Synthesis of new deoxycholic acid bis thiocarbazones under solvent-free conditions using microwave irradiation

Article abstract of DOI:10.3184/174751911X12995267948561

A simple method for the synthesis of new deoxycholic acid bis thiocarbazones under solvent-free conditions using microwave irradiation has been developed. Its main advantages are short reaction times, good conversions and the environmentally friendly nature of the process. Their structures were characterised by ¹H NMR, IR, ESI-MS spectra and elemental analysis. The preliminary results indicate that some of these compounds possess inhibitory effects against Escherichia coli.

Full text of DOI:10.3184/174751911X12995267948561

198 RESEARCH PAPER
APRIL, 198–201
JOURNAL OF CHEMICAL RESEARCH 2011
Synthesis of new deoxycholic acid bis thiocarbazones under solvent-free
conditions using microwave irradiation
Zhichuan Shi, Zhigang Zhao*, Xingli Liu and Lili Wu
College of Chemistry and Environmental Protection Engineering, Southwest University for Nationalities, Chengdu 610041, P. R. China
A simple method for the synthesis of new deoxycholic acid bis thiocarbazones under solvent-free conditions using
microwave irradiation has been developed. Its main advantages are short reaction times, good conversions and the
environmentally friendly nature of the process. Their structures were characterised by 1H NMR, IR, ESI-MS spectra
and elemental analysis. The preliminary results indicate that some of these compounds possess inhibitory effects
against Escherichia coli.
Keywords: bis thiocarbazones, microwave irradiation, solvent-free condition, deoxycholic acid
Thiosemicarbazones have received considerable attention
because of their biological activity and industrial application
especially those which contain Schiff bases structure.1 The
biological activity of thiosemicarbazones was exploited in
the 1960s using N-methylisatin-β-thiosemicarbazone, which
was effective as prophylactic agent against smallpox2,3 and
vaccinia.4 3-Aminopyridine-2-carboxaldehyde thiosemicarba-
zone is now being evaluated in clinical trials against several
malignancies.5 Currently, derivatives of thiosemicarbazones
and their metal complexes have been reported as antibacterial,
antitumor, antiviral and antimalarial agent.6–8 In addition,
steroidal thiosemicarbazone Schiff bases derivatives have
attracted considerable interest because they exhibit a wide
variety of biological activities. Steroidal Schiff bases have
a good inhibitory effect9–12 in vitro against Staphylococcus
aureus, Staphylococcus pyogenes, Salmonella typhimurium
and Escherichia coli.
With increasing public concern over environmental degra-
dation, the use of environmentally benign solvents like water
and solvent-free reactions represent important green proce-
dures from both the economic and synthetic point of view.
Microwave-assisted organic synthesis has proven to be a
valuable tool for reducing reaction times, giving cleaner
reactions, improvingyields, simplifyingwork-upanddesigning
energy-saving protocols.13 The development of “green chemis-
try”, has now shifted to less cumbersome microwave solvent-
free methods, which gives facile reactions that provide high
yields of pure products, thus elimininating or minimising the
use of organic solvents.14,15
δ 11.43 and 11.86 ppm can be assigned to the protons of the
NH. A singlet due to the other NH proton was observed at
10.41–10.84 ppm. In addition, the singlets at 0.99–1.00 ppm,
1.03–1.04 ppm and the doublet at 0.77 ppm were the
characteristic of steroidal structure. The singlet at 3.58 ppm
assigned to the protons of the COOCH3.
In searching for the best conditions, we also carried out a
series of experiments, to optimise the microwave irradiation
power, time and support. We used the synthesis of 5a for
example and we found that the highest yield was obtained
when the time was 4.5 min at 450 W and using neutral
aluminum oxide as the solid support.
