Unsymmetrical triazolyl-naphthyridinyl-pyridine bridged highly active copper complexes supported on reduced graphene oxide and their application in water

Article abstract of DOI:10.1039/c9gc02086a

A novel unsymmetrical triazolyl-naphthyridinyl-pyridine ligand was designed and synthesized, and employed in the synthesis of a heterogeneous copper complex on reduced graphene oxide. The resulting copper composite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX). This supported copper catalyst containing unsymmetrical triazolyl-naphthyridinyl-pyridine (only 0.1 mol%) showed excellent catalytic activity in water with good recyclability. Various functionalized quinoline derivatives were successfully synthesized in high yields through the green strategy in water. Other heterocyclic compounds, such as pyridine, 2-(pyridin-2-yl)quinoline, 1,8-naphthyridine, 5,6-dihydronaphtho[1,2-b][1,8]naphthyridine and 2-(pyridin-2-yl)-1,8-naphthyridine derivatives, were achieved in water with more than 80% yields. Mechanism studies revealed that this transformation occurs via dehydrogenation, condensation, and transfer hydrogenation and dehydrogenation processes which was supported by a deuterium labeling experiment.

Full text of DOI:10.1039/c9gc02086a

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DOI: 10.1039/C9GC02086A
Table of Contents
OH
TNP-Cu-HGR
OH
NH2
+
X
N
H2O
X
Y
Y
Water as solvent
Reusable of catalyst
Highly efficient
X, Y = C, N
N
N
N
N
N
N
N
N
N
N
N
N
A clean method for the synthesis of functionalized quinolines in water with recovered copper catalyst
was developed.

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ARTICLE
Unsymmetrical triazolyl-naphthyridinyl-pyridine bridged high
active copper complexes supported on reduced graphene oxide
and the application in water†
Received 00th January 20xx,
Accepted 00th January 20xx
Wenkang Hu,a Yilin Zhang,b Haiyan Zhu,a Dongdong Ye,a and Dawei Wang*a
DOI: 10.1039/x0xx00000x
Novel unsymmetrical triazolyl-naphthyridinyl-pyridine ligand was designed and synthesized, and
employed in heterogeneous copper complex on reduced graphene oxide. The resulting copper
composite was characterized by scanning electron microscopy (SEM), transmission electron
microscopy (TEM), X-ray photoelectron spectrometry (XPS) and energy dispersive X-ray (EDX).
This supported copper catalyst containing unsymmetrical triazolyl-naphthyridinyl-pyridine (only
0.1 mol%) showed excellent catalytic activity in water with good recyclability. Various
functionalized quinoline derivatives were successfully synthesized in high yields through the green
strategy in water. Other heterocyclic compounds, such as, pyridine, 2-(pyridin-2-yl)quinoline, 1,8-
naphthyridine, 5,6-dihydronaphtho[1,2-b][1,8]naphthyridine and 2-(pyridin-2-yl)-1,8-naphthyridine
derivatives were achieved in water with more than 80% yields. Mechanism studies revealed this
transformation undergoes dehydrogenation, condensation, transfer hydrogenation and
dehydrogenation processes which was supported by deuterium labeling experiment.
www.rsc.org/
stable starting materials to achieve quinolines synthesis is
highly desirable.3
Introduction
Borrowing hydrogen and dehydrogenation reactions
have been known as an efficient tool in synthetic
chemistry during the past several years,4,5 which can start
with simple alcohols. Catalyst usually plays a crucial role
in these reactions, and can be used to determine the
occurrence of the reaction.6,7 Although several classical
borrowing hydrogen reactions, such as amine with
alcohols, ketones with alcohols, have been well
developed,8,9 the synthesis of quinolines based on
borrowing hydrogen or dehydrogenation strategy remains
highly challenging, particularly with recyclable catalysts
in water. Recently, we designed and synthesized several
novel triazole based ligands, which have revealed
excellent catalytic activity in the reactions of
alcohol/amine, alcohol/ketone and amine/amine.10
However, none of the developed catalysts have shown
activity to date for the synthesis of quinoline derivatives,
even in harsh conditions.
