The synthesis of quinolines: via denitrogenative palladium-catalyzed cascade reaction of o -aminocinnamonitriles with arylhydrazines

Article abstract of DOI:10.1039/d0ra01043j

The first example of the palladium-catalyzed cascade reaction of o-aminocinnamonitriles with arylhydrazines has been achieved, providing an efficient synthetic pathway to access quinolines with moderate to good yields. Preliminary mechanistic experiments

Full text of DOI:10.1039/d0ra01043j

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The synthesis of quinolines via denitrogenative
palladium-catalyzed cascade reaction of o-
aminocinnamonitriles with arylhydrazines†
Cite this: RSC Adv., 2020, 10, 8586
c
b
Jing Xie,a Hang Huang,b Tong Xu,c Renhao Li,d Jiuxi Chen
*
*
and Xueting Ye
Received 3rd February 2020
Accepted 20th February 2020
The first example of the palladium-catalyzed cascade reaction of o-aminocinnamonitriles with
arylhydrazines has been achieved, providing an efficient synthetic pathway to access quinolines with
moderate to good yields. Preliminary mechanistic experiments indicate that this cascade process
involves sequential denitrogenative addition followed by an intramolecular cyclization.
DOI: 10.1039/d0ra01043j
rsc.li/rsc-advances
metal-catalyzed a series of tandem addition/cyclization reac-
tion of nitriles with organoboron reagents for the synthesis of
Introduction
structurally diverse 5-membered, 6-membered, and 7-
membered N-heterocycles.8 In addition, arylhydrazines are used
as an important class of molecular building blocks in both
synthetic and medicinal chemistry for preparing various
nitrogen-containing compounds because of their high reac-
tivity, low cost, and ready availability.9 Recent progresses in the
development of using arylhydrazines as aryl source by deni-
trogenation have been documented.10 Despite the remarkable
advances in transition-metal-catalyzed addition reactions of
nitriles with arylating reagents into a valuable array of products
to date, less attention has been paid to the using arylhydrazines
as aryl sources by denitrogenation presumably due to the high
dissociation energy from direct activation of the C–N bond.11 To
our knowledge, only two examples of denitrogenative
palladium-catalyzed reaction of nitriles with arylhydrazines for
the synthesis of aryl ketones have been reported (Scheme 1a).12
Quinoline derivatives have become increasingly popular in the
past few years due to their ubiquity in natural products, bioactive
compounds, and other functional molecules. For example,
quinoline scaffolds are privileged structures in medicinal
chemistry, and therapeutic agents with such cores on the market
or in clinical trials for the treatment of urological malignancies
such as renal cell carcinoma (e.g., lenvatinib,1 cabozantinib2) and
the treatment of head and neck cancer (e.g., camptothecin3)
(Fig. 1). Therefore, the development of the effective methods for
the synthesis of quinolines has been actively pursued during the
past several decades.4 However, less attention has been paid to
the preparation of quinolines from nitriles.
Nitriles are well-known as solvents or ligands in organome-
tallic reactions because of the inherently inert nature of the
C^N bond.5 For example, acetonitrile or benzonitrile are
usually used as solvents or ligands in many transition-metal-
catalyzed reactions.6 The development of transition-metal-
catalyzed inert C^N bond activation and further trans-
formation has received signicant attention from organic
chemists because nitriles are normally very stable and abun-
dant and cheap feedstock chemicals. Substantial progress
towards this goal made in recent years, the transition-metal-
catalyzed transformation of nitriles offers an attractive route
for the synthesis of arylketones or further cyclization products
by several other groups.7 Our group also developed transition-
We envisioned that
a Pd-catalyzed sequential deni-
trogenative addition followed by an intramolecular dehydrative
cyclization of readily available o-aminocinnamonitriles with
arylhydrazines would result in a tandem procedure for the
preparation of 2-arylquinolines (Scheme 1b). It is worth noting
that the amino group cannot approach the carbonyl group to
achieve the intramolecular cyclization because of the steric
conguration. Recently, Cheon group developed the synthesis
of 2-substituted quinolines by the dehydrative cyclization of 2-
aminostyryl ketones.13 These strategies involve the change of
unreactive (E)-2-aminostyryl ketones into the unstable but
reactive Z-conguration intermediate to undergo dehydrative
cyclization reaction by using iodide13a or benzylamine13b as the
nucleophilic catalyst. Recently, we reported the Pd-catalyzed
tandem reaction of 2-aminostyryl nitriles with arylboronic
acids for the synthesis of 2-arylquinolines.14 As part of the
continuing efforts in our laboratory toward the development of
novel transformations of nitriles,8,14 we herein report the rst
example of the denitrogenative Pd-catalyzed cascade reaction of
aDepartment of Stomatology, The First Affiliated Hospital of Wenzhou Medical
University, Wenzhou 325000, China
bDepartment of Urology, The First Affiliated Hospital of Wenzhou Medical University,
Wenzhou 325000, China. E-mail: yexueting001@163.com
cCollege of Chemistry & Materials Engineering, Wenzhou University, Wenzhou 325000,
China. E-mail: jiuxichen@wzu.edu.cn
dSchool of Pharmaceutical Sciences, Wenzhou Medical University, Wenzhou 325000,
China
† Electronic supplementary information (ESI) available: 1H and 13C NMR spectra
for products. See DOI: 10.1039/d0ra01043j
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Fig. 1 Representative bioactive quinoline derivatives.
