An efficient synthesis of ferrocenyl substituted 3-cyanopyridine derivatives under ultrasound irradiation

Article abstract of DOI:10.1016/j.jorganchem.2005.09.046

An efficient synthesis of 2-alkoxy-4-aryl-6-ferrocenyl-3-cyanopyridines via the condensation of ferrocenyl substituted chalcones with malononitrile in a freshly prepared sodium alkoxide solution under ultrasound irradiation was investigated. Especially noteworthy, the reaction of 1-ferrocenyl-3-(pyridin-2- yl)prop-2-ene-1-one with malononitrile afforded 2-alkoxy-4-pyridyl-6- ferrocenylpyridine, with the loss of CN group on the 3-position of pyridine ring was first observed.

Full text of DOI:10.1016/j.jorganchem.2005.09.046

Journal of Organometallic Chemistry 691 (2006) 1356–1360
www.elsevier.com/locate/jorganchem
An efficient synthesis of ferrocenyl substituted
3-cyanopyridine derivatives under ultrasound irradiation
*
Wei-Juan Zhou, Shun-Jun Ji , Zhi-Liang Shen
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry and Chemical Engineering, Suzhou (Soochow) University,
Suzhou 215123, China
Received 20 June 2005; received in revised form 20 September 2005; accepted 21 September 2005
Available online 27 January 2006
Abstract
An efficient synthesis of 2-alkoxy-4-aryl-6-ferrocenyl-3-cyanopyridines via the condensation of ferrocenyl substituted chalcones with
malononitrile in a freshly prepared sodium alkoxide solution under ultrasound irradiation was investigated. Especially noteworthy, the
reaction of 1-ferrocenyl-3-(pyridin-2-yl)prop-2-ene-1-one with malononitrile afforded 2-alkoxy-4-pyridyl-6-ferrocenylpyridine, with the
loss of CN group on the 3-position of pyridine ring was first observed.
Ó 2005 Elsevier B.V. All rights reserved.
Keywords: Ferrocene; Heterocycle; Cyanopyridine; Ultrasound irradiation
1. Introduction
the synthesis of ferrocene-containing compounds with spe-
cial properties and usefulness [10], herein we wish to report
the synthesis of ferrocenyl substituted 3-cyanopyridine
compounds via the condensation of ferrocenyl substituted
chalcone with malononitrile in a freshly prepared sodium
alkoxide solution.
A survey of the literature shows that various organic
reactions could be accelerated by ultrasonic irradiation
with a higher yield, shorter reaction time and milder condi-
tions [11,12]. Therefore, an ultrasound-assisted method
was applied to the reaction of chalcone 1(a–j) and malon-
onitrile 2 in our research (Schemes 1–3).
Metallocenes are known to exhibit a wide range of bio-
logical activity [1]. Among them, ferrocene has attracted
special attention since it is neutral, chemically stable,
non-toxic and able to cross cell membranes [2]. In fact, it
is now well established that the incorporation of ferrocene
units in organic molecules introduces significant and new
properties in these materials [3]. In addition, it has been
demonstrated that molecules containing cyanopyridine
moiety may be able to work as ligands towards transi-
tion-metal ions [4], new drugs [5], and significant intermedi-
ates for the synthesis of important vitamins [6] such as
nicotinic acids [7] and nicotinamides [8]. To the best of
our knowledge, although the synthesis of 3-cyanopyridine
compounds via the condensation of chalcone with malono-
nitrile has been studied previously [5,9], such kind of reac-
tion with ferrocenyl (Fc) substituent has not been
investigated till now. In continuation of our efforts for
2. Results and discussion
Initial studies were focused on the reaction of ferrocenyl
substituted chalcone 1a with malononitrile 2 in various
freshly prepared sodium alkoxide solutions under ultra-
sound irradiation (Scheme 1).
First, the reaction of 1a with 2 proceeded smoothly to
afford the corresponding product 3, 2-alkoxy-4-(4-meth-
oxyphenyl)-6-ferrocenyl-3-cyanopyridine, in moderate
yields in the presence of different sodium alkoxide solutions
*
Corresponding author. Tel.: +86 512 65880086; fax: +86 512
65880307.