Quinoline derivatives, known as an ubiquitous class of
heterocyclic compounds, are widely distributed in
alkaloids and natural products, and have demonstrated
various pharmaceutical and biological properties, such as
antiviral, antitumor, antibacterial and antimalarial.1
Although synthetic routes to quinoline derivatives have
been extensively explored, most methods relies on
condensation reactions between amines and aldehydes in
the presence of strong base or acid under harsh
conditions.2
Development
of
innovative
and
environmentally benign conditions, such as water or
solvent-free conditions, employing easily available and
a.Key Laboratory of Synthetic and Biological Colloids, Ministry of
Education, School of Chemical and Material Engineering, Jiangnan
University, Wuxi 214122, China. E-mail: wangdw@jiangnan.edu.cn
Unsymmetrical tridentate ligands possess special
properties and have exhibited high efficiency as tuner
moderator to adjust catalyst reactivity in synthesis
(Scheme 1).11,12 The unsymmetrical tridentate ligands
have attracted much attention from the synthetic
b.C. Eugene Bennett Department of Chemistry, West Virginia University,
Morgantown, West Virginia 26506, United States.
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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J. Name., 2013, 00, 1-8 | 1
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community and significant progress has been made on
Journal Name
Subsequently, graphene oxide (GO) was VsieywnAtrhticelesOiznleinde
their applications during the past several decades.13,14 from natural graphene by the modified Hummers
Recently, we reported the use of indazolyl-pyridinyl- method.17 The reduced graphene oxide (rGO) was
triazole as an effective ligand for iridium-catalyzed prepared with the addition of hydrazine monohydrate to
coupling reactions between amines through transfer GO. Finally, rGO and copper complex was evenly
DOI: 10.1039/C9GC02086A
hydrogenation
followed
by
dehydrogenation.15 dispersed in DMSO and stirred under N2 atmosphere at
o
Nevertheless, the high cost of iridium has limited its 160 C for 24 h, leading to the supported catalysts TNP-
wide application. Herein, we reported the synthesis of an Cu@rGO (3% loading, w/w) (for more details, see the
unsymmetrical triazolyl-naphthyridinyl-pyridine ligand and SI).
the corresponding heterogeneous copper complex on
reduced graphene oxide (rGO) was characterized
Characterization of composite TNP-Cu@rGO.
thoroughly. This heterogeneous copper catalyst exhibited
After a series of preparation, the supported copper
excellent catalytic activity for the synthesis of quinoline
derivatives in water with good recyclability.
catalysts (TNP-Cu@rGO) were successively characterized by
scanning electron microscopy (SEM), transmission electron
microscopy (TEM), energy dispersive X-ray (EDX), and X-
ray photoelectron spectrometry (XPS). SEM spectra of rGO
and TNP-Cu@rGO are shown in Fig.1 (a) and (b),
respectively. And TEM spectra were shown in Fig. 1 (c) and
(d). It can be seen that copper complex was evenly supported
on rGO from the above spectra (for more figures, see the SI).
Unsymmetrical strategy
Strong coordinating side
Y
Highly or low active ?
M
X
Z
Weak coordinating side
Scheme 1. The unsymmetrical tridentate ligand strategy.
Results and discussion
Synthesis of triazolyl-naphthyridinyl-pyridine ligand
and heterogeneous catalyst TNP-Cu@rGO.
Triazolyl-naphthyridinyl-pyridine was synthesized in
two steps (Scheme 2). Initially, 2-amino-3-pyridine-
carboxaldehyde and 2-acetyl-6-bromopyridine, dissolved
in methanol, were mixed with potassium hydroxide
solution and stirred for 10 hours at 60 oC, leading to 2-(6-
bromopyridin-2-yl)-1,8-naphthyridine (L1).16 Then,
purified L1 was allowed to react with 1,2,4-triazole at
Fig. 1. (a): SEM images of rGO; (b) : SEM images of TNP-
Cu@rGO; (c): TEM images of rGO; (d): TEM images of
TNP-Cu@rGO.
o
160 C for 16 hours, using K2CO3, CuI and L-proline as
additives and DMSO as solvent. Finally, triazolyl-
naphthyridinyl-pyridine (TNP, L2) was obtained.15 With
this TNP ligand in hand, the copper complex TNP-Cu
was prepared with Cu(CH3CN)4PF6 in MeOH at room
temperature for 16 h (for more details, see the SI).
KOH, 60 o
MeOH, 10 h
C
O
Br
N
+
N
Br
N
N
NH2
O
L1
, 97%
N
N
N
CuI, L-proline
,
HN
N
N
N
N
N
DMSO, K2CO3, 160 o
16 h, N2
C
N
L2
, 65%
Scheme 2. The synthesis of triazolyl-naphthyridinyl-pyridine.
