Microwave-assisted one-pot synthesis of 3-amino-1-aryl-8-bromo-2,4-dicyano- 9H-fluorenes in water

Article abstract of DOI:10.1080/00397911.2010.517377

A series of novel 3-amino-1-aryl-8-bromo-2,4-dicyano-9H-fluorenes derivatives were prepared using arylaldehyde, 4-bromo-indanone, malononitrile, and sodium hydroxide as the reactants in water via one-pot synthesis under microwave irradiation. A green and

Full text of DOI:10.1080/00397911.2010.517377

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Microwave-Assisted One-Pot Synthesis of
3-Amino-1-aryl-8-bromo-2,4-dicyano-9H-
fluorenes in Water
Yixin Zhou a , Jianqiang Wang a , Renjun Du a , Guohua Zhang a , Wei
Wang a & Cheng Guo a
a College of Sciences , Nanjing University of Technology , Nanjing ,
China
Published online: 27 Jul 2011.
To cite this article: Yixin Zhou , Jianqiang Wang , Renjun Du , Guohua Zhang , Wei Wang & Cheng Guo
(2011) Microwave-Assisted One-Pot Synthesis of 3-Amino-1-aryl-8-bromo-2,4-dicyano-9H-fluorenes
in Water, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 41:21, 3169-3176, DOI: 10.1080/00397911.2010.517377
To link to this article: http://dx.doi.org/10.1080/00397911.2010.517377
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Synthetic Communications1, 41: 3169–3176, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.517377
MICROWAVE-ASSISTED ONE-POT SYNTHESIS
OF 3-AMINO-1-ARYL-8-BROMO-2,4-DICYANO-
9H-FLUORENES IN WATER
Yixin Zhou, Jianqiang Wang, Renjun Du, Guohua Zhang,
Wei Wang, and Cheng Guo
College of Sciences, Nanjing University of Technology, Nanjing, China
GRAPHICAL ABSTRACT
Abstract A series of novel 3-amino-1-aryl-8-bromo -2,4-dicyano-9H-fluorenes derivatives
were prepared using arylaldehyde, 4-bromo-indanone, malononitrile, and sodium hydroxide
as the reactants in water via one-pot synthesis under microwave irradiation. A green and
efficient method was successfully developed via microwave irradiation. The method
possesses several advantages, such as environmental friendliness, shorter reaction time,
and simple workup procedure.
Keywords Fluorene; microwave irradiation; synthesis; water
INTRODUCTION
In recent years, microwave-assisted organic synthesis as a green method has
become an important research field.[1–7] Compared with other expensive toxic
organic solvents, the inexpensive and pollution-free aqueous medium has been
eagerly applied in microwave irradiation.[8–10] Moreover, the water as solvent pro-
vides us with a convenient way to separate the product from the reaction system.
3-Amino-1-aryl-2,4-dicyano-9H-fluorenes are typical acceptor-donor-acceptor
(A-D-A) systems, which have been found exhibit strong fluorescence in previous
studies.[11,12] A-D-A systems comprise one electron donor and two electron acceptors
in the extensive study of photo-induced intramolecular electron transfer,[13,14] which
has potential applications in electron devices such as light-emitting diodes[15,16] and
field-effect transistors.[17] Besides, 9H-fluorene derivatives have a strong inhibitory
effect on cholesterol biosynthesis[18] and anti-inflammatory activity.[19]
Received May 17, 2010.
Address correspondence to Cheng Guo, College of Sciences, Nanjing University of Technology,
Nanjing 210009, China. E-mail: guocheng@njut.edu.cn
3169