E-mail address: shunjun@suda.edu.cn (S.-J. Ji).
0022-328X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.09.046

W.-J. Zhou et al. / Journal of Organometallic Chemistry 691 (2006) 1356–1360
1357
OMe
irradiation (Scheme 2). And the results were listed in Table
2.
As shown in Table 2, both the phenyl ring substituted
chalcones (entries 1–4, Table 2), and the heterocyclic ring
containing chalcones (entries 5–8, Table 2) reacted effi-
ciently with malononitrile to afford the target products.
In all cases, the reaction proceeded smoothly to give ferr-
ocenyl substituted 3-cyanopyridine derivatives in moderate
to good yields. All the products were satisfactorily charac-
O
CN
OR
CN
CN
RONa/ROH
US
N
Fe
+
OMe
Fe
3(a-d)
1a
2
Scheme 1.
1
terized by their H NMR, IR and HRMS.
Unexpectedly when 1-ferrocenyl-3-(pyridine-2-yl)prop-
2-ene-1-one (1j) was subjected to the same reaction
conditions, the formation of 2-alkoxy-4-pyridyl-6-ferroce-
nylpyridine (4(j–l), Scheme 3) was observed, instead of
the corresponding 3-cyanopyridine product. The structure
of 4k has been determined by its IR, HRMS and 1H
NMR. An additional singlet at 7.57 ppm (Hb) has been
Ar
CN
O
Ar
CN EtONa/EtOH
N
OEt
+
Fe
US
CN
Fe
1
1(b-i)
2
observed in the H NMR spectrum other than the com-
4(b-i)
monly-observed singlet at about 7.00 ppm (Ha). Together
with the disappearance of the strong absorption at about
2220 cmÀ1 that attributed to CN stretching in the IR spec-
trum, and the mass information, we can confirm the struc-
ture of 4k evidently.
Scheme 2.
N
Propelled by these encouraging results, we optimized the
reaction by running in various alcohols as solvents. As
showing the results obtained in entries 1–3 (Table 3), the
reactions proceeded smoothly under ultrasound irradiation
to generate the corresponding de-cyano-ferrocenyl substi-
tuted pyridines with good yields. And the highest yield
was obtained in ethanol (entry 2, Table 3). In addition,
the effect of ultrasonication is clearly manifested in the
de-cyanation reaction, with a significant yield reduction
of 4k (entry 4, Table 3).
O
Hb
Ha
CN
CN
RONa/ROH
US
+
N
OR
N
Fe
Fe
1j
2
(j-l)
4
Scheme 3.
under ultrasonication (entries 1–4, Table 1). Although the
yields were almost the same in different alcoholic solvents,
considering the reaction time and the demand for an innox-
ious and low-cost solvent, ethanol proved to be the best
one among them.
However, when ethyl cyanoacetate was applied to this
reaction instead of malononitrile, several by-products were
obtained other than the usual cyano-ferrocenyl substituted
pyridine and the de-cyano-ferrocenyl substituted pyridine.
Second, we investigated the effect of reaction time on the
yield. The reaction was carried out for a longer duration,
the yield was no significant increasing (entry 5, Table 1).
And also it was found that the reaction without ultrasonic
irradiation for a longer duration, with no compromise in
yield.
3. Conclusion
In conclusion, we have described a mild, efficient and
ultrasound-assisted method for the synthesis of a new series
of ferrocenyl substituted pyridine derivatives which might
be able to work as important intermediates, ligands for
transition-metal ions and potential new drugs. With regard
to the different results obtained for substrate 1j, the further
research is now in progress to explain the phenomena.