2 | J. Name., 2013, 00, 1-8
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(Table 1, entries 9-11). In addition, we also found that
100 C is the optimum temperature, while the reaction
remains either incomplete or reduced yield at low and
high temperatures. (Table 1, entries 14, 15, 16). To our
delight, the yield can be significantly improved after the
addition of tetrabutylammonium halides, and TBAB is
more effective than TBAF and TBAI (Table 1, entries
View Article Online
DOI: 10.1039/C9GC02086A
Fig. 2. EDX spectrum of TNP-Cu@rGO.
o
In Fig. 2, it can be seen that a characteristic peak of
copper was found at 0.93 KeV in the EDX spectrum.
Additionally, the characteristic peaks of oxygen were found at
0.52 KeV, while carbon was seen at 0.27 KeV.
The chemical compositions and surface chemical states of
the TNP-Cu@rGO composites were further studied by X-ray 17-19). The control experiment revealed that this
photoelectron spectroscopy. The wide XPS spectra
demonstrated the presence of C, N, O and Cu elements, and
binding energy of Cu2+ was found at 931.1 and 951.1 eV (Fig.
3) (for further analysis, please see the SI for details).
reaction couldn’t take place in absence of the catalyst in
water (Table 1, entries 2-3). It should be noted that the
reaction couldn’t happen under solvent-free conditions
(Table 1, entry 13). Thus, the optimal conditions were
established to have TBAB as the additive, KOH as base
and refluxing in water for 12 hours.
Table 1. Optimization of reaction conditions. a, b
OH
base (1 equiv)
OH
catalyst (0.1 mol %)
+
N
solvent
NH2
3a
1a
2a
Entry
1
Catalyst
Solvent
Base
-
Yield [%]b
-
-
-
H2O
H2O
<5
<5
<5
7
2
K2CO3
KOH
K2CO3
KOH
KOH
-
3
H2O
4
Cu(CH3CN)4PF6
Cu(CH3CN)4PF6
TNP-Cu
H2O
5
H2O
16
32
<5
41
37
29
42
<10c
<5
76
6
H2O
7
rGO
H2O
8
TNP-Cu@rGO
TNP-Cu@rGO
TNP-Cu@rGO
TNP-Cu@rGO
TNP-Cu@rGO
TNP-Cu@rGO
TNP-Cu@rGO
H2O
K2CO3
t-BuOK
t-BuOK
t-BuOK
t-BuOK
KOH
KOH
9
MeCN
Toluene
Dioxane
Dioxane
-
10
11
12
13
14
Fig. 3. XPS spectra of TNP-Cu@rGO.
Catalytic activity
Firstly, we investigated the catalytic activity of the
TNP-Cu@rGO based on the hydrogen-borrowing
reaction of o-aminobenzylmethanol with 1-phenylethanol.
After a set of controlled experiments, it was indicated
that TNP-Cu@rGO has superior activity in water,
however, organic solvents such as acetonitrile, toluene
and dioxane has led to reduced yield and conversion.
H2O
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than 3ak, the reaction also proceeded welVliewunArdticelerOntlhinee
optimized conditions with TNP-Cu@rGO, providing the
desired products 3ag and 3ah in 81% and 82% yield,
respectively (Table 3).
15
16
17
18
19
20
TNP-Cu@rGO
TNP-Cu@rGO
TNP-Cu@rGO
TNP-Cu@rGO
TNP-Cu@rGO
-
H2O
H2O
H2O
H2O
H2O
H2O
KOH
KOH
KOH
KOH
KOH
KOH
43d
71e
88f
DOI: 10.1039/C9GC02086A
Table 3. Substrate expansion a
78g
83h
<5 f
N
N
N
N
N
N
3ah,
3af,
3ag,
82 %
73 %
81 %
N
N
a
N
Reactions conditions: 1a (1 mmol), 2a (1.2 mmol), catalyst (0.1
N
N
N
o
mol%, 3% loading, w/w), base (1.0 equiv.), solvent (2 mL), 100 C
or reflux, 12 h. b Yields of isolated product. c N2 atmosphere. d 60 oC.
e 120 oC. f TBAB (20 mol%). g TBAF (20 mol%). h TBAI (20 mol%).