3170
Y. ZHOU ET AL.
Scheme 1. Synthesis of 4 in water under MWI.
Many synthetic methods for the preparation of 2,4-dicyano-9H-fluorenes
have been reported.[20–22] However, some methods need longer reaction time, more
complex original materials, organic base catalyst, and organic solvent. Keeping in
view the importance of 3-amino-1-aryl-2,4-dicyano-9H-fluorenes and recent trends
of using of environmentally friendly techniques, a green method to synthesize a
series of new 3-amino-1-aryl-8-bromo-2,4-dicyano-9H-fluorenes 4 in water was
developed under microwave irradiation (MWI) from arylaldehyde 1, 4-bromo-
indan-1-one 2, malononitrile 3, and sodium hydroxide (Scheme 1). To optimize
the reaction condition, a comparison was done between MWI and conventional
heating.
RESULTS AND DISCUSSION
To optimize the reaction conditions, the effects of different reaction time and
MWI power were investigated in the synthesis of 4a. The reactions of benzaldehyde
1a (2 mmol), 4-bromo-indan-1-one 2 (2 mmol), malononitrile 3 (4.5 mmol), and
sodium hydroxide (5 mmol) were carried out in water at 100 ꢀC. The results showed
that the yield of product 4a was improved as the MWI time was increased from 3 to
7 min in an increment of 2 min each time. However, as the reaction time increased
continuously, the yield of the products was decreasing. Therefore, 7 min was chosen
for all the further reactions (Fig. 1).
The MWI power was optimized by carrying out the experiment at 250 to 450 W
in increments of 50 W, and the reaction time and temperature was 7 min and 100 ꢀC
respectively. The results showed that MWI at 400 W gave the best yield (Fig. 2).
Furthermore, we tested the same reaction in different solvents under the
optimized reaction conditions, namely, 100 ꢀC at MWI power of 400 W for 7 min
(Table 1). We found that the reaction carried out in water gave the greatest yield.
Considering the nontoxic and inexpensive character of water, we chose water as
the optimum solvent.
Under these reaction conditions, we synthesized a series of products of
3-amino-1-aryl-8-bromo-2,4-dicyano-9H-fluorenes 4 (Table 2).
We performed the synthesis of 4 under both MWI and classical heating
conditions. Compared with the 6–7 h reaction using conventional heating, little time
was needed under MWI. Moreover, a greater yield was obtained when we performed
the reaction using MWI (Table 3). Therefore, MWI exhibited several advantages
over classical heating.

SYNTHESIS OF 2,4-DICYANO-9H-FLUORENES IN WATER
3171
Figure 1. Effect of MWI time on the yield of 4a.
Figure 2. Effect of MWI power on the yield of 4a.
Table 1. Investigation of solvent in the synthesis of 4a (C6H5)
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
MeOH
EtOH
H2O
6
7
7
7
67.8
56.3
74.4
64.5
EtOH=H2O ¼ 1:1
Note. The product 4a was synthesized under MWI at 100 ꢀC and the MWI
power was 400 W.

3172
Y. ZHOU ET AL.
Table 2. Synthesis of 4 in water under MWI
Compound
Ar
M
Mp (ꢀC)
Yield (%)
4a
4b
4c
4d
4e
4f
C6H5
C21H12BrN3
C22H14BrN3
C19H10BrN3O
C25H14BrN3
C19H10BrN3S
C20H11BrN4
C21H10BrF2N3
C21H11BrFN3
268–270
299–300
234–236
298–300
223–225
301–303
224–226
289–291
74.4
54.4
77.2
69.7
81.6
48.7
89.0
52.1
3-CH3C6H4
2-C4H3O
1-C10H7
2-C4H3S
4-C5H4N
3,4-(F)2C6H3
3-FC6H4
4g
4h
Table 3. Comparison of reaction times and yields for compounds 4 using microwave and classical
methods
Reaction time
Yield (%)
Classical heating
Compound
Microwave (min)
Classical heating (h)
Microwave
4a
4b
4c
4d
4e
4f
7
7
6
7
7
7
6
7
6
74.4
54.4
77.2
69.7
81.6
48.7
89.0
52.1
68.4
45.9
54.0
63.1
74.9
41.5
72.8
46.6
6
6
6
6
6
4g
4h
6.5
6.5
The reaction was assumed to proceed via a mechanism of Knoevenagel
condensation, Michael addition, cyclization, and elimination. Aldehyde 1 and ketone
2 reacted with malononitrile in the presence of a base to give 2-arylidenemalonodini-
triles 5 and 2-(4-bromo-2,3-dihydroinden-1-ylidene)malononitrile 6, and Michael
addition reaction of 6 and 5 afforded intermediate 7, which undergoes intramolecu-
lar cyclization, isomerization, and elimination to finally afford 3-amino-1-aryl-8-
bromo-2,4-dicyano-9H-fluorenes 4 (Scheme 2).
Scheme 2. Mechanisms of the reaction.

