Green and high efficient synthesis of triaza-benzo[b]fluoren-6-one derivatives in water under microwave irradiation

Article abstract of DOI:10.1002/jhet.5570450218

(Chemical Equation Presented) Triaza-benzo[b]fluoren-6-one derivatives were synthesized via the three-component reaction of aldehyde, cyclohexane-1,3-dione compound and 2-aminobenzimidazole in water under microwave irradiation. The new protocol has the advantages of excellent yield, low cost, reduced environment impact, wide scope and convenient procedure.

Full text of DOI:10.1002/jhet.5570450218

Mar-Apr 2008
411
Green and High Efficient Synthesis of Triaza-benzo[b]fluoren-6-one
Derivatives in Water under Microwave Irradiation
Qingqing Shaoa, Shujiang Tu*a, Chunmei Lia, Longji Caoa, Dianxiang Zhoua,
Qian Wangb, Bo Jianga, Yan Zhanga, Wenjuan Haoa
aSchool of Chemistry and Chemical Engineering, Xuzhou Normal University, Key Laboratory of
Biotechnology on Medical Plant, Xuzhou, Jiangsu 221116, PR China
bXuzhou Medical College, Jiangsu 221004, PR China
Received June 28, 2007
R1
O
O
H
N
N
H2O
MWI
R2
R2
R2
R2
+
NH2
R1CHO
+
N
N
N
H
O
Triaza-benzo[b]fluoren-6-one derivatives were synthesized via the three-component reaction of
aldehyde, cyclohexane-1,3-dione compound and 2-aminobenzimidazole in water under microwave
irradiation. The new protocol has the advantages of excellent yield, low cost, reduced environment impact,
wide scope and convenient procedure.
J. Heterocyclic Chem., 45, 411 (2008).
in combination with microwave irradiation [16] wherein
activation of reactions can be achieved.
INTRODUCTION
The concept of “green chemistry” has been widely
adopted to meet the fundamental scientific challenges of
protecting human health and the environment while
simultaneously achieving commercial viability [1]. The
emerging area of green chemistry envisages minimum
hazard as the performance criteria while designing new
chemical processes. One of the thrust areas for achieving
this target is to explore alternative reaction conditions and
reaction media to accomplish the desired chemical
transformations with minimum byproducts and waste
generation, as well as eliminating the use of volatile and
toxic organic solvents [2].
Braulio Insuasty [17] and co-workers have reported the
reaction of aromatic aldehyde, 2-aminobenzimidazole and
5,5-dimethylcyclohexane-1,3-dione in absolute ethanol
(Scheme 1). Their protocol gave moderate yields (60%-
86%) except for the limitation: (i) narrow scope of only
aromatic aldehyde, and only 5,5-dimethylcyclohexane-
1,3-dione as the cyclic active methylene compound, (ii)
organic solvent, (iii) long reaction time. Therefore, it is
urgent to develop a more efficient and greener protocol to
prepare triaza-benzo[b]fluoren-6-one compounds.
Scheme 1
Organic reactions accelerated under the influence of
microwave (MW) irradiation have attracted considerable
attention in the past decade for the efficient and relatively
friendlier synthesis of a variety of organic compounds [3].
The use of MW irradiation for the formation of several
carbon-heteroatom and carbon-carbon bonds has been
successfully demonstrated [4].
Nitrogen-containing heterocycles are known subunits in
many natural products and biologically active pharma-
ceuticals [5]. Varied biological activities have been
attributed to triaza-benzo[b]fluoren-6-one compounds,
including analgesic, antiinflamatory, antipyretic [6-8],
antimicrobial [9], anticonvulsant [10], fungicidal [11],
antidepressant or other central nervous system affecting
activities [12], and recently two original triaza-benzo[b]-
fluoren-6-one compounds were described as a new class
of potent antitumour compounds [13].
O
Ar
O
Ar
H
N
N
absolute ethanol
+
NH2
N
O
N
H
O
N
We wish to report here the synthesis of triaza-
benzo[b]fluoren-6-one derivatives occurring in aqueous
media upon microwave irradiation in a simple and
straight-forward manner (Scheme 2).
Scheme 2
R1
O
O
H
N
N
H2O
MWI
R2
R2
R2
R2
R1CHO
NH2
+
+
N
N
N
H
O
1
3
2
4
Developing efficient, selective and eco-friendly
synthetic methods for applications in complex organic
preparations is the ultimate goal of several research
groups, including ours [14]. Among alternative, friendlier
solvents, water is very benign [15] and has been utilized
RESULTS AND DISCUSSION
To optimize the reaction temperature, the
synthesis of 4a was performed using water as the

412
Q. Shao, S. Tu,C. Li, L. Cao, D. Zhou, Q. Wang, B. Jiang, Y. Zhang, W. Hao
Vol 45
Scheme 3
R2
..
R2
HO
H
N
H
N
3
-H2O
R1CHO
NH2
N
CHR1
O
+
N
N
2
1
5
R2
R2
R2
R2
N
..
NH2
CHR1
..
HO
H
O
O
N
H
H
N
O
O
N
O
NH CHR1
NH CHR1
N
N
R2
R2
7
6
8
R2
R2
R2
R2
R2
R2
OH
NH
O
NH
O
O
-H2O
..
