A highly efficient microwave-assisted synthesis of chromeno-[3,4-b][4,7] phenanthroline derivatives through multicomponent reactions in water

Article abstract of DOI:10.1002/jhet.5570450330

(Chemical Equation Presented) A short and simple synthesis of chromeno[3,4-b][4,7]phenanfhroline derivatives was accomplished by three-component reactions involving an aromatic aldehyde, 6-aminoquinoline and 4-hydroxycoumarin in water, under microwave irradiation without use of any catalyst. This protocol has the advantages of short reaction time, high yields, low cost and being environmental-friendly as well as easy operation.

Full text of DOI:10.1002/jhet.5570450330

May-Jun 2008
831
A Highly Efficient Microwave-assisted Synthesis of Chromeno-
[3,4-b][4,7]phenanthroline Derivatives Through Multicomponent
Reactions in Water
Qiya Zhuang, Dianxiang Zhou, Shujiang Tu,* Chunmei Li, Longji Cao, Qingqing Shao
School of Chemistry and Chemical Engineering, Xuzhou Normal University, Key Laboratory of Biotechnology
for Medicinal Plant, Xuzhou, Jiangsu, 221116, P. R. China
Received October 22, 2007
O
R
OH
O
N
H2N
H2O
MWI
O
RCHO
+
+
N
H
O
N
A short and simple synthesis of chromeno[3,4-b][4,7]phenanthroline derivatives was accomplished by
three-component reactions involving an aromatic aldehyde, 6-aminoquinoline and 4-hydroxycoumarin in
water, under microwave irradiation without use of any catalyst. This protocol has the advantages of short
reaction time, high yields, low cost and being environmental-friendly as well as easy operation.
J. Heterocyclic Chem., 45, 831 (2008).
inhibitors of the enzymes [20] and fungicides [21]. Hence,
the preparation of this heterocyclic unit has gained much
attention.
INTRODUCTION
Multicomponent reactions, in which multiple reactions
are combined into one synthetic operation, have been
extensively used in synthetic chemistry for the formation
of carbon-carbon and carbon-heteroatom bonds [1]. Such
reactions offer a wide range of possibilities for the
efficient construction of highly complex molecules in a
single procedural step, thus avoiding complicated
purification operations and allowing savings both of
solvents and of reagents. The use of water as a solvent has
many advantages in organic synthesis, both from
economical and from environmental points of view [2].
Water has therefore become an attractive medium for
many organic reactions, not only as the need for drying
reactants, expensive catalysts, and solvents can be
circumvented, but also for its unique reactivity and
selectivity [3,4]. Many important types of heterocyclic
compounds, such as triazines [5], acridines [6], quinolines
[7], pyridines [8], indoles [9], pyrazines [10], furans [11],
and pyrimidines [12], have been synthesized in aqueous
medium. The synthesis of new and important types of
heterocyclic compounds in water continues to attract wide
attention among synthetic chemists.
Chromenes [22] and 4,7-phenanthroline [23] derivatives
have been reported widely in the literature. For example,
Martinez [24] and co-works have reported the reaction of
aldehydes, β-naphthylamine and 4-hydroxycoumarin in
ethanol. Their protocol have inevitable drawbacks such
as: (i) narrow application scope of substrates, (ii) using
organic solvent and low yields, (iii) long reaction time
and two-step reaction. Therefore, it is urgent to develop a
more efficient and greener protocol to prepare similar
skeleton compounds.
Herein, we describe a simple multicomponent reaction
involving an aldehyde 1, 6-aminoquinoline 2, and 4-
hydroxycoumarin 3 in water under microwave irradiation
(MWI) without use of any catalyst to synthesize the
chromeno[3,4-b][4,7]phenanthroline
derivatives
4
(Scheme 1).
Scheme 1
RCHO
O
R
OH
1
N
H2N
O
H2O
Chromenes and their derivatives are important
compounds, which are found to possess antiestrogenic
activity and are devoid of any agonistic activity [13], and
are evaluated for potassium channel opening and
hypotensive activities [14], vasodilator and
antihypertensive activities [15], β-adrenolytic activity
[16], antimicrobial activity [17], and biological activity of
high-affinity retinoic acid receptor antagonist [18].
