Adducts of diketene, alcohols, and aldehydes: Useful building blocks for 3,4-dihydropyrimidinones and 1,4-dihydropyridines

Article abstract of DOI:10.1055/s-0030-1258291

A novel, one-pot, solvent-free synthesis of 3,4-dihydropyrimidin-2-(1H)-one and 1,4-dihydropyridines derivatives via a four-component cyclocondensation reaction of diketene, alcohol, and aldehyde with urea or ammonium acetate is presented. Georg Thieme Ve

Full text of DOI:10.1055/s-0030-1258291

PAPER
4057
Adducts of Diketene, Alcohols, and Aldehydes: Useful Building Blocks for
3,4-Dihydropyrimidinones and 1,4-Dihydropyridines
Four-Component
C
b
ondensation
d
s
to
D
ihydro
o
pyrimidinone
l
s
and 1
a
,4-Dihydro
l
pyridi
ines Alizadeh,* Sadegh Rostamnia
Department of Chemistry, Tarbiat Modares University, P.O. Box 14115-175, Tehran, Iran
Fax +98(21)88006544; E-mail: abdol_alizad@yahoo.com; E-mail: aalizadeh@modares.ac.ir
Received 20 August 2010; revised 26 August 2010
adducts with new and interesting chemistry to overcome
limitations due to the presence of general acids such as
sulfuric acid or trifluoroacetic acid. This new solvent-free
or ‘neat’ method is based on the use of diketene as an in
situ source of various b-keto esters in the four-component
synthesis of dihydropyrimidinones and 1,4-dihydropy-
ridines. The solvent-free approach, simplicity, and variety
of derivatives available (using various aldehydes and al-
cohols) of the four-component procedure presented here
makes it an interesting alternative to three-component ap-
proaches.
Abstract: A novel, one-pot, solvent-free synthesis of 3,4-dihydro-
pyrimidin-2-(1H)-one and 1,4-dihydropyridines derivatives via a
four-component cyclocondensation reaction of diketene, alcohol,
and aldehyde with urea or ammonium acetate is presented.
Key words: dihydropyridines, dihydropyrimidines, diketene, mul-
ticomponent reaction, neat condition
Functionalized dihydropyrimidinones have recently
emerged as an integral part of several calcium channel
blockers, antihypertensives, and a1-adrenergic antago-
nists.1a,b Particularly, aryl-3,4-dihydropyrimidinones ex-
hibit a wide spectrum of biological activity such as
antiviral, antitumor, antibacterial, and anti-inflammatory
behavior1c,d and they are used as a starting point for the
preparation of complex heterocyclic scaffolds with phar-
macological properties.1e These reasons have motivated
researchers to extend the scope of the Biginelli-type reac-
tion to other 1,3-dicarbonyl compounds such as b-ketolac-
tones,1f b-diamides,1g and cyclic diketones.1h
O
O
H2N
N
NH
O2N
O2N
MeO2C
CO2Me
O
Oi-Pr
N
H
Nifedipine
SQ32926
1,4-Dihydropyridines are among the most widely used
drugs. The heterocyclic ring in 1,4-dihydropyridines is a
common feature of various bioactive compounds such as
anticonvulsant, antidiabatic, antianxiety, antidepressive,
antitumor, analgesic, seditative, vasodilator, bronchodila-
tor, hypnotic, and anti-inflammatory agents.2a,b Some de-
rivatives of 1,4-dihydropyridines, such as Nifedipine and
Lacidipine (Figure 1), are used commercially as calcium
channel blockers for the treatment of cardiovascular
diseases2c including hypertension. They are also known as
neuroprotectants, used for anti-platelet treatment of
aggregators, and are important in the treatment of
Alzheimer’s disease as anti-ischemic agents.2d
CO2t-Bu
EtO2C
CO2Et
N
H
Lacidipine
Figure 1 Examples of biologically active dihydropyrimidinone and
1,4-dihydropyridine derivatives
The three-component synthesis of dihydropyrimidinones
and 1,4-dihydropyridines via Biginelli and Hantzsch con-
ditions has been studied.3,4 Chiba, Sato, and Kato,5 report-
ed the halogenation of diketene in a multistep synthesis to
generate the halomethyl-dicarbonyl group through
Biginelli heterocyclization. To our surprise, the one-pot
reaction between diketene, urea, and an aldehyde in the
presence of trifluoroacetic acid as a catalyst and methanol
as a solvent, produced the Biginelli product, e.g. 3,4-dihy-
dropyrimidin-2(1H)-ones. Also, this study showed that
methanol is a main component of this reaction. Based on
this finding, we have explored the potential of solvent-
free diketene/alcohol/aldehyde adducts for four-compo-
nent condensation of this adduct with ammonium acetate
and urea under reflux conditions.
