One-Pot Three-Component Synthesis of 2-Amino Pyrimidines in Aqueous PEG-400 at Ambient Temperature

Article abstract of DOI:10.1002/jhet.673

Amino pyrimidines have been synthesized by a one-pot procedure under environmentally friendly reaction conditions at room temperature. The use of aqueous PEG-400 circumvents the problems associated with the toxic, hazardous organic solvents and oxidizing agents.

Full text of DOI:10.1002/jhet.673

Month 2016 One-Pot Three-Component Synthesis of 2-Amino Pyrimidines in Aqueous
PEG-400 at Ambient Temperature
*
Dhanaji V. Jawale, Umesh R. Pratap, Manisha R. Bhosale, and Ramrao A. Mane
Department of Chemistry, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad 431004, Maharashtra, India
E-mail: manera@indiatimes.com
Received June 5, 2010
DOI 10.1002/jhet.673
Published online 00 Month 2016 in Wiley Online Library (wileyonlinelibrary.com).
Amino pyrimidines have been synthesized by a one-pot procedure under environmentally friendly reac-
tion conditions at room temperature. The use of aqueous PEG-400 circumvents the problems associated with
the toxic, hazardous organic solvents and oxidizing agents.
J. Heterocyclic Chem., 00, 00 (2016).
INTRODUCTION
sulfonium salts, and imidazolium derivatives, which make
the routes time-consuming. Also, they need toxic, hazard-
ous, flammable solvents and oxidizing agents. Recently,
Zhuang et al. [20] have reported a one-pot improved
method for the synthesis of 2-amino pyrimidines, but it
does not solve the problem potentially.
Literature reveals that poly(ethylene glycols) (PEGs)
have become popular reaction media in the synthetic or-
ganic chemistry since the last decade. PEGs are known as
non-toxic, inexpensive, non-flammable, and non-ionic liq-
uid reaction media of low volatility [21]. This kind of sol-
vent system fully meets the demands of green chemistry
[22] and is found to be useful for various organic transfor-
mations [23]. PEG-400 has been found as an accelerator in
various synthetic reactions [24].
Multicomponent reactions have gained much importance
in organic chemistry as they reduce the steps and reaction
time and also improve the yields of the products [25].
Considering the drawbacks of existing synthetic routes
of pyrimidines, need of incorporation of green tools like
nonvolatile organic solvents, namely, PEGs, CO2(SC), wa-
ter, and ionic liquids, and the importance of multicompo-
nent one-pot synthetic approach for expediting organic
transformation by safer way, here, it was thought worth-
while to develop a convenient route for the synthesis of
amino pyrimidines.
In continuation of our earlier work carried out to develop
the convenient synthetic protocols for the synthesis of bio-
active heterocycles by applying green tools [26] and con-
sidering the aforementioned urgent need, here, we report
on eco-sustainable one-pot synthetic protocol for the bioac-
tive amino pyrimidines using aq. PEG-400 as medium and
accelerator.
Pyrimidines display a broad spectrum of biological activ-
ities in the field of medicinal chemistry [1]. Lobeglitazone
[2], sulfadimidine [3], and bacimethrin [4] (Fig. 1) have
pyrimidines moieties and antidiabetic, antibacterial, and
antibiotic activities, respectively. Naturally occurring
L-lathrine elicits wide range of biological activities such as
hypoglycemic and antitumor activities [5]. Some pyrimi-
dines are valuable drugs for the treatment of hyperthyroid-
ism, acute leukemia in children, and adult granulocytic
leukemia [6]. Several biological activities are associated
with polysubstituted pyrimidines [7]. Pyrimidines act as
the inhibitors [8] of c-Jun N-terminal kinase, estrogen
receptor–coactivator binding, vascular endothelial growth
factor receptor, and Hsp90 molecular chaperone, and they
also act as antagonists of calcium-sensing receptor [9]. The
polysubstituted pyrimidines are also used for the treatment
of hypoxemia [10], neurosis [11], and neuropathy [12].
They also act as potential antitumor agents [13].
