t, 3 H, J = 7.0 Hz), 2.50 (s, 3 H),
3.95 (q, 2 H, J = 7.0 Hz), 4.25 (d, 1 H, J = 6.0 Hz), 6.05 (dd, 1 H,
J = 16.4 Hz), 6.2 (d, 1 H, J = 16.4 Hz), 7.25 (m, 5 H), 7.45 (d, 1 H,
NH, J = 1.7 Hz), 8.95 (br s, NH).
EIMS: m/z (%) = 304 (M+), 275, 258, 231, 183, 155, 137, 110, 69.
IR (KBr): = 3356, 3222, 2975, 1700, 1642, 1490, 1225, 1093, 795
cm–1.
EIMS: m/z (%) = 286 (M+), 252, 224, 196, 149, 84.
2c
Solid; mp mp 174–176°C (Lit.10 mp 177°C).
Synthesis 2001, No. 9, 1341–1345 ISSN 0039-7881 © Thieme Stuttgart · New York

1344
J. S. Yadav et al.
PAPER
IR (KBr): = 3335, 3242, 3098, 2978, 1689, 1642, 1492, 1373,
1218, 1121, 785 cm–1.
EIMS: m/z = 253 (M+), 209, 183, 155, 137, 91, 40.
IR (KBr): = 3249, 2933, 1730, 1646, 1433, 1331, 1288, 1086, 779
cm–1.
2j
Solid; mp 207–208°C (Lit.10 mp 208°C).
2q
1H NMR (DMSO-d6): = 1.15 (t, 3 H, J = 6.9 Hz), 2.30 (s, 3 H),
4.20 (q, 2 H, J = 6.9 Hz), 5.30 (d, 1 H, J = 1.8 Hz), 6.85 (m, 2 H),
7.15 (m, 1 H), 7.30 (br s, NH), 8.90 (br s, NH).
Solid; mp 158°C (Lit.9 mp 159°C).
1H NMR (DMSO-d6): = 0.90 (t, 3 H, J = 6.8 Hz), 3.85 (q, 2 H,
J = 6.8 Hz), 5.45 (d, 1 H, J = 1.8 Hz), 6.55 (br s, 1 H, NH), 7.30–7.40
(m, 10 H), 7.80 (br s, 1 H, NH).
EIMS: m/z = 266 (M+), 238, 221, 193, 145, 117, 83.
IR (KBr): = 3245, 3120, 1720, 1690, 1535, 1460 cm–1.
EIMS: m/z (%) = 322 (M+), 294, 278, 249, 185, 157, 138, 91, 77, 69.
IR (KBr): = 3215, 3085, 2978, 1697, 1650 cm–1.
2k
Solid; mp 206–208°C (Lit.9 mp 205°C).
2r
1H NMR (DMSO-d6): = 1.17 (t, 3 H, J = 7.0 Hz), 2.35 (s, 3 H),
4.18 (q, 2 H, J = 7.0 Hz), 5.30 (d, 1 H, J = 2.0 Hz), 6.10 (d, 1H,
J = 2.1 Hz), 6.33 (s, 1 H), 7.30 (m, 1 H), 7.82 (br s, NH), 9.21 (br s,
NH).
EIMS: m/z = 250 (M+), 221, 205, 177, 134, 80, 67.
IR (KBr): = 3268, 3118, 1716, 1681, 1591, 1485 cm–1.
Solid; mp 210–211°C (Lit.9 mp 209°C).
1H NMR (DMSO-d6): = 2.25 (s, 3 H), 3.60 (s, 3 H), 5.25 (d, 1 H,
J = 1.7 Hz), 7.20–7.35 (m, 6 H), 9.05 (br s, 1 H, NH).
EIMS: m/z (%) = 246 (M+), 219, 161, 134, 91, 69, 42.
IR (KBr): = 3255, 3120, 2958, 1725, 1680, 1653, 1518, 1462,
1238, 1140, 1095, 790 cm–1.
2l
2s
Solid; mp 182–184°C (Lit.7 mp 186–187°C).
Solid; mp 241–243°C.
