Synthesis of new ferrocene bis thiocarbazones under solvent-free conditions using microwave

Article abstract of DOI:10.3184/174751911X13043447062703

A simple efficient method for the synthesis of new ferrocene bis thiocarbazones via microwave irradiation under solvent-free conditions has been developed. Compared to the conventional method, its major advantages are short reaction times, good conversions and actually accorded the green synthesis technology. The structures of target compounds were confirmed by ¹H NMR, IR, ESI-MS spectra data and elemental analysis. Preliminary bioassay results showed that some of these compounds possess inhibitory effects against S. aureus, S. pyogenes and E. coli bacteria.

Full text of DOI:10.3184/174751911X13043447062703

278 RESEARCH PAPER
MAY, 278–281
JOURNAL OF CHEMICAL RESEARCH 2011
Synthesis of new ferrocene bis thiocarbazones under solvent-free
conditions using microwave
Guohua Li, Zhichuan Shi, Xiaorui Li and Zhigang Zhao*
College of Chemistry and Environmental Protection Engineering, Southwest University for Nationalities, Chengdu 610041, P. R. China
A simple efficient method for the synthesis of new ferrocene bis thiocarbazones via microwave irradiation under
solvent-free conditions has been developed. Compared to the conventional method, its major advantages are
short reaction times, good conversions and actually accorded the green synthesis technology. The structures of
target compounds were confirmed by 1H NMR, IR, ESI-MS spectra data and elemental analysis. Preliminary bioassay
results showed that some of these compounds possess inhibitory effects against S. aureus, S. pyogenes and E. coli
bacteria.
Keywords: ferrocene, bis thiocarbazones, microwave irradiation, solvent-free conditions
Ferrocene derivatives are important compounds that have
attracted attention owing to their remarkable biological,
medical and microbiological properties.1 Incorporation of a
ferrocene fragment into the molecule of an organic compound
often leads to unexpected biological activity, which is due
to their different structure.2–4 For example, ferrocenic pyrrolo
[1, 2-a]quinoxaline derivatives possess antimalarial activity,5
ferrocenyl chalcone derivatives have antitumor activity6 and
other ferrocenyl derivatives are antimycobacterial agents.7
Thiocarbazones are considered to be one of the most
important scaffolds and are embedded in many biologically
activecompounds.8 Ferrocenylmodificationsofthiocarbazones
could lead to significant change in biological activity.9
Environmental concerns have led to the use of
environmentally benign solvents such as water and solvent-
free reactions in green chemical procedures with both the
economic and synthetic advanyages. Microwave-assisted
solvent-free synthesis is an environmentally friendly synthetic
method which is widely used in organic synthesis. It can reduce
reaction times affording cleaner reactions, enhanced
conversions and simplified work-up.10–12 It clearly constitutes
an eco-friendly green approach.13,14
As shown in Table 1, it is obvious that microwave irradia-
tion greatly decreased the reaction time from 360–600 min to
3–5 min. The yields also increased from 55–72% to 86–94%.
Consequently, the use of microwave technology in conjunction
with the use of solvent-free conditions allowed an expeditious
and efficient procedures for their synthesis.
In vitro antibacterial activity
Compounds 4a, 4b, 4e and 4j were evaluated for their in vitro
antibacterial activity against Staphylococcus aureus, Staphylo-
coccus pyogenes and Escherichia coli using an agar dilution
method. The preliminary results seemed promising and these
thiocarbazones showed good inhibitory effect. More research
work is underway.
In conclusion, we have used an inexpensive, nonpoisonous,
and highly effective method for the preparation of ferrocene
bis thiocarbazones. Its major advantages are short reaction
times, good conversions and follow a green synthetic
technology. In addition, these compounds may have good anti-
bacterial activity which needs further research. The importance
of such work lies in the possibility that the new compounds
might be useful in designing more potent antibacterial agents
with therapeutic uses.