demonstrated that the steric effect of the substituent had an
obvious impact on the reaction. For example, the reactions of 1a
with para- and meta-tolylhydrazine afforded 85% and 79%
yields of 3b and 3c, respectively, while the ortho-tolylhydrazine
gave the desired product 3d with a diminished yield of 52%.
Moderately electron-withdrawing halogens, such as uoro (3e–
3f), chloro (3g), and bromo (3h) groups, were compatible with
this reaction, providing 42–76% yields. The substrate bearing
Table 1 Optimization of reaction conditionsa
Scheme 1 Design of new approach to quinolines.
o-aminocinnamonitriles with arylhydrazines to afford 2-aryl-
quinolines (Scheme 1b).
Results and discussion
Entry [Pd]
Ligand Additive
Solvent
Yieldb (%)
We begin our investigation with readily available (E)-3-(2-
aminophenyl)but-2-enenitrile (1a) and phenylhydrazine (2a) for
the optimization of reaction conditions (Table 1).
1
2
Pd(PPh3)4
Pd(OM)2
L1
L1
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
TFA
AcOH
THF
THF
THF
THF
THF
THF
THF
2-MeTHF
DMF
DMA
1,4-Dioxane 23
Toluene
H2O
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
0
12
19
17
31
21
23
37
41
47
We initially found that the desired product 2-phenylquino-
line (3a) could be obtained in 12% yield under the combination
of Pd(OAc)2, triuoroacetic acid (TFA) and 2,20-bipyridine (L1) in
THF under air atmosphere (entry 2). Various palladium cata-
lysts were tested (entries 3–7) and PdCl2 exhibited the highest
catalytic reactivity in 31% yield (entry 5). Delightedly, the yield
of 3a could be improved to 56% using toluene as the solvent.
Other solvents, including DMF, dimethylacetamide (DMA), 1,4-
dioxane and H2O were less efficient (entries 8–13). Replacement
of L1 with other bidentate N-ligands (entries 13–19), resulted in
lower yields. However, trace amounts of 3a was detected when
sterically hindered ligands, such as 6,60-dimethyl-2,20-bipyr-
idine (L4) and 2,9-dimethyl-1,10-phenanthroline (L5) were used
(entries 16–17). An investigation of the effect of additive
revealed that the yield of 3a was greatly increased to 81% under
O2 atmosphere (entry 23). The product 3a was not observed if
either Pd catalyst or ligand was absent (entries 24 and 25).
Having the optimized reaction conditions in hand, we
examined the substrates scope of this cascade reaction. First,
the cascade reaction of (E)-3-(2-aminophenyl)but-2-enenitrile
(1a) with different arylhydrazines were evaluated under opti-
mized conditions (Table 2). The reactivities of para-, meta-, and
ortho-tolylhydrazine were evaluated, and the results
3
4
Pd(CF3CO2)2 L1
Pd(PPh3)2Cl2 L1
5
6
7
8
PdCl2
Pd2(dba)3
Pd(acac)2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
PdCl2
L1
L1
L1
L1
L1
L1
L1
L1
L1
L2
L3
L4
L5
L6
L7
L1
L1
L1
L1
L1
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
56
18
53
51
Trace
Trace
41
51
Trace
33
TsOH$H2O Toluene
MsOH
TfOH
TfOH
TfOH
Toluene
Toluene
Toluene
Toluene
21
79(81)c
0
PdC12
0
a
Conditions: 1a (0.3 mmol), 2a (0.6 mmol), Pd catalyst (10 mol%),
ligand (20 mol%), additive (2 equiv.), solvent (2 mL), 90 ꢀC, 24 h, air.
b
Isolated yield. c Under O2.