NH2
O
R1
N
R1
N
N
R1
N
N
N
10
9
4
solvent at temperatures ranging from 70 °C to 95 °C,
with an increment of 5 °C each time. The yield of
product 4a was increased and the reaction time was
shortened when the temperature was increased from
70 °C to 85 °C. The yield leveled off when the
temperature was further increased to 90 °C and 95
°C. Therefore, the most suitable temperature should
be 85 °C.
It is shown in Table 1 that the reaction in water and in
organic solvents of glycol and DMF afforded satisfying
results, similarly. Water could be chosen as efficient and
green solvent.
Microwave irradiation power was also optimized for
the synthesis of 4a. The most suitable initial irradiation
power was 250 W.
Based on these optimized reaction conditions, a series
of triaza-benzo[b]fluoren-6-one derivatives was synthe-
sized by the reaction of equimolecular amounts of
aldehyde, cyclohexane-1,3-dione compound and 2-amino-
benzimidazole in water under microwave irradiation. The
protocol could be applied not only to the aromatic
aldehydes with either electron-withdrawing groups or
electron-donating groups, but also to aliphatic aldehydes,
which highlighted the wide scope of this three-component
condensation. Furthermore, the procedure is easy to
operate and the workup procedure is just simple filtration.
A series of triaza-benzo[b]fluoren-6-one derivatives was
synthesized. The results are summerized in Table 2.
The reaction of 4-chlorobenzaldehyde, 2-aminobenz-
imidazole, and cyclohexane-1,3-dione in water under
conventional and MW heating conditions was investi-
gated to demonstrate the specific microwave effect. We
found that the reaction under conventional heating
condition gave rise to a moderate yield (59%) within 40
min of reaction time. However, the same reaction under
In collection with Braulio’s work, as well as to test the
effect of water as solvent under microwave irradiation, we
also examined the same reaction of synthesis of 4a under
microwave irradiation using ethyleneglycol, ethanol,
glacial acetic acid and DMF as solvent, respectively. The
results were summarized in Table 1.
Table 1
The comparison of water and organic solvents.
No
Solvent
temp (oC)
Time (min)
Yield(%)
1
2
3
4
5
Water
Glycol
DMF
85
85
85
85
85
3
94
94
93
76
50
5
4
EtOH
HOAc
10
20

Mar-Apr 2008
Green and High Efficient Synthesis of Triaza-benzo[b]fluoren-6-one Derivatives
413
Table 2
Synthesis of 4 in water under Microwave Irradiation Conditions at 85 °C
No
1
2
3
4
5
6
7
8
4
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
R1
4-ClC6H4
4-BrC6H4
R2
H
H
H
H
H
H
H
H
H
H
H
H
H
H
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
Time(min)
Yield(%)
94a
Mp(°C)
>300a
3
3
4
4
2
3
2
3
2
2
3
3
4
4
4
4
4
3
4
4
4
3
3
3
4
93a
>300a
3,4-OCH2OC6H3
CH3CH2CH2CH2
2-ClC6H4
C6H5
4-FC6H4
4-N(CH3)2C6H4
3-BrC6H4
4-NO2C6H4
4-CH3C6H4
3-NO2C6H4
4-CH3OC6H4
3,4-(CH3O)2C6H3
4-ClC6H4
93a
>300a
92a
>300a
97a
>300a
93a
>300a
94a
>300a
92a
>300a
9
94a
>300a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
93a
>300a
91a
>300a
93a
>300a
92a
>300a
93a
>300a
94a(60)b
93a(64)b
94a(68)b
92a
>300a(393)b
>300a(368)b
>300a(369)b
>300a
C6H5
4-BrC6H4
2-ClC6H4
4-CH3OC6H4
3,4-OCH2OC6H3
3,4-(CH3O)2C6H3
2,4-Cl2C6H3
3-BrC6H4
94a(70)b
94a
>300a(389)b
>300a
4t
4u
4v
4w
4x
4y
95a
>300a
95a
>300a
94a
>300a
4-FC6H4
4-CH3C6H4
95a
>300a
92a
>300a
a Isolated yield and melting point; b literature yield and melting point
microwave irradiation for only 3 min afforded excellent
product yield (94%). Microwave-assisted reaction
exhibited several advantages over the conventional
heating by not only significantly reducing the reaction
time but also by improving the reaction yield
dramatically.
In conclusion, we have developed a three-component
reaction of aldehyde, cyclohexane-1,3-dione compound
and 2-aminobenzimidazole in water under microwave
irradiation conditions for the synthesis of triaza-
benzo[b]fluoren-6-one derivatives. Particularly valuable
features of this method include excellent yields of the
products, shorter reaction time, reduced environmental
impact, and straightforward procedure.
The formation of triaza-benzo[b]fluoren-6-one deriva-
tives 4 could be explained by the reaction sequence
presented in Scheme 3. It is easier for aldehydes to react
with 2-aminobenzimidazole than with cyclic β-dicarbonyl
compounds. Therefore, we proposed that the reaction
proceeded via a sequence of condensation, addition,
elimination, addition, cyclization and dehydration. First, the
condensation of aldehyde and 2-aminobenzimidazole gave
Schiff base 5. The addition of Schiff base to cyclohexane-
1,3-dione compounds, then after elimination furnished the
intermediate product 8. Then the addition of 2-aminobenz-
imidazole to 8 gave the intermediate product 9, which upon
intermolecular cyclization and dehydration gave rise to 4.