With the above observations, the following studies were
chosen to be conducted in EtOH system under ultrasonic
Table 1
The reaction of chalcone 1a with malononitrile 2 in different alcoholic
solventsa
4. Experimental
Entry
Solvent
Time (h)
Product
Yield (%)b
1
2
3
4
5
a
MeOH
n-PrOH
n-BuOH
EtOH
18
10
5
4
8
3a
3c
3d
3b
3b
67
66
67
68
70
Melting points were determined on a XT-5A digital
melting points apparatus and uncorrected. IR Spectra were
obtained on a Nicolet FT-IR500 spectrophotometer using
KBr pellets. Elemental analyses were performed on a
Carlo-Erba 1110 Elemental analysis instrument. 1H
NMR was recorded on Varian Inova 400 MHz NMR spec-
trometer in CDCl3. High resolution mass spectra were
EtOH
Reactions were carried out under ultrasound irradiation unless
otherwise stated.
b
Isolated yields.

1358
W.-J. Zhou et al. / Journal of Organometallic Chemistry 691 (2006) 1356–1360
Table 2
Reactions of various ferrocenyl substituted chalcones with malononitrile in ethanola
Entry
1
Chalcone
O
Product
Time (h)
5
Yield (%)b
66
Fc
1b
CN
O
Fc
N
4b
O
2
3
3
4
64
71
Fc
CN
O
1c
Fc
N
O
4c
O
O
O
O
Fc
1d
CN
O
Fc
N
4d
Cl
O
4
2
73
Fc
Cl
1e
CN
O
Fc
N
4e
S
O
5
6
6
4
68
65
Fc
CN
S
1f
Fc
N
O
4f
Br
Br
O
O
S
Fc
S
1g
CN
O
Fc
Fc
N
N
4g
4h
71
70
7
8
a
5
5
S
Fc
CN
O
S
1h
O
O
Fc
O
1i
CN
O
Fc
N
4i
Reactions were carried out under ultrasound irradiation.
Isolated yields.
b
obtained using GCT-TOF instrument. Ultrasonication was
performed in a KQ-250E ultrasonic cleaner with a fre-
quency of 40 KHz and a normal power of 250 W. Ferroce-
nyl substituted chalcones 1(a–j) were prepared as
previously reported [13]. Other reagents were obtained
from commercial sources and used without purification.
5 mL alcohol), was immersed into the water bath of an
ultrasonic cleaner at 50–60 °C, the reaction progress was
monitored by TLC. At the end of the reaction, removing
the solvent under reduced pressure, then the residue was
purified by column chromatography over a silica gel col-
umn using ethyl acetate–petroleum ether as eluent to give
the products. The reaction time and the yields are listed
in Tables 1–3. The analytical data of new products are as
following:
4.1. General procedure
A mixture of ferrocenyl substituted chalcone 1(a–j)
(0.5 mmol) and malononitrile 2 (0.5 mmol) in a freshly pre-
pared sodium alkoxide solution (1 mmol of sodium in
2-Methoxy-4-(4-methoxy-phenyl)-6-ferrocenyl-nicotino-
nitrile (3a): brown solid; m.p.: 166–167 °C; IR (KBr): m
1
2954, 2220 (CN) cmÀ1; H NMR (400 MHz, CDCl3): d

W.-J. Zhou et al. / Journal of Organometallic Chemistry 691 (2006) 1356–1360
1359
(CN) cmÀ1 1H NMR (400 MHz, CDCl3): d 1.52 (t,
;
Table 3
The reaction of chalcone 1j with malononitrile 2 in various solventsa
J = 6.8 Hz, 3H), 4.09 (s, 5H), 4.50 (s, 2H), 4.58–4.63 (m,
2H), 4.97 (s, 2H), 6.07 (s, 2H), 6.95 (s, 1H), 6.97 (d,
J = 3.2 Hz, 1H), 7.11 (s, 1H), 7.15 (d, J = 8.0 Hz, 1H);
HRMS [Found: m/z, 452.0802 (M+); Calcd. for
C25H20FeN2O3: M, 452.0823].