+
N
H
MWI
O
N
O
2
3
4
RESULTS AND DISCUSSION
Compounds of 4,7-phenanthroline series possess high
and versatile biological activity, such as antiallergic and
antitumor activities [19]. And they are also used as
Choosing an appropriate solvent is of crucial
importance for a successful organic synthesis. To search
for the optimal solvent, the microwave-assisted reaction

832
Q. Zhuang, D. Zhou, S. Tu, C. Li, L. Cao, Q. Shao
Vol 45
between 4-chlorobenzaldehyde (1b, 1.0 mmol), 6-
aminoquinoline (2, 1.0 mmol) and 4-hydroxycoumarin
(3, 1.0 mmol) was examined in ethylene glycol, glacial
acetic acid, ethanol, N,N-dimethylformamide and water
as solvents (2.0 mL) at 100 °C, respectively. All the
reactions were carried out at the maximum power of 250
W and the results are summarized in Table 1.
aldehydes either with electron-donating groups (such as
alkoxyl groups) or with electron-withdrawing groups
(such as nitro or halide groups), but also to heterocyclic
aldehyde, such as thiophene-2-carbaldehyde (Table 2,
entry 13), with excellent yields under same conditions, so
we conclude that the electronic nature of the substituents
has no significant effect on this reaction.
As can be seen in Table 1, the reactions with ethylene
glycol or water as the solvent gave higher yields and
required shorter reaction times than those with AcOH,
DMF or EtOH (Table1, entries 1−5). Water was thus
chosen as the solvent for all further microwave-assisted
reactions, as it is environmentally friendly and allows
toxic organic reagents to be avoided.
To further optimize the reaction temperature, the
same three reagents were allowed to react in water at
temperatures ranging from 110 to 150 °C, with an
increment of 10 °C each time. The results are shown in
Table 1. The yield of product 4b was increased and the
reaction time was shortened as the temperature was
increased from 110 °C to 140 °C (Table 1, entries 6-9).
However, further increase of the temperature to 140-150
°C failed to improve the yield of product 4b (Table 1,
entry 10). Therefore, 140 °C was chosen as the reaction
temperature for all further microwave-assisted reactions.
Although the detailed mechanism of the above reaction
remains to be fully clarified, the formation of
chromeno[3,4-b][4,7]phenanthroline derivatives 4 could
be explained by the possible mechanism presented in
Scheme 2.
All the products in this study were characterized by mp
and by IR and 1H NMR spectroscopy, as well as by
elemental analyses.
In summary, we have developed a simple three-
component reaction involving an aldehyde, 6-
aminoquinoline, and 4-hydroxycoumarin for the synthesis
of chromeno[3,4-b][4,7]phenanthroline derivatives in
high-temperature water under microwave irradiation
condition. This green procedure offers several advantages
including operational simplicity, clean reactions,
increased safety for small-scale high-speed synthesis, and
minimal environmental impact that makes it a useful and
attractive process for the synthesis of these compounds.
The new series of chromeno[3,4-b][4,7]phenanthroline
derivatives may provide new classes of biologically active
compounds for biomedical screening. This work is
currently in progress and the results will be reported in
due course.
Table 1
Optimization of reaction conditions of compound 4b.
Entry
Solvent
T / °C
Time / min
Yield / %
1
2
Glycol
AcOH
EtOH
DMF
water
water
water
water
water
water
100
100
100
100
100
110
120
130
140
150
9
10
12
11
9
85
80
75
81
84
86
89
91
93
92
3
EXPERIMENTAL
4
5
Microwave irradiation was carried out with an EmrysTM Creator
microwave oven from Personal Chemistry, Uppsala, Sweden.
Melting points were determined in open capillaries and were
uncorrected. IR spectra were taken with a FT-IR-Tensor 27
6
8
7
7
8
7
9
6
10
6
1
spectrometer in KBr pellets and are reported in cm-1. H NMR
spectra were measured with
spectrometer in DMSO-d6 with chemical shifts (δ) given in ppm
relative to TMS as internal standard. Elemental analysis was
a Bruker DPX 400 MHz
The maximum power of microwave irradiation was
optimized by carrying out the same reaction for the
synthesis of 4b at powers of 100, 150, 200, 250 and 300
W respectively, using water as solvent at 140 °C. When
the power was at 100−200 W, the times taken for the
temperature to reach 140 °C were too long. Microwave
irradiation at 250 W gave the highest yield and the
maximum temperature reached during the reaction was
141 °C. Therefore, a microwave power of 250 W was
chosen as the optimal power.
determined with
instrument.
