Simple one-pot three-component synthesis of 2-Oxo-1,11b-dihydro-2H- pyrimido[2,1-α]isoquinolines

Article abstract of DOI:10.1055/s-2004-815991

Isoquinoline reacts smoothly with dialkyl acetylenedicarboxylates in the presence of isocyanates to produce dialkyl 2-oxo-1,11b-dihydro-2H-pyrimido[2,1- a]isoquinoline-3,4-dicarboxylates in good yields.

Full text of DOI:10.1055/s-2004-815991

PAPER
861
Simple One-Pot Three-Component Synthesis of 2-Oxo-1,11b-dihydro-2H-py-
rimido[2,1-a]isoquinolines
One-Pot Synthesis of
2
e
-Oxo-1,11b
h
-dihydro-2
H
d
-pyrimido[2
i
,1-
a
]isoquino
A
lines dib,*a Mehdi Mollahosseini,a Hossine Yavari,a Mohammad Hosein Sayahi,a Hamid Reza Bijanzadehb
a
Department of Chemistry, Faculty of Science, University of Tehran, Tehran, Iran
Fax +98(21)6495291; E-mail: madib@khayam.ut.ac.ir
b
Department of Chemistry, University of Tarbiat Modarres, Tehran, Iran
Received 20 January 2004
development of new routes in heterocyclic synthesis,11 in
this paper, we wish to report a simple synthesis of func-
tionalized pyrimido[2,1-a]isoquinolines.
Abstract: Isoquinoline reacts smoothly with dialkyl acetylenedi-
carboxylates in the presence of isocyanates to produce dialkyl 2-
oxo-1,11b-dihydro-2H-pyrimido[2,1-a]isoquinoline-3,4-dicarbox-
ylates in good yields.
The reaction of isoquinoline (1) and dialkyl acetylenedi-
Key words: isocyanates, cyclizations, heterocycles, quinolines, carboxylates (2) in the presence of isocyanates (3) pro-
isoquinolines, alkynes
ceeds smoothly in dichloromethane at ambient
temperature to produce dialkyl 2-oxo-1,11b-dihydro-2H-
pyrimido[2,1-a]isoquinoline-3,4-dicarboxylates (4) in
75–99% yields (Scheme 1).
The development of simple synthetic routes for widely
used organic compounds from readily available reagents
is one of the major tasks in organic synthesis.1 Bridgehead
nitrogen heterocycles are of interest because they consti-
tute an important class of natural and unnatural products,
many of which exhibit useful biological activity.2,3 The in-
terest in fused bicyclic 6-6 systems with one ring junction
and one extra nitrogen atom, stems from the appearance of
saturated and partially saturated pyrido[1,2-a]pyrimidine
ring systems and their 8,9-benzo analogues (pyrimi-
do[2,1-a]isoquinolines) in many biologically active com-
pounds and natural products,3–10 some of which are key
intermediates for the synthesis of rutaecarpine alkaloids,
some have characteristic pharmacological properties such
as analgesic, antiallergic, antiasthmatic, and antipsychotic
agents, and some are neutral hydrogen chloride acceptors
in organic synthesis.3 As part of our current studies on the
The reactions were carried out by first mixing isoquino-
line and the isocyanate and then the acetylenic ester was
added slowly, proceeding spontaneously in CH2Cl2, and
were complete within an hour (see experimental).
The structures of compounds 4a–g were deduced from
their elemental analyses and their IR, H NMR and 13C
1
NMR spectra. The mass spectrum of 4a displayed the mo-
lecular ion (M+) peak at m/z = 390, which is consistent
with the 1:1:1 adduct of isoquinoline, dimethyl acetylene-
1
dicarboxylate (DMAD) and phenyl isocyanate. The H
NMR spectrum of 4a exhibited three singlets readily rec-
ognized as arising from two methoxy (d = 3.87 and 3.98)
and the methine (d = 6.55) protons, an AB quartet system
for two vinylic protons of the enamine moiety of isoquin-
oline ring (d = 6.01 and 6.56, J = 7.8 Hz), and the charac-
teristic multiplets for the aromatic protons (d = 6.6–7.2).
