Mild and efficient one-pot three-component synthesis of benzopyrimidoquinoline-tetraone derivatives in ionic liquids

Article abstract of DOI:10.3184/174751912X13384724679874

An efficient one-pot synthesis of 5-aryl-5,12-dihydrobenzo[g]pyrimido[4,5- b]quinoline-2,4,6,11(1H,3H)-tetraone derivatives via three-component reaction of aromatic aldehydes, 2-hydroxy-1,4-naphthoquinone and 6-aminouracil in ionic liquid [bmim]BF₄

Full text of DOI:10.3184/174751912X13384724679874

JOURNAL OF CHEMICAL RESEARCH 2012
RESEARCH PAPER 453
AUGUST, 453–456
Mild and efficient one-pot three-component synthesis of
benzopyrimidoquinoline-tetraone derivatives in ionic liquids
Bai-Xiang Du, Bo Zhao, Gan Cai, Yu-Ling Li* and Xiang-Shan Wang
School of Chemistry and Chemical Engineering, Jiangsu Key Laboratory of Green Synthetic Chemistry for Functional Materials,
Xuzhou Normal University, Xuzhou Jiangsu 221116, P. R. China
An efficient one-pot synthesis of 5-aryl-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetraone
derivatives via three-component reaction of aromatic aldehydes, 2-hydroxy-1,4-naphthoquinone and 6-aminouracil
in ionic liquid [bmim]BF4 is reported. This method had the advantages of easier work-up, environmentally benign
procedure, high yields and ease of recovery and reuse of reaction media.
Keywords: multicomponent reactions, ionic liquid, pyrimidoquinoline
Over the past decade, multicomponent reactions (MCRs) have
become one of the most efficient tools for synthesising highly
complex molecules and introducing molecular diversity from
simple starting materials in a single synthetic operation.1
MCRs have been widely used in organic, combinatorial, and
medicinal chemistry because of their advantages such as
convenience and high degree of atom economy.2
with the added benefit of the ease of recovery and reuse of
these ionic liquids.14
In view of the importance of pyrimidoquinolines for diverse
therapeutic activity and in continuation of developing environ-
mentally benign methodologies for synthesis of heterocyclic
compounds, we now report a novel three-component one-pot
synthesis of well functionalised pyrimidoquinolines in ionic
liquid medium (Scheme 1).15–17 When three components of
aromatic aldehyde 1, 2-hydroxy-1,4-naphthoquinone 2 and
6-aminouracil 3 were treated in ionic liquids [bmim]BF4 at
80 °C for a few hours (Scheme 1), the pyrimidoquinolines
derivatives 4 were obtained in high yields (80–95%). To the
best of our knowledge, this is the first report on such a synthe-
sis of 5-aryl-5, 12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
2,4,6,11(1H,3H)-tetraone derivatives.
Heterocyclic compounds containing nitrogen atoms are
widespread in nature, and are valuable in the design and
discovery of new biologically active compounds. Their appli-
cations to pharmaceuticals, agrochemicals, and functional
materials are becoming increasingly important. For example,
pyrimidoquinolines have diverse pharmacological activities
such as anticancer,3 antibacterial,4 antimicrobial,5 antiallergic,6
anti-inflammatory,7 and antimalerial activity.8 For the prepara-
tion of these complex molecules much effort has been directed
towards the synthetic manipulation of pyrimidoquinolines.
Zoorob synthesised pyrimidoquinolines by the reaction of
benzoylethylbarbituric acids with aniline derivatives by reflux-
ing in xylene in the presence of a catalytic amount of p-toluene
sulfonic acid.9 Shi synthesised pyrimido[4,5-b]quinoline
derivatives via the three-component reaction in water in the
presence of triethylbenzylammonium chloride (TEBAC).10 Tu
reported a simple and efficient synthesis of benzoquinolinopy-
rimidine derivatives via a three-component reaction in mixed
solvent of acetic acid and glycol under microwave irradiation
at 120 °C.11 Singh reported the synthesis of pyrimidoquino-
lines via t-BuOK catalysed cyclisation reaction of 2-chloro-
quinoline-3-carbonitriles and guanidine hydrochlorides in high
yields in ethyl alcohol at 90 °C.12 These methods usually
require forcing conditions, long reaction times, complex
synthetic pathways and often react in organic solvents or by
catalysis. Therefore, development of simple and safe method-
ologies for the synthesis of pyrimidoquinolines is of prime
interest from the synthetic and environment points of view.