SYNTHESIS OF 2,4-DICYANO-9H-FLUORENES IN WATER
3173
Figure 3. Crystal structure of the product 4a.
All the structures of the products were confirmed by means of Fourier trans-
form infrared (FTIR) and1H NMR analysis. Furthermore, the structure of 4a was
established by the x-ray crystallographic analysis (Fig. 3).
In conclusion, we developed a green method for the synthesis of 3-amino-1-
aryl-8-bromo-2,4-dicyano-9H-fluorenes using an inexpensive original material under
MWI and got a series of new products, some of which were never reported in litera-
ture. Above all, the use of water leads to a new and nontoxic method for the organic
reaction.
EXPERIMENTAL
The melting points were determined on an X-4 microscopic melting-point
apparatus and are uncorrected. The reactions were monitored by means of thin-layer
chromatography (TLC). IR spectra were measured on a FIR-360 spectrometer.
1H NMR spectra were measured on a Bruker DRX500 NMR spectrometer using
tetramethylsilane (TMS) as an internal standard and dimethylsulfoxide (DMSO-d6)
as solvent. Elemental analyses were carried out using a Vario EL III analyzer.
Reactions were carried out in a WF-4000 M microwave reaction system.
General Procedure for the Preparation of 3-Amino-1-aryl-8-
bromo-2,4-dicyano-9H-fluorenes (4)
A flask (50 ml) charged with arylaldehyde 1 (2 mmol), 4-bromo-indan-1-one 2
(2 mmol), malononitrile 3 (4.5 mmol), sodium hydroxide (5 mmol), and water (10 ml)
was placed in microwave reaction system, connected with refluxing equipment. The
mixture was irradiated for 6–7 min at 100 ꢀC with the output of 400 W. After
completion of the reaction (monitored by TLC), the mixture was kept at room tem-
perature for several hours, filtered to give precipitation, and washed with ethanol.