As shown in Table 1, we carried out a comparison of
the synthesis of 5a–j between microwave irradiation in the
solvent-free conditions and conventional heating. It was easy
to show that microwave irradiation greatly decreased the reac-
tion time from 360–540 min to 4.0–6.5 min. Furthermore,
the yields increased from 49–67% to 87–92%. Consequently,
the use of microwave technology in conjunction with the use
of solvent-free conditions allows expeditious and efficient
procedures in organic synthesis.
The in vitro antibacterial activities of compounds 5a, 5b
and 5e were examined using cultures of S. aureus, S. pyogenes
and E. coli. Amoxicillin (30 µg) was used as the standard drug.
The MIC was evaluated by the macro-dilution test using stan-
dard inoculums of 10−5 CFU mL−1. Serial dilutions of the test
compounds, previously dissolved in DMSO were prepared
to give final concentrations of 512, 256, 128, 64, 32, 16, 8, 4,
2 and 1 µg mL−1. To each tube was added 100 µL of 24 h old
inoculums. The MIC which inhibits the visible growth after
18 h, was determined visually after incubation for 18 h, at
37°C. The result is presented in Table 2. These compounds
have good inhibitory activity against E. coli. Further
antibacterial activities are under study.
Our research group has been working on microwave
solvent-free synthesis.16–18 As far as we know, no one has
examined the microwave solvent-free synthesis of deoxycholic
acid bis thiocarbazones. We now report good yields in the
synthesis of new deoxycholic acid bis thiocarbazones under
microwave assisted solvent-free conditions using neutral
aluminum oxide as a mineral support. The synthetic route is
depicted in Scheme 1.
In conclusion, we have developed a rapid and efficient eco-
friendly method for the preparation of bisthiocarbazones. The
reaction was conducted in the presence of neutral aluminum
oxide, without using solvent, and assisted by microwave
irradiation. The salient features of this method include the
simple reaction set-ups, high yields of products, and short
reaction time. The importance of such work lies in the
possibility that the new compounds might be more helpful in
designing more potent antibacterial agents for therapeutic
use.
Results and discussion
The structures of all the compounds 5a–j were confirmed by
IR, Mass, 1H NMR and elementary analysis. Their mass spec-
tra showed the expected molecular peaks in high intensity. The
IR spectra of these compounds exhibited a characteristic strong
absorption at 3141–3453 cm−1 due to N–H stretching vibration;
The strong bands in the region 1691–1740 cm−1 indicated the
absorption of C=O groups. Strong absorption bands falling
within the range of 1517–1635 cm−1 and the range of 1213–
1274 cm−1 were assigned to the C=N and C=S groups
Experimental
Melting points were determined on a micro-melting point apparatus
and the thermometer was uncorrected. IR spectra were obtained
1
on 1700 PerkinElmer FTIR using KBr disks. H NMR spectra were
1
respectively. In the H NMR spectra, the singlet between
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
* Correspondent. E-mail: zzg63129@yahoo.com.cn

JOURNAL OF CHEMICAL RESEARCH 2011 199
Scheme 1 The synthetic route of the bis thiocarbazones 5a–j.
Table 1 Synthetic comparison of bis thiocarbazones 5a–j
between solvent-free conditions under microwave irradiation
and conventional heating
Table 2 MIC (µg mL−1) of bis thiocarbazones and positive
amoxicillin control
Compd
S. aureus
S. pyogenes
E. coli
a
Compd Conventional method Microwave method tC/tMW
5a
128
64
256
64
128
32
64
32
32
32
5b
t/min
Yield/%
t/min
Yield/%
5e
64
5a
5b
5c
5d
5e
5f
360
480
420
420
540
480
540
420
540
480
62
58
67
49
57
52
60
54
50
49
4.5
6.0
4.0
4.5
6.5
6.0
5.5
4.5
6.0
5.0
89
91
87
88
92
90
89
88
92
90
80
80
Amoxicillin
32
105
93
were performed in a commercial microwave reaction (XH-100A,
100-1000W, Beijing XiangHu Science and Technology Development
Co. Ltd, Beijing, P.R. China). All the solvents were purified before
use. Compound 3 was prepared by a known procedure.19
83
80
5g
5h
5i
98
93
190
96
Preparation of substituted benzaldehyde thiocarbohydrazones 2a–j20
The aromatic aldehyde (10 mmol) in ethanol (40 mL) was added
dropwise to the solution of thiocarbohydrazide (15 mmol) in H2O
5j
tC, Conventional method time; tMW, microwave method time.

