First synthesis of ferrocenyl-substituted 1,2-dihydro-2-oxopyridine-3- carbonitriles

Article abstract of DOI:10.1002/hlca.201300015

In the present investigation, the first incorporation of both ferrocene scaffold and 1,2-dihydro-2-oxopyridine-3-carbonitrile pharmacophore leading to a series of structurally novel ferrocene-based hybrids has been achieved, involving the condensation reaction of ferrocenyl substituted chalcones with 2-cyanoacetamide in a freshly prepared EtONa solution at 70°. The molecular structures of these newly synthesized products were confirmed by IR, and ¹H- and ¹³C-NMR analyses.

Full text of DOI:10.1002/hlca.201300015

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First Synthesis of Ferrocenyl-Substituted 1,2-Dihydro-2-oxopyridine-3-
carbonitriles
by Hong Zhang, Yang Li, and Wentao Gao*
Institute of Superfine Chemicals, Bohai University, Jinzhou 121000, P. R. China
(phone/fax: þ 86-416-3400266; e-mail: bhuzh@163.com)
In the present investigation, the first incorporation of both ferrocene scaffold and 1,2-dihydro-2-
oxopyridine-3-carbonitrile pharmacophore leading to a series of structurally novel ferrocene-based
hybrids has been achieved, involving the condensation reaction of ferrocenyl substituted chalcones with
2-cyanoacetamide in a freshly prepared EtONa solution at 708. The molecular structures of these newly
synthesized products were confirmed by IR, and 1H- and 13C-NMR analyses.
Introduction. – Molecules containing the 2-oxopyridine-3-carbonitrile moiety have
received considerable interest from the medicinal community due to their potent
biological properties, particularly anticancer, antimicrobial, antidepressant, and
cardiotonic activities [1 – 4]. Among the successful examples as drug candidates
possessing the 1,2-dihydro-2-oxopyridine-3-carbonitrile nucleus are milrinone (1),
which has been introduced to the clinic for the treatment of congestive heart failure [5].
The recently reported oncogenic serine/threonine kinase PIM-1 inhibitor 2 and survivin
inhibitor 3 also contain this carbonitrile [6][7]. Compound 4 with this ring system was
also reported to display robust in vivo activity in a sleepꢀwake electroencephalogram
(sw-EEG) [8].
These examples emphasize the importance of 1,2-dihydro-2-oxopyridine-3-carbo-
nitrile as key pharmacophores in bioactive small molecules. Apart from these, 2-
oxopyridine-3-carbonitrile derivatives also serve as important intermediates in the
synthesis of many biologically active compounds such as pyridone-containing
farnesyltransferase inhibitors [9]. Not surprisingly, the mentioned framework has
been an attractive synthetic target, and strategies for accessing new scaffolds of 2-
oxopyridine-3-carbonitrile are of great interest to synthetic chemists [10 – 13].
ꢀ 2013 Verlag Helvetica Chimica Acta AG, Zꢁrich

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On the other hand, it is well-established that the interchange of an aromatic or
heterocyclic ring with the ferrocene nucleus in some organic compounds possessing a
certain property (e.g., biological activity) might lead to products with enhanced or
unexpected chemical and pharmacological properties compared to that of the parent
compound. This fact could be rationalized as being due to the unique properties of the
ferrocene nucleus such as membrane permeation, aqueous stability, anomalous
metabolism, and redox behavior [14 – 16]. The incorporation of the ferrocene unit
into a heterocyclic molecule according to classical methods of organic chemistry has
been recognized as an attractive way to endow a novel molecule functionally [17][18].
For example, Zhao and Liu demonstrated that the modification of ailanthoidol by a
ferrocenyl group enhanced its ability to quench radicals and to protect DNA against
radical-induced oxidation [19]. Thus, introduction of the ferrocene unit into bioactive
heterocyclic skeletons would be a challenge for medicinal applications. Therefore, it is
of high interest to synthesize ferroceneꢀheterocycle hybrids to expand the structure
diversity for current medicinal chemistry needs.