However, a number of the reported protocols for the
synthesis of dihydropyrimidinones3 and 1,4-dihydro-
pyridines4 in high yields require solvents and catalysts,
such as heavy metals, that are not acceptable in the con-
text of cost or green chemistry. However, developments in
this area require solvent-free methods and diversity in re-
agents that are potentially superior to existing methods
with regard to generality, simplicity, high yields, and han-
dling. In this respect, we are interested in introducing
potential solvent-free or ‘neat’ diketene/alcohol/aldehyde
SYNTHESIS 2010, No. 23, pp 4057–4060
x
x.
x
x
.
2
0
1
0
Earlier we reported the application of the in situ 1,3-dicar-
bonyl generated from diketene and alcohols or amines
Advanced online publication: 08.10.2010
DOI: 10.1055/s-0030-1258291; Art ID: Z21010SS
© Georg Thieme Verlag Stuttgart · New York

4058
A. Alizadeh, S. Rostamnia
PAPER
leading to the synthesis of novel furans or hydrazine The reaction was found to be general, with ammonium
enaminones, pyrans, and others.6 Recently, we have acetate affording the 1,4-dihydropyridine products 4 in
shown that solvolytic and non-solvolytic ring-opening re- good yields. The results are summarized in Table 2.
actions of diketene are facilitated.6 Here we wish to report
the use of diketene, alcohols 2, and aldehydes 1 under sol-
Although we have not established the mechanism of these
reactions, a possible explanation is proposed in Scheme 1.
vent-free conditions, with general catalysts such as sulfu-
On the basis of the established chemistry of diketene,6,7 it
ric or trifluoroacetic acid for the one-pot synthesis of 3,4-
is reasonable to assume that the dihydropyrimidinones 3
and 1,4-dihydropyridines 4 apparently result from the ini-
dihydropyrimidinones 3 and 1,4-dihydropyridines 4 via
four-component Biginelli-type and Hantzsch-type con-
tial addition of the alcohol or aldehyde to diketene to gen-
densation protocols, respectively.
eration in situ 1,3-dicarbonyl 5 and unsaturated adduct 6
The solvent-free reaction of diketene, arylaldehydes 1, under acidic and reflux conditions, followed by Biginelli
and alcohols 2, with urea in the presence of a catalytic and Hantzsch conditions. These in situ generated interme-
amount of trifluoroacetic acid undergoes a Biginelli cy- diates under the reaction conditions give the correspond-
clocondensation reaction at reflux to produce 3,4-dihy- ing 3,4-dihydropyrimidinones and 1,4-dihydropyridines
dropyrimidin-2(1H)-one derivatives 3 in 76–91% yields derivatives (Tables 1 and 2).
(Table 1).
In summary, we have described a novel, one-pot, solvent-
free synthesis of 3,4-dihydropyrimidin-2(1H)-one and
1,4-dihydropyridine derivatives via a four-component cy-
clocondensation reaction of diketene, alcohol, and alde-
hyde with urea or ammonium acetate. In addition, the
present method has the advantage that, not only is the re-
action performed under one-pot, solvent-free conditions,
but also, in addition to the aldehyde component, the alco-
hol component can be modified to achieve the synthesis of
a variety of derivatives. The simplicity, variety of deriva-
tives available, use of general acids of this four-compo-
nent procedure makes it an interesting alternative to three-
component approaches.