3ai,
3aj,
3ak,
57 %
89 %
84 %
a Reagents and conditions: 1 (1 mmol), 2 (1.2 mmol), TNP-Cu@rGO
(0.1 mol%, 3% loading, w/w), KOH (1.0 equiv.), TBAB (20 mol%),
H2O (2 mL), 100 oC, 12 h. b Yields of isolated product.
The substrate scope of this hydrogen-borrowing
reaction was investigated under the optimized reaction
condition. We found that substrates containing either
electron-withdrawing groups or electron-donating groups
proceed well in this reaction leading to good to excellent
yields. However, ortho-substituted substrates (3g, 3v)
were only obtained in moderate yields from the reaction
because of steric hindrance issue.
Encouraged by the promising results based on
unsymmetrical tridentate ligand strategy, we next
employed this novel TNP-Cu@rGO to the reaction
between amines and alcohols, and the results were
summarized in Table 4. Gratifyingly, substrates bearing
various electron-withdrawing or electron-donating
substituents could be applied in this TNP-Cu@rGO
catalyzed transformation, producing a great variety of
functionalized secondary amines in good to high yield.
Notably, substrates containing -F, -Cl or -Br groups on
the para- or meta-position of the benzene ring of the
amines or alcohols proceeded smoothly in this reaction,
giving the functionalization amines in satisfying yield.
Table 2. Substrate expansiona
TNP-Cu@rGO (0.1 mol%)
KOH (1.0 mmol)
OH
R1
OH
NH2
R1
+
N
R2
R2
TBAB, H2O
100 oC, 12 h
3
1
2
1
R2=p-Me, 86 %
3a
, R =H, 88 %
3f
,
3g
3h
1
R1
2
3b
3c
3d
, R =3-Me, 86 %
, R =o-Me, 66 %
Table 4. Substrate expansion of borrowing hydrogen
reaction a
1
2
, R =5-Me, 87 %
, R =p-F, 85 %
N
1
, R =5-Cl, 83 %
3i
,
R2=p-Cl, 84 %
1
3e,
R =6-Cl, 85 %
3j
,
R2=m-Cl, 81 %
2
N
TNP-Cu@rGO (0.1 mol%)
H
KOH (1.0 mmol)
R2
R2
NH2
3k,
R =p-Br, 83 %
N
R2=m-CF3, 82 %
OH
2
3l
3p
,
, R =p-Br, 82 %
+
2
2
N
H2O, 100 oC, 10 h
3m
3n
3q
3r
,R =p-CF3, 86 %
R2
, R =p-OMe, 85 %
R1
R2
2
R1
6g
2
5
4
, R =3,5-(CF3)2, 85 %
, R =3,5-(CF3)2, 80 %
6
2
3o
, R =p-OMe, 87 %
2
1
Cl
6a
6b
6c
6d
, R =4-OMe, 89 %
, R = H, 87 %
2
1
2
Cl
6h
, R =3-Me, 86 %
R2=3-Cl, 83 %
3v
, R =4-tBu, 89 %
, R =o-Me, 65 %
2
3s
, R =p-Me, 86 %
1
2
H
N
6i
,
, R =2-Me, 79 %
3w
, R =p-F, 81 %
2
3t
, R =m-Cl, 81 %
,
R2=4-Br, 85 %
2
1
1
N
N
6j
, R =3-Cl, 81 %
3x
3y
R2
R2
, R =m-OMe, 84 %
R2=3,5-(CF3)2, 85 %
R1
3u
,
6e,
6f,
R2
R =4-COOMe, 88 %
R2=4-CN, 80%
1
2
H
N
6k,
6l,
R =4-F, 83 %
, R =m-CF3, 79 %
R1=3, 4-(CH3)2, 78 %
Cl
1
3z
, R =H, 88 %
1
2
R1
6m,
6n,
6o,
R =2-NO2, 79 %
S
1
3aa
3ab
H
N
, R =3-Me, 85 %
6p,
2
R = H, 88 %
R =3-NO2, 82 %
1
N
N
N
1
, R =5-Cl, 82 %
6q
2
, R =3-Cl, 85 %
R =2,4-(Cl)2, 78 %
R1
1
3ae
, 67 %
3ac,
R =6-Cl, 84 %
3ad,
82 %
F
H
H
N
H
N
a Reagents and conditions: 1 (1 mmol), 2 (1.2 mmol), TNP-Cu@rGO
(0.1 mol%, 3% loading, w/w), KOH (1.0 equiv.), TBAB (20 mol%),
H2O (2 mL), 100 oC, 12 h. b Yields of isolated product.