Considering the above mentioned findings, we conceived that the incorporation of
the ferrocene scaffold into the 2-oxopyridine-3-carbonitrile pharmacophore, leading to
a series of structurally novel compounds as possible drug-like candidates, would be of
synthetic importance. A literature survey revealed that there are a number of reports
for the synthesis of 1,2-dihydro-2-oxopyridine-3-carbonitrile derivatives, and consid-
erable attention has been focused on the synthesis of aryl or hetaryl substituted 2-
oxopyridine-3-carbonitrile. Although the importance of both 2-oxopyridine-3-carbo-
nitrile and ferrocene core compounds is undisputed, surprisingly, the synthesis of
ferrocenyl-substituted 2-oxopyridine-3-carbonitrile has not been achieved so far. Thus,
in continuation of our efforts to synthesize highly interesting types of heterocycles
[20 – 23], herein report the synthesis of a system, which combines these two impor-
tant components via the condensation of a ferrocenyl substituted chalcone with 2-
cyanoacetamide.
Results and Discussion. – The synthetic sequence employed in our laboratories for
preparation of 6-ferrocenyl-1,2-dihydro-2-oxo-4-phenylpyridine-3-carbonitriles, 3a –
3f, is outlined in Scheme 1. The starting compounds, ferrocenyl chalcones, were
prepared as previously described in [24][25].
Scheme 1

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The condensation of a chalcone or enone with 2-cyanoacetamide for the synthesis
of 1,2-dihydro-2-oxopyridine-3-carbonitrile derivatives is a well-known reaction. Prior
to the current investigation, a number of examples involving this reaction have been
reported [26 – 32]. For example, it has been reported that the condensation reaction of
chalcones with 2-cyanoacetamide using a catalytic amount of piperidine in EtOH [27]
or BuOH [29] yielded the 1,2-dihydro-2-oxopyridine-3-carbonitrile. However, in our
attempts to follow the method, we did not observe any trace of the expected product,
but only undefined mixtures. Further investigation towards the cyclocondensation
reaction was conducted according to reported methods using DMSO/tBuOK system
under an O2 atmosphere [28][31]. Unfortunately, the attempts in our case were also
unfruitful, and no promising result was obtained even after refluxing for a prolonged
period (24 h). Recently, Ji and co-workers described the synthesis of ferrocenyl
substituted pyridine-3-carbonitriles via the condensation of ferrocenyl substituted
chalcones with malononitrile [33]. On this basis, we presumed that this approach can be
extended for our synthesis. Thus, we first investigated the reaction of ferrocenylchal-
cone 1a with 1.1 equiv. of 2-cyanoacetamide (2a) using EtONa/EtOH at 508, but this
led to a modest yield of 31% of 3a. Interestingly, a further increase of the reaction
temperature led to a significant increase in the yield of 3a, reaching 62% at a
temperature of 708. However, at temperatures > 708, by-products were formed as
observed on TLC, which reduced the yield of the desired products. After complete
formation of the product as monitored by TLC, H2O was added, the mixture was
acidified with 10% AcOH, and the precipitate, which separated on standing, was
collected. Recrystallization from EtOH gave the product in 62% yield. In addition, in
our case, the use of microwave irradiation did not further improve the yield, in contrast
to the literature results. To retain the simplicity of the procedure, no further changes in
reaction conditions were tested and the above mentioned condition was chosen for the
following work.
To further investigate the viability of the transformation, the reaction was tested
with other substituted ferrocenylchalcones 1b – 1f in a similar fashion. This reaction
invariably led to the formation of the corresponding 6-ferrocenyl-1,2-dihydro-2-
oxopyridine-3-carbonitriles 3b – 3f in acceptable yields, and the results of this series of
experiments are compiled in the Table.