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Table 2 Denitrogenative Pd-catalyzed cascade reaction of 1a with
(3l–3m), chloro (3n–3p) and bromo (3q) moieties, were also
compatible, affording the corresponding desired products with
moderate to good yields. Treatment of a strong electron-
withdrawing triuoromethyl substituent with 2a delivered
product 3r in 36% yield. Finally, several representative examples
of substituents (R2) on the carbon–carbon double bond were
investigated. The R2-substituted products 3t, 3u and 3u was
obtained in 71%, 62% and 57% yields, respectively, compared
to relatively low yield of the product 3s in 51% yield. It is worth
noting that the presence of the halogen in the products (e.g., 3h,
3q) is very useful for further synthetic elaborations by cross-
coupling reaction thereby broadening the diversity of the
products.
arylhydrazinesa
To gain insight into the mechanism of this cascade reaction,
several control experiments were conducted (Scheme 2). The
desired product 3a was not detected when the reaction was
performed under N2 atmosphere (Scheme 2a), which revealed
that the reaction required the presence of oxygen. As expected,
the reactions of (E)-3-(2-aminophenyl)-1-phenylprop-2-en-1-one
(4a) under optimized conditions in the absence of phenyl-
hydrazine achieved the product 2-phenylquinoline (3r) in 72%
yield, indicating that 4a was proposed as a possible interme-
diate for this transformation (Scheme 2b). The cyclization of 4a
gave the desired product 3r in 65% yield in the absence of TfOH
(Scheme 2c). The cyclization of 4a could also proceed to afford
3r in 63% yield in the absence of PdCl2/L1 (Scheme 2d).
However, we attempted to perform the reaction in the absence
of palladium catalyst and additive failed to give 3r (Scheme 2e).
On the basis of the above experimental results and previous
reports,12a a possible reaction mechanism for the formation of
quinolines is shown in Scheme 3. The rst step may involve
metathesis between the palladium catalyst and arylhydrazide to
form the palladiaziridine intermediate A, which is followed by
the coordination of cyano group affording intermediate B.
Oxidative addition of the intermediate B to palladium(0) species
to give the corresponding two palladium(II) centered interme-
diate C via C–N bond cleavage. Thereaer, cracking of the
intermediate C gives the intermediate D and the palladiazir-
idine intermediate E, which would be decomposed into palla-
dium(0), N2 and H2O in the presence of oxygen. Then,
carbopalladation of the cyano group affords the imine-Pd
intermediate F. Protonation of F by TfOH gives the imine
intermediate G and regenerates palladium(II) species. Hydro-
lysis of G under acidic conditions would deliver the ketone
intermediate H. Finally, the ketone intermediate H undergoes
C–C bond E/Z congurational tautomerization to give I in the
presence of TfOH and/or palladium(II) species, which is fol-
lowed by intramolecular cyclization to generate the desired
quinolines 3.
a
Conditions: 1a (0.3 mmol), 2 (0.6 mmol), PdCl2 (10 mol%), L1
(20 mol%), toluene (2 mL), TfOH (2 equiv.), 90 ꢀC, 24 h, O2, isolated
yield.
Table
3 Denitrogenative Pd-catalyzed reaction of o-amino-
cinnamonitriles with arylhydrazinesa
a
Conditions: 1 (0.3 mmol), 2 (0.6 mmol), PdCl2 (10 mol%), L1
(20 mol%), toluene (2 mL), TfOH (2 equiv.), 90 ꢀC, 24 h, O2, isolated
yield.
a strong electron-withdrawing group (e.g., CF3) could also be
well tolerated, albeit giving the desired 3i in a slightly lower
yield.
We next turned our attention to the effect of the reactions
between substituted o-aminocinnamonitriles (1) and phenyl-
hydrazine (2a) under standard conditions (Table 3). First, the
inuence of a variety of functional groups (R1) on the phenyl
ring of the 2-(benzylideneamino)benzonitriles was evaluated.
Both electron-donating groups, such as methyl (3j) and methoxy
(3k) moieties, and electron-withdrawing groups, such as uoro
Conclusions
In summary, we have developed a new and complementary
strategy for the synthesis of 2-arylquinolines in moderate to
good yields by palladium-catalyzed cascade denitrogenative
addition and intramolecular cyclization of o-amino-
cinnamonitriles with arylhydrazines.