200 JOURNAL OF CHEMICAL RESEARCH 2011
Table 3 The melting points of substituted benzaldehyde
thiocarbohydrazones 2a–j
aluminium oxide (0.3 g) were placed in a porcelain mortar, are then
concentrated acetic acid (two drops) was added. After grinding, the
mixture was put in a round-bottom flask (25 mL) in a microwave
oven. It was irradiated for 4–6.5 min at 300–600 W. The reaction
mixture was cooled to room temperature and was dissolved in DMSO
and filtered. The filtrate was added to water and the product was
formed. The product was recrystallised from ethanol in 87–92%
yields. The physical and spectra data of the compounds 5a–j are as
follows.
Product
Formula
M.p./ °C
Lit. m.p./ °C
2a
2b
2c
2d
2e
2f
C8H10N4S
196–197
210–211
210–211
199–200
208–209
206–207
209–210
200–201
211–212
217–218
19820
—
C8H9ClN4S
C8H10N4OS
C9H12N4OS
C8H9FN4S
C8H9N5O2S
C8H9ClN4S
C8H10N4OS
C8H9BrN4S
C8H10N4OS
21020
198–20022
—
204–20621
21020
—
5a: White solid, yield 89%, m.p. 132–133°C, [α]2D0 = +136.7
(c 0.10, CH2Cl2); IR (KBr)(cm−1): 3328, 3249, 2934, 2867, 1735,
1704, 1635, 1518, 1236, 1171, 1065, 758; 1H NMR (400 MHz,
DMSO-d6) δ: 11.44 (s, 1H, NH), 10.55 (s, 1H, NH), 8.10 (s, 1H,
=CH), 7.72 (s, 2H, ArH), 7.47–7.40 (m, 3H, ArH), 3.58 (s, 3H,
COOCH3), 1.03 (s, 3H, 19-CH3), 0.99 (s, 3H, 18-CH3), 0.77 (d, 3H,
J = 6.4 Hz, 21-CH3); ESI-MS m/z (%): 1157 ([2M+1]+, 100). Ana1.
Calcd for C33H46N4O3S: C, 68.48; H, 8.01; N, 9.68. Found: C, 68.32;
H, 8.10; N 9.63%.
2g
2h
2i
—
2j
21820
(50 mL) and acetic acid (1 mL) over 1 h under reflux. After the
addition, the mixture was refluxed further for 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 product. The
analytical data for 2b, 2e, 2h and 2i are given below. The melting
point of benzaldehyde thiocarbohydrazones 2a–j are shown in
Table 3.
5b: Yellow solid, yield 91%, m.p. 153–154°C, [α]2D0 = +156.7
(c 0.10, CH2Cl2); IR (KBr)(cm−1): 3431, 3338, 3217, 2932, 2865,
1737, 1699, 1595, 1516, 1214, 1089, 830; 1H NMR (400 MHz,
DMSO-d6) δ: 11.43 (s, 1H, NH), 10.59 (s, 1H, NH), 8.07 (s, 1H,
=CH), 7.73 (d, 2H, J = 14 Hz, ArH), 7.51 (d, 2H, J = 8 Hz, ArH), 3.58
(s, 3H, COOCH3), 1.03 (s, 3H, 19-CH3), 0.99 (s, 3H, 18-CH3), 0.77
(d, 3H, J = 6.4 Hz, 21-CH3); ESI-MS m/z (%): 613 ([M+1]+, 100).