a Perkin-Elmer 240c elemental analysis
General procedure for the one-pot synthesis of chromeno-
[3,4-b][4,7]phenanthroline derivatives 4 in water under
microwave irradiation condition. Typically, in a 10-mL
EmrysTM reaction vial, aldehydes 1 (1 mmol), 6-aminoquinoline
2 (1 mmol), 4-hydroxycoumarin 3 (1 mmol) and water (2 mL)
were mixed and then capped. The mixture was irradiated for a
given time at 140 °C under microwave irradiation (initial power
Under these optimized reaction conditions [water, 140
°C, 250 W (Maximum power)] a series of chromeno[3,4-
b][4,7]phenanthroline derivatives 4 were synthesized. The
results are summarized in Table 2. As shown in Table 2,
this methodology can be applied not only to aromatic
200
W and maximum power 250W). Upon completion,
monitored by TLC, the reaction mixture was filtered to give the
crude product, which was further purified by recrystallization
from EtOH (95%) to give pure chromeno[3,4-b][4,7]-
phenanthroline derivatives 4.

May-Jun 2008
A Highly Efficient Microwave-assisted Synthesis
833
of Chromeno-[3,4-b][4,7]phenanthroline Derivatives
Table 2
Synthesis of 4 in water under microwave irradiation at 140 °C
Entry
Product
R
Time/min
Yield/ %
Mp / °C
1
2
3
4a
4b
4c
4d
4e
4f
4g
4h
4i
4-FC6H4
4-ClC6H4
4-BrC6H4
4-CH3OC6H4
4-NO2C6H4
3-NO2C6H4
4-CH3C6H4
C6H5
6
6
5
5
6
5
5
5
5
6
6
5
5
93
93
94
95
94
95
95
94
94
93
94
95
95
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
>300
4
5
6
7
8
9
3,4-(CH3O)2C6H3
2,4-Cl2C6H3
3,4-OCH2OC6H3
4-OH-3-NO2C6H3
thien-2-yl
10
11
12
13
4j
4k
4l
4m
778, 617 cm-1; Hnmr: δ 10.27 (s, 1H, NH), 8.73-8.74 (m, 1H,
ArH), 8.41 (t, 2H, ArH, J = 9.6 Hz), 7.95-8.02 (m, 2H, ArH),
7.67 (t, 1H, ArH, J = 7.6 Hz), 7.44-7.51 (m, 2H, ArH), 7.38-7.41
(m, 3H, ArH), 7.31-7.33 (m, 2H, ArH), 5.94 (s, 1H, CH). Anal.
Calcd for C25H15BrN2O2: C, 65.95; H, 3.32; N, 6.15. Found C,
65.90; H, 3.35; N, 6.07.
1
Scheme 2
O
R
OH
O
-H2O
RCHO
+
O
O
O
1
3
5
N
14-(4-Methoxyphenyl)-7H-chromeno[3,4-b][4,7]phenanthro-
lin-13(14H)-one (4d). This compound was obtained according
to the above general procedure; ir (potassium bromide): 3231,
3184, 3014, 1659, 1637, 1605, 1571, 1469, 1321, 1259, 1056,
H2N
O
O
R
O
H2N
R
1
789 616 cm-1; Hnmr: δ 10.21 (s, 1H, NH), 8.71-8.72 (m, 1H,
N
O
O
O
ArH), 8.37-8.44 (m, 2H, ArH), 7.93-8.00 (m, 2H, ArH), 7.65 (t,
1H, ArH, J = 7.6 Hz), 7.43-7.50 (m, 2H, ArH), 7.39 (d, 1H,
ArH, J = 8.4 Hz), 7.26 (d, 2H, ArH, J = 8.4 Hz), 6.74 (d, 2H,
ArH, J = 8.4 Hz), 5.87 (s, 1H, CH), 3.61 (s, 3H, OCH3). Anal.
Calcd for C26H18N2O3: C, 76.83; H, 4.46; N, 6.89. Found C,
76.89; H, 4.50; N, 6.80.
