SnCl4/SiO2: An efficient heterogeneous alternative for one-pot synthesis of β-acetamidoketones

Article abstract of DOI:10.1002/jccs.200900056

Enolizable ketones have been reacted in a one-pot method with aromatic aldehydes, acetyl chloride and acetonitrile at room temperature in the presence of SnCl₄/SiO₂ to furnish the corresponding β-acetamidoketones in improved yields.

Full text of DOI:10.1002/jccs.200900056

386
Journal of the Chinese Chemical Society, 2009, 56, 386-391
SnCl4/SiO2: An Efficient Heterogeneous Alternative for One-pot Synthesis
of b-Acetamidoketones
Bi Bi Fatemeh Mirjalili,a,* Mohammad M. Hashemi,b Bahareh Sadeghic and Hamideh Emtiazia
aDepartment of Chemistry, College of Science, Yazd, University, Yazd, P.O. Box 89195-741, Iran
bDepartment of Chemistry, Sharif University of Technology, P.O. Box 11365-9516, Tehran, Iran
cFaculty of Chemistry, Islamic Azad University, Science and Research Campus, Tehran, Iran
Enolizable ketones have been reacted in a one-pot method with aromatic aldehydes, acetyl chloride
and acetonitrile at room temperature in the presence of SnCl4/SiO2 to furnish the corresponding b-acet-
amidoketones in improved yields. Acetylation of an aromatic hydroxyl group was observed while using
4-hydroxybenzaldehyde or vanillin and the corresponding b-acetamidoketones were isolated in an excel-
lent yield.
Keywords: Tin chloride (SnCl4); b-Acetamidoketones; One-pot synthesis; SnCl4/SiO2.
INTRODUCTION
b-Acetamidoketones are valuable building blocks for
bly the silica supported SnCl4 will have a surface species
-
such as Si-OSnCl3 or the ion pair Si-OSnCl4 H+. Tin tetra-
the preparation of b-amino ketones or b-amino alcohols
such as antibiotic nikkomycins1,2 and neopolyoxines.3 Re-
cently, Iqbal et al. have developed a new route based on
condensation of aromatic aldehydes, enolizable ketones
and acetonitrile in the presence of acetyl chloride and a cat-
alytic amount of an acid such as CoCl24 or montmorillonite
K-10 clay.6 As a result, many catalysts such as CeCl3.
7H2O,7 silica sulfuric acid,8 H6P2W18O62,9 K5CoW12O40.
3H2O,10 ZnO,11 sulfated zirconia,12 FeCl3,13 some hetero-
poly acids,14,15 silica supported H3PW12O40,16 nano ZnO,17
sulfamic acid,18 Sc(OTf)3,19 SnCl2.2H2O20 and Nafion-H21
have been applied in this one-pot reaction. Many authors
have erroneously reported that b-acetamidoketones could
be prepared by the Dakin-West reaction,7-16 but, as we
clearly know, in the Dakin-West reaction, a-acetamidoke-
tones were prepared.22
chloride (SnCl4) is used extensively in organic syntheses as
a Lewis acid for enhancing a variety of organic reactions
such as Friedel-Crafts alkylation,23 the Mukaiyama-Mi-
chael reaction,24 the Diels-Alder reaction,25 the ene reac-
tion,26 the arotamization of enamines,27 the rearrangement
of 2,3-epoxy alcohol derivatives,28 the dimerization of 1-
naphthols to 2,2¢-binaphthoquinones,29 the allylation of
a-benzyloxyaldehydes30 and the formation of 1,2-dioxo-
lanes,31 among others. Because of the importance of solid
acids in organic synthesis,32-37 herein, we report an efficient
and simple procedure for synthesis of b-acetamidoketones
using SnCl4/SiO2 as catalyst.
RESULTS AND DISCUSSION
In order to utilize SnCl4 as a catalyst in the synthesis
of b-acetamidoketones, the reaction of 2-chlorobenzalde-
hyde and 4-chloroacetophenone was examined in the pres-
ence of several catalysts and under various conditions (Ta-
ble 1). According to the obtained data, the 70% SnCl4/SiO2
(10 mol%) in the presence of acetylchloride and aceto-
nitrile was the best system for b-acetamidoketone forma-
tion (Table 1, entry 9). Therefore, various aromatic alde-
hydes and ketones were transformed into the correspond-
ing b-acetamidoketones in the presence of 70% SnCl4/SiO2
as a catalyst without the formation of any side products and
with improved yields (Table 2).