3174
Y. ZHOU ET AL.
The crystalline product was obtained from recrystallization with ethanol. All the
1
products were characterized by FTIR and H NMR.
3-Amino-8-bromo-1-phenyl-2,4-dicyano-9H-fluorene (4a)
Yellow crystals; FTIR (KBr): n 3449, 3343, 3237, 2210, 1636, 1559, 1467, 1367,
1305, 1287, 1121, 798, 759, 709, 696. 1H NMR (300 MHz, DMSO-d6): d 3.63 (s, 2H,
CH2), 6.81 (s, 2H, NH2), 7.50–7.58 (m, 6H, ArH), 7.73 (d, 1H, ArH), 8.35 (d, 1H,
ArH). Anal. calcd. for C21H12BrN3: C, 65.30; H, 3.13; N, 10.88. Found: C, 65.48;
H, 3.06; N, 10.81.
3-Amino-8-bromo-1-(3-methylphenyl)-2,4-dicyano-9H-fluorene (4b)
Pale yellow crystals; FTIR (KBr): n 3475, 3351, 3237, 2210, 1635, 1558, 1467,
1387, 1364, 1307, 1287, 1122, 796, 759, 724, 697. 1H NMR (300 MHz, DMSO-d6): d
2.41 (s, 3H, CH3), 3.63 (s, 2H, CH2), 6.80 (s, 2H, NH2), 7.35–7.56 (m, 5H, ArH), 7.74
(d, 1H, ArH), 8.35 (d, 1H, ArH). Anal. calcd. for C22H14BrN3: C, 66.01; H, 3.53; N,
10.50. Found: C, 66.17; H, 3.60; N, 10.30.
3-Amino-8-bromo-1-(Furan-2-yl)-2,4-dicyano-9H-fluorene (4c)
Yellow crystals; FTIR (KBr): n 3444, 3348, 3238, 2208, 1639, 1561, 1547, 1480,
1423, 1384, 1359, 1307, 1126, 1029, 787, 756. 1H NMR (300 MHz, DMSO-d6): d 4.00
(s, 2H, CH2), 6.78 (s, 2H, NH2), 7.38–7.77 (m, 4H, ArH), 8.11 (d, 1H, ArH), 8.33
(d, 1H, ArH). Anal. calcd. for C19H10BrN3O: C, 60.66; H, 2.68; N, 11.17. Found:
C, 60.85; H, 2.62; N, 11.11.
3-Amino-8-bromo-1-(Naphthalene-1-yl)-2,4-dicyano-9H-fluorene (4d)
Yellow crystals; IR (KBr): n 3470, 3412, 3346, 3236, 3082, 2207, 1633, 1555,
1515, 1464, 1406, 1376, 1289, 1126, 792, 759, 708. H NMR (300 MHz, DMSO-d6):
1
d 4.02 (s, 2H, CH2), 6.93 (s, 2H, NH2), 7.48–7.74 (m, 6H, ArH), 7.94–8.14 (m, 3H,
ArH), 8.39 (d, 1H, ArH). Anal. calcd. for C25H14BrN3: C, 68.82; H, 3.23; N, 9.63.
Found: C, 67.00; H, 3.15; N, 9.51.
3-Amino-8-bromo-1-(Thiophen-2-yl)-2,4-dicyano-9H-fluorene (4e)
Yellow crystals; FTIR (KBr): n 3456, 3412, 3357, 3232, 2211, 1631, 1557, 1524,
1386, 1363, 1282, 1123, 1082, 803, 775, 759, 716. 1H NMR (300 MHz, DMSO-d6): d
3.83 (s, 2H, CH2), 6.85 (s, 2H, NH2), 7.31 (t, 1H, ArH), 7.52–7.60 (m, 2H, ArH), 7.77
(d, 1H, ArH), 7.91 (d, 1H, ArH), 8.36 (d, 1H, ArH). Anal. calcd. for C19H10BrN3S:
C, 58.17; H, 2.57; N, 10.71. Found: C, 58.08; H, 2.62; N, 10.75.
3-Amino-8-bromo-1-(Pyridine-4-yl)-2,4-dicyano-9H-fluorene (4f)
Yellow crystals; FTIR (KBr): n 3483, 3388, 3250, 2210, 1662, 1559, 1466, 1409,
1365, 1306, 1283, 1123, 1044, 830, 796, 7757, 693. 1H NMR (300 MHz, DMSO-d6): d