Ana1. Calcd for C33H45ClN4O3S: C, 64.63; H, 7.40; N, 9.14. Found:
C, 64.54; H, 7.31; N 9.07%.
2b: Yellow solid, yield 75%, m.p. 210–211°C, IR (KBr)(cm−1):
1
3311, 3273, 3153, 2968, 1597, 1543, 1505, 1249, 1079; H NMR
(400 MHz, DMSO-d6) δ: 11.50 (s, 1H, NH), 9.93 (s, 1H, NH), 7.98 (s,
1H, =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 (%): 267 ([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%.
5c: Yellow solid, yield 87%, m.p. 188–189°C, [α]2D0 = +201.7
(c 0.10, CH2Cl2); IR (KBr)(cm−1): 3309, 2930, 2868, 1738, 1700,
1606, 1536, 1508, 1275, 1224, 1165, 830; 1H NMR (400 MHz,
DMSO-d6) δ: 11.53 (s, 1H, NH), 10.41 (s, 1H, NH), 9.93 (s, 1H, OH),
8.00 (s, 1H, =CH), 7.54 (d, 2H, J = 5.2 Hz, ArH), 6.81 (t, 2H, J = 13.4
Hz, ArH), 3.58 (s, 3H, COOCH3), 1.03 (s, 3H, 19-CH3), 0.99 (s, 3H,
18-CH3), 0.77 (d, 3H, J = 6.4 Hz, 21-CH3); ESI-MS m/z (%): 1189
([2M+1]+, 100). Ana1. Calcd for C33H46N4O4S: C, 66.64; H, 7.79;
N, 9.42. Found: C, 66.60; H, 7.72; N, 9.47%.
2e: white solid, yield 72%, 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%.
2h: Yellow solid, yield 70%, m.p. 200–201°C, IR (KBr)(cm−1):
5d: Yellow solid, yield 88%, m.p. 126–127°C, [α]2D0 = +163.0
(c 0.10, CH2Cl2); IR (KBr)(cm−1): 3319, 3215, 2935, 2868, 1735,
1704, 1605, 1506, 1250, 1170, 832; 1H NMR (400 MHz, DMSO-d6)
δ: 11.43 (s, 1H, NH), 10.46 (s, 1H, NH), 8.05 (s, 1H, =CH), 7.66
(d, 2H, J = 6.4 Hz, ArH), 7.01 (d, 2H, J = 8.4 Hz, ArH), 3.80 (s, 3H,
Ar-OCH3), 3.58 (s, 3H, COOCH3), 1.03 (s, 3H, 19-CH3), 0.99 (s, 3H,
18-CH3), 0.77 (d, 3H, J = 6.4 Hz, 21-CH3); ESI-MS m/z (%): 631
([M+23]+, 100). Ana1. Calcd for C33H48N4O4S: C, 67.07; H, 7.95; N,
9.20. Found: C, 66.98; H, 7.93; N, 9.17%.
1
3241, 3174, 2983, 1609, 1580, 1515, 1279, 1158, 1011; H 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%.
2i: Yellow solid, yield 79%, m.p. 211–212°C, IR (KBr)(cm−1):
1
3253, 3168, 2997, 1619, 1589, 1530, 1484, 1244, 1067; H 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%.
5e: White solid, yield 92%, m.p. 139–140°C, [α]2D0 = +187.0 (c 0.10,
CH2Cl2); IR (KBr)(cm−1): 3453, 3270, 3136, 2932, 2867, 1736, 1707,
1603, 1535, 1503, 1232, 1156, 837; 1H NMR (400 MHz, DMSO-d6)
δ: 11.69 (s, 1H, NH), 10.56 (s, 1H, NH), 8.09 (s, 1H, =CH), 7.79
(s, 2H, ArH), 7.29 (t, 2H, J = 8.4 Hz, ArH), 3.58 (s, 3H, COOCH3),
1.03 (s, 3H, 19-CH3), 1.00 (s, 3H, 18-CH3), 0.77 (d, 3H, J = 6.4 Hz,
21-CH3); ESI-MS m/z (%): 1193 ([2M+1]+, 100). Ana1. Calcd for
C33H45FN4O3S: C, 66.41; H, 7.60; N, 9.39. Found: C, 66.39; H, 7.61;
N, 9.37%.