Stannic chloride or tin chloride (SnCl4), a thin, color-
less and fuming liquid, is used in industry and in organic
synthesis. Since stannic chloride is a liquid with a high spe-
cific gravity that fumes in air and reacts with the moisture
in the air to form solid hydrates and HCl, the handling and
the usability of SnCl4 as a liquid form is laborious, and the
supported form is indeed preferable. It has been claimed
that the supported SnCl4 is a solid superacid. If the complex
SnCl4 in MeOH is used to prepare a silica-supported SnCl4
catalyst, Brönsted surface sites will be obtained and proba-
* Corresponding author. E-mail: fmirjalili@yazduni.ac.ir

SnCl4/SiO2: An Efficient Alternative Synthesis of b-Acetamidoketones
J. Chin. Chem. Soc., Vol. 56, No. 2, 2009 387
were obtained as a by-product; also, a mixture of chalcone,
acetyl chloride and acetonitrile in the presence of a catalyst
failed to generate any b-acetamidoketones. In the absence
of acetyl chloride or benzoyl chloride, the reaction failed to
provide the desired product, obviously indicating that they
play a necessary role in this reaction, although they are not
involved in the final product. When benzylcyanide or phen-
ylcyanide was used instead of acetonitrile, the correspond-
ing b-amidoketones such as b-phenylacetamidoketone or
b-benzamidoketone were obtained. Note that neither a
mixture of 4-methylbenzaldehyde, 4-nitroacetophenone,
aceticanhydride and acetonitrile in the presence of SnCl4/
SiO2, nor a mixture of 4-methylbenzaldehyde acylal, 4-
nitroacetophenone and SnCl4/SiO2 in acetonitrile could
produce any of the corresponding b-acetamido ketones
(Scheme I).
Table 1. Standardisation of reaction conditions for one-pot
formation of b-acetamidoketone from 2-chlorobenz-
aldehyde (1 mmol) and 4-chloroacetophenone (1 mmol)
Acetyl Aceto-
Yield
Entry chloride nitrile
Catalyst (mmol)
(%)a
(mL)
(mL)
1
1
1
1
FeCl3 (10 mol%)
46
55
60
62
80
63
74
81
89
68
2
1
AlCl3 (10 mol%)
ZnCl2 (10 mol%)
ZrCl4 (10 mol%)
SnCl4 (10 mol%)
3
1
1
4
1
1
5
1
1
.
6
1
1
BF3 Et2O (10 mol%)
7
0.3
0.3
0.3
1
0.3
0.7
1
70% SnCl4/SiO2 (10 mol%)
70% SnCl4/SiO2 (10 mol%)
70% SnCl4/SiO2 (10 mol%)
70% SnCl4/SiO2 (10 mol%)
8
The proposed mechanism for the formation of SnCl4/
SiO2 catalyzed b-acetamidoketone is illustrated in Scheme
II. Condensation of acid chloride and aldehyde in the pres-
ence of the acidic catalyst (A+) produces an intermediate (I)
which then reacts with nitrile to produce (II) after the elimi-
nation of A+ and Cl-. Intermediate (II) rearranges into the
cyclic intermediate (III). Next, the enol form of ketone at-
tacks (III) to form (IV) and then (V) with an exchange of
H+. The nucleophilic attack of (V) accompanied by tauto-
merization gives the desired b-acetamidoketone.
9
10
11
12
13
14
15
16
17
18
19
20
0.3
1
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
70% SnCl4/Al2O3 (10 mol%) 76
1
70% SnCl4/TiO2 (10 mol%)
70% SnCl4/ZrO2 (10 mol%)
60% SnCl4/SiO2 (10 mol%)
50% SnCl4/SiO2 (10 mol%)
80% SnCl4/SiO2 (10 mol%)
70% SnCl4/SiO2 (8 mol%)
70% SnCl4/SiO2 (5 mol%)
70% SnCl4/SiO2 (14 mol%)
70% SnCl4/SiO2 (18 mol%)
72
45
80
75
90
82
74
91
89
1
1
1
1
1
1
1
1
a Isolated yield
CONCLUSION
In conclusion, a significantly important and new cata-
lytic activity of SnCl4/SiO2 has been studied for the synthe-
sis of b-acetamido ketones in excellent yields. A mild reac-
tion condition, a simple experimental procedure, an easy
work-up and scale up and also improved yields of products
are some strong features of this reported method.