Scheme 1
SYNTHESIS 2004, No. 6, pp 0861–0864
x
x
.
x
x
.2
0
0
4
Advanced online publication: 25.02.2004
DOI: 10.1055/s-2004-815991; Art ID: P01004SS
© Georg Thieme Verlag Stuttgart · New York

862
M. Adib et al.
PAPER
13
The proton-decoupled C NMR spectrum of 4a showed acceptable one-pot method for the preparation of func-
20 distinct resonances in agreement with the proposed tionalized pyrimido[2,1-a]isoquinolines.
structure.
Although we have not established the mechanism of the
reaction between isoquinoline and acetylenic esters in the
presence of isocyanates in an experimental manner, a pos-
sible explanation is proposed in Scheme 2. The first step
may involve addition of isoquinoline to the acetylenic es-
ter and formation of the 1:1 adduct 5. Subsequent nucleo-
philic attack of the adduct to the isocyanate would yield
Isoquinoline, quinoline, dialkyl acetylenedicarboxylates and isocy-
anates were obtained from Merck and were used without further pu-
rification. Mps were measured on an Electrothermal 9100
apparatus. Elemental analyses for C, H and N were performed using
a Heraeus CHN-O-Rapid analyzer. Mass spectra were recorded on
a Finnigan-Matt 8430 mass spectrometer operating at an ionization
potential of 20 eV. 1H and 13C NMR spectra were measured (CDCl3
solution) with a Bruker DRX-500 Avance spectrometer at 500.1
the 1:1:1 adduct 6. The observed product is formed from and 125.8 MHz, respectively. IR spectra were recorded on a Shi-
madzu IR-460 spectrometer. Chromatography columns were pre-
the intramolecular addition of the nitrogen to the isoquin-
pared from Merck silica gel 60 mesh.
olinium moiety.
Compounds 4 and 7; General Procedure
To a magnetically stirred solution of isoquinoline or quinoline
(0.129 g, 1 mmol) and the appropriate isocyanate (1 mmol) in
CH2Cl2 (5 mL) was added dropwise a mixture of the appropriate di-
alkyl acetylenedicarboxylate (1 mmol) in CH2Cl2 (2 mL) at –5 ºC
for 10 min. The reaction mixture was allowed to warm to r.t. and
stirred for 1 h. The solvent was removed under reduced pressure.
For compounds 4a–c,e the residue was crystallized from hexane–
EtOAc (1:1), and for compounds 4d,f,g, and 7 the product was pu-
rified by column chromatography (hexane–EtOAc, 2:1) and then
crystallized from hexane–EtOAc (1:1).
Dimethyl 2-Oxo-1-phenyl-1,11b-dihydro-2H-pyrimido[2,1-
a]isoquinoline-3,4-dicarboxylate (4a)
Yield: 0.39 g (99%); yellow crystals; mp 153–155 ºC (decomp).
IR (KBr): 1731, 1699, 1664, 1537, 1234 cm–1.
Scheme 2
1H NMR (500 MHz, CDCl3): d = 3.87 and 3.98 (6 H, 2 s, 2 ×
When this reaction was carried out with quinoline, the
TLC and 1H NMR spectra of the reaction mixture showed
OCH3), 6.01 (1 H, d, J = 7.8 Hz, NCH=CH), 6.55 (1 H, s, NCHN),
6.56 (1 H, d, J = 7.8 Hz, NCH=CH), 6.70 (1 H, d, J = 7.7 Hz, CH),
6.82–6.89 (3 H, m, 3 CH), 7.02 (1 H, t, J = 7.1 Hz, CH), 7.05–7.08
(3 H, m, 3 CH), 7.12 (1 H, t, J = 7.2 Hz, CH).