Entry
Solvent
Time (h)
Product
Yield (%)b
1
2
3
4
a
MeOH
EtOH
n-PrOH
EtOH
18
4
5
4j
81
98
80
49c
4k
4l
8
4k
2-Ethoxy-4-(4-chloro-phenyl)-6-ferrocenyl-nicotinonit-
rile (4e): brown solid; m.p.: 158–159 °C; IR (KBr): m 2971,
Reactions were carried out under ultrasonication unless otherwise
stated.
1
2216 (CN) cmÀ1; H NMR (400 MHz, CDCl3): d 1.44 (t,
b
Isolated yields.
c
J = 6.8 Hz, 3H), 4.01 (s, 5H), 4.43 (s, 2H), 4.50–4.56 (m,
2H), 4.89 (s, 2H), 6.90 (s, 1H), 7.43 (d, J = 8.8 Hz, 2H),
7.50 (d, J = 8.4 Hz, 2H), HRMS [Found: m/z, 442.0530
(M+); Calcd. for C24H1935ClFeN2O: M, 442.0535; Found:
m/z, 444.0490 (M+); Calcd. for C24H1937ClFeN2O: M,
444.0506].
The reaction was performed without ultrasound irradiation (other
conditions were the same as entry 2).
3.89 (s, 3H), 4.09 (s, 5H), 4.14 (s, 3H), 4.50 (s, 2H), 4.98 (s,
2H), 7.04 (s, 1H), 7.06 (d, J = 8.8 Hz, 2H), 7.62 (d,
J = 8.4 Hz, 2H); HRMS [Found: m/z, 424.0880 (M+);
Calcd. for C24H20FeN2O2: M, 424.0874].
2-Ethoxy-4-(2-thienyl)-6-ferrocenyl-nicotinonitrile (4f):
brown solid; m.p.: 131–133 °C; IR (KBr): m 2966, 2218
(CN) cmÀ1 1H NMR (400 MHz, CDCl3): d 1.53 (t,
;
2-Ethoxy-4-(4-methoxy-phenyl)-6-ferrocenyl-nicotinonit-
rile (3b): brown solid; m.p.: 162–163 °C; IR (KBr): m 2960,
J = 5.6 Hz, 3H), 4.08 (s, 5H), 4.50 (s, 2H), 4.57–4.63 (m,
2H), 4.96 (s, 2H), 7.08 (s, 1H), 7.48 (d, J = 2.8 Hz, 1H),
7.51 (d, J = 4.8 Hz, 1H), 7.92 (s, 1H); HRMS [Found: m/
z, 414.0354 (M+); Calcd. for C22H18FeN2OS: M, 414.0489].
2-Ethoxy-4-(4-bromo-2-thienyl)-6-ferrocenyl-nicotinonit-
rile (4g): brown solid; m.p.: 112–113 °C; IR (KBr): m 2973,
2219 (CN) cmÀ1; H NMR (400 MHz, CDCl3): d 1.52 (t,
1
J = 6.8 Hz, 3H), 3.89 (s, 3H), 4.09 (s, 5H), 4.50 (s, 2H),
4.60–4.62 (m, 2H), 4.97 (s, 2H), 7.01 (s, 1H), 7.06 (d,
J = 8.8 Hz, 2H), 7.62 (d, J = 8.8 Hz, 2H); HRMS [Found:
m/z, 438.1041 (M+); Calcd. for C25H22FeN2O2: M,
438.1031].
1
2215 (CN) cmÀ1; H NMR (400 MHz, CDCl3): d 1.52 (t,
2-Propoxy-4-(4-methoxy-phenyl)-6-ferrocenyl-nicotino-
nitrile (3c): brown solid; m.p.: 129–131 °C; IR (KBr): m
J = 7.0 Hz, 3H), 4.10 (s, 5H), 4.53 (s, 2H), 4.58–4.63 (m,
2H), 4.97 (s, 2H), 7.07 (s, 1H), 7.43 (s, 1H), 7.75 (s, 1H);
HRMS [Found: m/z, 491.9568 (M+); Calcd. for
C22H1779BrFeN2OS: M, 491.9594 m/z, 493.9555 (M+);
Calcd. for C22H1781BrFeN2OS: M, 493.9574].