Table 1 Solvent-Free Four-Component Biginelli-Type Condensa-
tion
O
O
O
HN
NH
TFA (10 mol%)
reflux
NH2
ArCHO + ROH
+
+
H2N
O
Ar
1
2
COOR
3
Product Ar
R
Mp (°C)
Found
Yielda (%)
Reported
3a
3b
3c
3d
3e
3f
Ph
Ph
Me
Et
205–208 207–2103b
199–204 201–2033b
253–255 252–2533i
213–216 215–2183b
208–211 208–2103k
195–196 192–1933g
205–207 204–2073g
212–214 210–2123g
236–238 235–2373b
210–212 207–2103b
85
76
83
84
83
82
89
84
91
88
Table 2 Solvent-Free Four-Component Hantzsch-Type Condensa-
tion
Ar
O
2-ClC6H4
2-ClC6H4
3-ClC6H4
3-ClC6H4
4-ClC6H4
4-ClC6H4
Me
Et
H2SO4
(10 mol%)
RO2C
CO2R
+ ArCHO + ROH + NH4OAc
O
reflux
1
N
H
4
2
Me
Et
Product R
Ar
Ph
Mp (°C)
Found
Yielda (%)
3g
3h
3i
Me
Et
Reported
–
4a
4b
4c
4d
4e
4f
Me
162–164
80
70
71
82
78
4-O2NC6H4 Me
4-O2NC6H4 Et
Me
Me
Me
Me
Et
2-MeOC6H4 159–161 170–1714b
3-MeOC6H4 165–167 168–1704b
3j
a Isolated and unoptimized yields.
4-ClC6H4
4-O2NC6H4
Ph
155–157
–
160–162 165–1684c
O
O
155–157 154–1594d,e 83
126–128 125–1264f,g 75
ROH
H+
ArCHO
ROH
OR
O
O
O
O
5
4g
4h
4i
Et
2-ClC6H4
3-ClC6H4
4-ClC6H4
4-O2NC6H4
O
OR
reflux
O
Et
125–127 120–1214d
75
Ar
Et
146–148 144–1484d,g 77
128–130 129–1324d,g 81
ArCHO
6
Ar
4j
Et
Scheme 1 Plausible mechanisms for the formation of dicarbonyl 5
and unsaturated adduct 6
a Isolated and unoptimized yields.
Synthesis 2010, No. 23, 4057–4060 © Thieme Stuttgart · New York

PAPER
Four-Component Condensations to Dihydropyrimidinones and 1,4-Dihydropyridines
4059
25 °C and the solid was washed with cooled H2O and petroleum
ether–Et2O; yield: 0.24 g (80%).
IR (KBr): 3287, 1700, 1656, 1463, 1213, 1105 cm–1.
1H NMR (500.13 MHz, DMSO-d6): d = 2.28 (s, 6 H), 3.54 (s, 6 H),
4.89 (s, 1 H), 7.09–7.45 (m, 5 H), 8.87 (s, 1 H).
Diketene, aldehydes, alcohols, NH4OAc, and urea were obtained
from Merck (Germany) and Fluka (Switzerland). Melting points
1
were measured on an Electrothermal 9100 apparatus. H and 13C
NMR spectra were measured (CDCl3 or DMSO-d6 soln) with a
Bruker DRX-500 Avance spectrometer at 500.1 and 125.8 MHz, re-
spectively. IR spectra were recorded on a Shimadzu IR-460 spectro-
photometer.
13C NMR (125.7 MHz, DMSO-d6): d = 18.47, 37.27, 51.10, 101.23,
127.27, 127.31, 128.37, 129.69, 146.13, 148.29, 168.64.
In Table 1, identification of the products 3a and 3h was ascertained
by high field 1H and 13C NMR, IR and comparison with available
mp and spectroscopic literature data and 3i by 1H NMR, IR, and mp
data. Compounds 3b–g,j were characterized by comparison of their
IR, and mp with literature data.
