Zinc-catalyzed multicomponent reactions: Facile synthesis of fully substituted pyridines

Article abstract of DOI:10.1080/00397911.2018.1463545

A first example of environmentally benign zinc complex catalyzed one-pot four-component reaction between malononitrile, ketone, ammonium acetate and aromatic aldehyde for the facile synthesis of fully substituted pyridines just within 2 min in environment

Full text of DOI:10.1080/00397911.2018.1463545

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
Zinc-catalyzed multicomponent reactions: Facile
synthesis of fully substituted pyridines
Ramaiah Konakanchi, Shravankumar Kankala & Laxma Reddy Kotha
To cite this article: Ramaiah Konakanchi, Shravankumar Kankala & Laxma Reddy Kotha (2018):
Zinc-catalyzed multicomponent reactions: Facile synthesis of fully substituted pyridines, Synthetic
Communications, DOI: 10.1080/00397911.2018.1463545
To link to this article: https://doi.org/10.1080/00397911.2018.1463545
Published online: 29 May 2018.
Submit your article to this journal
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=lsyc20

R
SYNTHETIC COMMUNICATIONSV
https://doi.org/10.1080/00397911.2018.1463545
Zinc-catalyzed multicomponent reactions: Facile synthesis
of fully substituted pyridines
Ramaiah Konakanchia, Shravankumar Kankalab and Laxma Reddy Kothaa
b
aDepartment of Chemistry, National Institute of Technology, Warangal, India; Department of Chemistry,
Kakatiya University, Warangal, India
ABSTRACT
ARTICLE HISTORY
Received 7 February 2018
A first example of environmentally benign zinc complex catalyzed
one-pot four-component reaction between malononitrile, ketone,
ammonium acetate and aromatic aldehyde for the facile synthesis of
fully substituted pyridines just within 2 min in environmentally
friendly solvent ethanol has been optimized.
KEYWORDS
Atom economy; fully
substituted pyridines; green
chemistry; multicomponent
reaction; zinc catalyst
GRAPHICAL ABSTRACT
Introduction
Zinc is one of the highly abundant, cheaper and low toxic metals of the periodic table.
It can be easily separated/extracted in high purity from the corresponding minerals than
many other metals. The biological relevance of zinc makes it an essential trace element
to regulate the enzymatic function of both animal and plant kingdom. Besides, at pre-
sent the current research in ‘green chemistry’ is focusing on the use of cheaper and low
toxic metals as catalysts or stoichiometric reagents to develop environmentally sustain-
able protocols in organic synthesis and pharmaceutical synthesis.[1] In line of these
precedents, the use of zinc based catalysts (homogeneous/heterogeneous) and reagents
would be a good choice to meet the requirements of green chemistry.[1b,2]
CONTACT Laxma Reddy Kotha
laxmareddychem12@gmail.com
Department of Chemistry, National Institute of
Technology, Warangal 506004, India.
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsyc.
Supplemental data for this article can be accessed on the publisher's website.
ß 2018 Taylor & Francis