1
2962, 2219 (CN) cmÀ1; H NMR (400 MHz, CDCl3): d
1.13 (t, J = 7.4 Hz, 3H), 1.92–1.94 (m, 2H), 3.89 (s, 3H),
4.09 (s, 5H), 4.48–4.50 (m, 4H), 4.97 (s, 2H), 7.01 (s, 1H),
7.06 (d, J = 8.4 Hz, 2H), 7.62 (d, J = 8.4 Hz, 2H); HRMS
[Found: m/z, 452.1203 (M+); Calcd. for C26H24FeN2O2:
M, 452.1187].
2-Ethoxy-4-(4-methyl-2-thienyl)-6-ferrocenyl-nicotino-
nitrile (4h): brown solid; m.p.: 117–118 °C; IR (KBr): m
1
2976, 2218 (CN) cmÀ1; H NMR (400 MHz, CDCl3): d
2-Butoxy-4-(4-methoxy-phenyl)-6-ferrocenyl-nicotinonit-
rile (3d): brown solid; m.p.: 84–86 °C; IR (KBr): nu 2954,
1.52 (t, J = 7.0 Hz, 3H), 2.34 (s, 3H), 4.09 (s, 5H), 4.50
(s, 2H), 4.58–4.63 (m, 2H), 4.95 (s, 2H), 6.99 (s, 1H), 7.01
(s, 1H), 7.40 (d, J = 6.0 Hz, 1H); HRMS [Found: m/z,
428.0629 (M+); Calcd. for C23H20FeN2OS: M, 428.0646].
2-Ethoxy-4-(furan-2-yl)-6-ferrocenyl-nicotinonitrile (4i):
brown solid; m.p.:115–117 °C; IR (KBr): m 2962, 2217 (CN)
1
2220 (CN) cmÀ1; H NMR (400 MHz, CDCl3): d 1.02 (t,
J = 7.2 Hz, 3H), 1.55 (s, 2H), 1.85–1.88 (m, 2H), 3.77 (s,
3H), 4.07 (s, 5H), 4.47 (s, 2H), 4.53 (t, J = 6.4 Hz, 2H),
4.94 (s, 2H), 6.99 (s, 1H), 7.03 (d, J = 8.8 Hz, 2H), 7.60
(d, J = 8.8 Hz, 2H); HRMS [Found: m/z, 466.1371 (M+);
Calcd. for C27H26FeN2O2: M, 466.1344].
1
cmÀ1; H NMR (400 MHz, CDCl3): d 1.51 (t, J = 7.6 Hz,
3H), 4.10 (s, 5H), 4.51 (s, 2H), 4.57–4.62 (m, 2H), 5.00 (s,
2H), 6.63 (s, 1H), 7.40 (s, 1H), 7.59 (d, J = 3.6 Hz, 1H),
7.64 (s, 1H); HRMS [Found: m/z, 398.0696 (M+); Calcd.
for C22H18FeN2O2: M, 398.0718].
2-Ethoxy-4-(4-methy-phenyl)-6-ferrocenyl-nicotinonitrile
(4b): brown solid; m.p.: 90–92 °C; IR (KBr): m 2963, 2217
(CN) cmÀ1 1H NMR (400 MHz, CDCl3): d 1.54 (t,
;
J = 8.2 Hz, 3H), 2.45 (s, 3H), 4.09 (s, 5H), 4.50 (s, 2H),
4.60–4.61 (d, J = 5.2 Hz, 2H), 4.97 (s, 2H), 7.02 (s, 1H),
7.34 (d, J = 6.4 Hz, 2H), 7.55 (d, J = 6.8 Hz, 2H); HRMS
[Found: m/z, 422.1091 (M+); Calcd. for C25H22FeN2O:
M, 422.1082].