Recently ionic liquids have been used as environmentally
benign solvents for a broad range of inorganic and organic
reactions.13 A nice feature of ionic liquid is that yields can be
optimised by changing the anions or properties of the cation.
In addition, several ionic liquids show enhancement in
reaction rates and selectivity, compared to organic solvents
Results and discussion
The study was initiated by using 4-chloroaldehyde, 2-hydroxy-
1,4-naphthoquinone and 6-aminouracil as model substrates for
the preparation of 4a in various reaction conditions (Table 1).
We examined several traditional solvents and ionic liquids. It
was found that no conversion to product occurred even after
24 h in organic solvent such as EtOH, DMF, CH3CN at reflux
temperature (Table 1, entry 1). There was a remarkable tem-
perature effect in this reaction; for the ionic liquid [bmim]BF4,
no conversion to the product occurred even after 24 h at room
temperature, but the yield of product 4a improved and the
reaction time was shortened as the temperature increased.
The yield levelled off when temperature was further increased
to 90 °C (Table 1, entries 4–8). Therefore, 80 °C was chosen as
the most suitable reaction temperature. The effect of reaction
time on the yields of product 4a in ionic liquid [bmim]BF4 was
also investigated. The reactions were performed in ionic liquid
[bmim]BF4 for 8, 10, or 12 h at 80 °C (Table 1, entries 7, 9 and
10), leading to 4a in 88%, 95%, and 93% yields, respectively.
Thus, the optimal reaction time is 10 h. Different ionic liquids
were also studied at 80 °C as shown in Table 1. On the basis of
results in Table 1, we could conclude that [bmim]BF4 was the
best ionic liquid for this reaction.
To generalise the feasibility of this protocol, a range of
structurally diverse aldehydes bearing electron donating and
Scheme 1 The reaction of 1, 2 and 3 in ionic liquid [bmim]BF4.
* Correspondent. E-mail: ylli19722@163.com

454 JOURNAL OF CHEMICAL RESEARCH 2012
Table 1 Optimisation of the reaction conditions for synthesis
of 4aa
withdrawing substituents were transformed in ionic liquid
[bmim]BF4 with 2-hydroxy-1,4-naphthoquinone and 6-amino-
uracil under optimised conditions. The results indicated that
aldehydes carrying both electron-withdrawing and electron-
donating substituents were converted to their corresponding
derivatives in good yields under optimal conditions described
above. At the same time, we have also observed delicate
electronic effects: aldehydes with electron-withdrawing groups
reacted rapidly, while electron donating groups decreased the
reactivity, requiring longer reaction times. The results are
summarised in Table 2. All the products were characterised by
melting points, 1H NMR, IR and HRMS.
To explain the mechanism of this one-pot, multicomponent
reaction, we tentatively propose a plausible reaction mecha-
nism which is illustrated in Scheme 2. Firstly, Knoevenagel
condensation of aromatic aldehyde 1 with 2-hydroxy-1,4-
naphthoquinone 2 could lead to the formation of intermediate
5. Then, nucleophilic addition between 5 and 3 would give
Schiff’s base 6 which would undergo a electrocyclic reaction
to give intermediate 7. Finally, the product 4 was obtained by
a rapid imine–enamine tautomerisation.
Entry
Temp/°C
Medium
Time/h
Yield/%b
1
2
Reflux
Reflux
Reflux
rt
EtOH
24
24
24
24
24
12
10
10
8
12
10
10
10
10
10
10
0
0
DMF
3
CH3CN
0
4
[bmim]BF4
[bmim]BF4
[bmim]BF4
[bmim]BF4
[bmim]BF4
[bmim]BF4
[bmim]BF4
[emim]Br
[pmim]Br
[bmim]Br
[emim]BF4
[pmim]BF4
[bmim]PF6
0
5
40
30
55
95
94
88
93
35
40
30
80
82
85
6
60
7
80
8
90
9
80
10
11
12
13
14
15
16
80
80
80
80
80
80
80
a Reaction condition: 2 mL of ionic liquid, 1 mmol 4-chloroalde-
hyde, 1 mmol 2-hydroxy-1,4-naphthoquinone, 1 mmol 6-
aminouracil.
b Isolated yields.