Synthesis of methyl 3,12-dioxocholan-24-oate (4)17
Pyridinium chlorochromate (PCC) (3.03 mmol) was added to a solu-
tion of methyl 3,12- dihydroxycholanate 2 (0.25 g, 0.615 mmol) in
dried CH2Cl2 (20 mL) at room temperature. The reaction was com-
pleted in 12 h. The solvent was removed under reduced pressure, and
the crude product was purified by chromatography on silica gel using
ethyl acetate to give white solid, yield 84%; m.p. 135–136°C (lit.23
m.p. 133–135°C); [α]2D0 = +12.15 (c 0.12, CH2Cl2); IR (KBr) (cm−1):
2967, 2930, 2868, 1738, 1709, 1220, 1175; 1H NMR (400 MHz,
CDCl3) δ: 3.69 (s, 3H, COOCH3), 1.11 (s, 3H, 19-CH3), 1.06 (d, 3H,
J = 6.4 Hz, 21-CH3), 0.86 (s, 3H, 18-CH3); ESI-MS m/z (%): 827
([2M+23]+, 100).
5f: Yellow solid, yield 90%, m.p. 167–168°C, [α]2D0 = +141.7
(c 0.10, CH2Cl2); IR (KBr)(cm−1): 3244, 3141, 2948, 2868, 1736,
1704, 1517, 1339, 1244, 1169, 1104, 854; 1H NMR (400 MHz,
DMSO-d6) δ: 11.74 (s, 1H, NH), 10.77 (s, 1H, NH), 8.29 (d, 2H, J =
5.2 Hz, ArH), 8.15 (s, 1H, =CH), 8.08-7.91 (m, 2H, ArH), 3.58 (s, 3H,
COOCH3), 1.03 (s, 3H, 19-CH3), 1.00 (s, 3H, 18-CH3), 0.77 (d, 3H,
J = 6.4 Hz, 21-CH3); ESI-MS m/z (%): 1247 ([2M+1]+, 100). Ana1.
Calcd for C33H45N5O5S: C, 63.54; H, 7.27; N, 11.23. Found: C, 63.40;
H, 7.18; N, 11.14%.
Preparation of bisthiocarbazones 5a–j
5g: White solid, yield 89%, m.p. 190–191°C, [α]2D0 = +84.0 (c 0.10,
CH2Cl2); IR (KBr)(cm−1): 3317, 3179, 2937, 2866, 1731, 1692, 1591,
1515, 1272, 1228, 1098, 760; 1H NMR (400 MHz, DMSO-d6) δ: 11.86
(s, 1H, NH), 10.55 (s, 1H, NH), 8.50 (s, 1H, =CH), 8.04 (s, 1H, ArH),
7.55–7.50 (m, 1H, ArH), 7.43 (t, 2H, J = 5.6 Hz, ArH), 3.58 (s, 3H,
COOCH3), 1.03 (s, 3H, 19-CH3), 0.99 (s, 3H, 18-CH3), 0.77 (d, 3H,
J = 5.6 Hz, 21-CH3); ESI-MS m/z> (%): 1225 ([2M+1]+, 100). Ana1.
Calcd for C33H45ClN4O3S: C, 64.63; H, 7.40; N, 9.14. Found: C, 64.57;
H, 7.38; N, 9.17%.
Conventional method
The steroidal ketone (4) (0.1 g, 0.26 mmol) and the substituted benz-
aldehyde thiocarbohydrazones (2a–j) (0.258 mmol) were dissolved in
10 mL ethanol. After completely dissolving, two drops of acetic acid
were added. The mixture was stirred for 3–5 h at 80°C. After cooling
the products were filtered and recrystallised from ethanol in 49–67%
yields.