Dimethyl 4-(4-Chlorophenyl)-2,6-dimethyl-1,4-dihydropyri-
dine-3,5-dicarboxylate (4d)
Yield: 0.27 g (82%).
IR (KBr): 3329, 1697, 1650, 1470, 1219, 1127 cm–1.
1H NMR (500.13 MHz, CDCl3): d = 2.35 (s, 6 H), 3.67 (s, 6 H), 4.99
(s, 1 H), 5.73 (s, 1 H), 7.19–7.28 (m, 4 H).
13C NMR (125.7 MHz, CDCl3): d = 19.56, 39.01, 50.99, 103.73,
128.14, 129.07, 131.84, 144.22, 145.98, 167.81.
In Table 2, identification of the products 4a,d,f, and 4h–j was ascer-
tained by high field 1H and 13C NMR and IR and comparison with
available mp and spectroscopic literature data. Compounds 4b,c
and 4e–j were characterized by comparison of their mp with litera-
ture data.
Methyl 6-Methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimi-
dine-5-carboxylate (3a); Typical Procedure
Diethyl 2,6-Dimethyl-4-phenyl-1,4-dihydropyridine-3,5-dicar-
boxylate (4f)
Yield: 0.27 g (83%).
IR (KBr): 3342, 1700, 1657, 1473, 1198, 1129 cm–1.
Equivalent amounts of neat adduct diketene (0.084 g, 1 mmol),
MeOH (0.032 g, 1 mmol), and benzaldehyde (0.106 g, 1 mmol) in
TFA (10 mol%) were magnetically stirred at reflux for 10 min, urea
(0.06 g, 1 mmol) was added, and then the mixture was refluxed with
stirring for the appropriate time (TLC monitoring). The reaction
was cooled to 25 °C and the solid was washed with cooled H2O and
petroleum ether–Et2O; yield: 0.21 g (85%).
3
1H NMR (500.13 MHz, CDCl3): d = 1.23 (t, JHH = 7.0 Hz, 6 H),
2.34 (s, 6 H), 4.12 (q, 3JHH = 7.0 Hz, 4 H), 4.91 (s, 1 H), 5.68 (s, 1
H), 7.07–7.43 (m, 5 H).
13C NMR (125.7 MHz, CDCl3): d = 14.91, 19.56, 39.43, 59.82,
103.14, 127.25, 127.32, 128.34, 129.61, 146.19, 148.25, 167.34.
IR (KBr): 3320, 3315, 1700, 1661, 1585, 1420 cm–1.
1H NMR (500.1 MHz, CDCl3): d = 2.36 (s, CH3), 3.63 (s, OCH3),
5.41 (d, 3JHH = 2.1 Hz, CHNH), 5.53 (br, NH), 7.25–7.34 (m, C6H5),
7.56 (br, NH).
13C NMR (125.7 MHz, CDCl3): d = 14.08, 55.78, 60.36, 101.43,
126.49, 128.03, 128.81, 143.55, 146.21, 152.79, 166.04.
Diethyl 4-(3-Chlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-
3,5-dicarboxylate (4h)
Yield: 0.27 g (75%).
IR (KBr): 3320, 1690, 1642, 1475, 1200, 1136 cm–1.
3
1H NMR (500.13 MHz, CDCl3): d = 1.25 (t, JHH = 7.1 Hz, 6 H),
2.37 (s, 6 H), 4.13 (q, 3JHH = 7.1 Hz, 4 H), 4.99 (s, 1 H), 5.62 (s, 1
Ethyl 4-(4-Chlorophenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydro-
pyrimidine-5-carboxylate (3h)
Yield: 0.25 g (84%).
IR (KBr): 3290, 3185, 1692, 1641, 1533, 1433 cm–1.
H), 7.11–7.29 (m, 4 H).
13C NMR (125.7 MHz, CDCl3): d = 15.18, 19.61, 39.74, 59.81,
103.82, 126.25, 126.31, 128.29, 129.04, 1433.60, 144.02, 149.73,
167.30.