Considering the pharmaceutical activities associated
with pyrimidines, chemists have paid more attention to de-
velop efficient/convenient synthetic routes for obtaining
them in high yields. The various routes presently in use
for obtaining 2,4,6-trisubstituted pyrimidines are well
reviewed by Heravi et al. [14]. The cyclocondensation of
chalcones with amidines at refluxed conditions in presence
of triethylamine in ethanol [15], KOH in ethanol [16] or in
methanol [17], in presence of peroxide [18], sodium
isopropoxide in isopropanol [6], and dimethylformamide
[19] is the most widely way for the synthesis of pyrimi-
dines. These synthetic routes have drawbacks, as they need
amidines, unsaturated ketones, aryl-β-vinyl imines,
© 2016 Wiley Periodicals, Inc.

D. V. Jawale, U. R. Pratap, M. R. Bhosale, and R. A. Mane
Vol 000
Figure 1. Biologically active amino pyrimidines.
RESULTS AND DISCUSSION
Table 1
Selection of the medium for the synthesis of 4e.
We have developed an environmentally benign one-pot
synthetic protocol for the synthesis of polysubstituted
amino pyrimidines 4 by allowing the interactions of aro-
matic aldehydes 1, aromatic acetophenones 2, and guani-
dine hydrochloride 3 in aq. PEG-400 at room temperature
(Scheme 1, Table 1).
Before developing the aforementioned one-pot route, we
performed the condensation of freshly prepared 3-(4-
chlorophenyl)-1-(4-methoxyphenyl) prop-2-en-1-one and
guanidine hydrochloride in alkaline ethanolic medium at re-
flux for 6–7 h and obtained the amino pyrimidine (4e) with
65% yield. Further, the attempt was made to carry out the
aforementioned model reaction, replacing ethanol with
90% aq. PEG-400. It was found that the reaction was ac-
complished within 4 h at room temperature, giving better
yield, of 78% of the amino pyrimidines (4e).
Keeping these results in mind, an attempt was
made to cyclocondense the three components—aromatic al-
dehyde (1e), acetophenone (2e), and guanidine
hydrochloride (3)—using KOH in different solvents,
namely, dimethylformamide, methanol, ethanol, and
isopropanol at room temperature and obtained the titled 2-
amino pyrimidine (4e) with moderate yields, and results
are shown in Table 1. Most of the solvents employed have
been volatile, toxic, flammable, and corrosive. Therefore,
to provide green medium, the aforementioned referred
model multicomponent condensation was performed by
Solvent
Timea (h)
Yieldb (%)
DMF
Methanol
Ethanol
Isopropanol
PEG-400
90% aq. PEG-400
30
24
24
24
24
10
47
55
60
68
80
89
DMF, dimethylformamide.
aReaction carried at room temperature.
bIsolated yields.
stirring the compounds in PEG-400 as green, safer medium.
It was found that the cyclocondensation was completed
within 24h, giving 80% yield of the 2-amino pyrimidine
(4e).
In another attempt, the multicomponent one-pot conden-
sation was run using 90% aq. PEG-400, and we noticed that
the condensation was completed within 10h at room temper-
ature and gave 89% yield of 2-amino pyrimidines (Table 1).
To optimize the medium composition, we performed the
condensation using various aq. solutions of PEG-400, and
results are summarized in Table 2. From this, it was noticed
that for the reference reaction, the best composition of the
medium for obtaining excellent yield in reduced time was
90% aq. PEG-400, and results are summarized in Table 2.
Using this composition of aq. PEG-400, the other reac-
tions were performed at room temperature, and we obtained
Scheme 1. One-pot synthesis of amino pyrimidines in aq. PEG-400 at room temperature.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2016
One-Pot Three-Component Synthesis of 2-Amino Pyrimidines in Aqueous
PEG-400 at Ambient Temperature
Table 2
Table 4
Aqueous solutions of PEG-400.
Recovering and reusability of aq. PEG-400.
% of aq. PEG-400 (v/v)
Timea (h)
Yieldb (%)
Batch
Yielda (%)
100
95
90
85
80
24
12
10
13
15
80
85
89
80
78
Fresh
1st
2nd
3rd
89
80
75
70
aIsolated yield.
aReaction carried at room temperature.
bIsolated yields.
the intermolecular H-bondings between the terminal H of
hydroxyl group of PEG and carbonyl oxygen of aldehydes
and the H-bonding between ethereal oxygen of PEG-400
and enolic hydroxyl group of acetophenones, respectively.