5h: White solid, yield 88%, m.p. 206–207°C, [α]2D0 = +100.3 (c 0.10,
CH2Cl2); IR (KBr)(cm−1): 3314, 3208, 2971, 2941, 2869, 1732, 1691,
1588, 1531, 1450, 1244, 1096, 779; 1H NMR (400 MHz, DMSO-d6)
Microwave irradiation method
The steroidal ketone (4) (0.1 g, 0.258 mmol) and the substituted
benzaldehyde thiocarbohydrazones (2a–j) (0.258 mmol) and neutral

JOURNAL OF CHEMICAL RESEARCH 2011 201
References
δ: 11.65 (s, 1H, NH), 10.52 (s, 1H, NH), 9.64 (t, 1H, J = 6.8 Hz, OH),
8.42 (s, 1H, =CH), 7.26–7.22 (m, 1H, ArH), 7.14 (s, 2H, ArH), 6.82
(d, 1H, J = 7.6 Hz, ArH), 3.58 (s, 3H, COOCH3), 1.04 (s, 3H, 19-CH3),
1.00 (s, 3H, 18-CH3), 0.77 (d, 3H, J = 6.8 Hz, 21-CH3); ESI-MS m/z
(%): 595 ([M+1]+, 100). Ana1. Calcd for C33H46N4O4S: C, 66.64;
H, 7.79; N, 9.42. Found: C, 66.57; H, 7.68; N, 9.37%.
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CH2Cl2); IR (KBr)(cm−1): 3448, 3311, 3229, 3046, 2931, 2868, 1740,
1694, 1587, 1517, 1213, 1102, 819; 1H NMR (400 MHz, DMSO-d6)
δ: 11.74 (s, 1H, NH), 10.46 (s, 1H, NH), 8.06 (s, 1H, =CH), 7.69
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397.
1
1534, 1276, 1228, 1158, 755; H NMR (400 MHz, DMSO-d6) δ:
11.76 (s, 1H, OH), 11.67 (s, 1H, NH), 10.84 (s, 1H, NH), 8.70 (s, 1H,
=CH), 7.35 (s, 1H, ArH), 7.29 (t, 1H, J = 8.0 Hz, ArH), 6.91 (t, 2H,
J = 4.4 Hz, ArH), 3.58 (s, 3H, COOCH3), 1.03 (s, 3H, 19-CH3), 0.99
(s, 3H, 18-CH3), 0.77 (d, 3H, J = 5.6 Hz, 21-CH3); ESI-MS m/z (%):
1189 ([2M+1]+, 100). Ana1. Calcd for C33H46N4O4S: C, 66.64; H,
7.79; N, 9.42. Found: C, 66.59; H, 7.81; N, 9.39%.
17 Z.G. Zhao, X.L. Liu, L.L. Liu and G.H. Li, J. Chem. Res., 2010, 34, 455.
18 X.X. Zhao, Z.G. Zhao and X.L. Liu, Chin. Chem. Lett., 2009, 20, 397.
19 Y. Chen, Z.G. Zhao, X.L. Liu and Z.C. Shi, J. Chem. Res., 2010, 34, 416.
20 V.V. Dabholkar and T.D. Ravi, Indian J. Chem., 2010, 49B, 593.
21 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.
We thank the State Administration of Foreign Experts Affairs
the P.R. of China (Project No.2009-15) for financial support.
Received 20 January 2011; accepted 3 March 2011
Paper 1100538 doi: 10.3184/174751911X12995267948561
Published online: 3 May 2011
22 Z. Li, X. Feng and Y.L. Zhao, J. Heterocyclic Chem., 2008, 45, 1489.
23 B. Koechlin and T. Reichstein, Helv. Chim. Acta, 1942, 25, 918.

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