3
1H NMR (500.1 MHz, CDCl3): d = 1.17 (d, JHH = 7.1 Hz,
OCH2CH3), 2.33 (s, CH3), 4.08 (d, 3JHH = 7.1 Hz, OCH2CH3), 5.37
(d, 3JHH = 2.0 Hz, CHNH), 6.08 (br, NH), 7.24 (d, 3JHH = 8.1 Hz, 2
Diethyl 4-(4-Chlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-
3,5-dicarboxylate (4i)
Yield: 0.28 g (77%).
3
CH of C6H4), 7.28 (d, JHH = 8.1 Hz, 2 CH of C6H4), 8.26 (br,
NHCH).
IR (KBr): 3345, 1695, 1649, 1480, 1210, 1137 cm–1.
13C NMR (125.7 MHz, CDCl3): d = 14.17, 18.64, 55.12, 60.14,
3
1H NMR (500.13 MHz, CDCl3): d = 1.22 (t, JHH = 7.2 Hz, 6 H),
101.17, 128.03, 128.88, 132.16, 142.24, 146.47, 153.39, 165.44.
2.33 (s, 6 H), 4.09 (q, 3JHH = 7.2 Hz, 4 H), 4.96 (s, 1 H), 5.65 (s, 1
H), 7.17 (d, 3JHH = 8.4 Hz, 2 H), 7.21 (d, 3JHH = 8.4 Hz, 2 H).
Methyl 6-Methyl-4-(4-nitrophenyl)-2-oxo-1,2,3,4-tetrahydro-
pyrimidine-5-carboxylate (3i)
Yield: 0.26 g (91%).
IR (KBr): 3345, 3090, 1706, 1631, 1507, 1425 cm–1.
13C NMR (125.7 MHz, CDCl3): d = 14.26, 19.58, 39.31, 59.80,
103.10, 128.31, 129.42, 131.73, 143.88, 146.32, 167.39.
1H NMR (500.1 MHz, CDCl3): d = 2.45 (s, CH3), 3.73 (s, OCH3),
Diethyl 2,6-Dimethyl-4-(4-nitrophenyl)-1,4-dihydropyridine-
3,5-dicarboxylate (4j)
Yield: 0.30 g (81%).
3
5.60 (s, CHNH), 5.75 (br, NH), 7.58 (d, JHH = 7.6 Hz, 2 CH of
C6H4), 7.26 (d, 3JHH = 7.6 Hz, 2 CH of C6H4), 8.37 (br, NHCH).
IR (KBr): 3324, 1695, 1647, 1473, 1205, 1131 cm–1.
Dimethyl 2,6-Dimethyl-4-phenyl-1,4-dihydropyridine-3,5-di-
carboxylate (4a); Typical Procedure
Neat adduct diketene (0.17 g, 2 mmol), MeOH (0.032 g, 1 mmol),
and benzaldehyde (0.106 g, 1 mmol) in H2SO4 (10 mol%) were
stirred magnetically at reflux for 10 min, NH4OAc (0.077 g, 1
mmol) was added, and then the mixture was refluxed with stirring
the appropriate time (TLC monitoring). The reaction was cooled to
3
1H NMR (500.13 MHz, CDCl3): d = 1.24 (t, JHH = 7.1 Hz, 6 H),
2.31 (s, 6 H), 4.19 (q, 3JHH = 7.1 Hz, 4 H), 4.76 (s, 1 H), 5.67 (s, 1
H), 7.53 (d, 3JHH = 7.9 Hz, 2 H), 8.12 (d, 3JHH = 8.4 Hz, 2 H).
13C NMR (125.7 MHz, CDCl3): d = 14.81, 19.56, 39.37, 59.84,
103.41, 124.1, 128.73, 145.5, 146.92, 156.3, 167.32.
Synthesis 2010, No. 23, 4057–4060 © Thieme Stuttgart · New York

4060
A. Alizadeh, S. Rostamnia
PAPER
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Synthesis 2010, No. 23, 4057–4060 © Thieme Stuttgart · New York