Nickel complexes as efficient catalysts in multicomponent synthesis of tetrahydropyridine derivatives

Article abstract of DOI:10.1080/00397911.2020.1803357

Ni(Salen) complexes as an efficient, homogeneous catalysts revealed a catalytic activity toward the one-pot synthesis of tetrahydropyridine derivatives through the pseudo five-component reactions of aromatic aldehydes, aromatic amines, and β-ketoesters in ethanol at room temperature. Mild reaction conditions, good yields, high diastereoseletivity, operational simplicity, and the absence of tedious separation procedures, clean reaction profiles, high atom economy, inexpensive starting materials, and environmentally benign catalyst are the key advantages of the present MCRs protocol.

Full text of DOI:10.1080/00397911.2020.1803357

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/lsyc20
Nickel complexes as efficient catalysts in
multicomponent synthesis of tetrahydropyridine
derivatives
Andrei N. Yankin & Maksim V. Dmitriev
To cite this article: Andrei N. Yankin & Maksim V. Dmitriev (2020): Nickel complexes as efficient
catalysts in multicomponent synthesis of tetrahydropyridine derivatives, Synthetic Communications,
DOI: 10.1080/00397911.2020.1803357
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https://doi.org/10.1080/00397911.2020.1803357
Nickel complexes as efficient catalysts in multicomponent
synthesis of tetrahydropyridine derivatives
a
b
Andrei N. Yankin
and Maksim V. Dmitriev
a
b
Department of Physics and Engineering, ITMO University, St. Petersburg, Russia; Departament of
Organic Chemistry, Perm State National Research University, Perm, Russia
ABSTRACT
ARTICLE HISTORY
Ni(Salen) complexes as an efficient, homogeneous catalysts revealed
a catalytic activity toward the one-pot synthesis of tetrahydropyri-
dine derivatives through the pseudo five-component reactions of
aromatic aldehydes, aromatic amines, and b-ketoesters in ethanol at
room temperature. Mild reaction conditions, good yields, high dia-
stereoseletivity, operational simplicity, and the absence of tedious
separation procedures, clean reaction profiles, high atom economy,
inexpensive starting materials, and environmentally benign catalyst
are the key advantages of the present MCRs protocol.
Received 16 June 2020
KEYWORDS
Heterocycles; Lewis acids;
nickel complexes; one-pot
synthesis;
tetrahydropyridines
GRAPHICAL ABSTRACT
Introduction
The development of new metal catalysts has been of wide interest in synthetic method-
[
1]
ology. Schiff bases are widely used as ligands in coordination chemistry and cataly-
[
2]
sis,
and their complexes can be accessed by a variety of methodologies. As
representative in the class of Schiff complexes, salen metal complexes have been
explored in many applications, from material science and catalysis to coordination
[
3]
chemistry.
The easy to prepare salen metal complexes have been used in the
development of catalysts for numerous reactions, which are widely used for the
[
4–9]
synthesis of practically significant compounds.
Salen derivatives have demonstrated
their huge application as ligands for catalysis, since, associated to a large variety
of metallic salts, they were able to promote formation of various C–C, C–heteroatom,
[
10]
or heteroatom–heteroatom bonds.
CONTACT Andrei N. Yankin
andrei.yankin@metalab.ifmo.ru
Department of Physics and Engineering, ITMO
University, Lomonosova St. 9, St. Petersburg, Russia.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