Table. Cyclocondensation Reaction of Ferrocenylchalcones with 2-Cyanoacetamide
Entry
3a – 3f
R
Time [h]
Yield [%]a)
1
2
3
4
5
6
3a
3b
3c
3d
3e
3f
H
5
8
8
4
4
4
62
59
61
67
70
65
4-Me
4-MeO
4-Cl
4-CN
2,6-Cl2
a) Yields of the isolated products.
Both electron-donating (Me and MeO) and electron-withdrawing (Cl and CN)
substituents of 1b – 1f were all well-tolerated when reacting with 2a, providing the

Helvetica Chimica Acta – Vol. 96 (2013)
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corresponding 3b – 3f in acceptable yields. But it is noteworthy that 1b and 1c with
electron-donating substituents required slightly longer reaction times for complete
conversion (Entries 2 and 3).
To the best of our knowledge, ferrocene substitution at C(6) of 1,2-dihydro-2-
oxopyridine-3-carbonitrile has not previously been reported. The structures of the
compounds 3a – 3f were confirmed via spectroscopic methods and elemental analyses,
with the results being in good agreement with the expected compounds. For instance,
the IR spectrum of compound 3b clearly exhibited the absorption bands characteristic
of the 2-oxopyridine C¼O group at 1629 cmꢀ1, of the CN group at 2216 cmꢀ1, and of the
NH group at 3455 cmꢀ1. The main features of its 1H-NMR spectrum were the presence
of the signals corresponding to HꢀC(5) and NH of the 2-oxopyridine ring at 6.49 and
13.18 ppm, respectively, which is consistent with the assigned structure of 3b. In the 1H-
decoupled 13C-NMR spectrum, the signal for the C¼O group appeared at 164.28 ppm,
while the CN signal was detected at 116.65 ppm. All these observations are consistent
with the chemical shifts of similar types of 2-oxopyridine-3-carbonitrile [13][27][31],
and thus, clearly indicated the formation of the desired product. Finally, the obtained
elemental analysis values are also in agreement with calculated data.
On the basis of these experiments, a mechanistic proposal portraying the probable
sequence of events for the formation of the title compounds is outlined in Scheme 2.
Condensation of the two fragments involves in the first step the formation of the
Michael adduct A, which undergoes subsequent intramolecular nucleophilic cyclization
with participation of the amide N-atom and the chalcone C¼O group to form the
Scheme 2

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dihydro-2-oxopyridine-3-carbonitrile C via B by elimination of H2O. Subsequently, the
species would be converted to an anion of the type D in the presence of excess EtONa,
which, in the presence of an oxidant such as O2, is further converted to radical anion E
via single-electron transfer [31][34]. Finally, aromatization of E by loss of an H-atom
results in the formation of product 3.
1H-NMR Spectroscopy was used to monitor the reaction. However, neither the
Michael adduct A nor the cyclized intermediate C was detected. The result indicated
that the generated intermediate A was highly reactive and underwent spontaneous
cyclization with the subsequent dehydration and aromatization to provide the final 1,2-
dihydro-2-oxopyridine-3-carbonitrile. It is worthy to mention that Carles et al. [34]
observed that the condensation of an enone with 2-cyanoacetamide derivatives in the
t
presence of BuOK yielded ꢂdescyano pyridine-2-onesꢃ in the absence of an O2
atmosphere via ꢂdecyanidative aromatizationꢃ. However, under our reaction condi-
tions, the transformation leading to ꢂdescyano pyridin-2onesꢃ was not observed,
probably because the O2 concentration in solution was sufficient to promote rapid
oxidation of C. An example that is particularly relevant to the present discussion is
described in [29], where 1,2-dihydro-2-oxopyridine-3-carbonitrile derivatives could
also be obtained in refluxing BuOH in the absence of O2.