Consequently, acetylation of an aromatic hydroxyl
group was observed while using 4-hydroxybenzaldehyde
or vanillin, and the corresponding b-acetamidoketones were
isolated in an excellent yield. 4-Dimethylamino benzalde-
hyde, however, was inert to the present reaction conditions.
The preparative efficacy of this one-pot synthesis was fur-
ther checked by scaling-up (5 fold) of the reaction of benz-
aldehyde with acetophenone and other ingredients which
proceeded with an 80% yield. Previously, four types of
mechanisms for the Iqbal procedure for b-acetamidoketone
formation were proposed.6,7,9,11,17,18 In some cases,7,11,17 b-
acetoxyketone was offered as an intermediate product that
converted into b-acetamidoketone with acetonitrile. In our
investigation, when the reaction was not subjected to aceto-
nitrile, no b-acetoxyketone was formed and only a crossed
aldol condensation reaction occurred. Meanwhile, in the
preparation of b-acetamidoketones, no b-acetoxyketones
EXPERIMENTAL
General
SnCl4, aldehydes, ketones and other necessary chem-
ical compounds were purchased from Fluka and Merck
companies. Some products were known and were charac-
terized by IR and 1H-NMR and by comparing their physical
properties with those reported in the literature. IR spectras
were run on a Shimadzu IR-470 spectrometer. 1H-NMR
was obtained using a Bruker Avance 400 and 300 MHz
spectrometer and mass spectras was obtained on a Fifons
(TRIO 10000) spectrometer. Melting points were deter-

388 J. Chin. Chem. Soc., Vol. 56, No. 2, 2009
Mirjalili et al.
Table 2. One-pot condensation of aldehydes, ketones, acetyl chloride and acetonitrile to give the
a
corresponding b-acetamidoketones catalyzed by 70% SnCl4/SiO2
Entry
Product (3)
R1,R2,R3=H, R4=Ph
Time (h) Reference Yieldb (%) m.p (°C)
1
7.5
7
9
12
8
82
89
79
80
80
78
79
79
84
85
92
85
83
79
104-105
97-98
2
R1,R2,R3=H, R4=4-NO2-C6H4
R1=Cl, R2,R3=H, R4=Ph
3
9
135-136
89-91
4
R1=H, R2=OCH3, R3=OCOCH3, R4=Ph
R1,R2=H, R3=CH3, R4=4-NO2-C6H4
R2,R3=H, R1=OCH3, R4=4-NO2-C6H4
R1,R3=H, R2=NO2, R4=4-NO2-C6H4
R1,R3=H, R2=NO2, R4=4-Cl -C6H4
R3,R2=H, R1=Cl, R4=3-OCH3-C6H4
R2,R1=H, R3=Cl, R4=Ph
10
5.5
6
-
5
12
-
84-85
6
145-146
105-106
145-146
101-103
148-149
168-169
171-172
192-193
110-111
7
4
12
7
8
9
9
9.5
8
-
10
11
12
13
14
9
R2,R3=H, R1=Cl, R4=4-Cl-C6H4
R1,R3=H, R2=Cl, R4=4-NO2-C6H4
R2,R3=H, R1=Cl, R4=4-Br-C6H4
R1,R2=H, R3=OCH3, R4=Ph
9
-
5
-
8
-
10
9
a Molar ratio of aldehyde (mmol):ketone (mmol):acetyl chloride (mL):acetonitrile (mL): 70%
SnCl4/SiO2 (g) [mmol] equal to 1:1:0.3:1:0.04 [0.1]
b Isolated yield.
mined with a Barnstead Electrothermal melting point appa-
ratus.
tallization or by preparative thin layer chromatography
(eluent:n-hexane:ethylacetate).