To test the proposed mechanism, we carried out the
synthesis of 4a in two steps, first of which was to get the
pure Schiffe base 5, which was characterized by IR and
1H NMR spectral data, and then reacted with 3 under
similar conditions. The target compound of 4a was
obtained with yield similar to the one-pot reaction. That
fact supported the proposed mechanism (Scheme 3).
In this study, all the products were characterized by
EXPERIMENTAL
Microwave irradiation was carried out in a monomodal
EmrysTM Creator from Personal Chemistry, Uppsala, Sweden.
Melting points were determined in open capillaries and are
uncorrected. ir spectra were recorded on a TENSOR 27
1
spectrometer in KBr. H nmr spectra were measured on a DPX
400 spectrometer operating at 400 MHz, using DMSO-d6 as
solvent and TMS as internal standard. Elemental analyses were
determined by using a Perkin-Elmer 240c elemental analysis
instrument.
General Procedure for the synthesis of triaza-
benzo[b]fluoren-6-one derivatives (4a-4y). In
a 10-mL
EmrysTM reaction vial, aldehyde (1 mmol), cyclic β-dicarbonyl
compound (1 mmol), 2-aminobenzimidazole (1 mmol) and
water (2 mL) were mixed and then capped. After irradiation
for 2-4 min, the reaction mixture was cooled to room
temperature. After pouring the liquid (water), the mixture was
further purified by crystallized from 95% EtOH.
5-(4-Chloro-phenyl)-5,8,9,10-tetrahydro-7H-4b,10,11-tri-
aza-benzo[b]fluoren-6-one (4a). This compound was obtained
according to above general procedure; ir (potassium bromide):
1
melting point, ir and H nmr spectral data, as well as
elemental analyses.

414
Q. Shao, S. Tu,C. Li, L. Cao, D. Zhou, Q. Wang, B. Jiang, Y. Zhang, W. Hao
Vol 45
3225, 3041, 2950, 2890, 1674, 1569, 1187, 977, 834, 747 cm-1;
1H nmr (DMSO-d6): δ 11.16 (s, 1H, NH), 7.39-7.29 (m, 6H,
ArH), 7.06 (t, 1H, J = 7.2 Hz, ArH), 6.96 (t, 1H, J = 7.6 Hz,
ArH), 6.45 (s, 1H, CH), 2.69-2.67 (m, 2H, CH2), 2.33-2.20 (m,
2H, CH2), 1.97-1.85 (m, 2H, CH2). Anal calcd. for C20H16ClN3O:
C, 68.67; H, 4.61; N, 12.01. Found: C, 68.69; H, 4.60; N, 12.00.
5-(4-Bromo-phenyl)-5,8,9,10-tetrahydro-7H-4b,10,11-tri-
aza-benzo[b]fluoren-6-one (4b). This compound was obtained
according to above general procedure; ir (potassium bromide):
ArH), 7.20 (d, 1H, J = 7.6 Hz, ArH), 7.04-6.99 (m, 3H, ArH),
6.92 (t, 1H, J = 7.2 Hz, ArH), 6.41 (s, 1H, CH), 2.65-2.63 (m,
2H, CH2), 2.31-2.15 (m, 2H, CH2), 1.97-1.83 (m, 2H, CH2).
Anal calcd. for C20H16FN3O: C, 72.06; H, 4.84; N, 12.61.
Found: C, 72.08; H, 4.83; N,12.60.
5-(4-Dimethylamino-phenyl)-5,8,9,10-tetrahydro-7H-4b,
10,11-triaza-benzo[b]fluoren-6-one (4h). This compound was
obtained according to above general procedure; ir (potassium
1
bromide): 3224, 3043, 2995, 1645, 1522, 949, 820 cm-1; H nmr
1
3222, 3093, 2952, 1644, 1436, 1072, 884, 748 cm-1; H nmr
(DMSO-d6): δ 10.96 (s, 1H, NH), 7.30 (d, 1H, J = 4.0 Hz, ArH),
7.21 (d, 1H, J = 8.0 Hz, ArH), 7.07 (d, 2H, J = 8.8 Hz, ArH),
6.99 (t, 1H, J = 7.2 Hz, ArH), 6.91 (t, 1H, J = 7.2 Hz, ArH), 6.50
(d, 2H, J = 8.8 Hz, ArH), 6.25 (s, 1H, CH), 2.75 (s, 6H, 2CH3),
2.65-2.63 (m, 2H, CH2), 2.29-2.15 (m, 2H, CH2), 1.95-1.90 (m,
2H, CH2). Anal calcd. for C22H22N4O: C, 73.72; H, 6.19; N,
15.63. Found: C, 73.74; H, 6.18; N, 15.62.
(DMSO-d6): δ 11.18 (s, 1H, NH), 7.44 (d, 2H, J = 8.0 Hz, ArH),
7.38 (d, 1H, J = 8.0 Hz, ArH), 7.29 (d, 2H, J = 8.4 Hz, ArH),
7.23 (d, 1H, J = 8.0 Hz, ArH), 7.06 (t, 1H, J = 8.0 Hz, ArH) ,
6.96 (t, 1H, J = 7.6 Hz, ArH), 6.44 (s, 1H, CH), 2.69-2.67 (m,
2H, CH2), 2.30-2.21 (m, 2H, CH2), 1.99-1.83 (m, 2H, CH2). Anal
calcd. for C20H16BrN3O: C, 60.93; H, 4.09; N, 10.66. Found: C,
60.94; H, 4.09; N, 10.68.