2
R. KONAKANCHI ET AL.
Figure 1. Structure of Zn(ANA)2Cl2 complex.
Since the discovery of first organometallic diethyl zinc, a variety of catalytic and stoi-
chiometric reagent applications of zinc compounds have been found in organic synthesis.
For instance, the use of zinc in Negishi coupling, Reformatskii and Fukuyama reactions
has been recognized as breakthrough reactions of organic synthesis.[3,4] However, as com-
pared to other metals, the use of zinc compounds in organic synthesis is still under
developing stage due to its position in the periodic table, where zinc is placed between
transition and main group elements. The filled d-orbital electronic configuration provides
zinc a different chemistry than those of other d-block elements and more related chemis-
try to main group elements, which is quite simple and predictable. However, recent
trends in green chemistry have been strongly recommending the development of cheaper
and low toxic zinc based organic transformations of C–C, C-heteroatom bond forming
reactions for sustainable environment.[1c,5]
The concept of multicomponent reaction (MCR) is one type of modern perspective
emerged in green chemistry, wherein three or more than three components reacts in
one-pot through sequential reactions and provides selectively the desired product by
reducing the waste. MCRs are indeed cost-effective, time-saving and environmentally
benign as compared to step-by-step reactions of traditional organic synthesis in achiev-
ing the desired final/target product. Majority of MCRs require a multifunctional
catalyst to control the selectivity in the sequential reactions. At present, catalyzed MCRs
are in common practice to synthesize a variety heterocycles and heteroatomic
organic compounds.[6]
We are interested in developing a facile MCR protocol to synthesize highly substi-
tuted pyridines in view of their intriguing applications in medicinal and materials chem-
istry.[7] The use of a variety of homogeneous and heterogeneous catalysts has been
reported previously to synthesize various densely substituted pyridines via traditional
organic synthesis or MCR synthesis.[8,10a,10b]
Results and discussion
Herein we report usefulness of homogeneous Zn(ANA)2Cl2 complex (ANA ¼ 2-
Aminonicotinaldehyde; Fig. 1) as catalyst for the one-pot four-component condensation of
malononitrile, ketone and ammonium acetate as partners to aromatic aldehydes to form a
variety of fully substituted pyridines in environmentally friendly solvent ethanol (EtOH;
Scheme 1) at room temperature (RT) conditions. It is a considerable topic that the green
aspect is connected not only with the use of water as reaction medium but also with the
possibility to use other green solvents such as ethanol to improve the yields and selectivity.

R
SYNTHETIC COMMUNICATIONSV
3
Scheme 1. Synthesis of fully substituted pyridines.
The Zn(ANA)2Cl2 complex was prepared on mixing freshly prepared solutions of
ANA dissolved in 20 ml ethanol and Zinc chloride tetrahydrate (ZnCl2.4H2O) dissolved
in 10 ml ethanol, at reflux temperature for about 3 h. At the end of the reaction excess
ethanol was removed by vacuum and filtered after cooling to obtain pure Zn(ANA)2Cl2
complex. The Zn(ANA)2Cl2 complex has been reported by us recently[9] and now we
extend the studies to explore its catalytic ability in MCR. It is worth noting that previ-
ously there were only few reports found in literature about the catalytic MCR synthesis
of fully substituted pyridines. However, there was no information about the use of zinc
catalysts in the MCR synthesis of fully substituted pyridines.
Initially we choose to probe a four-component sequential one-pot reaction (MCR)
between benzaldehyde (Compound 1a) malononitrile (Compound 2), ammonium acetate
(Compound 3) and 2-butanone (Compound 4; acyclic ketone) in ethanol in the presence
of different zinc salts and a Zn(ANA)2Cl2 complex for the synthesis of substituted pyri-
dine (Compound 5a). The details of the reaction and the results are given in Table 1.
The intended MCR was not observed in the absence of catalyst at RT conditions in
ethanol (Table 1, Entry1). Later, we have investigated the above MCR in the presence of
different zinc salts including zinc acetate (Zn(OAc)2), zinc trifluoromethanesulfonate
(Zn(OTf)2), zinc chloride (ZnCl2), zinc nitrate (Zn(NO3)2), zinc bromide (ZnBr2), zinc tet-
rafluoroborate hydrate (Zn(BF4)2), zinc iodide (ZnI2;Table 1, Entries 2–8) and copper salts
cupric chloride (CuCl2) and copper(II) bromide (CuBr2) as catalysts (Table 1, Entries 9,
10) at RT conditions. However, we have noticed that the simple zinc salts and copper salts
did not facilitate the intended MCR at RT. In this situation, when Zn(ANA)2Cl2 (Fig. 1)
was employed as a catalyst, there was a dramatic acceleration in the proposed MCR at RT
only and yielded the expected/desired substituted pyridine (Compound 5a) selectively just
in 2 min in good yield (92%, Table 1, Entry 11). It is also important to note that the above
Zn(ANA)2Cl2 catalyzed reaction was observed to be sluggish and non-selective in non-
protic solvents, tetrahydrofuran (THF), acetonitrile (CH3CN), dichloromethane (DCM),
dioxane, benzene (Table 1, Entries 12–16). This information outlines that the choice of
solvent is also one of the key factors in this catalyzed MCR.
Literature information reveals that there were few similar MCR strategies (malononi-
trile, ketone, ammonium acetate and aromatic aldehyde) were developed with or without
using catalysts.[10,11] However, except the one with the use of Ag(I)-NHC catalysts[10a]
,
those remained methodologies reported the requirement of refluxing or microwave con-
ditions and longer reaction times.[11] Our results indicates the efficiency of zinc catalyst
(Zn(ANA)2Cl2) in catalyzing the MCR at just RT conditions to produce Compound 5a