13C NMR (125 MHz, CDCl3): d = 52.32 and 53.68 (2 × OCH3),
70.92 (NCHN), 107.82 (NC=C), 108.49 (NCH=CH), 122.75 (CH),
122.84 (C), 125.73, 126.82, and 127.12 (3 × CH), 128.13 (CHortho),
128.57 (CHmeta), 128.75 and 129.32 (2 × CH), 129.39 (C), 135.19
(Cipso), 147.94 (NC=C), 159.24, 162.91, and 164.80 (3 × C=O).
MS: m/z (%) = 390 (M+, 12), 331 (10), 313 (18), 183 (20), 155 (65),
129 (100).
a combination of starting materials and numerous prod-
ucts and the yields of 3H-pyrimido[1,2-a]quinoline deriv-
atives were less than 20%, only with DMAD and 3-
chloro-4-methylphenyl isocyanate could we obtain dime-
thyl 3-oxo-4-(3-chloro-4-methylphenyl)-4,4a-dihydro-
3H-pyrimido[1,2-a]quinoline-1,2-dicarboxylate (7) in
65% yield (Scheme 3).
The structure of compound 7 was deduced from its ele-
1
mental analysis, mass spectrum, IR, H NMR and 13C
NMR spectral data (see experimental).
Anal. Calcd for C22H18N2O5 (390.40): C, 67.69; H, 4.65; N, 7.18.
Found: C, 67.7; H, 4.6; N, 7.1.
In summary, the present method has the advantages that
not only is the reaction performed under neutral condi-
tions, but also the substances can be mixed without any
activation or modification. The simplicity of the present
procedure makes it an interesting alternative to other ap-
proaches.3,10 The procedure described here provides an
Dimethyl 2-Oxo-1-(3,4-dichlorophenyl)-1,11b-dihydro-2H-py-
rimido[2,1-a]isoquinoline-3,4-dicarboxylate (4b)
Yield: 0.41 g (90%); yellow crystals; mp 124–125 ºC.
IR (KBr): 1739, 1656, 1633, 1531, 1242 cm–1.
1H NMR (500 MHz, CDCl3): d = 3.88 and 3.99 (6 H, 2 s, 2 ×
OCH3), 6.05 (1 H, d, J = 7.8 Hz, NCH=CH), 6.54 (1 H, s, NCHN),
Scheme 3
Synthesis 2004, No. 6, 861–864 © Thieme Stuttgart · New York

PAPER
One-Pot Synthesis of 2-Oxo-1,11b-dihydro-2H-pyrimido[2,1-a]isoquinolines
863
6.56 (1 H, d, J = 7.8 Hz, NCH=CH), 6.63 (1 H, dd, 3J = 8.5, 4J = 1.9
Hz, CH), 6.71 (1 H, d, J = 7.8 Hz, CH), 6.98 (1 H, t, J = 7.6 Hz,
CH), 7.06 (1 H, d, 4J = 1.9 Hz, CH), 7.10 (1 H, d, J = 8.7 Hz, CH),
7.12 (1 H, d, J = 8.0 Hz, CH), 7.19 (1 H, t, J = 7.5 Hz, CH).
13C NMR (125 MHz, CDCl3): d = 52.42 and 53.78 (2 × OCH3),
70.73 (NCHN), 107.33 (NC=C), 108.62 (NCH=CH), 122.21 (C),
122.77, 126.05, 127.53, 127.69, and 128.44 (5 × CH), 129.36 (C),
129.55, 129.89, and 130.46 (3 × CH), 130.79 and 131.83 (2 × C),
134.48 (CipsoN), 148.41 (NC=C), 158.93, 162.66, and 164.49 (3 ×
C=O).
6.58 (1 H, s, NCHN), 6.60 (1 H, d, J = 7.8 Hz, NCH=CH), 6.72 (1
H, d, J = 7.7 Hz, CH), 6.8–6.9 (3 H, m, 3 CH), 7.0–7.2 (5 H, m, 5
CH).