5-(3-Bromo-phenyl)-5,8,9,10-tetrahydro-7H-4b,10,11-tri-
aza-benzo[b]fluoren-6-one (4i). This compound was obtained
according to above general procedure; ir (potassium bromide):
5-Benzo[d][1,3]dioxol-5-yl-5,8,9,10-tetrahydro-7H-4b,10,
11-triaza-benzo[b]fluoren-6-one (4c). This compound was
obtained according to above general procedure; ir (potassium
1
3220, 3048, 2891, 1647, 1571, 996, 890 cm-1; H nmr (DMSO-
1
bromide): 3224, 3095, 2942, 2831, 1642, 1360, 785 cm-1; H
d6): δ 11.16 (s, 1H, NH), 7.55 (s, 1H, ArH), 7.36-7.31 (m, 2H,
ArH), 7.24-7.13 (m, 3H, ArH), 7.02 (t, 1H, J = 7.6 Hz, ArH),
6.94 (t, 1H, J = 7.6 Hz, ArH), 6.41 (s, 1H, CH), 2.66-2.63 (m,
2H, CH2), 2.28-2.18 (m, 2H, CH2), 1.95-1.80 (m, 2H, CH2). Anal
calcd. for C20H16BrN3O: C, 60.93; H, 4.09; N, 10.66. Found: C,
60.92; H, 4.10; N, 10.65.
nmr (DMSO-d6): δ 11.11 (s, 1H, NH), 7.38 (d, 1H, J = 7.6 Hz,
ArH), 7.36 (d, 1H, J = 7.6 Hz, ArH), 7.07 (t, 1H, J = 7.6 Hz,
ArH), 6.98 (t, 1H, J = 8.0 Hz, ArH), 6.87 (s, 1H, ArH), 6.82-
6.75(m, 2H, ArH), 6.36 (s, 1H, CH), 5.92 (d, 2H, J = 8.4 Hz,
OCH2O), 2.70-2.69 (m, 2H, CH2), 2.27-2.25 (m, 2H, CH2), 1.88-
1.86 (m, 2H, CH2). Anal calcd. for C21H17N3O3: C, 70.18; H,
4.77; N, 11.69. Found: C, 70.16; H, 4.78; N, 11.70.
5-Butyl-5,8,9,10-tetrahydro-7H-4b,10,11-triaza-benzo[b]-
fluoren-6-one (4d). This compound was obtained according to
above general procedure; ir (potassium bromide): 3100, 2955,
2868, 1655, 1132, 739 cm-1; 1H nmr (DMSO-d6): δ 10.77 (s, 1H,
NH), 7.48 (d, 1H, J = 7.2 Hz, ArH), 7.40 (d, 1H, J = 6.8 Hz,
ArH), 7.13-7.07 (m, 2H, ArH), 5.60 (s, 1H, CH), 2.62-2.60 (m,
2H, CH2), 2.35-2.33 (m, 2H, CH2), 2.01-1.92 (m, 3H, CH), 1.75-
1.67 (m, 1H, CH), 1.06-1.03 (m, 3H, CH), 0.68-0.65 (m, 4H,
CH). Anal calcd. for C18H21N3O: C, 73.19; H, 7.17; N, 14.23.
Found: C, 73.21; H, 7.16; N, 14.22.
5-(4-Nitro-phenyl)-5,8,9,10-tetrahydro-7H-4b,10,11-tri-
aza-benzo[b]fluoren-6-one (4j). This compound was obtained
according to above general procedure; ir (potassium bromide):
1
3223, 3040, 2949, 1646, 1515, 898, 822 cm-1; H nmr (DMSO-
d6): δ 11.25 (s, 1H, NH), 8.06 (d, 2H, J = 8.8 Hz, ArH), 7.56 (d,
2H, J = 8.8 Hz, ArH), 7.35 (d, 1H, J = 8.0 Hz, ArH), 7.17 (d,
1H, J = 7.6 Hz, ArH), 7.02 (t, 1H, J = 7.2 Hz, ArH), 6.92 (t, 1H,
J = 8.0 Hz, ArH), 6.59 (s, 1H, CH), 2.68-2.65 (m, 2H, CH2),
2.31-2.15 (m, 2H, CH2), 1.97-1.80 (m, 2H, CH2). Anal calcd. for
C20H16N4O3: C, 66.66; H, 4.48; N, 15.55. Found: C, 66.68; H,
4.47; N, 15.56.