Preparation of silica-supported SnCl4
Data for b-acetamido-b-(3-methoxy, 4-acetoxy-phenyl)
5 mL of ethanol containig 1 mL of SnCl4 and 1 g of
preheated silica gel was stirred for 1 h at room tempera-
ture. The slurry was dried slowly on a rotary evaporator at
40 °C. The obtained solid (70% SnCl4/SiO2) was dried at
an ambient temperature for 2 h and then stored in a dry
container.
propiophenone (Table 2, entry 4)
1H NMR (CDCl3, 400 MHz): d 2.1 (s, 3H), 2.3 (s,
3H), 3.5 (dd, J = 6 and 16.8 Hz, 1H), 3.7 (dd, J = 5.6 and
16.8 Hz, 1H), 3.8 (s, 3H), 5.6 (dd, J = 6 and 5.6 Hz, 1H), 6.9
(d, J = 8 Hz, 1H), 7.0 (d, J = 8 Hz, 1H), 7.1 (s, 1H), 7.5 (t, J
= 7.6 Hz, 2H), 7.6 (t, J = 7.6 Hz, 1H), 8 (d, J = 7.6 Hz, 2H),
8.6 (sbr, 1H). 13C-NMR (CDCl3, 100 MHz): d 21.6, 24.38,
44.35, 51.09, 57.02, 112.6, 119.32, 123.95, 129.31, 129.91,
134.82, 137.57, 140.09, 141.09, 152.19, 170, 172, 200. IR
(KBr, cm-1) 3279, 3135, 2930, 1767, 1684, 1651, 1508,
1414, 1367, 1302, 1195, 1121, 1025.
General procedure for one-pot synthesis of b-acet-
amidoketones using 70% SnCl4/SiO2
Enolizable ketone (1 mmol), aromatic aldehyde (1
mmol), acetyl chloride (0.3 mL), acetonitrile (1 mL) and
70% SnCl4/SiO2 (0.04 g, 0.1 mmol of SnCl4) were placed in
a round bottom flask. The materials were mixed at an ambi-
ent temperature. The progression of the reaction was fol-
lowed by TLC (eluent:n-hexane:ethylacetate). After the
completion of reaction, the mixture was poured into 30 mL
ice water. The oily solid was isolated and washed with di-
ethyl ether to remove any residual starting materials. The
pure product was obtained from ethanol and water by crys-
Data for b-acetamido-b-(2-methoxy)-4-nitro propio-
phenone (Table 2, entry 6)
1H NMR (CDCl3, 300 MHz): d 2 (s, 3H), 3.55 (dd, J =
6.9 and 17.5 Hz, 1H), 3.6 (dd, J = 6.5 and 17.5 Hz, 1H), 3.9
(s, 3H), 5.7 (dd, J = 6.9 and 16 Hz, 1H), 6.7 (d, J = 6.9 Hz,
1H), 6.9 (m, 2H), 8.1 (m, 3H), 8.3 (m, 3H); IR (KBr, cm-1)
3260, 1684, 1637, 1545, 1510, 1337, 1234, 837, 742; MS

SnCl4/SiO2: An Efficient Alternative Synthesis of b-Acetamidoketones
J. Chin. Chem. Soc., Vol. 56, No. 2, 2009 389
Scheme I Various reactions as evidence for verification of the proposed mechanisms
Scheme II The proposed mechanism for the formation of SnCl4/SiO2 catalyzed b-acetamidoketone

390 J. Chin. Chem. Soc., Vol. 56, No. 2, 2009
Mirjalili et al.
(m/z, %) 344 (M+2+, 1.87), 342 (M+, 10.65), 299 (100), 150
(85), 107 (25), 77 (17.8), 43 (27.6, CH3-CºO+).
Data for b-acetamido-b-(2-chloro)-3-methoxy propio-
phenone (Table 2, entry 9)
1H NMR (CDCl3, 300 MHz): d 2 (s, 3H), 3.45 (dd, J =
17 and 5.7 Hz, 1H), 3.77 (dd, J = 17 and 6 Hz, 1H), 3.84 (s,
3H), 5.82 (dd, J = 15 and 6 Hz, 1H), 6.93 (dbr, J = 6.7 Hz,
1H), 6.9-7.5 (m, 8H). IR (KBr, cm-1) 3265, 1681, 1643,
1547, 1284, 1002, 747; MS (m/z, %) 332 (M+, 3.75), 296
(83), 135 (100), 107 (49), 77 (94), 43 (73, CH3-CºO+).