This, therefore, accelerates the Claisen–Schmidt condensa-
tion at room temperature, leading to the intermediates 2-
propen-1-ones (chalcones). The in situ generated chalcones
might be then undergone 1,4 successive Michael addition
with guanidine. The rate of this Michael addition has been
accelerated because of H-bonding between amino hydro-
gen of guanidine and ethereal oxygen of PEG-400, enhanc-
ing the nucleophilic character of nitrogen of the guanidine
and the electrophilic character of carbonyl carbon of the
chalcones.
excellent yields of the 2-amino pyrimidines by using multi-
components; acetophenones, aryl aldehydes, guanidine
hydrochloride, and KOH data are shown in Table 3.
The developed synthetic strategy for amino pyrimidines
has been economical by recovering and recycling PEG-400
for the same reaction sequences. After completion of the
cyclocondensation, the reaction mass was poured into ice
water, and the obtained solid was filtered. Recovery of
PEG-400 was made by removing water from the aqueous
filtrate using vacuum distillation [27]. The recovered
PEG-400 has been reused for the same reaction sequence
and gave moderate to excellent yield of amino pyrimidine
(4e) (Table 4).
The following is a possible explanation for the rate ac-
celeration of the condensation by aq. PEG-400 leading in
the formation of amino pyrimidines. PEG-400 might have
a dual role: (i) PEG-400 is a nonvolatile unique solvent
for many of the organic substrates as it has the ability to
dissolve hydrophilic and hydrophobic solutes. The multi-
components, therefore, would have been dissolved at room
temperature in 90% aq. PEG-400, forming concentrate ho-
mogenous mass, which would have helped to accelerate
the rate of the condensation. (ii) Here, PEG-400 might
ameliorate the electrophilic character of carbonyl carbon
of aromatic aldehydes and also enhances the nucleophilic
character of α carbon of the acetophenones by forming
CONCLUSION
Thus, we have developed an economical, eco-
sustainable, scalable, and safer one-pot synthetic protocol
for the synthesis of polysubstituted amino pyrimidines
using aq. PEG-400 as medium and accelerator. The fasci-
nating scope of this synthetic strategy to afford the amino
pyrimidines alleviates the use of toxic, hazardous organic
solvents and oxidizing agents.
EXPERIMENTAL
Aromatic acetophenones, aromatic aldehydes, guanidine
hydrochloride, KOH, and PEG-400 were obtained from
SD Fine-Chem Limited, Spectrochem, and Merck. The
1H-NMR and 13C-NMR spectra were recorded at
400 MHz on Geol. The mass spectra were recorded on
Shimadzu GCMS. The melting points were taken in open
capillary and are uncorrected.
General experimental procedure for 2-amino-4,6
diarylpyrimidines 4 (a–g). Potassium hydroxide (20mmol)
was dissolved in 90% aq. PEG-400 solution (10mL). To the
aforementioned solution, acetophenones (10mmol) were
added, and the reaction content was stirred for 0.5h. After
that, aromatic aldehydes (10mmol) were introduced to the
stirred mass, and stirring was then continued at room
temperature for 5.3h. The completion of the reaction was
Table 3
One-pot synthesis of amino pyrimidines in aq. PEG-400.
Melting
points (°C)
Yieldb
(%)
R1
R2
Productsa
4-CH3
4-F
4-Cl
2-Cl
4-Cl
4-CH3
4-Br
4-OCH3
H
H
H
H
4a
4b
4c
4d
4e
4f
119–120
118–120
146–147
120–122
148–149
128–129
153–155
180–182
85
82
87
86
89
87
82
87
4-OCH3
4-OCH3
H
4g
4h
4-OH
aAll products are characterized by 1H-NMR and mass spectral analyses
and are in good agreement with those reported in the literature [18].
bIsolated yields.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

D. V. Jawale, U. R. Pratap, M. R. Bhosale, and R. A. Mane
Vol 000
[3] Shinogi. U S Patent 1959, 2 888 455.
[4] Reddick, J. J.; Saha, S.; Lee, J.; Melnick, J. S.; Perkins, J.;
Begley, T. P. Bioorg Med Chem Lett 2001, 11, 2245.
[5] (a) Adlington, R. M.; Baldwin, J. A.; Catterick, D.; Pritchard,
G. J. J Chem Soc Perkin Trans 1 1999 855; references cited therein;
(b) Rosenthal, G. A. Plant Nonprotein Amino and Imino Acids Biological,
Biochemical and Toxicological Properties; Academic: New York, NY,
1982; Vol 117; (c) Bell, E. A. Biochim Biophys Acta 1961, 47, 602.