5-p-Tolyl-5,8,9,10-tetrahydro-7H-4b,10,11-triaza-benzo-
[b]fluoren-6-one (4k). This compound was obtained according to
above general procedure; ir (potassium bromide): 3224, 3038,
5-(2-Chloro-phenyl)-5,8,9,10-tetrahydro-7H-4b,10,11-tri-
aza-benzo[b]fluoren-6-one (4e). This compound was obtained
according to above general procedure; ir (potassium bromide):
1
2950, 1645, 1514, 977, 829 cm-1; H nmr (DMSO-d6): δ 11.04 (s,
1
3222, 3093, 2952, 1644, 884, 748 cm-1; H nmr (DMSO-d6): δ
1H, NH), 7.31 (d, 1H, J = 7.6Hz, ArH), 7.20-7.14 (m, 3H, ArH),
7.01-6.98 (m, 3H, ArH), 6.90 (t, 1H, J = 7.6 Hz, ArH), 6.33 (s, 1H,
CH), 2.65-2.64 (m, 2H, CH2), 2.29-2.19 (m, 2H, CH2), 2.17 (s, 3H,
CH3), 1.93-1.80 (m, 2H, CH2). Anal calcd. for C21H19N3O: C,
76.57; H, 5.81; N, 12.76. Found: C, 76.55; H, 5.80; N, 12.77.
5-(3-Nitro-phenyl)-5,8,9,10-tetrahydro-7H-4b,10,11-tri-
aza-benzo[b]fluoren-6-one (4l). This compound was obtained
according to above general procedure; ir (potassium bromide):
3220, 3040, 2950, 1652, 1514, 1020, 744 cm-1; 1H nmr (DMSO-
d6): δ 11.30 (s, 1H, NH), 8.27 (s, 1H, ArH), 8.04(d, 1H, J = 8.4
Hz, ArH), 7.70 (d, 1H, J = 7.6 Hz, ArH), 7.55 (t, 1H, J = 8.0 Hz,
ArH), 7.40 (d, 1H, J = 7.6 Hz, ArH), 7.27 (d, 1H, J = 7.6 Hz,
ArH), 7.06 (t, 1H, J = 7.2 Hz, ArH), 6.96 (t, 1H, J = 7.6 Hz,
ArH), 6.67 (s, 1H, CH), 2.73-2.70 (m, 2H, CH2), 2.36-2.19 (m,
2H, CH2), 1.99-1.85 (m, 2H, CH2). Anal calcd. for C20H16N4O3:
C, 66.66; H, 4.48; N, 15.55. Found: C, 66.69; H, 4.49; N, 15.54.
5-(4-Methoxy-phenyl)-5,8,9,10-tetrahydro-7H-4b,10,11-
triaza-benzo[b]fluoren-6-one (4m). This compound was
obtained according to above general procedure; ir (potassium
11.24 (s, 1H, NH), 7.52-7.51 (m, 1H, ArH), 7.39-7.32 (m, 2H,
ArH), 7.27 (t, 1H, J = 7.6 Hz, ArH), 7.21 (t, 1H, J = 7.6 Hz,
ArH), 7.10-7.03 (m, 2H, ArH), 6.95 (t, 1H, J = 7.6 Hz, ArH),
6.66 (s, 1H, CH), 2.71-2.68 (m, 2H, CH2), 2.29-2.18 (m, 2H,
CH2), 2.01-1.83 (m, 2H, CH2). Anal calcd. for C20H16ClN3O: C,
68.67; H, 4.61; N, 12.01. Found: C, 68.69; H, 4.60; N, 12.02.
5-Phenyl-5,8,9,10-tetrahydro-7H-4b,10,11-triaza-benzo-
[b]fluoren-6-one (4f). This compound was obtained according to
above general procedure; ir (potassium bromide): 3226, 3029,
1
2957, 1653, 885, 749 cm-1; H nmr (DMSO-d6): δ 11.10 (s, 1H,
NH), 7.38-7.31 (m, 3H, ArH), 7.25-7.22 (m, 3H, ArH), 7.15 (t, 1H,
J = 7.6 Hz, ArH), 7.04 (t, 1H, J = 7.6 Hz, ArH), 6.95 (t, 1H, J = 7.6
Hz, ArH), 6.42 (s, 1H, CH), 2.71-2.70 (m, 2H, CH2), 2.32-2.20 (m,
2H, CH2), 2.00-1.86 (m, 2H, CH2). Anal calcd. for C20H17N3O: C,
76.17; H, 5.43; N, 13.32. Found: C, 76.16; H, 5.44; N, 13.33.