We have already synthesised a series of compounds under
solvent-free conditions using microwave methods.15–17 Our
previous work focused on the synthesis of steroidal
thiocarbazones18 and we have now turned our attention toward
ferrocenyl thiocarbazones. We report here the synthsis of novel
ferrocenyl bis thiocarbazones under microwave assisted
solvent-free conditions. The synthetic route is depicted in
Scheme 1.
Experimental
Melting points were determined on a micro-melting point apparatus
and the thermometer was uncorrected. IR spectra were obtained on
1
1700 PerkinElmer FTIR using KBr disks. H NMR spectra were
recorded on a Varian INOVA 400 MHz spectrometer using DMSO-d6
and CDCl3 as solvent and TMS as internal standard. Mass spectra
were determined on FinniganLCQDECA instrument. Elemental analysis
was performed on a Carlo-Erba-1106 auto analyzer. All reactions
were performed in a commercial scientific microwave oven (XH-
100A, 100-1000W, Beijing XiangHu Science and Technology
Development Co. Ltd, Beijing, P.R. China). All the chemicals and
solvents were dried and purified by standard methods.
Results and discussion
The structures of the compounds 4a–j were confirmed by IR,
1
mass, H NMR and elementary analysis. Their mass spectra
showed the expected molecular ions in high intensity. The IR
spectra of these compounds exhibited a characteristic strong
absorption at 3260–3526 cm−1 due to N–H stretching vibration;
The strong bands in the region 2928–3096 cm−1 indicated the
absorption of ferrocenyl C–H; The strong absorption bands
falling within the range of 1520–1615 cm−1 and the range
of 1215–1317 cm−1 were assigned to the C=N and C=S
respectively. In the 1H NMR spectra, the singlet peaks between
δ 11.59 and 12.56 ppm were assigned to the protons in the NH,
and a singlet peaks due to the other NH proton was observed at
10.71–10.97 ppm. In addition, the singlet peaks at 4.17–4.38
ppm, 4.44–4.74 ppm and 4.82–4.99 ppm were characteristic
of ferrocene structures. The singlet peaks between δ 2.28 and
2.43 ppm were assigned to the protons of the CH3 group.
Synthesis of substituted benzaldehyde thiocarbohydrazones 2a–j19
A solution of thiocarbohydrazide (15 mmol) in H2O (50 mL) and
acetic acid (1 mL), was treated with aromatic aldehyde (10 mmol) in
ethanol (40 mL) dropwise over 1 h under reflux. After the addition,
the mixture was refluxed for a further 3 h. Then the precipitate was
collected by filtration and washed with water (3×10 mL). The resulting
solid was recrystallised from ethanol to give the pure product. The
analytical data for 2c, 2f, 2g and 2h are given below. The melting
point of benzaldehyde thiocarbohydrazones 2a–j was shown in
Table 2.
2c: Yellow solid, yield 72%, m.p. 200–201 °C, IR (KBr)(cm−1):
3241, 3174, 2983, 1609, 1580, 1515, 1279, 1158, 1011; 1H NMR (400
MHz, DMSO-d6) δ: 11.34 (s, 1H, NH), 9.72 (s, 1H, NH), 9.48 (s, 1H,
OH), 7.92 (s, 1H, =CH), 7.24–7.16 (m, 3H, ArH), 6.79 (d, 1H, J = 7.6
Hz, ArH), 4.85 (s, 2H, NH2); ESI-MS m/z (%): 421 ([2M+1]+, 100).
Ana1. Calcd for C8H10N4OS: C, 45.70; H, 4.79; N, 26.65. Found:
C, 45.57; H, 4.82; N, 26.69%.
* Correspondent. E-mail: zzg63129@yahoo.com.cn

JOURNAL OF CHEMICAL RESEARCH 2011 279
Scheme 1 The synthetic route of the bis thiocarbazones 4a–j.