SYNTHESIS OF 2,4-DICYANO-9H-FLUORENES IN WATER
3175
3.67 (s, 2H, CH2), 6.93 (s, 2H, NH2), 7.55 (t, 1H, ArH), 7.65 (d, 2H, ArH), 7.77 (d, 1H,
ArH), 8.37 (d, 1H, ArH), 8.81 (d, 2H, ArH). Anal. calcd. for C20H11BrN4: C, 62.03; H,
2.86; N, 14.47. Found: C, 62.14; H, 2.80; N, 14.38.
3-Amino-8-bromo-1-(3,4-difluorophenyl)-2,4-dicyano-9H-fluorene (4g)
Pale yellow crystals; FTIR (KBr): n 3461, 3414, 3238, 2210, 1707, 1636, 1601,
1518, 1428, 1382, 1306, 1268, 1119, 983, 797, 771, 741. 1H NMR (300 MHz,
DMSO-d6): d 3.67 (s, 2H, CH2), 6.90 (s, 2H, NH2), 7.44–7.98 (m, 5H, ArH), 8.35
(d, 1H, ArH). Anal. calcd. for C21H10BrF2N3: C, 59.74; H, 2.39; N, 9.95. Found:
C, 59.92; H, 2.32; N, 9.87.
3-Amino-8-bromo-1-(3-fluorophenyl)-2,4-dicyano-9H-fluorene (4h)
Pale yellow crystals; FTIR (KBr): n 3458, 3342, 3237, 2208, 1636, 1572, 1468,
1400, 1378, 1308, 1258, 1121, 876, 794, 761, 716, 688. 1H NMR (300 MHz,
DMSO-d6): d 3.66 (s, 2H, CH2), 6.90 (s, 2H, NH2), 7.38–7.45 (m, 2H, ArH), 7.54
(t, 2H, ArH), 7.60–7.68 (m, 1H, ArH), 7.76 (d, 1H, ArH), 8.35 (d, 1H, ArH). Anal.
calcd. for C21H11BrFN3: C, 62.40; H, 2.74; N, 10.39. Found: C, 62.56; H, 2.69; N,
10.33.
X-Ray Structure Determination of 4a
Yellow block crystals, C21H12BrN3, M ¼ 386.25, 0.20ꢁ 0.10ꢁ 0.10mm, monocli-
ꢀ
˚
˚
˚
nic, space group P21=N, a ¼ 10.437(2) A, b ¼ 7.2840(15) A, c ¼ 22.025(4) A, a ¼ 90.00 ,
b ¼ 90.45(3) , c ¼ 90.00 , V ¼ 1674.4(6) A , Z ¼ 4, Dc¼ 1.532 g cmꢂ3. F (000) ¼ 776, m
3
ꢀ
ꢀ
˚
(Mo Ka) ¼ 2.463 mmꢂ1. Intensity data were collected using a Nonius CAD4 diffract-
˚
ometer at 293(2) K, graphite monochromator Mo Ka radiation (k ¼ 0.71073 A), using
w=2q scan mode with 1.85ꢀ < h < 25.26ꢀ. A total of 3219 reflections were collected with
3043 unique ones (Rint ¼ 0.0621), of which 1603 reflections were observed with I > 2r
(I). The final R and wR values were 0.0660 and 0.1185, s ¼ 1.009, (D=r)max ¼ 0.000.
REFERENCES
1. Young, D. D.; Torres-Kolbus, J.; Deiters, A. Microwave-assisted synthesis of unnatural
amino acids. Bioorg. Med. Chem. Lett. 2008, 18, 5478–5480.
2. Lidstro¨m, P.; Tierney, J.; Wathey, B.; Westman, J. Microwave-assisted organic
synthesis—A review. Tetrahedron 2001, 57, 9225–9283.
3. Caddick, S. Microwave-assisted organic reactions. Tetrahedron 1995, 51, 10403–10432.
4. Singh, A. K.; Shukla, S. K.; Ahamad, I.; Quraishi, M. A. Solvent-free microwave-assisted
synthesis of 1H-indole-2,3-dione derivatives. J. Heterocycl. Chem. 2009, 46, 571–574.
5. Shi, F.; Zhou, D.; Tu, S.; Shao, Q.; Li, C.; Cao, L. An efficient microwave-assisted
synthesis of furo-3,4-b 4,7-phenanthroline and indeno-2,1-b4,7-phenanthroline derivatives
in water. J. Heterocycl. Chem. 2008, 45, 1065–1070.
6. Reddy, T. R. K.; Mutter, R.; Heal, W.; Guo, K.; Gillet, V. J.; Pratt, S.; Chen, B. Library
design, synthesis, and screening: Pyridine dicarbonitriles as potential prion disease
therapeutics. J. Med. Chem. 2006, 49, 607–615.