Conclusions. – We have described a facile synthesis of a new series of ferrocenyl-
substituted 1,2-dihydro-2-oxopyridine-3-carbonitrile derivatives. In view of the syner-
gism of both the ferrocene ring system and pyridine-3-carbonitrile moiety in a single
molecule, the newly synthesized compounds would likely possess significant biological
activities and could be employed in the developement of lead compounds. The
biological activities of the synthesized compounds are under investigation. Addition-
ally, it should be emphasized that these compounds belong to a new class of 1,2-
dihydro-2-oxopyridine-3-carbonitrile systems, and thus, a further investigation of the
synthetic potential of these scaffolds should provide access to significant chemical
diversity via further derivatization reactions.
Experimental Part
General. M.p.: WRS-1B melting-point apparatus; uncorrected. IR Spectra: Shimadzu FT-IR-8400S
(Shimadzu, Japan) spectrophotometer; KBr pellets; ˜n in cmꢀ1. 1H- and 13C-NMR spectra: Bruker Avance
spectrometer, at 400 and 100 Mhz, resp., with CDCl3 or (D6)DMSO as solvent; d in ppm rel. to Me4Si as
internal standard, J in Hz. Elemental analyses: EL-III element analyzer.
General Procedure for the Preparation of 4-Aryl-6-ferrocenyl-1,2-dihydro-2-oxopyridine-3-carbo-
nitriles 3a – 3f. A mixture of one of the selected ferrocenyl chalcones 1a – 1f (1.0 mmol) [24][25] and 2-
cyanoacetamide (2a; 92.4 mg, 1.1 mmol) in 8 ml of a freshly prepared EtONa (68.0 mg, 1 mmol) soln. in
EtOH was stirred at 708. After the completion of the reaction (TLC), the mixture was acidified with 10%
AcOH, and the resulting solid, which precipitated on standing, was collected. Recrystallization from
EtOH gave the corresponding product (59 – 70% yields).
6-Ferrocenyl-1,2-dihydro-2-oxo-4-phenylpyridine-3-carbonitrile (3a). Yield: 235 mg (62%). Purple
needles. M.p. 246 – 2488. IR (KBr): 3449 (NH), 3103, 2217 (CN), 1633 (C¼O), 1588, 1535, 1491, 1444,
1378. 1H-NMR (400 MHz, CDCl3): 4.30 (s, 5 H, ferrocenyl (Fc)); 4.67 (s, 2 H, Fc); 5.11 (s, 2 H, Fc); 6.48
(s, C5NH); 7.55 – 7.58 (m, 3 H, Ph); 7.69 – 7.71 (m, 2 arom. H); 12.50 (s, NH). 13C-NMR (100 MHz,
CDCl3): 67.0; 68.0; 70.3; 70.9; 95.5; 102.8; 113.9; 127.2; 129.2; 129.7; 138.6; 147.9; 153.9; 165.2. Anal. calc.
for C22H16FeN2O (380.22): C 69.50, H 4.24, N 7.37; found: C 65.62, H 4.13, N 7.56.

Helvetica Chimica Acta – Vol. 96 (2013)
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6-Ferrocenyl-1,2-dihydro-4-(4-methylphenyl)-2-oxopyridine-3-carbonitrile (3b). Yield: 232 mg
(59%). Purple needles. M.p. 256 – 2588. IR (KBr): 3455 (NH), 3101, 2916, 2848, 2216 (CN), 1629
(C¼O), 1590, 1528, 1487, 1447, 1381. 1H-NMR (400 MHz, CDCl3): 2.44 (s, Me); 4.27 (s, 5 H, Fc); 4.64 (s,
2 H, Fc); 5.17 (s, 2 H, Fc); 6.49 (s, C5NH); 7.42 (d, J ¼ 8.4, 2 arom. H); 7.61 (d, J ¼ 8.4, 2 arom. H); 13.18
(s, NH). 13C-NMR (100 MHz, CDCl3): 21.5; 29.7; 68.0; 70.7; 72.4; 74.5; 92.7; 104.7; 116.7; 128.0; 129.6;
131.5; 140.9; 154.5; 160.1; 164.3. Anal. calc. for C23H18FeN2O (394.25): C 70.07, H 4.60, N 7.11; found: C
69.84, H 4.42, N 7.27.