2
A. N. YANKIN AND M. V. DMITRIEV
Figure 1. Representative compounds containing the tetrahydropyridine moiety.
The synthesis of tetrahydropyridine derivatives is an important area of research, since
[
11,12]
these scaffolds are core motifs in numerous natural products
and find applications as
[13]
[14,15]
dophamine D4-receptor agonist
and also exhibit antibacterial,
anti-inflamma-
[16]
[17]
[16]
[18]
[19,20]
[21]
tory,
anticancer,
anticonvulsant,
antitubercular,
antiartmic,
antipsyholic,
etc. activities. Moreover, tetrahydropyridine derivatives possess enzyme inhibitory activity
against acetylcholinesterase (AChE) which is believed to play an important role in the
[22]
development of Alzheimer’s disease.
Examples of well-known biologically active com-
pounds containing a tetrahydropyridine moiety are shown in Figure 1. Hence, the synthesis
of highly functionalized piperidines has evoked much attention as a result of which a num-
ber of methodologies have been developed involving a variety of cyclization techniques
such as one-pot pseudo five-component reactions of aromatic aldehydes, anilines, and
[15,23–25].
b-ketoesters under various reaction conditions.
Herein, we described the synthesis of tetrahydropyridine derivatives, where we
considered various Ni(Salen) complexes as catalysts, showing their effectiveness in
comparison with Lewis acids.
Result and discussion
Initially, we obtained a series of nickel salen complexes through two stage synthesis
(Scheme 1). At the first stage, ligand 3 was obtained via reaction salicylic aldehyde
derivatives 1 with ethylene diamine 2. Further, compound 3 was metalized via nickel(II)
[
26–29]
acetate (Ni(AcO) ) with the formation of complexes 4.
2
Standard reaction conditions were developed using the model reaction of ethylacetoa-
cetate 6b (10 mmol), aniline 5a (20 mmol), and benzaldehyde 7a (20 mmol) in ethanol
(10 mL) at room temperature in the presence of various Ni(SalEn) complexes 4a–g and
Lewis acids such as iron(III) chloride (FeCl ), bismuth(III) nitrate (Bi(NO ) ), and iod-
3
3 3
ine (I ), which were previously used as catalysts in the synthesizes various heterocyclic
2
[
30–34]
[15]
compounds,
obtained in the presence of Ni(SalEn) 4a (10 mol%) which gave tetrahydropyridine 8a
Table 1, entry 5) in 79% yield. Ni(Salen) complexes 4b–g with different substitutes in
including tetrahydropyridines
(Table 1). The best results were
(

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Scheme 1. Synthesis Ni(Salen) complexes.
Table 1. Catalyst screening for the synthesis of tetrahydropyridine 8a .
a
b
Entry
Catalyst
None
Time
Yield (%)
1
2
3
4
5
6
7
8
9
192 h
12 h
12 h
14 h
15 min
15 min
40 min
6 h
2 h
3 h
7 h
2 h
35
76
64
51
79
77
69
74
71
67
56
65
Bi(NO
FeCl
ꢀ6H
(10 mol%)
3
)
3
ꢀ5H
2
O (10 mol%)
O (10 mol%)
3
2
I
2
Ni(SalEn) (10 mol%)
Ni(SalEn) (20 mol%)
Ni(3-MeSalEn) (10 mol%)
Ni(4-MeSalEn)
Ni(3-MeOSalEn)
Ni(6-MeOSalEn)
4a
4a
4b
4c
4d
4e
4f
10
11
12
a
2
Ni(4-Et NSalEn)
Ni(SalPn)
4g
Reagents and conditions: benzaldehyde (20 mmol), ethylacetoacetate (10 mmol), aniline (20 mmol), catalyst, ethanol
10 mL), room temperature.
(
b
Isolated yield.
aromatic ring and diamine bridge showed a lower catalytic activity in comparison 4a,
apparently, probably due to the steric effect. Various solvents were tested for the
synthesis of 8a (Table 2) which revealed ethanol to be the best choice. The traces were
obtained when dimethyl sulfoxide (DMSO) and water were employed as solvents
(Table 2, entries 11 and 12).
To explore this reaction under the optimized conditions, a variety of aromatic alde-
hydes and amines containing electron donating or electron withdrawing substituents on
the aromatic ring (Me, OMe, tert-Bu, allyloxy, F, and thiophenyl) were reacted with
b-ketoesters (Table 3). A relationship between the nature of the substituents in the

4
A. N. YANKIN AND M. V. DMITRIEV
a
Table 2. Solvent screening for the synthesis of tetrahydropyridine 8a .
Entry
Solvent
Yield (%)
1
2
3
4
5
6
7
8
9
MeOH
EtOH
i-PrOH
THF
75
79
70
53
15
12
56
50
44
5
Traces
Traces
CH
CHCl
MeCN
Me CO
Cl
2 2
3
2
1,4-Dioxane
DMF
DMSO
1
1
1
a
0
1
2
Water
Reagents and conditions: benzaldehyde (20 mmol), ethylacetoacetate (10 mmol), aniline (20 mmol), Ni(SalEn) (10 mol%),
solvent (10 mL), room temperature.
b
Isolated yield.
a
Table 3. Synthesis of tetrahydropyridine 8a–h .
3
4
5
b
Entry
R
R
R
Product
Yield (%)
1
2
3
4
5
6
7
8
a
H
H
H
OMe
H
H
Me
H
OEt
OEt
OEt
OEt
O-tert-Bu
O-i-Pr
OEt
Ph
8a
8b
8c
8d
8e
8f
79
82
75
81
71
69
89
67
4-tert-Bu(C
6
H
4
)
Thiophen-2-yl
Thiophen-2-yl
Thiophen-2-yl
Thiophen-2-yl
4-OCH
4-F(C H )
2
CHCH
2
(C
6 4
H )
8g
8h
OEt
6 4
Reagents and conditions: aromatic aldehyde (20 mmol), b-ketoester (10 mmol), aromatic amine (20 mmol), Ni(SalEn)
10 mol%), ethanol (10 mL), room temperature.
(
b
Isolated yield.
aromatic ring and such as -F (Table 3, entry 8). the product yield was not observed.
However, the smallest product yield (67%) was obtained by electron-withdrawing
substituents.
1
13
All products were characterized by IR, H NMR, C NMR, elemental analysis, and
mass spectroscopic studies (see ESI). The relative anti-configuration of the product was
confirmed by comparing the physical and spectroscopic data of the known compounds
[
24]
with those in the literature,
compound 8g (Fig. 2, S27).
and also by single crystal X-ray analysis of the model
This is also important to mention here that the presence
[
35]
of the corresponding syn-diastereomer in the products could not be identified from the