5-(4-Fluoro-phenyl)-5,8,9,10-tetrahydro-7H-4b,10,11-tri-
aza-benzo[b]fluoren-6-one (4g). This compound was
obtained according to above general procedure; ir (potassium
1
1
bromide): 3227, 3043, 2956, 1644, 1510, 890, 759 cm-1; H
bromide): 3226, 3040, 2955, 1655, 1514, 1038, 748 cm-1; H
nmr (DMSO-d6): δ 11.10 (s, 1H, NH), 7.34-7.31 (m, 3H,
nmr (DMSO-d6): δ 11.09 (s, 1H, NH), 7.36 (d, 1H, J = 7.6 Hz,

Mar-Apr 2008
Green and High Efficient Synthesis of Triaza-benzo[b]fluoren-6-one Derivatives
415
ArH), 7.26-7.23 (m, 3H, ArH), 7.04(t, 1H, J = 7.6 Hz, ArH),
6.95(t, 1H, J = 7.6 Hz, ArH), 6.78 (d, 2H, J = 7.6 Hz, ArH), 6.37
(s, 1H, CH), 3.65(s, 3H, OCH3), 2.70-2.69 (m, 2H, CH2), 2.31-
2.20 (m, 2H, CH2), 1.99-1.85 (m, 2H, CH2). Anal calcd. for
C21H19N3O2: C, 73.03; H, 5.54; N, 12.17. Found: C, 73.05; H,
5.53; N, 12.18.
ArH), 6.96 (t, 1H, J = 8.0 Hz, ArH), 6.76 (d, 2H, J = 8.4 Hz,
ArH), 6.36 (s, 1H, CH), 3.66 (s, 3H, OCH3), 2.65-2.51 (m, 2H,
CH2) 2.28-2.03 (m, 2H, CH2), 1.06 (s, 3H, CH3), 0.95 (s, 3H,
CH3). Anal calcd. for C23H23N3O2: C, 73.97; H, 6.21; N, 11.25.
Found: C, 73.99; H, 6.20; N, 11.24.
5-Benzo[1,3]dioxol-5-yl-8,8-dimethyl-5,8,9,10-tetrahydro-
7H-4b,10,11-triaza-benzo[b]fluoren-6-one (4t). This compound
was obtained according to above general procedure; ir
(potassium bromide): 3228, 3095, 2966, 1644, 850, 791 cm-1;1H
nmr (DMSO-d6): δ 11.09 (s, 1H, NH), 7.38-7.31 (m, 2H, ArH),
7.06 (t, 1H, J = 7.2 Hz, ArH), 6.98 (t, 1H, J = 7.6 Hz, ArH), 6.89
(s, 1H, ArH),6.82-6.76 (m, 2H, ArH), 6.35 (s, 1H, CH), 5.93 (d,
2H, J = 8.0 Hz, OCH2O), 2.64-2.53 (m, 2H, CH2), 2.28-2.06 (m,
2H, CH2), 1.06 (s, 3H, CH3), 0.96 (s, 3H, CH3). Anal calcd. for
C23H21N3O3: C, 71.30; H, 5.46; N, 10.85. Found: C, 71.29; H,
5.44; N, 10.86.
5-(3,4-Dimethoxy-phenyl)-5,8,9,10-tetrahydro-7H-4b,10,11-
triaza-benzo[b]fluoren-6-one (4n). This compound was
obtained according to above general procedure; ir (potassium
1
bromide): 3226, 3095, 2904, 1654, 1516, 888, 738 cm-1; H nmr
(DMSO-d6): δ 11.08 (s, 1H, NH), 7.35 (t, 2H, J = 7.6 Hz, ArH),
7.06-7.03 (m, 2H, ArH), 6.97 (t, 1H, J = 7.6 Hz, ArH), 6.79-
6.70(m, 2H, ArH), 6.38 (s, 1H, CH), 3.70(s, 3H, OCH3), 3.64(s,
3H, OCH3), 2.69-2.67 (m, 2H, CH2), 2.32-2.20 (m, 2H, CH2),
2.06-1.86 (m, 2H, CH2). Anal calcd. for C22H21N3O3: C, 70.38;
H, 5.64; N, 11.19. Found: C, 70.36; H, 5.65; N, 11.20.
5-(4-Chloro-phenyl)-8, 8-dimethyl-5,8,9,10-tetrahydro-7H-
4b,10,11-triaza-benzo[b]fluoren-6-one (4o). This compound
was obtained according to above general procedure; ir
(potassium bromide): 3232, 3050, 2963, 2866, 1660, 1106, 890,
5-(3,4-Dimethoxy-phenyl)-8,8-dimethyl-5,8,9,10-tetrahydro-
7H-4b,10,11-triaza-benzo[b]fluoren-6-one (4u). This
compound was obtained according to above general procedure;
ir (potassium bromide): 3231, 3048, 2935, 2866, 1665, 1650,
891,759 cm-1; 1H nmr (DMSO-d6): δ 11.04 (s, 1H, NH), 7.36 (d,
2H, J = 8.4 Hz, ArH ), 7.07-6.96 (m, 3H, ArH), 6.79 (s, 2H,
ArH), 6.35 (s, 1H, CH), 3.68 (s, 3H, OCH3), 3.64 (s, 3H, OCH3),
2.67-2.51 (m, 2H, CH2), 2.30 (m, 2H, CH2), 1.07 (s, 3H, CH3),
0.96 (s, 3H, CH3). Anal calcd. for C24H25N3O3: C, 71.44; H, 6.25;
N, 10.41. Found: C, 71.46; H, 6.24; N, 10.42.