13C NMR (125 MHz, CDCl3): d = 13.81 and 14.15 (2 × CH2CH3),
61.34 and 63.16 (2 × CH2CH3), 70.91 (NCHN), 108.09
(NCH=CH), 109.04 (NC=C), 122.83 (C), 123.09, 125.62, 126.88,
and 127.02 (4 × CH), 128.18 (CHortho), 128.60 (CHmeta), 128.79 and
129.31 (2 × CH), 129.55 (C), 135.22 (Cipso), 147.23 (NC=C),
159.42, 162.32, and 164.13 (3 × C=O).
MS: m/z (%) = 418 (M+, 10), 345 (9), 255 (5), 212 (7), 182 (15), 155
(100), 129 (70), 93 (60).
MS: m/z (%) = 459 (M+, 10), 399 (15), 355 (5), 171 (45), 155 (60),
129 (100).
Anal. Calcd for C24H22N2O5 (418.45): C, 68.89; H, 5.30; N, 6.69.
Found: C, 68.8; H, 5.4; N, 6.7.
Anal. Calcd for C22H16Cl2N2O5 (459.28): C, 57.53; H, 3.51; N, 6.10.
Found: C, 57.5; H, 3.6; N, 6.1.
Diethyl 2-Oxo-1-(3,4-dichlorophenyl)-1,11b-dihydro-2H-py-
rimido[2,1-a]isoquinoline-3,4-dicarboxylate (4f)
Yield: 0.41 g (85%); yellow crystals; mp 138–143 ºC (decomp).
IR (KBr): 1741, 1666, 1606, 1542, 1471, 1292, 1226 cm–1.
Dimethyl 2-Oxo-1-(3-chloro-4-methylphenyl)-1,11b-dihydro-
2H-pyrimido[2,1-a]isoquinoline-3,4-dicarboxylate (4c)
Yield: 0.43 g (99%); yellow crystals; mp 147–150 ºC (decomp).
IR (KBr): 1741, 1693, 1635, 1525, 1238 cm–1.
1H NMR (500 MHz, CDCl3): d = 1.37 and 1.42 (6 H, 2 t, J = 7.1 Hz,
2 × CH2CH3), 4.36 (2 H, m, ABX3 system, CH2CH3), 4.47 (2 H, q,
J = 7.1 Hz, CH2CH3), 6.06 (1 H, d, J = 7.8 Hz, NCH=CH), 6.58 (1
H, s, NCHN), 6.61 (1 H, d, J = 7.8 Hz, NCH=CH), 6.68 (1 H, dd,
3J = 8.5, 4J = 2.0 Hz, CH), 6.74 (1 H, d, J = 7.8 Hz, CH), 7.00 (1 H,
1H NMR (500 MHz, CDCl3): d = 2.17 (3 H, s, ArCH3), 3.88 and
3.99 (6 H, 2 s, 2 × OCH3), 6.03 (1 H, d, J = 7.7 Hz, NCH=CH), 6.53
(1 H, s, NCHN), 6.55 (1 H, d, J = 7.7 Hz, NCH=CH), 6.60 (1 H, dd,
3J = 8.0, 4J = 1.5 Hz, CH), 6.74 (1 H, d, J = 7.7 Hz, CH), 6.88 (1 H,
4
4
d, J = 8.0 Hz, CH), 6.93 (1 H, d, J = 1.5 Hz, CH), 6.97 (1 H, t,
t, J = 7.6 Hz, CH), 7.05 (1 H, d, J = 2.0 Hz, CH), 7.12 (1 H, d,
J = 7.5 Hz, CH), 7.10 (1 H, d, J = 7.5 Hz, CH), 7.16 (1 H, t, J = 7.5
J = 9.0 Hz, CH), 7.14 (1 H, d, J = 9.0 Hz, CH), 7.21 (1 H, t, J = 7.5
Hz, CH).
Hz, CH).
13C NMR (125 MHz, CDCl3): d = 19.49 (ArCH3), 52.36 and 53.71
(2 ×OCH3), 70.84 (NCHN), 107.61 (NC=C), 108.57 (NCH=CH),
122.53 (C), 122.74, 125.84, 126.53, 127.39, 128.62, and 129.11 (6
× CH), 129.37 (C), 129.58 and 130.12 (2 CH), 133.54 and 133.76
(2 × C), 134.72 (CipsoN), 148.16 (NC=C), 159.15, 162.82, and
164.66 (3 × C=O).