Table 1 Synthetic comparison of compounds 4a–j between
solvent-free conditions under microwave irradiation and
conventional heating
=CH), 7.89 (d, 2H, J = 8.4 Hz, ArH), 7.45 (d, 2H, J = 8.4 Hz, ArH),
4.88 (s, 2H, NH2); ESI-MS m/z (%): 269 ([M+39]+, 100). Ana1. Calcd
for C8H9ClN4S: C, 42.01; H, 3.97; N, 24.50. Found: C, 41.94; H, 3.92;
N, 24.40%.
a
Compd Conventional method
Microwave method tC/tMW
2g: White solid, yield 74%, m.p. 208–209 °C, IR (KBr)(cm−1):
3300, 3151, 2976, 1598, 1504, 1268, 1205, 1074; 1H NMR (400 MHz,
DMSO-d6) δ: 11.46 (s, 1H, NH), 9.90 (s, 1H, NH), 7.99 (s, 1H, =CH),
7.94–7.91 (m, 2H, ArH), 7.24 (t, 2H, J = 8.8 Hz, ArH), 4.88 (s, 2H,
NH2); ESI-MS m/z (%): 235 ([M+23]+, 100). Ana1. Calcd for
C8H9FN4S: C, 45.27; H, 4.27; N, 26.40. Found: C, 45.17; H, 4.23;
N, 26.42%.
t/min
Yield/%
t/min
Yield/%
4a
4b
4c
4d
4e
4f
360
420
420
420
480
540
360
420
600
600
70
63
57
67
70
72
70
68
55
66
3
4
5
4
4
4
3
5
5
5
92
89
91
86
93
87
90
94
88
90
120
105
84
100
120
135
120
84
2h: Yellow solid, yield 80%, m.p. 211–212 °C, IR (KBr)(cm−1):
3253, 3168, 2997, 1619, 1589, 1530, 1484, 1244, 1067; 1H NMR (400
MHz, DMSO-d6) δ: 11.46 (s, 1H, NH), 9.90 (s, 1H, NH), 7.97 (s, 1H,
=CH), 7.81 (d, 2H, J = 8.4 Hz, ArH), 7.58 (d, 2H, J = 8.4 Hz, ArH),
4.87 (s, 2H, NH2); ESI-MS m/z (%): 545 ([2M+1]+, 100). Ana1. Calcd
for C8H9BrN4S: C, 35.18; H, 3.32; N, 20.51. Found: C, 35.09; H, 3.36;
N, 20.47%.
4g
4h
4i
120
120
4j
tC, Conventional method time; tMW, microwave method time.
Preparation of acetylferrocene (3)22
To a solution of ferrocene (2.23 g, 12 mmol) in dried CH2Cl2 (15 mL)
at 0 °C, a solution of acetylchloride (0.75 mL, 10 mmol) and
aluminium chloride (1.60 g, 10 mmol) in dried CH2Cl2 (15 mL) was
2f: Yellow solid, yield 78%, m.p. 210–211 °C, IR (KBr)(cm−1):
3311, 3273, 3153, 2968, 1597, 1543, 1505, 1249, 1079; 1H NMR (400
MHz, DMSO-d6) δ: 11.50 (s, 1H, NH), 9.93 (s, 1H, NH), 7.98 (s, 1H,

280 JOURNAL OF CHEMICAL RESEARCH 2011
Table 2 The melting points of substituted benzaldehyde
thiocarbohydrazones 2a–j
(s, 1H, OH), 8.09 (s, 1H, =CH), 7.66 (s, 2H, ArH), 6.87 (d, 2H, J = 7.6
Hz, ArH), 4.99 (s, 2H, H-2 H-5, Fc), 4.74 (s, 2H, H-3 H-4, Fc), 4.39
(s, 5H, Fc-unsubst. ring), 2.41 (s, 3H, CH3); ESI-MS m/z (%): 863
([2M+23]+, 100). Ana1. Calcd for C20H20FeN4OS: C, 57.15; H, 4.80;
N, 13.33. Found: C, 57.16; H, 4.81; N, 13.31%.