6-Ferrocenyl-1,2-dihydro-4-(4-methoxyphenyl)-2-oxopyridine-3-carbonitrile (3c). Yield: 250 mg
(61%). Purple needles. M.p. 240 – 2418. IR (KBr): 3440 (NH), 3104, 2918, 2850, 2217 (CN), 1632
(C¼O), 1598, 1528, 1489, 1447, 1386. 1H-NMR (400 MHz, (D6)DMSO): 3.86 (s, MeO); 4.21 (s, 5 H, Fc);
4.62 (s, 2 H, Fc); 5.30 (s, 2 H, Fc); 6.65 (s, C5NH); 7.13 (d, J ¼ 8.4, 2 arom. H); 7.69 (d, J ¼ 8.4, 2 arom. H);
12.21 (s, NH). 13C-NMR (100 MHz, (D6)DMSO): 55.9; 68.4; 70.7; 72.2; 75.1; 95.5; 103.7; 114.5; 118.0;
128.7; 130.3; 154.3; 159.1; 161.4; 162.5. Anal. calc. for C23H18FeN2O2 (410.25): C 67.34, H 4.42, N 6.83;
found: C 67.14, H 4.29, N 6.67.
4-(4-Chlorophenyl)-6-ferrocenyl-1,2-dihydro-2-oxopyridine-3-carbonitrile (3d). Yield: 277 mg
(67%). Purple needles. M.p. 262 – 2648. IR (KBr): 3459 (NH), 3105, 2213 (CN), 1629 (C¼O), 1595,
1527, 1487, 1445, 1422, 1383. 1H-NMR (400 MHz, (D6)DMSO): 4.22 (s, 5 H, Fc); 4.64 (s, 2 H, Fc); 5.31 (s,
2 H, Fc); 6.48 (s, C5NH); 7.66 (d, J ¼ 8.4, 2 arom. H); 7.71 (d, J ¼ 8.4, 2 arom. H); 12.36 (s, NH).
13C-NMR (100 MHz, (D6)DMSO): 68.4; 70.7; 72.5; 74.3; 96.2; 103.7; 117.5; 129.1; 129.2; 130.6; 132.3;
135.5; 158.4; 162.3. Anal. calc. for C22H15ClFeN2O (414.67): C 63.72, H 3.65, N 6.76; found: C 63.81, H
3.50, N 6.62.
4-(4-Cyanophenyl)-6-ferrocenyl-1,2-dihydro-2-oxopyridine-3-carbonitrile (3e). Yield: 283 mg
(70%). Orange needlels. M.p. 243 – 2458. IR (KBr): 3436 (NH), 3101, 2212 (CN), 2220 (CN), 1622
1
(C¼O), 1589, 1516, 1483, 1443, 1417, 1379. H-NMR (400 MHz, (D6)DMSO): 4.17 (s, 5 H, Fc); 4.48 (s,
2 H, Fc); 5.15 (s, 2 H, Fc); 6.41 (s, C5NH); 7.75 (d, J ¼ 8.8, 2 arom. H); 7.98 (d, J ¼ 8.8, 2 arom. H); 11.74
(s, NH). 13C-NMR (100 MHz, (D6)DMSO): 67.4; 68.1; 70.3; 70.9; 111.6; 119.1; 128.3; 129.8; 132.6; 133.2;
143.6; 152.6; 162.8; 163.7. Anal. calc. for C23H15FeN3O (405.23): C 68.17, H 3.73, N 10.37; found: C 68.39,
H 3.55, N 10.20.