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Figure 2. Molecular structure of compound 8g showing 50% probability displacement ellipsoids
CCDC 1919473).
(
1
H NMR of the product(s), indicating the reactions to be exclusively anti-
diastereoselective.
A probable mechanistic pathway for this five-component reaction is outlined in
Scheme 2, which is in analogy to the established mechanism as reported in the litera-
[
15,23–25]
ture.
Based on the presented mechanism, initially, the carbonyl groups of
b-ketoester 6 and aromatic aldehyde 7 were activated by Ni(Salen) as catalyst, which
made them susceptible to the nucleophilic attack of aromatic amine 5. Thereafter, the
activated 6 and 7 were separately condensed with 5 to give b-enaminone A and imine
B, respectively. Subsequently, an intermolecular Mannich reaction occurred between A
and B to generate intermediate C. Intermediate C was reacted with another molecule of
aldehyde 7 to give intermediate D through the elimination of one H O molecule.
2
Finally, tautomerization of D led to the formation of intermediate E, which instantan-
eously underwent an intramolecular Mannich reaction to offer the product F. Next,
upon tautomerization, F was converted to the more stable form of the desired tetrahy-
dropyridine 8.
Conclusion
In conclusion, a straightforward and efficient protocol for one-pot synthesis of function-
alized piperidine scaffolds has been developed in the presence of Ni(Salen) complexes as
catalyst via five-component tandem reaction of aromatic aldehydes, b-ketoesters, and
amines at room temperature. Mild reaction conditions, good yields, high diastereosele-
tivity, operational simplicity and the absence of tedious separation procedures, clean

6
A. N. YANKIN AND M. V. DMITRIEV
Scheme 2. Plausible mechanism for the formation of tetrahydropyridine derivatives 8.
reaction profiles, high atomeconomy, inexpensive starting materials, and environmen-
tally benign catalyst are the key advantages of the present MCRs protocol.
Experimental
General
IR spectra were recorded on FTIR-spectrometer «IRAffinity-1» (Shimadzu, Kyoto,
Japan). NMR spectra were recorded on Bruker AVANCE 400SX using DMSO-d and
6
CDCl as solvents, TMS as internal standard substance, with proton and carbon reso-
3
nances at 400 and 100 MHz, respectively. HR-ESI-MS spectra were recorded on
«
MaXis» mass spectrometer with accessories, Bruker Daltonik GmbH.
X-ray crystallographic analysis
The unit cell parameters and the X-ray diffraction intensities were measured on a
SuperNova diffractometer. The empirical absorption correction was introduced by
[
36]
[37]
multi-scan method using SCALE3 ABSPACK algorithm.
structure was solved with the SHELXT program
Using the Olex2,
and refined by the full-matrix least-
squares method in the anisotropic approximation for all non-hydrogen atoms with the
the
[
38]