4
R. KONAKANCHI ET AL.
Table 1. Optimization of reaction parameters for the synthesis of Compound 5a.
Entry
Catalyst
Solvent
Yield (%)a
1
2
3
4
5
6
7
8
No catalyst
Zn(OAc)2
Zn(OTf)2
ZnCl2
Zn(NO3)2
ZnBr2
Zn(BF4)2
ZnI2
CuCl2
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
THF
–
24
36
35
30
32
35
35
28
26
92
22
18
20
Trace
Trace
9
10
11
12
13
14
15
16
CuBr2
Zn(ANA)2Cl2
Zn(ANA)2Cl2
Zn(ANA)2Cl2
Zn(ANA)2Cl2
Zn(ANA)2Cl2
Zn(ANA)2Cl2
CH3CN
DCM
Dioxane
Benzene
aGC yields.
to meet the requirements of green catalysis. The solid product of Compound 5a
obtained in our work was further identified and quantified on the basis of its analytical
and spectral data (Refer the “Experimental” section).
Using the above optimized conditions (Zn(ANA)2Cl2, 2 mol%, 2 min, RT, ethanol) for
four-component MCR, we extended substrate scope to synthesize some diverse fully sub-
stituted pyridines. We have used various structurally different aldehydes (Compounds
1b–g), acyclic ketones (Compound 4) and cyclic ketones (Compound 6a–c)) in the MCR
to study the electronic effects. The results are summarized in Scheme 2. The results indi-
cate that the Zn(ANA)2Cl2 is highly also efficient in facilitating the MCRs of Scheme 2
and providing the good yields in shorter reaction times. The substrates of MCR bearing
electron donating or electron-withdrawing groups on the aromatic ring proceeded
smoothly and formed the corresponding fully substituted pyridines in good yields.
Structures of the substituted pyridines (Compounds 5(a–d) and 7(a–i), Scheme 2)
were established on the basis of elemental analysis and spectral data (1H and 13C NMR).
The details of the product characterization are presented in the “Experimental” section.
Finally, based on the results obtained in our work and previous reports concerning
the MCR synthesis of fully substituted pyridines including control experiments, a plaus-
ible mechanism has been deduced in Scheme 3. The reaction may proceed via forming
enamine (Compound A) the condensed product of ketone and ammonium acetate, then
activated by Zn(ANA)2Cl2, which then reacts with alkylidenemalononitrile (Compound
B; Compound C; Michael adduct). The Michael adduct then undergoes cycloaddition
and isomerization to give 1,4-dihydropyridine (Compound D). The subsequent oxidative
aromatization of 1,4-dihydropyridine (Compound D) under air atmosphere will produce

R
SYNTHETIC COMMUNICATIONSV
5
Scheme 2. Synthesized fully substituted pyridine derivatives.
the desired fully substituted pyridines (Compounds 5(a–d) and 7(a–i)) as shown in
Scheme 3.
Experimental
General
All commercially available reagents were used without further purification. Reaction sol-
vents were dried by standard methods before use. Purity of the compounds was checked
by thin layer chromatography (TLC) using Merck 60F254 silica gel plates. Elemental