3176
Y. ZHOU ET AL.
7. Paul, S.; Gupta, R.; Loupy, A. Improved synthesis of 2-amino-3-cyanopyridines in solvent
free conditions under microwave irradiation. J. Chem. Res., Sunop. 1998, 6, 330–331.
8. Burkett, B. A.; Ting, S. Z.; Gan, G. C. S.; Chai, C. L. L. Microwave-assisted synthesis of
azetidines in aqueous media. Tetrahedron Lett. 2009, 50, 6590–6592.
9. Jia, R.; Tu, S.; Zhang, Y.; Jiang, B.; Zhang, Y.; Yao, C.; Shi, F. An efficient and greener
approach to the synthesis of 3,5-dicyanopyridin-2 (1H)-one derivatives in aqueous media
under microwave irradiation conditions. J. Heterocycl. Chem. 2007, 44, 1177–1180.
10. Carpita, A.; Ribecai, A. Microwave-assisted synthesis of indole derivatives via cycloi-
somerization of 2-alkynylanilines in water without added catalysts, acids, or bases. Tetra-
hedron Lett. 2009, 50, 6877–6881.
11. Cui, S.-L.; Lin, X.-F.; Wang, Y.-G.. Parallel synthesis of strongly fluorescent polysubsti-
tuted 2,6-dicyanoanilines via microwave-promoted multicomponent reaction. J. Org.
Chem. 2005, 70, 2866–2869.
12. Chen, X.; Zhao, Z.; Liu, Y.; Lu, P.; Wang, Y.-G. Synthesis and properties of 1-(4-
aminophenyl)-2,4-dicyano-3-diethylamino-9,9-diethylfluorenes: Potential fluorescent
material. Chem. Lett. 2008, 37, 570–571.
13. Dumur, F.; Gautier, N.; Gallego-Planas, N.; Sahin, Y.; Levillain, E.; Mercier, N.
Hudhomme, P. Novel fused D-A dyad and A-D-A triad incorporating tetrathiafulvalene
and p-benzoquinone. J. Org. Chem. 2004, 69, 2164–2177.
14. Chen, X.-H.; Zhao, Z.; Liu, Y.; Lu, P.; Wang, Y.-G. Synthesis and properties of
1-(4-aminophenyl)-2,4-dicyano-3-diethylamino-9,9-diethyl-fluorenes: Potential fluor-
escent material. Chem. Lett. 2008, 37, 570–571.
15. Ochi, T.; Yamaguchi, Y.; Kobayashi, S.; Wakamiya, T.; Matsubara, Y.; Yoshida, Z.
Rod-shaped oligophenyleneethynylenes modified by donor and acceptor groups in a block
manner: Synthesis and light-emitting characteristics. Chem. Lett. 2007, 36, 794–795.
16. Kulkarni, A. P.; Kong, X.; Jenekhe, S. A. High-performance organic light-emitting diodes
based on intramolecular charge-transfer emission from donor–acceptor molecules:
Significance of electron–donor strength and molecular geometry. Adv. Funct. Mater.
2006, 16, 1057–1066.
17. Brown, A. R.; Pomp, A.; Hart, C. M.; de Leeuw, D. M. Logic gates made from polymer
transistors and their use in ring oscillators. Science 1995, 270, 972–974.
18. Ishihara, T.; Kakuta, H.; Moritani, H.; Ugawa, T.; Sakamoto, S.; Tsukamoto, S. I.;
Yanagisawa, I. Syntheses and biological evaluation of novel quinuclidine derivatives as
squalene synthase inhibitors. Bioorg. Med. Chem. 2003, 11, 2403–2414.
19. Weitzberg, M.; Burch, R. M. Pharmaceutical compositions and methods for treating
inflammation. WO Patent 9015602, 1990.
20. Wang, X.-S.; Zhang, M.-M.; Li, Q.; Yao, C.-S.; Tu, S.-J. An improved and clean pro-
cedure for the synthesis of one-donor poly-acceptors systems containing 2,6-dicyanoamine
moiety in aqueous media catalyzed by TEBAC in the presence and absence of K2CO3.
Tetrahedron 2007, 24, 5265–5273.
21. Rong, L.; Han, H.; Jiang, H.; Tu, S. Efficient and facile synthesis of 3-amino-1-aryl-
9H-fluorene-2,4-dicarbonitrile under solvent-free conditions. Synth. Commun. 2009, 39,
3493–3499.
22. Wang, X.-S.; Zhang, M.-M.; Li, Q.; Yao, C.-S.; Tu, S.-J. An improved and clean pro-
cedure for the synthesis of one-donor poly-acceptors systems containing 2,6-dicyanoamine
moiety in aqueous media catalyzed by TEBAC in the presence and absence of K2CO3.
Tetrahedron 2007, 63, 5265–5273.