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Scheme 2 Control experiments.
Scheme 3 Plausible reaction mechanism for the formation of quinolines.
room temperature. Chemical shis are given n d relative to TMS,
and the coupling constants J are given in hertz. The starting
materials o-aminocinnamonitriles15 and 4a16 were synthesized
according to the method described in the literatures. Column
chromatography was performed using EM silica gel 60 (300–400
mesh).
Experimental section
General methods
1
Melting points are uncorrected. H NMR and 13C NMR spectra
were measured on a 500 MHz spectrometer using CDCl3 as the
solvent with tetramethylsilane (TMS) as an internal standard at
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General procedure for the synthesis of quinolines
2-(4-Chlorophenyl)-4-methylquinoline (3g).22 White solid
(38.8 mg, 51%), mp 73–74 ꢀC. 1H-NMR (500 MHz, CDCl3) d 8.16
(d, J ¼ 10.5 Hz, 1H), 8.11–8.09 (m, 2H), 7.98 (d, J ¼ 10.5 Hz, 1H),
7.74–7.70 (m, 1H), 7.65 (s, 1H), 7.57–7.53 (m, 1H), 7.49–7.47 (m,
2H), 2.74 (s, 3H); 13C-NMR (125 MHz, CDCl3) d 155.5, 147.9,
144.9, 138.0, 135.3, 130.1, 129.4, 128.8, 128.6, 126.2, 126.1,
123.5, 119.1, 18.8.
Under O2 atmosphere, a Teon-valve-sealed Schlenk tube was
charged with o-aminocinnamonitriles and arylhydrazines,
PdCl2, L1, TfOH and toluene at room temperature. The reaction
mixture was stirred for 10 minutes at room temperature for
proper mixing of the reactants, and then heated at 90 ꢀC (oil
bath) with vigorous stirring for 24 hours. Aer the reaction
equilibrium, the mixture was poured into ethyl acetate, which
was washed with saturated NaHCO3 (2 ꢁ 10 mL) and then brine
(10 mL). The aqueous layer was extracted with ethyl acetate, the
combined organic layers were dried over anhydrous Na2SO4 and
evaporated under vacuum. The residue was puried by ash
column chromatography (hexane/ethyl acetate) to afford the
desired products.
2-(4-Bromophenyl)-4-methylquinoline (3h).21 White solid
(37.5 mg, 42%), mp 66–67 ꢀC. 1H-NMR (500 MHz, CDCl3) d 8.22–
8.15 (m, 2H), 8.05–8.03 (m, 1H), 8.00–7.98 (m, 1H), 7.74–7.71
(m, 1H), 7.66–7.63 (m, 2H), 7.57–7.51 (m, 2H), 2.77–2.76 (m,
3H); 13C-NMR (125 MHz, CDCl3) d 155.3, 148.0, 145.2, 141.8,
132.1, 130.6, 130.4, 130.3, 129.6, 127.4, 126.4, 126.1, 123.7,
123.1, 119.5, 19.0.
4-Methyl-2-(4-(triuoromethyl)phenyl)quinoline
(3i).23
4-Methyl-2-phenylquinoline (3a).17 White solid (53.2 mg,
1
Yellow oil (22.4 mg, 26%). 1H-NMR (500 MHz, CDCl3) d 8.27 (d, J
¼ 8.0 Hz, 2H), 8.20 (d, J ¼ 8.5 Hz, 1H), 8.02 (d, J ¼ 8.0 Hz, 1H),
7.78–7.24 (m, 4H), 7.60–7.57 (m, 1H), 2.79 (s, 3H); 13C-NMR (125
MHz, CDCl3) d 155.5, 148.0, 145.5, 143.0, 131.0 (d, J ¼ 32.5 Hz),
130.4, 129.7, 127.9, 127.5, 126.6, 125.7 (q, J ¼ 3.8 Hz), 124.2 (d, J
¼ 270.0 Hz), 123.7, 119.6, 19.0.
ꢀ
81%), mp 62–63 C. H-NMR (500 MHz, CDCl3) d 8.22 (d, J ¼
10.5 Hz, 1H), 8.19–8.17 (m, 2H), 7.97 (d, J ¼ 10.5 Hz, 1H), 7.75–
7.70 (m, 2H), 7.56–7.52 (m, 3H), 7.49–7.46 (m, 1H), 2.73 (s, 3H);
13C-NMR (125 MHz, CDCl3) d 157.0, 148.2, 144.8, 139.8, 130.3,
129.3, 129.2, 128.8, 127.6, 127.3, 126.0, 123.6, 119.7, 19.0.