1
776 cm-1; H nmr (DMSO-d6): δ 11.19 (s, 1H, NH), 7.39-7.31
(m, 5H, ArH), 7.25 (d, 1H, J = 8.4 Hz, ArH), 7.07 (t, 1H, J = 7.6
Hz, ArH), 6.98 (t, 1H, J = 7.6 Hz, ArH), 6.45 (s, 1H, CH), 2.67-
2.51 (m, 2H, CH2), 2.29-2.04 (m, 2H, CH2), 1.07 (s, 3H, CH3),
0.93 (s, 3H, CH3). Anal calcd. for C22H20ClN3O: C, 69.93; H,
5.33; N, 11.12. Found: C, 69.92; H, 5.33; N, 11.13.
8,8-Dimethyl-5-phenyl-5,8,9,10-tetrahydro-7H-4b,10,11-
triaza-benzo[b]fluoren-6-one (4p). This compound was
obtained according to above general procedure; ir (potassium
5-(3,4-Dichloro-phenyl)-8,8-dimethyl-5,8,9,10-tetrahydro-
7H-4b,10,11-triaza-benzo[b]fluoren-6-one (4v). This
compound was obtained according to above general procedure;
ir (potassium bromide): 3234, 3060, 2962, 1650, 891, 758 cm-1;
1H nmr (DMSO-d6): δ 11.25 (s, 1H, NH), 7.51-7.38 (m, 4H,
ArH), 7.09-6.90 (m, 3H, ArH), 6.67 (s, 1H, CH), 2.62-2.33 (m,
2H, CH2), 2.27-2.02(m, 2H, CH2), 1.07 (s, 3H, CH3), 0.97 (s,
3H, CH3). Anal calcd. for C22H19Cl2N3O: C, 64.09; H, 4.64; N,
10.19. Found: C, 64.11; H, 4.63; N, 10.19.
5-(3-Bromo-phenyl)-8,8-dimethyl-5,8,9,10-tetrahydro-7H-
4b,10,11-triaza-benzo[b]fluoren-6-one (4w). This compound
was obtained according to above general procedure; ir
(potassium bromide): 3222, 3048, 2944, 1650, 887, 743 cm-1; 1H
nmr (DMSO-d6): δ 11.17 (s, 1H, NH), 7.61 (s, 1H, ArH), 7.38 (t,
2H, J = 8.0 Hz, ArH), 7.31-6.98 (m, 3H, ArH), 7.08 (t, 1H, J =
7.6 Hz, ArH), 7.00 (t, 1H, J = 7.6 Hz, ArH), 6.46 (s, 1H, CH),
2.66-2.50 (m, 2H, CH2), 2.29-2.07 (m, 2H, CH2), 1.07(s, 3H,
CH3), 0.94(s, 3H, CH3). Anal calcd. for C22H20BrN3O: C, 62.57;
H, 4.77; N, 9.95. Found: C, 62.55; H, 4.78; N, 9.96.
1
bromide): 3228, 2956, 891, 838, 759 cm-1; H nmr (DMSO-d6):
δ 11.13 (s, 1H, NH), 7.38-7.33 (m, 3H, ArH), 7.28-7.23 (m, 3H,
ArH), 7.18-7.14 (m, 1H, ArH), 7.05 (t, 1H, J = 8.0 Hz, ArH),
6.96 (t, 1H, J = 7.6 Hz, ArH), 6.42 (s, 1H, CH), 2.67-2.50 (m,
2H, CH2), 2.29-2.04 (m, 2H, CH2), 1.06 (s, 3H, CH3), 0.93 (s,
3H, CH3). Anal calcd. for C22H21N3O: C, 76.94; H, 6.16; N,
12.24. Found: C, 76.93; H, 6.15; N, 12.25.
5-(4-Bromo-phenyl)-8,8-dimethyl-5,8,9,10-tetrahydro-7H-
4b,10,11-triaza-benzo[b]fluoren-6-one (4q). This compound
was obtained according to above general procedure; ir
(potassium bromide): 3232, 3048, 2932, 1648, 891, 740 cm-1; 1H
nmr (DMSO-d6): δ 11.17 (s, 1H, NH), 7.47-7.37 (m, 2H, ArH),
7.30-7.24 (m, 4H, ArH), 7.07 (t, 1H, J = 8.0 Hz, ArH), 6.97 (t,
1H, J = 8.0 Hz, ArH), 6.43 (s, 1H, CH), 2.67-2.66 (m, 2H, CH2),
2.28-2.04 (m, 2H, CH2), 1.06 (s, 3H, CH3), 0.93(s, 3H, CH3).
Anal calcd. for C22H20BrN3O: C, 62.57; H, 4.77; N, 9.95. Found:
C, 62.59; H, 4.78; N, 9.96.
5-(2-Chloro-phenyl)-8,8-dimethyl-5,8,9,10-tetrahydro-7H-
4b,10,11-triaza-benzo[b]fluoren-6-one (4r). This compound
was obtained according to above general procedure; ir
(potassium bromide): 3227, 3094, 2953, 1655, 890, 756 cm-1; 1H
nmr (DMSO-d6): δ 11.20 (s, 1H, NH), 7.39-7.09 (m, 6H, ArH),
7.06 (t, 1H, J = 7.6 Hz, ArH), 6.96 (t, 1H, J = 7.2 Hz, ArH), 6.67
(s, 1H, CH), 2.66-2.51 (m, 2H, CH2), 2.27-2.02 (m, 2H, CH2),
1.07 (s, 3H, CH3), 0.97 (s, 3H, CH3). Anal calcd. for
C22H20ClN3O: C, 69.93; H, 5.33; N, 11.12. Found: C, 69.92; H,
5.34; N, 11.10.