2-Methoxy-4-(2-pyridyl)-6-ferrocenyl-pyridine (4j): yel-
1
low solid; m.p.: 105–106 °C; IR (KBr): m 2940 cmÀ1; H
NMR (400 MHz, CDCl3): d 4.05 (s, 3H), 4.13 (s, 5H),
4.45 (s, 2H), 5.07 (s, 2H), 7.09 (s, 1H), 7.34 (s, 1H),
7.60 (s, 1H), 7.79 (s, 2H), 8.76 (s, 1H); HRMS [Found:
m/z, 370.0768 (M+); Calcd. for C21H18FeN2O: M,
370.0769].
2-Ethoxy-4-phenyl-6-ferrocenyl-nicotinonitrile
(4c):
brown solid; m.p.: 82–83 °C; IR (KBr): m 2976, 2219
1
(CN) cmÀ1; H NMR (400 MHz, CDCl3): d 1.53 (s, 3H),
2-Ethoxy-4-(2-pyridyl)-6-ferrocenyl-pyridine (4k): yel-
low solid; m.p.: 110–111 °C; IR (KBr): m 2971 (aromatic
4.10 (s, 5H), 4.51 (s, 2H), 4.61 (s, 2H), 4.98 (s, 2H), 7.04
(s, 1H), 7.53 (s, 3H), 7.64 (s, 2H); HRMS [Found: m/z,
408.0913 (M+); Calcd. for C24H20FeN2O: M, 408.0925].
2-Ethoxy-4-benzo[1,3]dioxol-6-ferrocenyl-nicotinonitrile
(4d): brown solid; m.p.: 99–100 °C; IR (KBr): m 2986, 2220
CH) cmÀ1 1H NMR (400 MHz, CDCl3): d 1.47 (t,
;
J = 6.8 Hz, 3H), 4.17 (s, 5H), 4.45 (s, 2H), 4.46–4.50 (m,
2H), 5.12 (s, 2H), 7.04 (s, 1H), 7.35 (t, J = 6.0 Hz, 1H),
7.57 (s, 1H), 7.78–7.82 (m, 2H), 8.75 (d, J = 4.4 Hz, 1H);

1360
W.-J. Zhou et al. / Journal of Organometallic Chemistry 691 (2006) 1356–1360
HRMS [Found: m/z, 384.0922 (M+); Calcd. for
C22H20FeN2O: M, 384.0925].
(c) V. Dobaria, J.R. Patel, H.H. Parekh, J. Indian Chem. Soc. 79 (2002)
772;
(d) J.M. Desai, V.H. Shah, Indian J. Chem., Sect. B 42 (2003)
382;
(e) J.M. Desai, V.H. Shah, Indian J. Chem., Sect. B 42 (2003)
2595;
(f) S. Rajvaidya, J. Vasavada, H.H. Parekh, Indian J. Chem., Sect.
B 43 (2004) 906.
2-Propoxy-4-(2-pyridyl)-6-ferrocenyl-pyridine (4l): yel-
low solid; m.p.: 70–71 °C; IR (KBr): m 2955 cmÀ1 1H
;
NMR (400 MHz, CDCl3): d 1.09 (s, 3H), 1.88 (s, 2H),
4.12 (s, 5H), 4.39–4.44 (m, 4H), 5.06 (s, 2H), 7.07 (s, 1H),
7.33 (s, 1H), 7.58 (s, 1H), 7.79 (s, 2H), 8.75 (s, 1H); HRMS
[Found: m/z, 389.1089 (M+); Calcd. for C23H22FeN2O: M,
389.1082].
[6] J.K. Landguist Comprehensive Heterocyclic Chemistry, vol. 1,
Pergamon Press, Oxford, England, 1984, p. 155.
[7] S.M. McElvain, M.A. Goese, J. Am. Chem. Soc. 63 (1941) 2283.
[8] B.F. Duesal, H.L. Friedman, US Patent 2471518, 1949.
[9] (a) D.V. Tyndall, T.A. Nakib, M.J. Meegan, Tetrahedron Lett. 29
(1988) 2703;
Acknowledgements
(b) M.M. Al-Arab, J. Heterocycl. Chem. 26 (1989) 1665.