13C NMR (125 MHz, CDCl3): d = 13.80 and 14.14 (2 × CH2CH3),
61.48 and 63.32 (2 × CH2CH3), 70.76 (NCHN), 107.29 (NC=C),
108.26 (NCH=CH), 122.21 (C), 123.10, 125.94, 127.55, 127.61,
and 128.47 (5 × CH), 129.53 (C), 129.61, 129.90, and 130.46 (3 ×
CH), 130.92 and 131.93 (2 × C), 134.52 (CipsoN), 147.80 (NC=C),
159.12, 162.07, and 163.71 (3 × C=O).
MS: m/z (%) = 438 (M+, 5), 393 (10), 226 (20), 155 (100).
MS: m/z (%) = 487 (M+, 5), 284 (40), 144 (10), 109 (55), 28 (100).
Anal. Calcd for C23H19ClN2O5 (438.87): C, 62.95; H, 4.36; N, 6.38.
Found: C, 62.9; H, 4.4; N, 6.4.
Anal. Calcd for C24H20Cl2N2O5 (487.34): C, 59.15; H, 4.14; N, 5.75.
Found: C, 59.1; H, 4.1; N, 5.8.
Dimethyl 2-Oxo-1-ethyl-1,11b-dihydro-2H-pyrimido[2,1-a]iso-
quinoline-3,4-dicarboxylate (4d)
Yield: 0.26 g (75%); yellow crystals; mp 80–83 ºC.
Diethyl 2-Oxo-1-(3-chloro-4-methylphenyl)-1,11b-dihydro-2H-
pyrimido[2,1-a]isoquinoline-3,4-dicarboxylate (4g)
Yield: 0.45 g (98%); yellow crystals; mp 87–90 ºC.
IR (KBr): 1740, 1660, 1630, 1533, 1240 cm–1.
IR (KBr): 1740, 1696, 1666, 1525, 1255 cm–1.
1H NMR (500 MHz, CDCl3): d = 1.43 (3 H, t, J = 7.2 Hz, CH2CH3),
3.07 (2 H, dq, AMX3 system, 2J = 10.0, 3J = 7.2 Hz, CH2CH3), 3.86
and 3.97 (6 H, 2 s, 2 × OCH3), 6.04 (1 H, d, J = 7.8 Hz, NCH=CH),
6.52 (1 H, s, NCHN), 6.58 (1 H, d, J = 7.8 Hz, NCH=CH), 6.69 (1
H, d, J = 7.8 Hz, CH), 6.96 (1 H, t, J = 7.6 Hz, CH), 7.14 (1 H, d,
J = 8.0 Hz, CH), 7.18 (1 H, t, J = 7.5 Hz, CH).
13C NMR (125 MHz, CDCl3): d = 14.12 (CH2CH3), 39.95
(CH2CH3), 52.48 and 53.84 (2 × OCH3), 70.22 (NCHN), 107.31
(NC=C), 108.74 (NCH=CH), 122.27 (CH), 122.85 (C), 125.15,
126.85, 127.23, and 129.25 (4 × CH), 129.38 (C), 147.46 (NC=C),
158.28, 162.77, and 164.53 (3 × C=O).
1H NMR (500 MHz, CDCl3): d = 1.35 and 1.39 (6 H, 2 t, J = 7.1 Hz,
2 × CH2CH3), 2.16 (3 H, s, ArCH3), 4.33 (2 H, m, ABX3 system,
CH2CH3), 4.44 (2 H, q, J = 7.1 Hz, CH2CH3), 6.01 (1 H, d, J = 7.7
Hz, NCH=CH), 6.53 (1 H, s, NCHN), 6.58 (1 H, d, J = 7.7 Hz,
NCH=CH), 6.61 (1 H, dd, 3J = 8.1, 4J = 1.4 Hz, CH), 6.73 (1 H, d,
J = 7.7 Hz, CH), 6.88 (1 H, d, J = 8.1 Hz, CH), 6.92 (2 H, m, 2 ×
CH), 7.08 (1 H, d, J = 7.6 Hz, CH), 7.14 (1 H, t, J = 7.5 Hz, CH).