[6] Agarwal, A.; Srivastava, K.; Puri, S. K.; Chauhan, P. M. S.
Bioorg Med Chem 2005, 13, 4645.
monitored by thin-layer chromatography. After confirming
in situ formation of the intermediates chalcones, guanidine
hydrochloride (12mmol) was added to the reaction mass
in portions. Then, the reaction content was further stirred
at room temperature for 4h until completion of the
condensation. The progress of the reaction was monitored
by thin-layer chromatography (TLC). It was then poured
into ice-cold water. Thus, obtained solid was filtered,
washed with water, and crystallized by using proper
solvents. PEG-400 was recovered from the filtrate by
vacuum distillation of the aqueous filtrate and recycled for
the same reaction sequences.
Experimental procedure for 2-amino-4-(4-hydroxyphenyl)-
6-(4-methoxyphenyl) pyrimidine 4i. Potassium hydroxide
(20 mmol) was dissolved in 90% aq. PEG-400 solution
(10 mL). To the aforementioned solution, 4-hydroxy
acetophenone was added, and the reaction content was
stirred for 0.5h. After that, 4-methoxy benzaldehyde
(10 mmol) was introduced to the stirred mass, and stirring
was then continued at room temperature for 5.3 h. The
completion of the reaction was monitored by thin-layer
chromatography. After confirming in situ formation of the
intermediate chalcone, guanidine hydrochloride (12 mmol)
and KOH (10 mmol) were added to the reaction mass in
portions. The reaction content was further stirred at room
temperature for 4 h until the completion of the
condensation. The completion was confirmed by thin-layer
chromatography. It was then poured into ice-cold water
and neutralized by HCl. Thus, obtained solid was filtered,
washed with water, and crystallized by using proper
solvents. PEG-400 was not recovered from the filtrate.
[7] (a) Dozorova, E. N.; Grizik, S. I.; Persianova, I. V.; Syubaev,
R. D.; Shvarts, G. Y.; Granik, V. G. Khim-Pharm Z 1985, 19, 154;
(b) Buchdunger, E.; Zimmermann, J.; Mett, H.; Meyer, T.; Muller, M.;
Drucker, B. J.; Lydon, N. B. Cancer Res 1996, 56, 100.
[8] (a) Alam, M.; Beevers, R. E.; Ceska, T.; Davenport, R. J.;
Dickson, K. M.; Fortunato, M.; Gowers, L.; Haughan, A. F.; James, L.
A.; Jones, M. W.; Kinsella, N.; Lowe, C.; Meissner, J. W.; Nicolas, A.
L.; Perry, B. G.; Phillips, D. J.; Pitt, W. R.; Platt, A.; Ratcliffe, A. J.;
Sharpe, A.; Tait, L. J Bioorg Med Chem Lett 2007, 17, 3463; (b)
Alexander, A.; Parent, J. R. G.; Katzenellenbogen, J. A. J Med Chem
2008, 51, 6512; (c) Harris, P. A.; Boloor, A.; Cheung, M.; Kumar, R.;
Crosby, R. M.; Davis-Ward, R. G.; Epperly, A. H.; Hinkle, K. W.; Hunter,
R. N.; Johnson, J. H.; Knick, V. B.; Laudeman, C. P.; Luttrell, D. K.;
Mook, R. A.; Nolte, R. T.; Rudolph, S. K.; Szewczyk, J. R.; Truesdale,
A. T.; Veal, J. M.; Wang, L.; Stafford, J. A. J Med Chem 2008, 51,
4632; (d) Brough, P. A.; Barril, J. B.; Chene, P.; Davies, N. G. M.;
Surgenor, A.; Valenti, M.; Walls, S.; Webb, P.; Mike, W.; Workman, P.;
Wright, L. J Med Chem 2009, 52, 4794.
[9] Yang, W.; Ruan, Z.; Wang, Y.; Kirk, K. V.; Ma, Z.; Arey, B.
J.; Cooper, C. B.; Seethala, R.; Feyen, J. H. M.; Dickson, J. K. Jr. J Med
Chem 2009, 52, 1204.
[10] Yasuji, S.; Masaichi, H.; Kataoka, K.; Hoshina, K.; Yamazaki,
N.; Kadota, T.; Yamaguchi, H. Japan Patent WO 9105784, A1 2, 1991.