4-(2,6-Dichlorophenyl)-6-ferrocenyl-1,2-dihydro-2-oxopyridine-3-carbonitrile (3f). Yield: 292 mg
(65%). Purple needles. M.p. 249 – 2518. IR (KBr): 3457 (NH), 3102, 2221 (CN), 1640 (C¼O), 1597,
1532, 1489, 1459, 1429, 1382. 1H-NMR (400 MHz, (D6)DMSO): 4.19 (s, 5 H, Fc); 4.66 (s, 2 H, Fc); 5.35 (s,
2 H, Fc); 6.72 (s, C5NH); 7.58 (d, J ¼ 8.4, 2 arom. H); 7.71 (t, J ¼ 8.4, 1 arom. H); 12.57 (s, NH). 13C-NMR
(100 MHz, (D6)DMSO): 68.7; 70.9; 72.9; 74.1; 97.7; 104.3; 116.1; 129.1; 132.3; 132.7; 155.5; 156.8; 161.8.
Anal. calc. for C22H14Cl2FeN2O (449.11): C 58.84, H 3.14, N 6.24; found: C 58.97, H 3.32, N 6.10.
We would like to acknowledge the financial support from the Natural Science Foundation of
Liaoning Province (Grant No. 201202001).
REFERENCES
[1] P. Thompson, V. C. Manganiello, E. Degerman, Curr. Topic Med. Chem. 2007, 7, 421.
[2] A. H. Abadi, D. A. Abouel-Ella, J. Lehmann, H. N. Tinsley, B. D. Gary, G. A. Piazza, M. A. O.
Abdel-Fattah, Eur. J. Med. Chem. 2010, 45, 90.
[3] A. H. Abadi, T. M. Ibrahim, K. M. Abouzid, J. Lehmann, H. N. Tinsley, B. D. Gary, G. A. Piazza,
Bioorg. Med. Chem. 2009, 17, 5974.
[4] M. Panunzio, M. A. Lentini, E. Campana, G. Martelli, E. Tamanini, P. Vicennati, Synth. Commun.
2004, 34, 345.
[5] G. Pastelin, R. Mendez, E. Kabela, A. Farah, Life Sci. 1983, 33, 1787.
[6] I. W. Cheney, S. Yan, T. Appleby, H. Walker, T. Vo, N. Yao, R. Hamatake, Z. Hong, J. Z. Wu, Bioorg.
Med. Chem. Lett. 2007, 17, 1679.
[7] M. D. Wendt, C. Sun, A. Kunzer, D. Sauer, K. Sarris, E. Hoff, L. Yu, D. G. Nettesheim, J. Chen, S. Jin,
K. M. Comess, Y. Fan, S. N. Anderson, B. Isaac, Bioorg. Med. Chem. Lett. 2007, 17, 3122.

2140
Helvetica Chimica Acta – Vol. 96 (2013)
[8] J. M. Cid, G. Duvey, G. Tresadern, V. Nhem, R. Furnari, P. Cluzeau, J. A. Vega, A. I. de Lucas, E.
´
Matesanz, J. M. Alonso, M. L. Linares, J. I. Andres, S. M. Poli, R. Lutjens, H. Himogai, J. P. Rocher,
G. J. Macdonald, D. Oehlrich, H. Lavreysen, A. Ahnaou, W. Drinkenburg, C. Mackie, A. A.
Trabanco, J. Med. Chem. 2012, 55, 2388.
[9] L. A. Hasvold, W. Wang, S. L. Gwaltney, T. W. Rockway, L. T. J. Nelson, R. A. Mantei, S. A.
Fakhoury, G. M. Sullivan, Q. Li, N. H. Lin, L. Wang, H. Zhang, J. Cohen, W. Z. Gu, K. Marsh, J.
Bauch, S. Rosenberg, H. L. Sham, Bioorg. Med. Chem. Lett. 2003, 13, 4001.