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[
39]
SHELXL program.
Hydrogen atoms were located from the Fourier synthesis of the
electron density and refined using a riding model.
General procedure for the preparation of complexes 4a–g
Corresponding salicylic aldehyde 1 (10mmol) and 1,2-diaminoethane 2 (5 mmol) were
mixed in MeOH (10mL). Reaction mixture was refluxed for 3 h, cooled down and filtered.
The ligand 3 obtained was redissolved in MeOH, and Ni(OAc) ꢀ4H O (0.88g, 5 mmol) was
2
2
added to the solution. The reaction mixture was stirring and refluxed for 3 h, cooled down,
filtered off, recrystallized from MeCN:EtOH (1:1) and dried in vacuo to obtain the desired
complex 4.
General procedure for the preparation of tetrahydropiridines 8a–h
A mixture of corresponding aromatic amine 5 (20 mmol), b-ketoester 2 (10 mmol) and
Ni(SalEn) 4a (10 mol%) in EtOH (10 mL) were stirred for 30 min at room temperature.
Then aromatic aldehyde 7 (20 mmol) was added to the solution. The reaction mixture
was stirring for 15 min, filtered off, recrystallized from EtOH:AcOEt (2:1) and dried in
vacuo to obtain the desired tetrahydropiridine 8.
Ethyl 2,6-bis(4-(allyloxy)phenyl)-1-p-tolyl-4-(p-tolylamino)-1,2,5,6-
tetrahydropyridine-3-carboxylate 8g
ꢁ
1
1
White crystalline solid; 89%. FTIR (KBr) ꢀ, cm : 3236 (NH), 1651 (C ¼ O). H NMR
ꢂ
(
400 MHz, CDCl , 25 C): d ¼ 1.47 (t, J(H,H) ¼ 7.1 Hz, 3H; OCH CH ), 2.19 (s, 3H;
3
H
2
3
5
Me), 2.30 (s, 3H; Me), 2.70–2.78 (m, 1H; C H H ), 2.83 (dd, J(H,H) ¼ 15.0, 5.5 Hz,
A
B
5
1
H; C H H ), 4.34 (dq, J(H,H) ¼ 10.9, 7.1 Hz, 1H; OCH H CH ), 4.45 (ddd, J(H,H) ¼
A
B
A
B
3
1
(
4.3, 9.0, 5.4 Hz, 1H; OCH H CH ), 4.55 (dd, J(H,H) ¼ 8.9, 3.4 Hz, 4H; OCH ), 5.07
A
6
B
3
2
d, J(H,H) ¼ 2.7 Hz, 1H; C H), 5.30 (dd, J(H,H) ¼ 5.3, 1.3 Hz, 1H; ¼CH H ), 5.32 (dd,
A
B
J(H,H) ¼ 5.3, 1.3 Hz, 1H; ¼CH H ), 5.40–5.43 (m, 1H; ¼CH H ), 5.45–5.48 (m, 1H;
A
B
A
B
¼
CH H ), 6.03–6.15 (m, 2H; ¼CH), 6.27 (d, J(H,H) ¼ 8.1 Hz, 2H; Ar-2CH), 6.35
A
B
2
(
s, 1H; C H), 6.47 (d, J(H,H) ¼ 8.6 Hz, 2H; Ar-2CH), 6.85 (dd, J(H,H) ¼ 8.6, 1.9 Hz,
4
2
(
H; Ar-4CH), 6.92 (dd, J(H,H) ¼ 14.9, 8.2 Hz, 4H; Ar-4CH), 7.09 (d, J(H,H) ¼ 8.6 Hz,
13
H; Ar-2CH), 7.25 (d, J(H,H) ¼ 8.6 Hz, 2H; Ar-2CH), 10.25 (s, 1H; NH). C NMR
ꢂ
6 2 3
2 3 2 2
5
100 MHz, CDCl , 25 C): d ¼ 14.8 (OCH CH ), 20.1 (Me), 20.9 (Me), 33.7 (C ), 54.7
3
H
2
3
(
C ), 57.5 (C ), 59.5 (OCH CH ), 68.9 (OCH ), 68.9 (OCH ), 97.9 (C ), 113.0, 114.3,
1
1
14.8, 117.6, 117.6, 125.0, 125.9, 127.5, 127.7, 129.4, 129.4, 133.4, 133.5, 135.2, 135.4,
4
35.5, 136.5, 145.0, 156.5, 157.0, 157.7 (C , –CH¼CH , C-Ar), 168.3 (CO). HRMS (ESI):
2
þ
calcd. for C H N O Na [M þ H] 615.3217, found 615.3192; calcd. for C H N O Na
4
0
43
2
4
40 42 2 4
þ
[MþNa] 637.3037, found 637.3012.
1
13
Full experimental details, elemental analysis, IR, HR-ESI-MS, H, and C NMR spec-
tra for all new compounds, crystal data and structure refinement for 8g. This material
can be found through the “Supplementary Content” section of this article’s webpage.

8
A. N. YANKIN AND M. V. DMITRIEV
Acknowledgments
Scientific research was performed at the Research Parks of St. Petersburg State University “Center
for Chemical Analysis and Materials Research” and “Educational Resource Center of Chemistry.”
ORCID
Andrei N. Yankin
Maksim V. Dmitriev
http://orcid.org/0000-0003-4221-5619
http://orcid.org/0000-0002-8817-0543
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