In our studies, the recycling of the ionic liquid [bmim]BF4
has also been investigated by using the preparation of 4a as a
model. Since the poor solubility of products in ionic liquids
and water, they were easily separated by simple filtration from
mixture of water and ionic liquid, the filtrate was then extracted
with ether and dried at 90 °C in vacuum for several hours to be
recycled. As shown in Fig. 1, the reaction medium could be
recycled at least six times without significant decrease of the
yields, which ranged from 95 to 88%.
Table 2 Synthesis of 4 in ionic liquid [bmim]BF4a
Entry
Ar
Products
Time/h
Yields/%b
1
2
4-ClC6H4
3-OCH3C6H4
2-OHC6H4
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
10
10
16
13
13
15
15
9
12
13
15
10
12
12
18
95
86
84
98
90
85
83
91
85
86
80
86
90
90
95
3
4
3-BrC6H4
5
3,4-(OCH3)2C6H3
4-OHC6H4
3,4-(OCH2O) C6H3
4-BrC6H4
Experimental
6
Melting points were determined in open capillaries without further
correction. IR spectra were recorded on a Tensor 27 spectrometer in
KBr. 1H NMR spectra were obtained from solution in DMSO-d6 with
Me4Si as an internal standard using a Bruker-400 spectrometer. HRMS
data were obtained using a MicroTOF-QII instrument.
7
8
9
3-ClC6H4
2-BrC6H4
2-OCH3C6H4
3,4-Cl2C6H3
2-ClC6H4
3-OHC6H4
4-CH3C6H4
10
11
12
13
14
15
Synthesis of 4; general procedure
A mixture of aromatic aldehyde 1 (1 mmol), 2-hydroxynaphthalene-
1,4-dione 2 (1 mmol), 6-aminouracil 3 (1 mmol) was stirred at 80 °C
for 9–18 h in ionic liquid [bmim]BF4 (2 mL). After completion of the
reaction as indicated by TLC, water (5 mL) was added and the product
was filtered off and washed with water. The remaining aqueous layer
containing the ionic liquid was extracted with ether (8 mL) for three
a Reaction condition: 2 mL ionic liquid, 1 mmol aromatic
aldehyde, 1 mmol 2-hydroxy-1,4-naphthoquinone, 1 mmol
6-aminouracil, 80 °C.
b Isolated yields.
Scheme 2 Reaction mechanism of 1, 2 and 3 in ionic liquid [bmim]BF4.

JOURNAL OF CHEMICAL RESEARCH 2012 455
5-(3,4-Methylelnedioxyphenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]
quinoline-2,4,6,11(1H,3H)-tetraone (4g): M.p. >300 °C; 1HNMR
(DMSO-d6, δ, ppm): 10.94 (s, 1H, NH), 10.18 (s, 1H, NH), 9.33 (s,
1H, NH), 8.05 (d, 1H, ArH, J = 7.6 Hz), 7.94 (d, 1H, ArH, J = 7.2 Hz),
7.83–7.85 (m, 2H, ArH), 6.88 (s, 1H, ArH), 6.75–6.77 (m, 2H, ArH),
5.92 (s, 2H, OCH2O), 5.02 (s, 1H, CH); IR (KBr, ν, cm−1): 3551, 3478,
3416, 3235, 1716, 1638, 1616; HRMS Calcd for C22H12N3O6 (M–H)−
requires 414.0725; found: 414.0738.
5-(4-Bromophenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
1
2,4,6,11(1H,3H)-tetraone (4h): M.p. >300 °C; HNMR (DMSO-d6,
δ, ppm): 10.96 (s, 1H, NH), 10.21 (s, 1H, NH), 9.38 (s, 1H, NH), 8.06
(d, 1H, ArH, J = 7.2 Hz), 7.92 (d, 1H, ArH, J = 7.2 Hz), 7.82–7.85
(m, 2H, ArH), 7.21–7.38 (m, 4H, ArH), 5.09 (s, 1H, CH); IR (KBr, ν,
cm−1): 3553, 3475, 3416, 3235, 1773, 1719, 1638; HRMS Calcd for
C21H11BrN3O4 (M–H)− requires 447.9933; found: 447.9937.