Data for b-acetamido-b-(2-chloro)-4-chloro propio-
phenone (Table 2, entry 11)
1H NMR (CDCl3, 400 MHz): d 2.1 (s, 3H), 3.5 (dd, J
= 16.8 and 5.6 Hz, 1H), 3.8 (dd, J = 16.8 and 6 Hz, 1H), 5.8
(sbr, 1H), 7.1 (sbr, 1H), 7.2 (m, 2H), 7.4 (d, J = 7.6, 1H), 7.6
(m, 3H), 7.9 (d, J = 8 Hz, 2H). 13C-NMR (CDCl3, 100
MHz): d 24.27, 42.88, 49.17, 128.28, 128.73, 129.46,
130.0, 130.18, 131.09, 133.59, 135.86, 139.13, 141.27,
173, 196. IR (KBr, cm-1) 3292, 1688, 1653, 1552, 1353,
1200, 814, 753. MS (m/z, %) 338 (M+2+, 1.87), 336 (M+,
2.5), 184 (3), 182 (10), 141 (24), 139 (100), 43 (25.6,
CH3-CºO+).
Received November 18, 2007.
REFERENCES
1. Barluenga, J.; Viado, A. L.; Aguilar, E.; Fustero, S.; Olano,
B. J. Org. Chem. 1993, 58, 5972.
2. Henderson, D. P.; Shelton, M. C.; Cotterill, I. C.; Toone, E. J.
J. Org.Chem. 1997, 62, 7910.
3. Uramoto, M.; Kobinata, K.; Isono, K.; Higashijima, T.;
Miyazawa, T.; Jenkins, E. E.; McCloskey, J. A. Tetrahedron
Lett. 1980, 21, 3395.
4. Mukhopadhaya, M.; Bhatia, B.; Iqbal, J. Tetrahedron Lett.
1997, 38, 1083.
5. Reddy, M. M.; Bhatia, B.; Iqbal, J. Tetrahedron Lett. 1995,
36, 4877.
6. Bahulayan, D.; Das, S. K.; Iqbal, J. J. Org. Chem. 2003, 68,
5735.
7. Khan, A. T.; Choudhury, L. H.; Parvin, T.; Asif Ali, M. Tet-
rahedron Lett. 2006, 47, 8137.
8. Khodaei, M. M.; Khosropour, A. R.; Fattahpour, P. Tetrahe-
dron Lett. 2005, 46, 2105.
9. Heravi, M. M.; Ranjbar, L.; Derikvand, F.; Bamoharram, F.
Catal. Commun. 2007, 8, 289.
10. Nagarapu, L.; Kantevari, S.; Cheemalapati, V. N.; Apuri, S.;
Kumari, V. J. Mol.Catal. A: Chem 2006, 264, 22.
11. Maghsoodlou, M. T.; Hassankhani, A.; Shaterian, H. R.;
Habibi-Khorasani, S. M.; Mosaddegh, E. Tetrahedron Lett.
2007, 48, 1729.
Data for b-acetamido-b-(3-chloro)-4-nitro propiophe-
none (Table 2, entry 12)
1H NMR (CDCl3, 300 MHz): d 2.05 (s, 3H), 3.5 (dd, J
= 17.1 and 6.6 Hz, 1H), 3.82 (dd, J = 17 and 5.1 Hz, 1H),
5.53 (m, 1H), 6.5 (dbr, J = 6.9 Hz, 1H), 7.24 (m, 3H), 7.34
(s, 1H), 8.07 (d, J = 8.7 Hz, 3H), 8.32 (d, J = 8.7 Hz, 2H). IR
(KBr, cm-1) 3235, 1687, 1641, 1546, 1530, 1316, 1156,
843, 688; MS (m/z, %) 346 (M+, 0.91), 311 (59), 150 (100),
77 (26), 43 (53, CH3-CºO+).
12. Das, B.; Krishnaiah, M.; Laxminarayana, K.; Reddy, K. R.
J. Mol. Catal. A: Chem. 2007, 270, 284.
13. Khan, A. T.; Parvin, T.; Choudhury, L. H. Tetrahedron 2007,
63, 5593.
14. Rafiee, E.; Tork, F.; Joshaghani, M. Bioorg. & Med. Chem.
Lett. 2006, 16, 1221.
15. Heravi, M. M.; Ranjbar, L.; Derikvand, F.; Bamoharram, F.
F. J. Mol. Catal. A:Chem. 2007, 271, 28.
16. Rafiee, E.; Shahbazi, F.; Joshaghani, M.; Tork, F. J. Mol.
Catal. A: Chem. 2005, 242, 129.