[11] Yokoyama, K.; Kato, S.; Kitahara, T.; Imuda, J.; Takei, M.;
Awaya, A.; Nakano, T.; Horigome, K.; Sasaki, T. Japan Patent JP
01040469, A2 10, 1989.
[12] Awaya, A.; Nakano, T.; Kobayashi, H.; Tan, K.; Horikomi, K.;
Sasaki, T.; Yokoyama, K.; Ohno, H.; Kato, K. Japan Patent WO 8704928,
A1 27, 1987.
[13] (a) Maquoi, E.; Sounni, N. E.; Devy, L.; Olivier, F.;
Frankenne, F.; Krell, H. W.; Grams, F.; Foidart, J. M.; Noel, A. Cancer
Res 2004, 10, 4038; (b) Huang, M.; Wang, Y.; Collins, M.; Mitchell, B.
S.; Graves, L. M. Mol Pharmacol 2002, 62, 463; (c) Von Bubnoff, N.;
Veach, D. R.; Miller, W. T.; Li, W.; Sanger, J.; Peschel, C.; Bornmann,
W. G.; Clarkson, B.; Duyster, J. Cancer Res 2003, 63, 6395.
[14] Majid, M. H.; Samaheh, S.; Hossein, A. O.; Rahim, H. S.;
Fatemeh, F. B. Tetrahedron Lett 2009, 50, 662.
[15] Bellura, E.; Langera, P. Tetrahedron 2006, 62, 5426.
[16] (a) Dodson, R. M.; Seyler, J. K. J Org Chem 1951, 16, 461;
(b) Kothari, S.; Singphal, M.; Vijayvergia, D.; Vyas, R.; Verma, B. L. J
Indian Chem Soc 2000, 77, 329.
Spectroscopic data of representative compound.
4-(4-
Chlorophenyl)-6-(4-methoxyphenyl)pyrimidin-2-amine (4e):
1H-NMR (δ ppm, 400MHz, DMSO-d6): 3.8 (s, 3H, –OCH3),
6.71 (s, 2H, –NH2), 7.05 (d, 2H, J=8Hz, Ar–H), 7.57 (d,
2H, J= 8Hz, pyrimidine-H), 7.68 (s, 1H, Ar–H), 8.21 (q, 4H,
J=8Hz, Ar–H); 13C-NMR (δ ppm, 100 MHz, DMSO-d6):
55.8 (–OCH3), 101.5, 114.4 (2× Ar–C), 129.1 (2×Ar–C),
129.2, 130.0 (2×Ar–C), 135.6 (2×Ar–C), 136.8 (2×Ar–C),
161.8, 163.8, 164.4, 165.2: gas chromatography mass
spectrometry (m/z): 312 [M+1], 314 [M+3].
[17] Mont, N.; Teixido, J.; Jose, I. B.; Kappeb, C. O. Tetrahedron
Lett 2003, 44, 5385.
[18] Laszlo, V.; Tamas, N.; Istvan, K.; Jordi, B.; Gyorgy, D.;
Laszlo, U.; Ferenc, D. Tetrahedron 2003, 59, 655.
[19] Zhichkin, P.; Fairfax, D. J.; Eisenbeisb, S. A. Synthesis 2002,
6, 29.
[20] Qiya, Z.; Hong, X. H.; Suhui, W.; Shuajiang, T.; Liangce, R.
Syn Commun 2009, 39, 516.
Acknowledgments. Authors are thankful to Professor D. B. Ingle
for his invaluable discussions and guidance. One of the authors,
D. V. Jawale, is also grateful to UGC, New Delhi, India, for
Research Fellowship in Sciences for meritorious students.
[21] (a) Harris, J. M. Poly(Ethylene Glycol) Chemistry, Biotechno-
logical and Biomedical Applications; Plenum Press: New York, 1992, pp
3; (b) Harris, J. M.; Zalipsky, S. Polyethylene Glycol: Chemistry and
Biological Application; ACS Books: Washington, DC, 1997.
[22] (a) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and
Practice; Oxford Science Publications: New York, 1998; (b) Anastas, P.
T.; Williamson, T. Green Chemistry: Frontiers in Benign Chemical Syn-
thesis and Processes; Oxford Science Publications: New York, 1998;
(c) Clark, J. H. Green Chem 1999, 1; (d) Clark, J. H. Chem Ber 1998, 43.