5-(3-Chlorophenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
1
2,4,6,11(1H,3H)-tetraone (4i): M.p. >300 °C; HNMR (DMSO-d6,
δ, ppm): 10.96 (s, 1H, NH), 10.21 (s, 1H, NH), 9.38 (s, 1H, NH), 8.05
(d, 1H, ArH, J = 7.2 Hz), 7.81–7.91 (m, 3H, ArH), 7.38 (s, 1H, ArH),
7.21–7.30 (m, 3H, ArH), 5.07 (s, 1H, CH); IR (KBr, ν, cm−1): 3552,
3481, 3415, 3235, 1719, 1662, 1637, 1617; HRMS Calcd for
C21H11ClN3O4 (M–H)− requires 404.0437; found: 404.0454.
Fig. 1 Reusability of ionic liquid [bmim]BF4.
times to remove organic impurity, and then dried under vacuum at
90 °C for about 15 h to afford ionic liquid, which was used in the
subsequent runs without further purification. The crude product was
purified by recrystallisation from DMF and H2O to give 4 as a red
powder.
5-(2-Bromophenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
1
2,4,6,11(1H,3H)-tetraone (4j): M.p. >300 °C; HNMR (DMSO-d6,
δ, ppm): 10.83 (s, 1H, NH), 10.17 (s, 1H, NH), 9.39 (s, 1H, NH), 8.04
(d, 1H, ArH, J = 6.8 Hz), 7.79–7.83 (m, 3H, ArH), 7.39–7.46 (m, 2H,
ArH), 7.24 (d, 1H, ArH, J = 7.2 Hz), 7.04 (d, 1H, ArH, J = 7.2 Hz),
5.43 (s, 1H, CH); IR (KBr, ν, cm−1): 3552, 3475, 3414, 3235, 1720,
1638, 1616; HRMS Calcd for C21H11BrN3O4 (M–H)− requires 447.9933;
found: 447.9967.
5-(4-Chlorophenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
1
2,4,6,11(1H,3H)-tetraone (4a): M.p. >300 °C; HNMR (DMSO-d6,
δ, ppm): 10.98 (s, 1H, NH), 10.21 (s, 1H, NH), 9.35 (s, 1H, NH), 8.05
(d, 1H, ArH, J = 7.2 Hz), 7.91 (d, 1H, ArH, J = 7.2 Hz), 7.81–7.84
(m, 2H, ArH), 7.36 (d, 2H, ArH, J = 8.4 Hz), 7.28 (d, 2H, ArH, J =
8.4 Hz), 5.09 (s, 1H, CH); IR (KBr, ν, cm−1): 3563, 3479, 3417, 3235,
1772, 1716, 1638, 1616; HRMS Calcd for C21H11ClN3O4 (M–H)−
requires 404.0437; found: 404.0447.
5-(2-Methoxyphenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
1
2,4,6,11(1H,3H)-tetraone (4k): M.p. >300 °C; HNMR (DMSO-d6,
δ, ppm): 10.77 (s, 1H, NH), 10.11 (s, 1H, NH), 9.37 (s, 1H, NH), 8.03
(d, 1H, ArH, J = 7.2 Hz), 7.78–7.85 (m, 3H, ArH), 7.31 (d, 1H, ArH,
J = 7.2 Hz), 7.12 (t, 1H, ArH, J = 7.6 Hz), 6.83–6.89 (m, 2H, ArH),
5.21 (s, 1H, CH), 3.67 (s, 3H, OCH3); IR (KBr, ν, cm−1): 3552, 3480,
3415, 3238, 3067, 1721, 1654, 1616; HRMS Calcd for C22H14N3O5
(M–H)− requires 400.0934; found: 400.0949.
5-(3-Methoxyphenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
1
2,4,6,11(1H,3H)-tetraone (4b): M.p. >300 °C; HNMR (DMSO-d6,
δ, ppm): 10.95 (s, 1H, NH), 10.20 (s, 1H, NH), 9.36 (s, 1H, NH), 8.05
(d, 1H, ArH, J = 7.2 Hz), 7.93 (d, 1H, ArH, J = 7.6 Hz), 7.81–7.85
(m, 2H, ArH), 7.14 (d, 1H, ArH, J = 8.0 Hz), 6.88 (d, 2H, ArH, J =
8.4 Hz), 6.73 (d, 1H, ArH, J = 8.4 Hz), 5.07 (s, 1H, CH), 3.69 (s, 3H,
OCH3); IR (KBr, ν, cm−1): 3649, 3553, 3416, 3235, 1718, 1638, 1617;
HRMS Calcd for C22H14N3O5 (M–H)− requires 400.0934; found:
400.0957.