6
R. KONAKANCHI ET AL.
Scheme 3. A plausible mechanism for the formation fully substituted pyridines.
1
analyses were obtained with an Elemental Analyser Perkin-Elmer 240C apparatus. H-
and 13C NMR spectra were recorded with a Mercuryplus 400 spectrometer (operating at
1
400 MHz for H and 100.58 MHz for 13C); chemical shifts were referenced to trimethyl
silane. Electron impact (EI) mass spectra (at an ionising voltage of 70 eV) were obtained
using a Shimadzu QP5050A quadrupole-based mass spectrometer.
Catalyst preparation
General procedure for the synthesis of [Zn(ANA)2Cl2] complex
The freshly purified ligand (0.488 g, 4 mmol) was dissolved in EtOH (20 ml) and added
ethanolic solution of ZnCl2.4H2O (0.273 g, 2 mmol) were stirred at reflux temperature
after mixing the solution for about 3 h. At the end of the reaction the excess ethanol
was removed in vacuum and filtered after cooling without further purification to obtain
75% yield. Yellow solid: mp 288–290 ꢀC; IR (KBr, cmꢁ1): 3412 (N–H), 1678 (C¼O),
1
1564(C¼N (py)). H NMR (400 MHz, DMSO): d ¼ 6.73–6.76 (m, 2H), 7.56 (s, 4H), 8.00
(d, J ¼ 8.0 Hz, 2H), 8.24 (d, J ¼ 8.0 Hz, 2H), 9.85 (s, 2H) ppm. 13C NMR (100 MHz,
DMSO): d ¼ 112.69, 113.49, 145.08, 155.31, 158.68and 194.10 ppm. Anal. calculated
(calcd; %) for Zn(C6H6N2O)2Cl2: Calcd: C, 37.85; H, 3.17and N, 14.72. Found: C, 37.80;
H, 3.15and N 14.69.

R
SYNTHETIC COMMUNICATIONSV
7
General procedure for the synthesis of pyridines (Compounds 5(a–d) and 7(a-i))
Aromatic aldehydes (Compound 1; 1 mmol) and malononitrile (1 mmol) was dissolved
in EtOH (10 ml) and added the ethanolic solution of cyclic ketone/ethyl methyl ketone
(Compounds 2(a–c) or 2d; 1.2 mmol), ammonium acetate (1.2 mmol) and catalyst
Zn(ANA)2Cl2 (2 mol%) were stirred over a period of 2 min at room temperature.
Complete consumption of starting material as judged by TLC and Gas chromatography
(GC) analysis. The reaction mass was filtered and washed with ethanol to obtained off-
white solid crude product which was subjected to recrystallization in hot ethyl acetate to
afford pure products (Compounds 5(a–d) and 7(a-i)).
2-Amino-5,6-dimethyl-4-phenyl-nicotinonitrile (5a): The product was obtained as off-
1
white solid: Yield (88%); mp 240–241 ꢀC; H NMR (400 MHz, CDCl3): d ¼ 1.95 (s, 3H,
CH3), 2.44 (s, 3H, CH3), 5.05 (s, 2H, NH2), and 7.23–7.50 (m, 5H) ppm. 13C NMR
(100 MHz, CDCl3): d ¼ 15.30, 23.72, 89.72, 116.80, 119.69, 128.33, 128.64, 128.77, 136.79,
153.86, 157.23 and 161.57 ppm. Anal. calcd (%) for C14H13N3: Calcd: C, 75.31; H,
5.87and N, 18.82. Found: C, 75.37; H, 5.89and N 18.78.
2-Amino-4-phenyl-6,7-dihydro-5H-cyclopenta[b]pyridine-3-carbonitrile (Compound 7a):
1
The product was obtained as off-white solid: Yield (92%); mp 220–221 ꢀC; H NMR
(400 MHz, CDCl3): d ¼ 1.90–1.98 (m, 2H), 2.60 (t, J ¼ 7.3 Hz, 2H), 2.80 (t, J ¼ 7.6 Hz,
2H), 6.66 (s, 2H, NH2), and 7.42–7.51 (m, 5H) ppm. 13C NMR (100 MHz, CDCl3):
d ¼ 22.22, 28.78, 34.50, 85.52, 117.39, 123.02, 128.24, 128.49, 128.92, 135.92, 149.16,
160.99, and 169.64 ppm. Anal. calcd (%) for C15H13N3: Calcd: C, 76.57; H, 5.57and N,
17.86. Found: C, 76.59; H, 5.58and N, 17.89.
Conclusion
In conclusion, we have demonstrated the usefulness of a cheaper, low toxic and environ-
mentally benign zinc metal complex, Zn(ANA)2Cl2 as catalyst in the MCR between alde-
hyde, ammonium acetate, ketone and malononitrile to produce a variety of fully
substituted pyridines in good yields. The use of ethanol is not only favored the fast
accomplishment of MCR at RT conditions, but also promoted the non-toxic solvents for
green chemical synthesis. Further studies are warranted to address the nature of the
active catalysts under these conditions. The presence of reactive ꢁCN and ꢁNH2 groups
at five and six positions, respectively, renders these compounds for further transforma-
tions towards more complex heterocycles.
Acknowledgements
RK thanks the MHRD, New Delhi for a research fellowship.
References
[1] Reviews on zinc catalysis: (a) Wu, X.-F. Chem. Asian J. 2012, 7, 2502–2509. (b) Enthaler, S.
ACS Catal. 2013, 3, 150–158. (c) Wu, X.-F.; Neumann, H. Adv. Synth. Catal. 2012, 354,
3141–3160. (d) Enthaler, S.; Wu, X.-F. Zinc Catalysis: Applications in Organic Synthesis;
ꢀ
ꢀ
Wiley, V. C. H: Weinheim, 2015. (e) Gonzalez, M. J.; Lopez, L. A.; Vicente, R. Tetrahedron
Lett. 2015, 56, 1600–1608.