Data for b-acetamido-b-(2-chloro)-4-bromo propio-
phenone (Table 2, entry 13)
1H NMR (CDCl3, 300 MHz): d 2.04 (s, 3H), 3.43 (dd,
J = 18 and 6 Hz, 1H), 3.73 (dd, J = 18 and 5.7 Hz, 1H), 5.81
(m, 1H), 6.88 (d, J = 7.8 Hz, 1H), 7.1 (t, J = 5.7 Hz, 2H), 7.2
(d, J = 7.2 Hz, 1H), 7.36 (d, J = 7.2 Hz, 3H), 7.59 (d, J = 8.1
Hz, 2H), 7.76 (d, J = 8.1 Hz, 2H). IR (KBr, cm-1) 3260,
1677, 1653, 1642, 1573, 1539, 1221, 801, 744; MS (m/z,
%) 382 (M+2+, 2.93), 380 (M+, 2.18), 346 (64), 344 (58),
183 (73), 43 (31, CH3-CºO+).
17. Mirjafary, Z.; Saeidian, H.; Sadeghi, A.; Matloubi Moghaddam,
F. Catal. Commun. 2008, 9, 299.
18. Heravi, M.; Ranjbar, L.; Derikvand, F.; Bamoharram, F. F. J.
Mol. Catal. A:Chem. 2007, 226.
19. Pandey, G.; Singh, R. P.; Garg, A.; Singh, V. K. Tetrahedron
Lett. 2005, 46, 2137.
20. Nagarapu, L.; Bantu, R.; Puttireddy, R. Appl. Catal. A: Gen.
2007, 304.
21. Yakaiah, T. V.; Lingaiah, B. P.; Venkat Reddy, G.; Narsaiah,
B.; Shanthan Rao, P. ARKIVOC 2007, 13, 227.
22. Dakin, H. D.; West, R. J. Biol. Chem. 1928, 78, 91.
23. Olah, G. A. Friedel–Crafts and Related Reactions; Wiley:
New York, 1964.
ACKNOWLEDGMENTS
Financial support for this work by the research affairs
of the Science and Research Campus of Islamic Azad Uni-
versity is gratefully acknowledged.
24. Sato, T.; Wakahara, Y.; Otera, J.; Nozaki, H.; Fukuzumi, S.
J. Am. Chem. Soc. 1991, 113, 4028.

SnCl4/SiO2: An Efficient Alternative Synthesis of b-Acetamidoketones
J. Chin. Chem. Soc., Vol. 56, No. 2, 2009 391
25. Maruoka, K.; Akakusa, M.; Saito, S.; Ooi, T.; Yamamoto, H.
J. Am. Chem. Soc.1994, 116, 6153.
32. Chou, S.-S. P.; Chu, C.-W. J. Chin. Chem. Soc. 1984, 31,
351.
26. Jin, J.; Smith, D. T.; Weinreb, S. M. J. Org. Chem. 1995, 60,
5366.
33. Lee, A. S.-Y.; Zhang, S.-L.; Pan, O.-G. J. Chin. Chem. Soc.
1997, 44, 625.
27. Bigdeli, M. A.; Rahmati, A.; Abbasi-Ghadim, H.; Mahdavinia,
G. H. Tetrahedron Lett. 2007, 48, 4575.
34. Zolfigol, M. A.; Niknam, K.; Nazari, F. J. Chin. Chem. Soc.
2006, 53, 669.
28. Kita, Y.; Matsuda, S.; Inoguchi, R.; Jnaneshwara, K.; Ganesh,
J.; Fujioka, H. Tetrahedron Lett. 2005, 46, 89.
29. Takeya, T.; Doi, H.; Ogata, T.; Iwao Okamoto, I.; Kotani, E.
Tetrahedron 2004, 60, 9049.
35. Zolfigol, M. A.; Mohammadpoor-Baltork, I.; Shiri, M. J.
Chin. Chem. Soc, 2006, 53, 545.
36. Mirjalili, B. F.; Zolfigol, M. A.; Bamoniri, A.; Zarei, A. J.
Chin. Chem. Soc, 2004, 51, 509.
30. Dubost, C.; Leroy, B.; Marko, I. E.; Tinant, B.; Declercq,
J.-P.; Justin Bryans, J. Tetrahedron 2004, 60, 7693.
31. Dussault, P. H.; Liu, X. Tetrahedron Lett. 1999, 40, 6553.
37. Sadeghi, B.; Mirjalili, B. F.; Hashemi, M. M. Tetrahedron
Lett. 2008, 49, 2575.