1H NMR (DMSO-d6): = 1.25 (t, 3 H, J = 7.2 Hz), 1.80 (m, 2 H),
2.25 (s, 3 H), 2.60–2.70 (m, 2 H), 4.15 (m, 2 H), 4.25 (m, 1 H), 7.10–
7.25 (m, 6 H), 8.80 (br s, 1 H, NH).
1H NMR (DMSO-d6): = 2.10 (s, 3 H), 2.25 (s, 3 H), 5.30 (d, 1 H,
J = 1.8 Hz), 7.20–7.30 (m, 5 H), 7.60 (br s, 1 H, NH), 9.05 (br s, 1
H, NH).
EIMS: m/z (%) = 288 (M+), 183, 155, 137, 91.
EIMS: m/z (%) = 230 (M+), 188, 154, 144, 115, 77, 43.
IR (KBr): = 3248, 3117, 2975, 1724, 1652, 1495, 1287, 1226,
1092, 778 cm–1.
IR (KBr): = 3286, 3251, 2920, 1703, 1675, 1598, 1414, 1327,
1235, 1105, 997, 965, 768 cm–1.
2m
Solid; mp 237–238°C (Lit.7 mp 235–237°C).
Acknowledgements
1H NMR (DMSO-d6): = 1.05 (m, 4 H), 1.25 (t, 3 H, J = 6.8 Hz),
1.45 (m, 3 H), 1.75 (m, 4 H), 2.3 (s, 3 H), 4.15 (m, 3 H), 6.15 (br s,
1 H, NH), 8.45 (br s, 1 H, NH).
BVS and RS thank CSIR, New Delhi for the award of a fellowship.
EIMS: m/z (%) = 266 (M+), 183, 137, 155, 40.
References
IR (KBr): = 3236, 3118, 2920, 2850, 1726, 1702, 1647, 1450,
1230, 1095, 789 cm–1.
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1799; and references cited therein.
2n
Solid; mp 170–171°C (Lit.9 172°C).
(4) (a) Atwal, K. S.; Rovnyak, G. C.; O’Reilly, B. C.; Schwartz,
J. J. Org. Chem. 1989, 54, 5898. (b) Atwal, K. S.; Swanson,
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1H NMR (DMSO-d6): = 1.25 (t, 3 H, J = 6.9 Hz), 2.32 (s, 3 H),
2.43 (s, 3 H), 4.10 (q, 2 H, J =6.9 Hz), 5.40 (d, 1H, J = 2.2 Hz), 6.95–
7.20 (m, 4 H), 7.61 (br s, NH), 9.10 (br s, NH).
EIMS: m/z = 274 (M+), 245, 229, 201, 155, 138, 91.
IR (KBr): = 3240, 3110, 1695, 1665, 1560 cm–1.
2o
Solid; mp 206–207°C (Lit.9 208°C).
1H NMR (DMSO-d6): = 1.20 (t, 3 H, J =7.0 Hz), 2.28 (s, 3 H), 4.05
(q, 2 H, J =7.0 Hz), 5.39 (d, 1H, J = 2.4 Hz), 7.52 (d, 2H, J =8.7 Hz),
7.35 (br s, NH), 8.23 (d, 2 H, J =8.7 Hz), 9.35 (br s, NH).
EIMS: m/z = 306 (M+), 276, 232, 183, 155, 137.
IR (KBr): = 3235, 3109, 2975, 1701, 1645, 1558 cm–1.
(6) Biginelli, P. Gazz. Chim. Ital. 1893, 23, 360.
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Tetrahedron Lett. 1995, 36, 7819. (c) Folkers, K.; Johnson,
T. B. J. Am. Chem. Soc. 1934, 1180.
2p
Solid; mp 161–162°C (Lit.10 mp 163°C).
1H NMR (DMSO-d6): = 0.95 (t, 3 H, J = 6.8 Hz), 1.25–1.40 (m, 9
H), 1.55 (m, 2 H), 2.30 (s, 3 H), 4.15 (m, 2 H), 4.25 (m, 1 H), 6.05
(br s, 1 H, NH), 8.55 (br s, 1 H, NH).
Synthesis 2001, No. 9, 1341–1345 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
LiClO4-Catalyzed One-Pot Synthesis of Dihydropyrimidinones
1345
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Synthesis 2001, No. 9, 1341–1345 ISSN 0039-7881 © Thieme Stuttgart · New York