8
R. KONAKANCHI ET AL.
[2] (a) Altman, E.; Stefanidis, G. D.; Gerven van, T.; Stankiewicz, A. Ind. Eng. Chem. Res.
2012, 51, 1612–1619. (b) Hosein, I. D.; Liddell, C. M. Langmuir. 2007, 23, 2892–2897.
(c) Shin-ichiro, F.; Yuki, Y.; Masahiko, A. J. Catal. 2013, 297, 137–141. (d) Cucciolito,
M. E.; Lega, M.; Papa, V.; Ruffo, F. Catal. Lett. 2016, 146, 1113–1117. (e) Wilson, K.;
Renson, A.; Clark. J. H. Catal. Lett. 1999, 61, 51–55.
[3] (a) Marie-France, L.; Damien, B.; Janine, C. Org. Lett. 2005, 7, 171–173. (b) Thapa, S.;
Vangala, A. S.; Giri, R. Synthesis. 2016, 48, 504–511.
[4] (a) Herrmann, W. A. Synthetic Methods of Organometallic and Inorganic Chemistry:
Catalysis; Verlag, G. T: Stuttgart, 2002. (b) Knochel, P.; Jones, P. Organozinc Reagents: A
Practical Approach; Oxford University Press: Oxford, 1999. (c) Sase, S.; Jaric, M.; Metzger,
A.; Malakhov, V.; Knochel, P. J. Org. Chem. 2008, 73, 7380–7382. (d) Hadei, N.; Kantchev,
E. A. B.; O’Brien, C. J.; Organ, M. G. Org. Lett. 2005, 7, 3805–3807. (e) Han, C.;
Buchwald. S. L. J. Am. Chem. Soc. 2009, 131, 7532–7533. (f) Diana, H.; Jeffrey, M. H.;
Robert, G.; Paul, K. ACS Catal. 2016, 6, 1540–1552. (g) Sailer, M.; Dumichi, K. I.;
Sorensen, J. L. Synthesis. 2015, 47, 79–82. (h) Wolf, C.; Moskowitz, M. J. Org. Chem. 2011,
76, 6372–6376. (i) Toshiaki, S.; Masahiko, S. Tetrahedron Lett. 2001, 42, 429–432.
[5] Krasovskiy, A.; Duplais, C.; Lipshutz, B. H. J. Am. Chem. Soc. 2009, 131, 15592–15593.
[6] (a) Zhang, X.; Xu, X.; Chen, G.; Yi, W. Org. Lett. 2016, 18, 4864–4867. (b) Chu, J. J.; Hu,
B. L.; Liao, Z. Y.; Zhang, X. G. J. Org. Chem. 2016, 81, 8647–8652. (c) Mou, X. Q.; Xu,
Z. L.; Xu, L.; Wang, S. H.; Zhang, B. H.; Zhang, D.; Wang, J.; Liu, W. T.; Bao, W. Org.
Lett. 2016, 18, 4032–4035. (d) Zhang, X.; Liu, W.; Sun, R.; Xu, X.; Wang, Z.; Yan, Y.
ꢀ
Synlett. 2016, 27, 1563–1568. (e) Patil, P.; Zhang, J.; Kurpiewska, K.; Kalinowska-Tłuscik,
€
J.; Domling, A. Synthesis. 2016, 48, 1122–1130. (f) Chandrasekhar, S.; Patro, V.; Chavan,
ꢀ
L. N.; Chegondi, R.; Gree, R. Tetrahedron Lett. 2014, 55, 5932–5935. (g) Brahmachari, G.;
Das, S. Tetrahedron Lett. 2012, 53, 1479–1484.
ꢀ
[7] (a) Chen, Q.; Leon, T.; Knochel, P. Angew. Chem. Int. Ed. 2014, 53, 8746–8750.
(b) Tummala, R. K. R.; Roger, M.; William, H.; Kai, G.; Valerie, J. G.; Steven, P.; Beining,