[10] (a) S.J. Ji, Z.L. Shen, D.G. Gu, S.Y. Wang, J. Organomet. Chem.
689 (2004) 1843;
We thank National Natural Science Foundation of Chi-
na (Nos. 20172039 and 20472062) and Natural Science
Foundation of Jiangsu Province (No. BK2004038) for
financial support.
(b) Z.L. Shen, S.J. Ji, D.G. Gu, J.M. Yang, Chin. Chem. Lett., in
press;
(c) J.M. Yang, S.J. Ji, D.G. Gu, Z.L. Shen, S.Y. Wang, J. Organomet.
Chem. 690 (2005) 2989.
References
[11] For review, see: J.L. Luche, Synthetic Organic Sonochemistry,
Plenum Press, New York, 1998.
[12] For examples, see: (a) J.Y. Winum, M. Kamal, A. Leydet, Tetrahe-
dron Lett. 37 (1996) 1781;
[1] N. Farrell, Transition Metal Complexes as Drugs and Therapeutic
Agents, Kluwer Academic, Dordrecht, Germany, 1989.
[2] K.E. Dombrowski, W. Baldwin, J.E. Sheats, J. Organomet. Chem.
302 (1986) 281.
[3] D. Astruc, Electron Transfer and Radical Processes in Transition-
Metal Chemistry, Verlag Chemie, New York, 1995.
[4] (a) A.D. Allen, C.V. Semoff, Chem. Commun. (1963) 621;
(b) L.A.P. Kane-Maguire, P.S. Sheridan, F. Basolo, R.G. Pearson, J.
Am. Chem. Soc. 90 (1968) 3203;
(b) J.T. Li, W.Z. Yang, S.X. Wang, S.H. Li, T.S. Li, Ultrason.
Sonochem. 9 (2002) 237;
(c) S.X. Wang, J.T. Li, W.Z. Yang, T.S. Li, Ultrason. Sonochem. 9
(2002) 159;
(d) J.T. Li, T.S. Li, L.J. Li, X. Cheng, Ultrason. Sonochem. 6 (1999)
199;
(e) Z. Qin, F. Chen, Y. Xie, Progr. Chem. 10 (1998) 65;
(f) J.T. Li, L.J. Li, T.S. Li, H.Z. Li, I.K. Li, Ultrason. Sonochem. 3
(1996) 141;
(g) J. Jayasree, J.M. Rao, Synth. Commun. 26 (1996) 3717;
(h) S.J. Ji, Z.L. Shen, D.G. Gu, X.Y. Huang, Ultrason. Sonochem.
12 (2005) 161;
(c) W. Hunts, J. Rasser, H. Yersin, J. Lumin. 72 (1997) 677;
(d) A.O. Alyoubi, Spectrochim. Acta, Part A 56 (2000) 2397.
[5] (a) T. Murata, M. Shimada, H. Kadono, S. Sakakibara, T. Yoshino,
T. Masuda, M. Shimazaki, T. Shintani, K. Fuchikami, K.B. Bacon,
K.B. Ziegelbauer, T.B. Lowinger, Bioorg. Med. Chem. Lett. 14
(2004) 4013;
(i) S.J. Ji, S.Y. Wang, Synlett 13 (2003) 2074;
(j) S.Y. Wang, S.J. Ji, T.P. Loh, Synlett 15 (2003) 2377;
(k) S.J. Ji, S.Y. Wang, Ultrason. Sonochem. 12 (2005) 339.
[13] S.J. Ji, Z.L. Shen, S.Y. Wang, Chin. Chem. Lett. 14 (2003) 663.
(b) T. Murata, M. Shimada, S. Sakakibara, T. Yoshino, T. Masuda, T.
Shintani, H. Sato, Y. Koriyama, K. Fukushima, N. Nunami, M.
Yamauchi,K.Fuchikami,H.Komura,A.Watanabe,K.B.Ziegelbauer,
K.B. Bacon, T.B. Lowinger, Bioorg. Med. Chem. Lett. 14 (2004) 4019;