N
6r,
6s,
6t,
75 %
84 %
78 %
a Reagents and conditions: 4 (1 mmol), 5 (1.1 mmol), TNP-Cu@rGO
(0.1 mol%, 3% loading, w/w), KOH (1.0 equiv.), H2O (2 mL), 100
oC, 10 h. b Yields of isolated product.
It is gratifying that 3-aminopropanol can also be
employed in this reaction, affording the valuable
compound 2-phenylpyridine (3af) and 2,2'-bipyridine
(3ai) in 73% and 57% yield respectively. Interestingly,
when using 1-pyridin-2-yl-ethanol as starting material,
the products (3aj, 3ak) can be obtained in excellent
yields. For product bearing naphthyridine group other
Mechanism exploration
Control experiments and activity exploration
4 | J. Name., 2013, 00, 1-8
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Motivated by the fact that the heterogeneous TNP-
Cu@rGO catalytic system revealed excellent activity in
the synthesis of quinolines in water, efforts were
subsequently made to understand the possible reaction
mechanism in this catalytic system. When we tried to use
Cu@rGO catalyst (Cu@rGO: copper salt was directly
supported on rGO, and the unsymmetrical TNP ligand
was absent) to catalyze quinoline synthesis, we found
that the copper salt cannot be supported on rGO without
the TNP ligand. However, when the unsymmetrical
tridentate ligand (triazolyl-naphthyridinyl-pyridine) was
introduced to the catalytic system, quinoline product was
found (Table 1, entry 14). The results were believed to be
highly beneficial for the development of green chemistry.
Recent studies also reported similar findings on the use
of unsymmetrical ligand strategy.11-14 Another advantage
was that this heterogeneous catalyst TNP-Cu@rGO
could be easily recovered and reused. Meanwhile, the
synergistic effect of the support and the triazolyl-
naphthyridinyl-pyridine ligand should be noted, as it may
relate to the high activity of the TNP-Cu@rGO catalyst.
Conventionally, 2,2,6,6-tetramethyl-1-piperidinyloxy
(TEMPO) is served as radical scavenger to determine the
possibility of free radical mechanism. In our study, the
competition experiments for radical progress were
conducted with 1.1 equivalent of TEMPO, in which 2-
phenylquinoline was smoothly isolated in a slightly
lower yield (Scheme 3). This result ruled out the
possibility of free-radical pathway during the quinoline
synthesis.
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DOI: 10.1039/C9GC02086A
[Cu]
O
OH
[Cu]
OH
NH2
O
+
NH2
[Cu]H2
1a'
1a
2a
2a'
O
O
OH
O
[Cu]H2
Ph
Ph
Ph
NH2
C
[Cu]
NH2
NH2
B
A
Pathway II
Pathway III
Pathway I
OH
OH
Ph
OH
Ph
OH
Ph
N
N
H
H
N
H
G
F
D
OH
N
Ph
N
Ph
N
Ph
H
E
3a
Scheme 4. The proposed mechanism for TNP-Cu@rGO
synthesis of quinolines.
The deuterium labeling experiment result indicated
that pathway III is one possible reaction mechanism
(Scheme 5). Additionally, the intermediate B was
isolated from this experiment, disclosed that pathway II
might also be possible. However, intermediate D was not
detected during this process, which implied the least
possibility of pathway I in the reaction mechanism.
93:7
H/D
91:9
H/D
OH
NH2
D
OH
cat [Cu] (1 mol%)
conditions
+
N
OH
TNP-Cu@rGO (0.1 mol%)
OH
1a
2a-d1
3a
KOH (1.0 mmol)
+
N
NH2
TBAB, H2O
Scheme 5. The deuterium labeling experiment.
radical scavenger
1a
3a
2a
Additionally, studies on Hammett plot equation were
conducted to better understand the synthesis of
quinolines in water. Several benzyl alcohols and (2-
aminophenyl)methanol were used to build the equation
and the Hammett plot was exhibited in Scheme 6. From
the result, it was found that this transformation is
significantly impacted by electronic effect. Meanwhile,
negative charge in the reaction center might be favorable
during the transition state of this transformation.