5-(2-Hydroxyphenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
2,4,6,11(1H,3H)-tetraone (4c): M.p. >300 °C; 1HNMR (DMSO-d6, δ,
ppm): 10.95 (s, 1H, NH), 10.23 (s, 1H, NH), 9.30 (s, 2H, NH+OH),
8.03 (d, 1H, ArH, J = 6.8 Hz), 7.92 (d, 1H, ArH, J = 7.2 Hz), 7.78–
7.85 (m, 2H, ArH), 7.01 (t, 1H, ArH, J = 8.0 Hz), 6.74 (d, 2H, ArH,
J = 6.8 Hz), 6.52 (t, 1H, ArH, J = 8.4 Hz), 5.01 (s, 1H, CH); IR (KBr,
ν, cm−1): 3553, 3480, 3414, 3235, 1719, 1638, 1616; HRMS Calcd for
C21H12N3O5 (M–H)− requires 386.0777; found: 386.0802.
5-(3-Bromophenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
2,4,6,11(1H,3H)-tetraone (4d): M.p. >300 °C; 1HNMR (DMSO-d6, δ,
ppm): 10.99 (s, 1H, NH), 10.22 (s, 1H, NH), 9.40 (s, 1H, NH), 7.82–
8.05 (m, 4H, ArH), 7.52 (s, 1H, ArH), 7.34 (d, 2H, ArH, J = 6.0 Hz),
7.20 (t, 1H, ArH, J = 6.8 Hz), 5.06 (s, 1H, CH); IR (KBr, ν, cm−1):
3551, 3478, 3411, 3235, 1730, 1654, 1614; HRMS Calcd for
C21H11BrN3O4 (M–H)− requires 447.9933; found: 447.9937.
5-(3,4-Dimethoxyphenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quino-
line-2,4,6,11(1H,3H)-tetraone (4e): M.p. >300 °C; 1HNMR (DMSO-
d6, δ, ppm): 10.94 (s, 1H, NH), 10.19 (s, 1H, NH), 9.32 (s, 1H, NH),
8.05 (d, 1H, ArH, J = 7.6 Hz), 7.93 (d, 1H, ArH, J = 7.6 Hz), 7.81–
7.85 (m, 2H, ArH), 6.93 (s, 1H, ArH), 6.77 (s, 2H, ArH), 5.04 (s, 1H,
CH), 3.70 (s, 3H, OCH3), 3.66 (s, 3H, OCH3); IR (KBr, ν, cm−1): 3563,
3478, 3416, 1714, 1638, 1617; HRMS Calcd for C23H16N3O6 (M–H)−
requires 430.1038; found: 430.1048.
5-(4-Hydroxyphenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
2,4,6,11(1H,3H)-tetraone (4f): M.p. >300 °C; 1HNMR (DMSO-d6, δ,
ppm): 10.92 (s, 1H, NH), 10.17 (s, 1H, NH), 9.28 (s, 2H, NH+OH),
8.03 (d, 1H, ArH, J = 7.2 Hz), 7.93 (d, 1H, ArH, J = 8.4 Hz), 7.80–
7.86 (m, 2H, ArH), 7.09 (d, 2H, ArH, J = 8.4 Hz), 6.60 (d, 2H, ArH,
J = 8.0 Hz), 4.98 (s, 1H, CH), IR (KBr, ν, cm−1): 3551, 3479, 3416,
3235, 1717; HRMS Calcd for C21H12N3O5 (M–H)− requires 386.0777;
found: 386.0783.
5-(3,4-Dichlorophenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
1
2,4,6,11(1H,3H)-tetraone (4l): M.p. >300 °C; HNMR (DMSO-d6,
δ, ppm): 10.98 (s, 1H, NH), 10.21 (s, 1H, NH), 9.40 (s, 1H, NH), 8.06
(d, 1H, ArH, J = 6.8 Hz), 7.91 (d, 1H, ArH, J = 6.8 Hz), 7.81–7.85
(m, 2H, ArH), 7.58 (d, 1H, ArH, J = 1.6 Hz), 7.48 (d, 1H, ArH, J =
8.4 Hz), 7.37(dd, 1H, ArH, J1 = 8.4 Hz, J2 = 1.6 Hz), 5.08 (s, 1H, CH);
IR (KBr, ν, cm−1): 3553, 3482, 3415, 3235, 1725, 1655, 1638, 1616;
HRMS Calcd for C21H10Cl2N3O4 (M–H)− requires 438.0049; found:
438.0041.