C. J. Med. Chem. 2006, 49, 607–615. (c) Roger, S.; Uwe, G.; Adrienne, M. H.; Luca, G.;
€
Jurgen, F.; Christoph, U.; Stefanie, D. K.; Roger, S.; Linjing, M.; Simon, M. A. J. Med.
Chem. 2015, 58, 4266–4277. (d) Lei, C. H.; Wang, D. X.; Zhao, L.; Zhu, J.; Wang, M. X. J.
Am. Chem. Soc. 2013, 135, 4708–4711. (e) Doebelin, C.; Wagner, P.; Bihel, F.; Humbert,
N.; Kenfack, C. A.; Mely, Y.; Bourguignon, J. J.; Schmitt, M. J. Org. Chem. 2014, 79,
908–918. (f) Guan, B. T.; Hou, Z. J. Am. Chem. Soc. 2011, 133, 18066–18069. (g) Meng,
X.; Wang, Y.; Yu, C.; Zhao, P. RSC Adv. 2014, 4, 27301–27307. (h) Mohan, D. C.; Rao,
S. N.; Adimurthy, S. J. Org. Chem. 2013, 78, 1266–1272. (i) Dhakshinamoorthy, A.; Garcia,
H. Chem. Soc. Rev. 2014, 43, 5750–5765. (j) Abdel-Mohsen, H. T.; Conrad, J.; Beifuss, U.
Green Chem. 2012, 14, 2686–2690. (k) Shi, Z.; Loh, T. P. Angew. Chem. Int. Ed. 2013, 52,
8584–8587. (l) Neely, J. M.; Rovis, T. J. Am. Chem. Soc. 2014, 136, 2735–2738. (m) Jiang,
Y.; Park, C. M.; Loh, T. P.; Org. Lett. 2014, 16, 3432–3435. (n) Stark, D. G.; Morrill, L. C.;
Yeh, P. P.; Slawin, A. M. Z.; O’Riordan, T. J. C.; Smith, A. D. Angew. Chem. Int. Ed. 2013,
52, 11642–11646. (o) Rostamnia, S.; Morsali, A. RSC Adv. 2014, 4, 10514–10518. (p) He,
Z.; Dobrovolsky, D.; Trinchera, P.; Yudin, A. K. Org. Lett. 2013, 15, 334–337.
(q) Ananthakrishnan, R.; Gazi, S. Catal. Sci. Technol. 2012, 2, 1463–1471.
[8] Homogenous-catalyzed, pyridine synthesis: (a) Zheng, L.; Ju, J.; Bin, Y.; Hua, R. J. Org.
Chem. 2012, 77, 5794–5800. (b) Wang, C.; Li, X.; Wu, F.; Wan, B. Angew. Chem. Int. Ed.
2011, 50, 7162–7166. (c) Xin, X.; Wang, Y.; Kumar, S.; Liu, X.; Lin, Y.; Dong, D. Org.
Biomol. Chem. 2010, 8, 3078–3082. (d) Jiang, B.; Hao, J.; Wang, X.; Shi, F.; Tu, S. J. J.
Comb. Chem. 2009, 11, 846–850. (e) Zhou, F.; Liu, X.; Zhang, N.; Liang, Y.; Zhang, R.;
Xin, X.; Dong, D. Org. Lett. 2013, 15, 5786–5789. (f) Sha, F.; Wu, L.; Huang, X. J. Org.
Chem. 2012, 77, 3754–3765. (g) Yamamoto, S.; Okamoto, K.; Murakoso, M.; Kuninobu,
Y.; Takai, K. Org. Lett. 2012, 14, 3182–3185. (h) Wang, C.; Wang, D.; Xu, F.; Pan, B.;
Wan, B. J. Org. Chem. 2013, 78, 3065–3072. (i) Thirumurugan, P.; Perumal, P. T.
Tetrahedron. 2009, 65, 7620–7629. (j) Raja, V. P. A.; Tenti, G.; Perumal, S.; Menꢀendez,
J. C. Chem. Commun. 2014, 50, 12270–12272. (k) Hao, Y.; Xu, X. P.; Chen, T.; Zhao,