2
5
6
O
R
O
R
N
N
O
O
-H2O
OH
N
H
N
H
14-(4-Nitrophenyl)-7H-chromeno[3,4-b][4,7]phenathrolin-
13(14H)-one (4e). This compound was obtained according to
the above general procedure; ir (potassium bromide): 3228,
3187, 3076, 1661, 1638, 1606, 1578, 1470, 1398, 1252, 1055,
4
7
14-(4-Fluorophenyl)-7H-chromeno[3,4-b][4,7]phenanthro-
lin-13(14H)-one (4a). This compound was obtained according
to the above general procedure; ir (potassium bromide): 3232,
3184, 3065, 1655, 1635, 1604, 1570, 1450, 1398, 1246, 1098,
1
766, 719 cm-1; Hnmr: δ 10.38 (s, 1H, NH), 8.73-8.74 (m, 1H,
ArH), 8.40-8.46 (m, 2H, ArH), 7.98-8.09 (m, 4H, ArH), 7.65-
7.70 (m, 3H, ArH), 7.44-7.52 (m, 2H, ArH), 7.40 (d, 1H, ArH, J
= 8.4 Hz), 6.12 (s, 1H, CH). Anal. Calcd for C25H15N3O4: C,
71.25; H, 3.59; N, 9.97. Found C, 71.35; H, 3.63; N, 9.90.
781, 616 cm-1; Hnmr: δ 10.24 (s, 1H, NH), 8.73-8.74 (m, 1H,
1
ArH), 8.39-8.44 (m, 2H, ArH), 7.95-8.02 (m, 2H, ArH), 7.66 (t,
1H, ArH, J = 7.6 Hz), 7.43-7.50 (m, 2H, ArH), 7.39-7.40 (m,
3H, ArH), 7.01 (t, 2H, ArH, J = 8.8 Hz), 5.96 (s, 1H, CH). Anal.
Calcd for C25H15FN2O2: C, 76.13; H, 3.83; N, 7.10. Found C,
76.02; H, 3.80; N, 7.02.
14-(3-Nitrophenyl)-7H-chromeno[3,4-b][4,7]phenathrolin-
13(14H)-one (4f). This compound was obtained according to the
above general procedure; ir (potassium bromide): 3231, 3138,
3076, 1658, 1635, 1605, 1558, 1468, 1375, 1246, 1056, 757, 615
1
cm-1; Hnmr: δ 10.37 (s, 1H, NH), 8.73 (s, 1H, ArH), 8.48 (d,
14-(4-Chlorophenyl)-7H-chromeno[3,4-b][4,7]phenanthro-
lin-13(14H)-one (4b). This compound was obtained according
to the above general procedure; ir (potassium bromide): 3230,
3184, 3067, 1657, 1635, 1602, 1572, 1468, 1322, 1247, 1089,
1H, ArH, J = 8.4 Hz), 8.41 (d, 1H, ArH, J = 7.6 Hz), 8.21 (s, 1H,
ArH), 7.99-8.06 (m, 2H, ArH), 7.95 (d, 1H, ArH, J = 8.4 Hz),
7.83 (d, 1H, ArH, J = 7.2 Hz), 7.67 (t, 1H, ArH, J = 7.6 Hz),
7.44-7.53 (m, 3H, ArH), 7.39 (d, 1H, ArH, J =7.6 Hz), 6.16 (s,
1H, CH). Anal. Calcd for C25H15N3O4: C, 71.25; H, 3.59; N,
9.97. Found C, 71.32; H, 3.64; N, 9.88.
780, 617 cm-1; Hnmr: δ 10.25 (s, 1H, NH), 8.72-8.73 (m, 1H,
1
ArH), 8.40 (t, 2H, ArH, J = 8.8 Hz), 7.95-8.02 (m, 2H, ArH),
7.66 (t, 1H, ArH, J = 7.6 Hz), 7.43-7.50 (m, 2H, ArH), 7.37-7.40
(m, 3H, ArH), 7.25 (d, 2H, ArH, J = 8.4 Hz), 5.95 (s, 1H, CH).
Anal. Calcd for C25H15ClN2O2: C, 73.08; H, 3.68; N, 6.82. Found
C, 73.18; H, 3.72; N, 6.89.