[10] L. ꢄhberg, J. Westman, Synlett 2001, 1296.
[11] K. Pradhan, P. Bhattacharyya, S. Paul, A. R. Das, Tetrahedron Lett. 2012, 53, 5840.
[12] A. M. Serry, S. Luik, S. Laufer, A. H. Abadi, J. Comb. Chem. 2010, 12, 559.
[13] S. S. Bisht, N. Jaiswal, A. Sharma, S. Fatima, R. Sharma, N. Rahuja, A. K. Srivastava, V. Bajpai, B.
Kumar, R. P. Tripathi, Carbohydr. Res. 2011, 346, 1191.
[14] R. P. Hanzlik, P. Soine, W. H. Soine, J. Med. Chem. 1979, 22, 424.
[15] G. Tabbꢅ, C. Cassino, G. Cavigiolio, D. Colangelo, A. Ghiglia, I. Viano, D. Osella, J. Med. Chem.
2002, 45, 5786.
[16] A. Pejovic, I. Damljanovic, D. Stevanovic, M. Vukicevic, S. B. Novakovic, G. A. Bogdanovic, N.
Radulovic, R. D. Vukicevic, Polyhedron 2012, 31, 789.
´
´
[17] J. Quirante, F. Dubar, A. Gonzalez, C. Lopez, M. Cascante, R. Cortes, I. Forfar, B. Pradines, C. Biot,
J. Organomet. Chem. 2011, 696, 1011.
[18] Y.-S. Xie, X.-H. Pan, B.-X. Zhao, J.-T. Liu, D.-S. Shin, J.-H. Zhang, L.-W. Zheng, J. Zhao, J.-Y. Miao,
J. Organomet. Chem. 2008, 693, 1367.
[19] C. Zhao, Z.-Q. Liu, Biochimie 2012, 94, 1805.
[20] W.-T. Gao, Y. Yan, Y. Li, Chem. Pap. 2012, 66, 691.
[21] W.-T. Gao, X.-P. Cheng, Y. Li, Heterocycles 2010, 81, 1923.
[22] W.-T. Gao, X.-P. Cheng, Y. Li, Chin. J. Org. Chem. 2010, 30, 456.
[23] Y. Li, W.-T. Gao, Beilstein J. Org. Chem. 2010, 6, 966.
[24] C. R. Hauser, J. K. Lindsay, J. Org. Chem. 1957, 22, 482.
[25] S.-J. Ji, Z.-L. Shen, S.-Y. Wang, Chin. Chem. Lett. 2003, 14, 663.
[26] J. L. Soto, C. Seoane, A. M. Mansilla, Org. Prep. Proc. Int. 1981, 13, 331.
[27] C. N. OꢃCallaghan, T. B. H. McMurry, C. J. Cardin, D. J. Wilcock, J. Chem. Soc., Perkin Tans. 1 1993,
2479.
[28] R. Jain, F. Roschangar; M. A.Ciufolini, Tetrahedron Lett. 1995, 36, 3307.
[29] H. I. El-Subbagh, S. M. Abu-Zaid, M. A. Mahran, F. A. Badria, A. M. Al-Obaid, J. Med. Chem.
2000, 43, 2915.
[30] C. G. Dave, D. A. Shah, Y. K. Agrawal, Indian J. Chem., Sect. B 2004, 43, 885.
[31] M. Nitta, T. Sakakida, H. Miyabara, H.Yamamoto, S. Naya, Org. Biomol. Chem. 2005, 3, 638.
[32] S. S. Chavan, M. S. Degani, Catal. Lett. 2011, 141, 1693.
[33] W.-J. Zhou, S.-J. Ji, Z.-L. Shen, J. Organomet. Chem. 2006, 691, 1356.
[34] L. Carles, K. Narkunan, S. Penlou, L. Rousset, D. Bouchu, M. A. Ciufolini, J. Org. Chem. 2002, 67,
4304.
Received January 10, 2013