5-(2-Chlorophenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
1
2,4,6,11(1H,3H)-tetraone (4m): M.p. >300 °C; HNMR (DMSO-d6,
δ, ppm): 10.93 (s, 1H, NH), 10.10 (s, 1H, NH), 9.30 (s, 1H, NH), 8.06
(d, 1H, ArH, J = 7.6 Hz), 7.93 (d, 1H, ArH, J = 7.2 Hz), 7.79–7.87 (m,
2H, ArH), 7.01 (t, 1H, ArH, J = 8.0 Hz), 6.74 (s, 2H, ArH), 6.52 (d,
1H, ArH, J = 8.0 Hz), 5.03 (s, 1H, CH); IR (KBr, ν, cm−1): 3551, 3481,
3413, 3236, 1717, 1660, 1637, 1616; HRMS Calcd for C21H11ClN3O4
(M–H)− requires 404.0437; found: 404.0444.
5-(3-Hydroxyphenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
1
2,4,6,11(1H,3H)-tetraone (4n): M.p. >300 °C; HNMR (DMSO-d6,
δ, ppm): 10.95 (s, 1H, NH), 10.11 (s, 1H, NH), 9.30 (s, 2H, NH+OH),
8.04 (d, 1H, ArH, J = 6.8 Hz), 7.93 (d, 1H, ArH, J = 6.8 Hz), 7.80–
7.86 (m, 2H, ArH), 7.01 (t, 1H, ArH, J = 7.0 Hz), 6.75 (s, 2H, ArH),
6.53 (d, 1H, ArH, J = 6.8 Hz), 5.02 (s, 1H, CH); IR (KBr, ν, cm−1):
3553, 3480, 3414, 3235, 1719, 1638, 1616; HRMS Calcd for
C21H12N3O5 (M–H)− requires 386.0777; found: 386.0779.
5-(4-Methylphenyl)-5,12-dihydrobenzo[g]pyrimido[4,5-b]quinoline-
1
2,4,6,11(1H,3H)-tetraone (4o): M.p. >300 °C; HNMR (DMSO-d6,
δ, ppm): 10.92 (s, 1H, NH), 10.20 (s, 1H, NH), 9.25 (s, 1H, NH), 8.03
(d, 1H, ArH, J = 6.8 Hz), 7.90 (d, 1H, ArH, J = 7.2 Hz), 7.78–7.85
(m, 2H, ArH), 7.20 (d, 2H, ArH, J = 8.0 Hz), 7.02 (d, 2H, ArH, J =
7.6 Hz), 5.05 (s, 1H, CH), 2.19 (s, 3H, CH3); IR (KBr, ν, cm−1): 3550,
3482, 3414, 3230, 1719, 1616; HRMS Calcd for C22H14N3O4 (M–H)−
requires 384.0985; found: 384.1002.

456 JOURNAL OF CHEMICAL RESEARCH 2012
Conclusion
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2
3
I. Ugi and S. Heck, Comb. Chem. High. T. Scr., 2001, 4, 1.
In summary, an efficient one-pot synthesis of 5-aryl-5,12-dihy
drobenzo[g]pyrimido[4,5-b]quinoline-2,4,6,11(1H,3H)-tetra-
one derivatives via three-component reaction of aromatic
aldehyde, 2-hydroxy-1,4-naphthoquinone and 6-aminouracil
in ionic liquid [bmim]BF4 is reported. The ionic liquid plays
a dual role as solvent and the promoter in this conversion.
The simple experimental and product isolation procedures
combined with ease of recovery and reuse of this reaction
media is expected to contribute to the development of a green
strategy for the synthesis of highly fictionalised pyrimido
[4,5-b]quinolines.
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We are grateful to the National Natural Science Foundation of
China (No. 21104064, 21172188), Natural Science Founda-
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Academic Program Development of Jiangsu Higher Education
Institutions for financial support.
Received 2 March 2012; accepted 4 May 2012
Paper 1201190 doi: 10.3184/174751912X13384724679874
Paublished online: 8 August 2012
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