14-(4-Bromophenyl)-7H-chromeno[3,4-b][4,7]phenanthro-
lin-13(14H)-one (4c). This compound was obtained according to
the above general procedure; ir (potassium bromide): 3230,
3019, 2927, 1658, 1635, 1603, 1571, 1468, 1322, 1285, 1087,
14-(4-Methylphenyl)-7H-chromeno[3,4-b][4,7]phenanthro-
lin-13(14H)-one (4g). This compound was obtained according
to the above general procedure; ir (potassium bromide): 3231,
3020, 2921, 1658, 1635, 1603, 1571, 1468, 1376, 1248, 1058,
1
763, 616 cm-1; Hnmr: δ 10.19 (s, 1H, NH), 8.71-8.72 (m, 1H,
ArH), 8.37-8.43 (m, 2H, ArH), 7.93-8.00 (m, 2H, ArH), 7.65 (t,
1H, ArH, J = 7.6 Hz), 7.42-7.49 (m, 2H, ArH), 7.38 (d, 1H,

834
Q. Zhuang, D. Zhou, S. Tu, C. Li, L. Cao, Q. Shao
Vol 45
ArH, J = 8.0 Hz), 7.23 (d, 2H, ArH, J = 7.6 Hz), 6.98 (d, 2H,
ArH, J = 7.6 Hz), 5.88 (s, 1H, CH), 2.13 (s, 3H, CH3). Anal.
Calcd for C26H18N2O2: C, 79.98; H, 4.65; N, 7.17. Found C,
79.90; H, 4.68; N, 7.10.
ArH), 8.52 (d, 1H, ArH, J = 8.4 Hz), 8.39 (d, 1H, ArH, J = 8.0
Hz), 8.03 (d, 1H, ArH, J = 8.8 Hz), 7.94 (d, 1H, ArH, J = 9.2
Hz), 7.69 (t, 1H, ArH, J = 7.6 Hz), 7.48-7.54 (m, 2H, ArH), 7.44
(d, 1H, ArH, J = 8.0 Hz), 7.20-7.22 (m, 1H, ArH), 6.86-6.87 (m,
1H, ArH), 6.79-6.81 (m, 1H, ArH), 6.29 (s, 1H, CH). Anal.
Calcd for C23H14N2O2S: C, 72.23; H, 3.69; N, 7.33; S, 8.38.
Found C, 72.31; H, 3.65; N, 7.39; S, 8.30.
14-Phenyl-7H-chromeno[3,4-b][4,7]phenanthrolin-13(14H)-
one (4h). This compound was obtained according to the above
general procedure; ir (potassium bromide): 3226, 3144, 3078,
1657, 1623, 1558, 1470, 1398, 1251, 1061, 923, 833, 753, 617
cm-1; 1Hnmr: δ 10.23 (s, 1H, NH), 8.72-8.73 (m, 1H, ArH), 8.38-
8.45 (m, 2H, ArH), 7.95-8.01 (m, 2H, ArH), 7.65 (t, 1H, ArH, J
= 8.0 Hz), 7.43-7.50 (m, 2H, ArH), 7.36-7.40 (m, 3H, ArH),
7.19 (t, 2H, ArH, J = 7.6 Hz), 7.07 (t, 1H, ArH, J = 7.2 Hz), 5.93
(s, 1H, CH). Anal. Calcd for C25H16N2O2: C, 79.77; H, 4.28; N,
7.44. Found C, 79.70; H, 4.30; N, 7.51.
Acknowledgements We are grateful to the financial support
from the National Natural Science Foundation of China (No.
20672090), the Natural Science Foundation of the Jiangsu
Province (No. BK2006033), and Six Kinds of Professional Elite
Foundation of the Jiangsu Province (No. 06-A-039).
REFERENCES
14-(3,4-Dimethoxyphenyl)-7H-chromeno[3,4-b][4,7]phen-
anthrolin-13(14H)-one (4i). This compound was obtained
according to the above general procedure; ir (potassium bromide):
3232, 3066, 2930, 1657, 1635, 1604, 1558, 1418, 1374, 1240,
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1
1058, 912, 762, 611 cm-1; Hnmr: δ 10.24 (s, 1H, NH), 8.73-8.74
(m, 1H, ArH), 8.48 (d, 1H, ArH, J = 8.4 Hz), 8.38 (d, 1H, ArH, J =
7.6 Hz), 7.94-8.01 (m, 2H, ArH), 7.66 (t, 1H, ArH, J = 7.6 Hz),
7.44-7.50 (m, 2H, ArH), 7.39 (d, 1H, ArH, J =8.4 Hz), 7.12 (s, 1H,
ArH), 6.65-6.73 (m, 2H, ArH), 5.88 (s, 1H, CH), 3.67 (s, 3H,
OCH3), 3.59 (s, 3H, OCH3). Anal. Calcd for C27H20N2O4: C, 74.30;
H, 4.62; N, 6.42. Found C, 74.38; H, 4.65; N, 6.49.