Entry
Compd
Formula
M.p./°C
Lit M.p./°C
1
2
2a
2b
2c
2d
2e
2f
C8H10N4S
196–197
217–218
200–201
210–211
209–210
210–211
208–209
211–212
206–207
199–200
19819
21819
—
4e: Pinky solid, yield 93%, m.p. 175–176 °C; IR (KBr)(cm−1):
3424, 3085, 2965, 1603, 1438, 1223, 1108, 1066, 834, 484; 1H NMR
(400 MHz, DMSO-d6) δ: 12.20 (s, 1H, NH); 10.75 (s, 1H, NH), 8.57
(s, 1H, =CH), 8.25–8.05 (m, 1H, ArH), 7.55 (t, 1H, J = 4.0 Hz, ArH),
7.47 (t, 2H, J = 3.6 Hz, ArH), 4.90 (s, 2H, H-2 H-5, Fc), 4.62 (s, 2H,
H-3 H-4, Fc), 4.33 (s, 5H, Fc-unsubst. ring), 2.34 (s, 3H, CH3); ESI-
MS m/z (%): 461 ([M+23]+, 100). Ana1. Calcd for C20H19ClFeN4S:
C, 54.75; H, 4.36; N, 12.77. Found: C, 54.73; H, 4.35; N, 12.79%.
4f: Pinky solid, yield 87%, m.p. 173–174 °C; IR (KBr)(cm−1):
3446, 3084, 2968, 1601, 1488, 1317, 1176, 1087, 825, 513; 1H NMR
(400 MHz, DMSO-d6) δ: 12.10 (s, 1H, NH); 10.87 (s, 1H, NH), 8.16
(s, 1H, =CH), 7.84 (s, 2H, ArH), 7.59–7.53 (m, 2H, ArH), 4.90 (s, 2H,
H-2 H-5, Fc), 4.64 (s, 2H, H-3 H-4, Fc), 4.33 (s, 5H, Fc-unsubst. ring),
2.35 (s, 3H, CH3); ESI-MS m/z (%): 461 ([M+23]+, 100). Ana1. Calcd
for C20H19ClFeN4S: C, 54.75; H, 4.36; N, 12.77. Found: C, 54.78;
H, 4.37; N, 12.70%.
C8H10N4OS
C8H10N4OS
3
4
C8H N4OS
21019
21019
—
10
5
C8H ClN4S
9
6
C8H9ClN4S
C8H9FN4S
C8H9BrN4S
C8H9N5O2S
C9H12N4OS
7
2g
2h
2i
—
—
8
9
204–20620
198–20021
10
2j
added dropwise. After being stirred at room temperature for 8 h, water
was added. The organic layer was separated and washed by water and
brine. The resulting solution was dried over anhydrous MgSO4 and
evaporated to dryness under vacuum. The crude product was purified
by chromatography on silica gel usingV(CH3COOC2H5):V(Petroleum
ether) =1: 10 to give an orange solid, yield 89%, m.p. 85–86 °C (lit.23
m.p. 87 °C); IR (KBr)(cm−1): 3436, 3090, 2924, 1657, 1454, 1107,
824, 496; 1H NMR (400 MHz, CDCl3) δ: 4.78 (t, 2H, J = 1.8 Hz, H-2
H-5, Fc), 4.52 (t, 2H, J = 1.8 Hz, H-3 H-4, Fc), 4.21 (s, 5H, Fc-unsubst.
ring), 2.40 (s, 3H, CH3); ESI-MS m/z (%): 229 ( [M+1]+, 100).
4g: Purple solid, yield 90%, m.p. 153–154 °C; IR (KBr)(cm−1):
3449, 3082, 2966, 1603, 1442, 1234, 1108, 1079, 834, 483; 1H NMR
(400 MHz, DMSO-d6) δ: 12.11 (s, 1H, NH); 10.89 (s, 1H, NH), 8.17
(s, 1H, =CH), 7.89 (s, 2H, ArH), 7.34 (t, 2H, J = 8.8 Hz, ArH), 4.91 (s,
2H, H-2 H-5, Fc), 4.67 (s, 2H, H-3 H-4, Fc), 4.35 (s, 5H, Fc-unsubst.
ring), 2.36 (s, 3H, CH3); ESI-MS m/z (%): 867 ([2M+23]+, 100). Ana1.