5-(4-Fluoro-phenyl)-8,8-dimethyl-5,8,9,10-tetrahydro-7H-
4b,10,11-triaza-benzo[b]fluoren-6-one (4x). This compound
was obtained according to above general procedure; ir
(potassium bromide): 3225, 3041, 2954, 2895, 1645, 846,748
1
cm-1; H nmr (DMSO-d6): δ 11.13 (s, 1H, NH), 7.40-7.36 (m,
3H, ArH), 7.26 (d, 1H, J = 7.6 Hz, ArH), 7.10-7.05 (m, 3H,
ArH), 6.97 (t, 1H, J = 7.6 Hz, ArH), 6.46 (s, 1H, CH), 2.65-2.51
(m, 2H, CH2), 2.29-2.05 (m, 2H, CH2), 1.07(s, 3H, CH3), 0.94(s,
3H, CH3). Anal calcd. for C22H20FN3O: C, 73.11; H, 5.58; N,
11.63. Found: C, 73.09; H, 5.57; N, 11.64.
8,8-Dimethyl-5-p-tolyl-5,8,9,10-tetrahydro-7H-4b,10,11-
triaza-benzo[b]fluoren-6-one (4y). This compound was
obtained according to above general procedure; ir (potassium
5-(4-Methoxy-phenyl)-8,8-dimethyl-5,8,9,10-tetrahydro-
7H-4b,10,11-triaza-benzo[b]fluoren-6-one (4s). This
compound was obtained according to above general procedure;
ir (potassium bromide): 3231, 3099, 2957, 2866, 1645, 838,737
1
bromide): 3232, 3049, 2958, 2895, 1647, 846,737 cm-1; H nmr
(DMSO-d6): δ 11.08 (s, 1H, NH), 7.36 (d, 1H, J = 8.6 Hz, ArH),
7.26-7.20 (m, 3H, ArH), 7.06-7.03 (m, 3H, ArH), 6.95 (t, 1H, J
= 7.6 Hz, ArH), 6.36 (s, 1H, CH), 2.66-2.53 (m, 2H, CH2), 2.28-
1
cm-1; H nmr (DMSO-d6): δ 11.08 (s, 1H, NH), 7.36 (d, 1H, J =
7.6 Hz, ArH), 7.28-7.24 (m, 3H, ArH), 7.04 (t, 1H, J = 7.6 Hz,

416
Q. Shao, S. Tu,C. Li, L. Cao, D. Zhou, Q. Wang, B. Jiang, Y. Zhang, W. Hao
Vol 45
Foundation India: Bangalore, India, 2002. (b) Varma, R. S. Organic
Synthesis using Microwave and Supported Reagents. In Microwaves in
organic Synthesis; Loupy, A., Ed.; Wiley-VCH: Weinheim, 2002; pp
181-218. (c) Larhed, M.; Moberg, C.; Hallberg, A. Acc. Chem. Res.
2002, 35, 717. (d) Varma, R. S. J. Heterocyclic. Chem. 1999, 36, 1565.
(e) Dallinger, D.; Kappe, C. O. Chem. Rev. 2007, 107, 2563.
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2.03 (m, 2H, CH2), 2.10 (s, 3H, CH3), 1.06 (s, 3H, CH3), 0.93 (s,
3H, CH3). Anal calcd. for C23H23N3O: C, 77.28; H, 6.49; N,
11.76. Found: C, 77.27; H, 6.50; N, 11.77.
(E)-N-(4-chlorobenzylidene)-1H-benzo(d)imidazol-2-amine
(Schiffe base 5). In a 10-mL EmrysTM reaction vial, 4-chloro-
benzaldehyde (1 mmol), 2-aminobenzimidazole (1 mmol) and
water (2 mL)were mixed and then capped. After irradiation for
1 min, the reaction mixture was cooled to room temperature.
Then the mixture was filtered to give the crude product, which
was further purified by recrystallization from 95% EtOH. Ir
(potassium bromide): 3245, 3078, 2973, 2764, 1684, 1585,
1389, 1090, 852cm-1; 1H nmr (DMSO-d6): δ 12.74 (s, 1H, NH),
9.47 (s, 1H, CH), 8.11-8.10 (d, 2H, J = 8.0 Hz, ArH), 7.67 (d,
2H, J = 8.0 Hz, ArH), 7.61-7.59 (m, 1H, ArH), 7.46-7.45(m, 1H,
ArH), 7.21-7.19(m, 2H, ArH). .Anal. calcd. for C14H10N3Cl: C,
65.76; H, 3.94; N, 16.43. Found: C, 65.73; H, 3.95; N, 16.42.
Acknowledgement. We thank the National Natural Science
Foundation of China (No. 20672090), the Nature Science
Foundation of the Jiangsu Province (No. BK 2006033) for
financial support, Six Kinds of Professional Elite Foundation of
the Jiangsu Province (No. 06-A-039), and project (No. 07KJ45)
supported by Xuzhou Medical College.
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