[23] (a) Vasudevan, V. N.; Rajendra, S. V. Green Chem 2001, 3,
146; (b) Haimov, A.; Neumann, R. Chem Commun 2002, 876; (c) Heiss,
REFERENCES AND NOTES
[1] Jain, K. S.; Chitre, T. S.; Miniyar, P. B.; Kathiravan, M. K.;
Bendre, V. S.; Veer, V. S.; Shahane, S. R.; Shishoo, C. J Current Sci
2006, 90, 25.
[2] Hong, W. L.; Joong, B. A.; Sung, K. K.; Soon, K. A.; Deok, C.
H. Org Process Res Dev 2007, 11, 190.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet

Month 2016
One-Pot Three-Component Synthesis of 2-Amino Pyrimidines in Aqueous
PEG-400 at Ambient Temperature
L.; Gais, H. J Tetrahedron Lett 1995, 36, 3833; (d) Chandrasekar, S.;
Narsihmulu, C.; Shameem, S. S. Chem Commun 2003, 1716;
(e) Tanemura, K.; Nishida, T. Y.; Horaguchi, T. Chem Lett 2005, 34,
576; (f) Kumar, R.; Chaudhary, P.; Nimesh, S. Green Chem 2006, 8,
356; (g) Ballini, R.; Luciano, B.; Alessandro, P. Green Chem 2008, 10,
1004; (h) Dickerson, T. J.; Reed, N. N.; Janda, K. D. Chem Rev 2002,
102, 3325.
[24] (a) Wang, S. L.; Hao, W. J.; Tu, S. J.; Zhang, X. H.; Cao, X.
D.; Yan, S.; Wu, S. S.; Han, Z. G.; Shi, F. J Heterocycl Chem 2009, 46,
664; (b) Zhou, W. J.; Wang, K. H.; Wang, J. X. J Org Chem 2009, 74,
5599; (c) Mao, J.; Hua, Q.; Xie, G.; Yao, Z.; Shi, D. Eur J Org Chem
2009, 14, 2262; (d) Burley, G. A.; Davies, D. L.; Griffith, G. A.; Lee,
M.; Singh, K. J Org Chem 2010, 75, 980; (e) Xu, C.; Wang, Z. Q.; Fu,
W. J.; Lou, X. H.; Li, Y. F.; Cen, F. F.; Ma, H. J.; Ji, B. M. Organometal-
lics 2009, 28, 1909; (f) Yadav, G. D.; Motirale, B. G. Org Process Res
Dev 2009, 13, 341; (g) Kidwai, M.; Bhatnagar, D. Tetrahedron Lett
2010, 51, 2700; (h) Victoria, F. N.; Radatz, C. S.; Sachini, M. R.; Jacob,
G.; Perin, G.; Eder Lenardao, J. Tetrahedron Lett 2009, 50, 6761;
(i) Dawane, B. S.; Konda, S. G.; Mandawad, G. G.; Shaikh, B. M. Eur J
Med Chem 2010, 45, 387; (j) Kidwai, M.; Bhatnagar, D.; Mishra, N. K.
Green Chem Lett Rev 2010, 3, 55.
[25] (a) James, D.; Stephen, F. M. Chem Eur J 2009, 15, 1300;
(b) Weber, L. Drug Discov Today 2002, 7, 143; (c) Domling, A. Curr Opin
Chem Biol 2002, 6, 306.
[26] (a) Mahalle, S. R.; Netankar, P. D.; Bondge, S. P.; Mane, R. A.
Green Chem Lett Rev 2008, 2, 103; (b) Pratap, U. R.; Mali, J. R.; Jawale,
D. V.; Mane, R. A. Tetrahedron Lett 2009, 50, 1352; (c) Mali, J. R.;
Pratap, U. R.; Netankar, P. D.; Mane, R. A. Tetrahedron Lett 2009, 50,
5025; (d) Jawale, D. V.; Lingampalle, D. L.; Pratap, U. R.; Mane, R. A.
Chin Chem Lett 2010, 21, 412.
[27] Santaniello, E.; Manzocchi, A.; Sozzani, P. Tetrahedron Lett
1979, 20, 4581.
Journal of Heterocyclic Chemistry
DOI 10.1002/jhet