Calcd for C20H19FFeN4S: C, 56.88; H, 4.53; N, 13.27. Found: C, 56.80;
H, 4.54; N, 13.29%.
Preparation of bis thiocarbazones 4a–j
4h: Purple solid, yield 94%, m.p. 151–152 °C; IR (KBr)(cm−1):
3440, 3081, 2973, 1609, 1440, 1261, 1107, 1068, 823, 491; 1H NMR
(400 MHz, DMSO-d6) δ: 12.15 (s, 1H, NH); 10.94 (s, 1H, NH), 8.13
(s, 1H, =CH), 7.84–7.78 (m, 2H, ArH), 7.69 (d, 2H, J = 6.4 Hz, ArH),
4.93 (s, 2H, H-2 H-5, Fc), 4.68 (s, 2H, H-3 H-4, Fc), 4.36 (s, 5H,
Fc-unsubst. ring), 2.37 (s, 3H, CH3); ESI-MS m/z (%): 989 ([2M+23]+,
100). Ana1. Calcd for C20H19BrFeN4S: C, 49.71; H, 3.96; N, 11.59.
Found: C, 49.75; H, 3.95; N, 11.57%.
Conventional method: Acetylferrocene (3) (0.114 g, 0.5 mmol) and
the substituted benzaldehyde thiocarbohydrazones (2a–j) (0.45 mmol)
were dissolved in ethanol (10 mL). After completely dissolving,
two drops of hydrochloric acid were added. The mixture was stirred
for 6–10 h at room temperature. The crude products were filtered and
recrystallised from DMSO and H2O to afford the pure products in
55–72% yields.
Microwave irradiation method: Acetylferrocene (3) (0.114 g,
0.5 mmol), substituted benzaldehyde thiocarbohydrazones (2a–j)
(0.45 mmol) and neutral aluminium oxide (0.3 g) were put in a porce-
lain mortar, then concentrated hydrochloric acid (two drops) was
added. After grinding, the mixture was put in a round-bottom flask
(25 mL) and then placed in the microwave oven. Then it was irradiated
for 3–5 min at 250–500W. The reaction mixture was cooled to room
temperature and dissolved in DMSO and filtered. Water was added
to the filtrate and the product was precipitated. The product was
recrystallised from DMSO and H2O in 86–94% yields. The physical
and spectroscopic data of the compounds 4a–j are as follows.
4a: Pink solid, yield 92%, m.p. 174–175 °C; IR (KBr)(cm−1): 3440,
4i: Brown solid, yield 88%, m.p. 154–155 °C; IR (KBr)(cm−1):
3441, 3082, 2963, 1610, 1439, 1243, 1088, 1005, 846, 500; 1H NMR
(400 MHz, DMSO-d6) δ: 12.56 (s, 1H, NH); 10.71 (s, 1H, NH), 8.69
(s, 1H, =CH), 8.30–8.22 (m, 2H, ArH), 8.08–8.01 (m, 2H, ArH), 4.82
(s, 2H, H-2 H-5, Fc), 4.47 (s, 2H, H-3 H-4, Fc), 4.20 (s, 5H,
Fc-unsubst. ring), 2.32 (s, 3H, CH3); ESI-MS m/z (%): 450 ([M+1]+,
100). Ana1. Calcd for C20H19FeN5O2S: C, 53.46; H, 4.26; N, 15.59.
Found: C, 53.41; H, 4.25; N, 15.60%.
4j: Pinky solid, yield 90%, m.p. 154–155 °C; IR (KBr)(cm−1):
3441, 3090, 2961, 1606, 1441, 1253, 1109, 1031, 831, 483; 1H NMR
(400 MHz, DMSO-d6) δ: 11.92 (s, 1H, NH); 10.71 (s, 1H, NH), 8.49
(s, 1H, =CH), 8.12 (s, 2H, ArH), 7.05 (d, 2H, J = 8.4 Hz, ArH), 4.87
(s, 2H, H-2 H-5, Fc), 4.59 (s, 2H, H-3 H-4, Fc), 4.31 (s, 5H,
Fc-unsubst. ring), 3.82 (s, 3H, -OCH3), 2.33 (s, 3H, CH3); ESI-MS
m/z (%): 891 ([2M+23]+, 100). Ana1. Calcd for C21H22FeN4OS:
C, 58.07; H, 5.11; N, 12.90. Found: C, 58.11; H, 5.10; N, 12.92%.