14-(2,4-Dichlorophenyl)-7H-chromeno[3,4-b][4,7]phenan-
throlin-13(14H)-one (4j). This compound was obtained
according to the above general procedure; ir (potassium
bromide): 3228, 3139, 3078, 1656, 1619, 1556, 1470, 1321,
1
1249, 1088, 965, 885, 757, 613 cm-1; Hnmr: δ 10.30 (s, 1H,
NH), 8.72-8.73 (m, 1H, ArH), 8.42 (t, 2H, ArH, J = 7.2 Hz),
7.92-8.00 (m, 2H, ArH), 7.67 (t, 1H, ArH, J = 7.6 Hz), 7.46-7.51
(m, 4H, ArH), 7.39 (d, 1H, ArH, J = 8.4 Hz), 7.25 (d, 1H, ArH, J
= 8.4 Hz), 6.18 (s, 1H, CH). Anal. Calcd for C25H14Cl2N2O2: C,
67.43; H, 3.17; N, 6.29. Found C, 67.36; H, 3.14; N, 6.36.
14-(Benzo[d][1,3]dioxol-6-yl)-7H-chromeno[3,4-b][4,7]-phen-
athrnolin-13(14H)-one (4k). This compound was obtained
according to the above general procedure; ir (potassium
bromide): 3232, 3186, 3067, 1659, 1635, 1530, 1469, 1322,
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2005, 53, 4130.
1
1247, 1099, 946, 852, 616 cm-1; Hnmr: δ 10.23 (s, 1H, NH),
8.73-8.74 (m, 1H, ArH), 8.47 (d, 1H, ArH, J = 8.8 Hz), 8.39 (d,
1H, ArH, J = 8.0 Hz), 7.94-8.01 (m, 2H, ArH), 7.66 (t, 1H, ArH,
J = 7.6 Hz), 7.45-7.50 (m, 2H, ArH), 7.40 (d, 1H, ArH, J = 8.4
Hz,), 6.94 (s, 1H, ArH), 6.70-6.78 (m, 2H, ArH), 5.88 (s, 1H,
CH), 5.86-5.87 (m, 2H, OCH2O). Anal. Calcd for C26H16N2O4:
C, 74.28; H, 3.84; N, 6.66. Found C, 74.20; H, 3.88; N, 6.74.
14-(4-Hydroxy-3-nitrophenyl)-7H-chromeno[3,4-b][4,7]-
phenanthrolin-13(14H)-one (4l). This compound was obtained
according to the above general procedure; ir (potassium
bromide): 3326, 3231, 3182, 3070, 1652, 1635, 1533, 1469,
[11] Wnorowski, A.; Yaylayan, V. A. J. Agric. Food Chem.
2000, 48, 3549.
[12] Bose, D. S.; Fatima, L.; Mereyala, H. B. J. Org. Chem.
2003, 68, 587.
1
1348, 1229, 1083, 922, 832, 617 cm-1; Hnmr: δ 10.82 (s, 1H,
[13] Hajela, K.; Kapil, R. S. Eur. J. Med. Chem. 1997, 32,
135.
OH), 10.31 (s, 1H, NH), 8.74-8.75 (m, 1H, ArH), 8.47 (d, 1H,
ArH, J = 8.4 Hz), 8.40 (d, 1H, ArH, J = 8.0 Hz), 7.92-8.04 (m,
2H, ArH), 7.88 (s, 1H, ArH), 7.67 (t, 1H, ArH, J =7.6 Hz,), 7.46-
7.51 (m, 3H, ArH), 7.41(d, 1H, ArH, J = 8.4 Hz), 6.94-6.98 (m,
1H, ArH), 5.97 (s, 1H, CH). Anal. Calcd for C25H15N3O5: C,
68.65; H, 3.46; N, 9.61. Found C, 68.60; H, 3.49; N, 9.68.
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14-(Thien-2-yl)-7H-chromeno[3,4-b][4,7]phenanthrolin-
13(14H)-one (4m). This compound was obtained according to
the above general procedure; ir (potassium bromide): 3234,
3143, 3066, 1656, 1636, 1529, 1469, 1321, 1249, 1079, 1051,
1
832, 617 cm-1; Hnmr: δ 10.39 (s, 1H, NH), 8.78-8.79 (m, 1H,

May-Jun 2008
A Highly Efficient Microwave-assisted Synthesis
835
of Chromeno-[3,4-b][4,7]phenanthroline Derivatives
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