13C NMR (125 MHz, CDCl3): d = 13.78 and 14.15 (2 × CH2CH3),
19.47 (ArCH3), 61.33 and 63.18 (2 × CH2CH3), 70.82 (NCHN),
108.11 (NCH=CH), 108.95 (NC=C), 122.53 (C), 123.11, 125.70,
126.61, 127.24, 128.63, and 129.13 (6 × CH), 129.53 (C), 129.55
and 130.13 (2 × CH), 133.52 and 133.87 (2 × C), 134.70 (CipsoN),
147.32 (NC=C), 159.26, 162.22, and 163.99 (3 × C=O).
MS: m/z (%) = 342 (M+, 2), 183 (10), 155 (51), 129 (100).
Anal. Calcd for C18H18N2O5 (342.35): C, 63.15; H, 5.30; N, 8.18.
Found: C, 63.2; H, 5.3; N, 8.2.
MS: m/z (%) = 466 (M+, 10), 394 (7), 284 (10), 226 (19), 155 (60),
129 (100).
Diethyl 2-Oxo-1-phenyl-1,11b-dihydro-2H-pyrimido[2,1-a]iso-
quinoline-3,4-dicarboxylate (4e)
Anal. Calcd for C25H23ClN2O5 (466.92): C, 64.31; H, 4.97; N, 6.00.
Found: C, 64.3; H, 5.0; N, 6.1.
Yield: 0.41 g (98%); yellow crystals; mp 140–143 ºC (decomp).
Dimethyl 3-Oxo-4-(3-chloro-4-methylphenyl)-4,4a-dihydro-
3H-pyrimido[1,2-a]quinoline-1,2-dicarboxylate (7)
Yield: 0.29 g (65%); yellow crystals; mp 164–167 ºC (decomp).
IR (KBr): 1741, 1691, 1668, 1527, 1494, 1290, 1251, 1228 cm–1.
IR (KBr): 1730, 1700, 1658, 1533, 1313, 1236 cm–1.
1H NMR (500 MHz, CDCl3): d = 1.36 and 1.41 (6 H, 2 t, J = 7.1
Hz, 2 × CH2CH3), 4.35 (2 H, m, ABX3 system, CH2CH3), 4.45 (2
H, q, J = 7.1 Hz, CH2CH3), 6.00 (1 H, d, J = 7.8 Hz, NCH=CH),
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M. Adib et al.
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1H NMR (500 MHz, CDCl3): d = 2.33 (3 H, s, ArCH3), 3.92 and
References
3
3
3.97 (6 H, 2 s, 2 × OCH3), 5.45 (1 H, dd, J = 10.0, J = 3.0 Hz,
N2CHCH=CH), 6.09 (1 H, d, J = 3.0 Hz, NCHN), 6.65 (1 H, d,
J = 10.0 Hz, N2CHCH=CH), 6.72 (1 H, d, J = 8.0 Hz, CH), 6.82 (1
H, d, J = 8.0 Hz, CH), 6.96 (1 H, d, 4J = 1.5 Hz, CH), 7.1–7.2 (4 H,
m, 4 × CH).
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(2 × OCH3), 69.64 (NCHN), 116.04 and 117.35 (2 × CH), 118.05
and 122.05 (2 × C), 124.12, 127.23, 128.41, 128.92, 129.77,
130.05, and 131.09 (7 × CH), 133.90, 134.25, 134.42, and 136.23
(4 × C), 145.29 (NC=C), 159.11, 163.19, and 164.24 (3 × C=O).
MS: m/z (%) = 438 (M+, 2), 379 (15), 226 (18), 155 (70), 129 (100).
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Acknowledgment
This research was supported by the Research Council of University
of Tehran as a research project (514/4/626).
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Synthesis 2004, No. 6, 861–864 © Thieme Stuttgart · New York