1
3081, 2973, 1609, 1440, 1261, 1107, 1068, 823, 491; H NMR (400
MHz, DMSO-d6) δ: 12.06 (s, 1H, NH), 10.81 (s, 1H, NH), 8.88 (s, 1H,
=CH), 7.81 (s, 2H, ArH), 7.48 (d, 3H, J = 6.4 Hz, ArH), 4.90 (s, 2H,
H-2 H-5, Fc), 4.62 (s, 2H, H-3 H-4, Fc), 4.32 (s, 5H, Fc-unsubst. ring),
2.43 (s, 3H, CH3); ESI-MS m/z (%): 405 ([M+1]+, 100). Ana1. Calcd
for C20H20FeN4S: C, 59.41; H, 4.99; N, 13.86. Found: C, 59.37;
H, 4.98; N, 13.83%.
4b: Yellow solid, yield 89%, m.p. 204–205 °C; IR (KBr)(cm−1):
3445, 3260, 2928, 1615, 1520, 1269, 1154, 1040, 838, 486; 1H NMR
(400 MHz, DMSO-d6) δ: 11.68 (s, 1H, OH), 11.59 (s, 1H, NH); 10.75
(s, 1H, NH), 8.76 (s, 1H, =CH), 7.39 (s, 1H, ArH), 7.33 (t, 1H, J = 7.8
Hz, ArH), 6.94 (t, 2H, J = 4.2 Hz, ArH), 4.91 (s, 2H, H-2 H-5, Fc),
4.44 (s, 2H, H-3 H-4, Fc), 4.23 (s, 5H, Fc-unsubst. ring), 2.28 (s, 3H,
CH3); ESI-MS m/z (%): 421 ([M+1]+, 100). Ana1. Calcd for
C20H20FeN4OS: C, 57.15; H, 4.80; N, 13.33. Found: C, 57.17; H, 4.81;
N, 13.30%.
We thank the Science and Technology Bureau of Si Chuan
Province (Project No.2011JY0035) for the financial support.
Received 18 March 2011; accepted 2 April 2011
Paper 1100621 doi: 10.3184/174751911X13043447062703
Published online: 1 June 2011
References
4c: Purple solid, yield 91%, m.p. 178–179 °C; IR (KBr)(cm−1):
3428, 3095, 2925, 1588, 1475, 1215, 1109, 1047, 833, 490; 1H NMR
(400 MHz, DMSO-d6) δ: 12.02 (s, 1H, NH); 10.77 (s, 1H, NH), 9.66
(s, 1H, OH), 8.48 (s, 1H, =CH), 7.28–7.20 (m, 3H, ArH), 6.86 (s, 1H,
ArH), 4.83 (s, 2H, H-2 H-5, Fc), 4.64 (s, 2H, H-3 H-4, Fc), 4.33 (s,
5H, Fc-unsubst. ring), 2.35 (s, 3H, CH3); ESI-MS m/z (%): 863
([2M+23]+, 100). Ana1. Calcd for C20H20FeN4OS: C, 57.15; H, 4.80;
N, 13.33. Found: C, 57.13; H, 4.79; N, 13.35%.
1
2
D.R. van Staveren and N. Metzler-Nolte, Chem. Rev., 2004, 104, 5931.
P.N. Kelly, A. Prêtre, S. Devoy, I.O. Rielly, R. Devery, A. Goel, J.F.
Gallagher, A.J. Lough and P.T.M. Kenny, J. Org. Chem., 2007, 69, 1327.