R
SYNTHETIC COMMUNICATIONSV
9
L. L.; Ji, S. J. Org. Biomol. Chem. 2012, 10, 724–728. (l) Hu, J.; Deng, Z.; Zhang, X.;
Zhang, F.; Zheng, H. Org. Biomol. Chem. 2014, 12, 4885–4889. (m) Shekarrao, K.;
Kaishap, P. P.; Gogoi, S.; Boruah, R. C. RSC Adv. 2014, 4, 14013–14023; Heterogenous-cat-
€
alyzed, pyridine synthesis: (n) Abahmane, L.; Knauer, A.; Ritter, U.; Kohler, J. M.; Grosz,
G. A. Chem. Eng. Technol. 2009, 32, 1799–1805. (o) Sandeep, V. H. S. B.; Suresh, M.;
Kranthi, K. G.; Sreekantha, B. J. Arab. J. Chem. 2017. (In press). (p) Sebenzile, S.; Suresh,
M.; Werner, E. V. Z.; Sreekantha. B. J. Ind. Eng. Chem. Res. 2017, 56, 11372–11379.
[9] Ramachary, M.; Ramaiah, K.; Ramu, G.; Nethaji, M.; Durgaiah, G.; Narsimha Reddy, Y.;
Laxma Reddy, K. Inorganica Chim. Acta. 2018, 469, 66–75.
[10] (a) Shravankumar, K.; Ramakanth, P.; Suresh M.; Chandra, S. V.; Sreekantha, B. J. RSC
Adv. 2015, 5, 105446–105452. (b) Ramakanth, P.; Suresh, M.; Vashen, M.; Werner,
E. V. Z.; Sreekantha, B. J. Tetrahedron Lett. 2014, 55, 4006–4010. (c) Tang, J.; Wang, L.;
Yao, Y.; Zhang, L.; Wang, W. Tetrahedron Lett. 2011, 52, 509–511. (d) Pagadala, R.;
Maddila, S.; Dasireddy, V. D. B. C.; Jonnalagadda, S. B. Catal. Commun. 2014, 45,
148–152. (e) Pagadala, R.; Maddila, S.; Rana, S.; Jonnalagadda, S. B. RSC Adv. 2014, 4,
6602–6607. (f) Pagadala, R.; Maddila, S.; Jonnalagadda, S. B. Ultrason. Sonochem. 2014, 21,
472–477.
[11] (a) Mungra, D. C.; Patel, M. P.; Patel, R. G. ARKIVOC. 2009, xiv, 64. (b) Shi, F.; Tu, S.;
Fang, F.; Li, T. ARKIVOC. 2005, i, 137.