With TEMPO: 81 %
No adical scavenger: 88 %
Scheme 3. The experiments with radical scavenger.
The proposed mechanism
Based on the preliminary explorations and literatures,
2b,2g,8b
we have proposed the mechanism of this
transformation which includes three possible pathways
(Scheme 4). The first pathway starts from aldol reaction
product A which undergoes cyclization to produce
intermediate E. Subsequent elimination of water from E
leads to the final product 3a. In the second pathway,
condensation product B is obtained from A and gives
product 3a via cyclization and elimination. The third
pathway involves borrowing hydrogen product C which
undergoes cyclization step to produce quinoline 3a.
OH
OH
TNP-Cu@rGO (0.1 mol%)
+
N
NH2
TBAB, H2O
100 oC, 1 h
R
R
1a
2
3
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DOI: 10.1039/C9GC02086A
KOH (1.0 mmol)
OH
OH
OH
TNP-Cu@rGO (0.1 mol%)
OH
+
N
TBAB, H2O
NH2
1a
2a
3a: 13.6 g,
: 10.0 g
82%
TNP-Cu@rGO (0.1 mol%)
KOH (1.0 mmol)
OH
N
N
+
TBAB, H2O
N
NH2
1ah
2ah
3ah: 14.5 g,
77%
: 10.0 g
TNP-Cu@rGO (0.1 mol%)
KOH (1.0 mmol)
OH
N
N
+
TBAB, H2O
N
N
NH2
N
1ah
2ak
3ak: 13.4 g,
80%
: 10.0 g
Scheme 8. The synthesis of several heterocyclic compounds
in large scale.
Scheme 6. Hammett plot of para-substituted 1-phenylethanol.
4. Conclusions
In conclusion, we designed and synthesized a novel
copper composite TNP-Cu@rGO from triazolyl-
naphthyridinyl-pyridine copper precursor. This copper
composite was supported on reduced graphene oxide
with no additional surfactant or reductant, and was
characterized by X-ray photo-electron spectrometry,
energy dispersive X-ray, scanning electron microscopy
and transmission electron microscopy. Importantly, it has
exhibited high efficiency in borrowing hydrogen reaction
between o-aminobenzyl alcohol and 1-phenylethanol
derivatives in water and air conditions.
Recyclability of the catalyst
Next, the composite TNP-Cu@rGO was washed and
centrifuged several times with water and EtOH, and dried
for reuse in the borrowing hydrogen reaction. As the
increasing recycling time, the reaction yield gradually
decreased (Scheme 7). To our delight, good yield could
be maintained when TNP-Cu@rGO catalyst was
recycled within five times. To further investigate the
leaching of TNP-Cu@rGO after the reactions, a series of
hot filtration experiments were conducted. The amount
of the TNP-Cu@rGO leaching into water for the reaction
of 1a and 2a at 100 °C was detected by contrasting the
content of Cu before and after each reaction cycle
through ICP analysis. The results showed that amount of
Cu leaching after the first run was 0.31% (w/w), and
even only 1.39% was obtained after the fifth cycle. Thus,
the results revealed that the leaching of TNP-Cu@rGO
was negligible, and TNP-Cu@rGO had good stability
and reactivity for the synthesis of quinolines.
Acknowledgements
We gratefully acknowledge financial support of this
work by the National Natural Science Foundation of
China (21776111, 21861039), the Fundamental Research
Funds for the Central Universities (JUSRP 51627B) and
MOE & SAFEA for the 111 Project (B13025).
Notes and references
OH
TNP-Cu@rGR (0.1 mol%)
OH
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KOH (1.0 mmol)
+
N
NH2
TBAB, H2O
100 oC, 12 h
1a
3a
2a
Recycled times
Yields
0
1
2
3
4
5
80%
88%
86%
84%
81%
81%
Scheme 7. Recycled experiments.
Finally, the gram scale synthesis of 2-phenylquinoline, 5,6-
dihydronaphtho[1,2-b][1,8]naphthyridine and 2-(pyridin-2-
yl)-1,8-naphthyridine were conducted and more than 10
grams products were achieved with this catalytic system. This
further explained that TNP-Cu@rGO catalytic system
exhibited high efficiency for the reaction of aminobenzyl
alcohols and 1-phenylethanols in water through borrowing
hydrogen strategy (Scheme 8).
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