A.J. Corry, A. Goel, S.R. Alley, P.N. Kelly, D.O. Sullivan, D. Savage and
P.T.M. Kenny, J. Org. Chem., 2007, 69, 1405.
A. Vessières, C. Corbet, J.M. Heldt, N. Lories, N. Jouy, I. Laïos,
G. Leclercq, G. Jaouen and R-A. Toillon, J. Inorg. Biochem., 2010, 104,
503.
3
4
5
6
J. Guillon, S. Moreau, E. Mouray, V. Sinou, I. Forfar, S.B. Fabre, V. Desplat,
D. Parzy, C. Jarry and P. Grellier, Bioorg. Med. Chem., 2008, 16, 9133.
Z. Ratkovic, Z.D. Juranic, T. Stanojkovic, D. Manojlovic, R.D. Vukicevic,
N. Radulovic and M.D. Joksovic, Bioorg. Chem., 2010, 38, 26.
4d: Purple solid, yield 86%, m.p. 160–161 °C; IR (KBr)(cm−1):
3526, 3096, 2970, 1610, 1448, 1270, 1105, 1070, 830, 491; 1H NMR
(400 MHz, DMSO-d6) δ: 12.01 (s, 1H, NH); 10.85 (s, 1H, NH), 10.32

JOURNAL OF CHEMICAL RESEARCH 2011 281
7
8
9
G.M. Maguene, J. Jakhlal, M. Ladyman, A. Vallin, D.A. Ralambomanana,
T. Bousquet, J. Maugein, J. Lebibi and L. Pélinski, Eur. J. Med. Chem.,
2011, 46, 31.
H. Huang, Q. Chen, X. Ku, L.H. Meng, L.P. Lin, X. Wang, C.H. Zhu,
Y. Wang, Z. Chen, M. Li, H.L. Jiang, K.X. Chen, J. Ding and H. Liu,
J. Med. Chem., 2010, 53, 3048.
15 Z.G. Zhao, X.L. Liu, Y. Chen and Z.C. Shi., J. Chem. Res., 2010, 34, 481.
16 L.L. Liu, J. Yang, Z.G. Zhao, P.Y. Shi and X.L. Liu, J. Chem. Res., 2010,
34, 57.
17 J. Yang, Y.Y. Cheng, Z.C. Shi and Z.G. Zhao, J. Chem. Res., 2010, 34,
680.
18 Z.G. Zhao, X.L. Liu, L.L. Liu and G.H. Li, J. Chem. Res., 2010, 34, 455.
19 V.V. Dabhlkar and T.D. Ravi, Indian. J. Chem., 2010, 49B, 593.
20 F. Han, Y.H. Bao, Z.G. Yang, T.M. Fyles, J.Z. Zhao, X.J. Peng, J.L. Fan,
Y.K. Wu and S.G. Sun, Chem. Eur. J., 2007, 13, 2880.
21 Z. Li, X. Feng and Y.L. Zhao, J. Heterocyclic Chem., 2008, 45, 1489.
22 J.X. Fang, Z. Jin, Z.M. Li and W. Liu, Appl. Organometal. Chem., 2003,
17, 145.
S. Yadav and R.V. Singh, Spectrochimica Acta Part A, 2011, 78, 298.
10 A. Aupoix, B. Pégot and G.V. Thanh, Tetrahedron, 2010, 66, 1352.
11 B. Krishnakumar, R. Velmurugan and M. Swaminathan, Catal. Commun.,
2011, 12, 375.
12 T.K.T. Truong and G.V. Thanh, Tetrahedron, 2010, 66, 5277.
13 V. Polshettiwar and R.S. Varma, Acc. Chem. Rev., 2008, 41, 629.
14 C.O. Kappe, Angew. Chem. Int. Ed., 2004, 43, 6250.
23 R. Wang, X. Hong and Z.X. Shan, Tetrahedron Lett., 2008, 49, 636.

Copyright of Journal of Chemical Research is the property of Science Reviews 2000 Ltd. and its content may
not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written
permission. However, users may print, download, or email articles for individual use.