4-Methyl-2-(p-tolyl)quinoline (3b).18 Yellow oil (59.4 mg,
1
6-Methyl-2-phenylquinoline (3j).24 White solid (42.7 mg,
65%), mp 68–69 ꢀC. 1H NMR (500 MHz, CDCl3) d 8.18–8.16 (m,
2H), 8.10 (d, J ¼ 11.0 Hz, 2H), 7.82 (d, J ¼ 11.0 Hz, 1H), 7.57–7.52
(m, 4H), 7.48–7.45 (m, 1H), 2.55 (s, 3H); 13C-NMR (125 MHz,
CDCl3) d 156.5, 146.8, 139.8, 136.2, 136.1, 132.0, 129.4, 129.2,
128.8, 127.5, 127.2, 126.3, 119.0, 21.6.
85%). H-NMR (500 MHz, CDCl3) d 8.20 (d, J ¼ 10.5 Hz, 1H),
8.09–8.07 (m, 2H), 7.98 (d, J ¼ 10.0 Hz, 1H), 7.74–7.70 (m, 2H),
7.55–7.51 (m, 1H), 7.34 (d, J ¼ 10.0 Hz, 2H), 2.74 (s, 3H), 2.45 (s,
3H); 13C-NMR (125 MHz, CDCl3) d 157.0, 148.1, 144.7, 139.3,
136.9, 130.2, 129.5, 129.3, 127.4, 127.2, 125.9, 123.6, 119.6, 21.3,
19.0.
6-Methoxy-2-phenylquinoline (3k).25 White solid (36.7 mg,
4-Methyl-2-(m-tolyl)quinoline (3c).18 Yellow oil (55.2 mg,
79%). 1H-NMR (500 MHz, CDCl3) d 8.22 (d, J ¼ 8.0 Hz, 1H), 8.02–
7.98 (m, 2H), 7.94 (d, J ¼ 8.0 Hz, 1H), 7.74–7.70 (m, 2H), 7.56–
7.52 (m, 1H), 7.44–7.41 (m, 1H), 7.29 (d, J ¼ 7.5 Hz, 1H), 2.75 (s,
3H), 2.50 (s, 3H); 13C-NMR (125 MHz, CDCl3) d 157.3, 148.1,
144.7, 139.8, 138.4, 130.3, 130.0, 129.3, 128.7, 128.3, 127.3,
126.0, 124.7, 123.6, 119.9, 21.6, 19.0.
1
ꢀ
52%), mp 125–126 C. H-NMR (500 MHz, CDCl3) d 8.15–8.14
(m, 1H), 8.13 (s, 1H), 8.11 (d, J ¼ 6.0 Hz, 1H), 8.08 (d, J ¼ 6.0 Hz,
1H), 7.83 (d, J ¼ 11.5 Hz, 1H), 7.52 (dd, J1 ¼ 9.5 Hz, J2 ¼ 9.0 Hz,
2H), 7.45 (d, J ¼ 9.5 Hz, 1H), 7.39 (dd, J1 ¼ 3.5 Hz, J2 ¼ 11.5 Hz,
1H), 7.08 (d, J ¼ 3.5 Hz, 1H), 3.94 (s, 3H); 13C-NMR (125 MHz,
CDCl3) d 157.8, 155.0, 144.4, 139.8, 135.5, 131.2, 128.9, 128.8,
128.2, 127.3, 122.3, 119.2, 105.1, 55.5.
4-Methyl-2-(o-tolyl)quinoline (3d).19 Yellow oil (36.3 mg,
52%). 1H NMR (500 MHz, CDCl3) d 8.20 (d, J ¼ 8.5 Hz, 1H), 8.04–
8.03 (m, 1H), 7.76–7.73 (m, 1H), 7.60–7.57 (m, 1H), 7.51–7.49
(m, 1H), 7.39 (s, 1H), 7.37–7.31 (m, 3H), 2.76 (s, 3H), 2.43 (s, 3H);
13C-NMR (125 MHz, CDCl3) d 160.3, 147.9, 144.3, 140.5, 136.0,
130.3, 130.0, 129.6, 129.3, 128.3, 126.0, 123.6, 123.1, 20.3, 18.8.
2-(4-Fluorophenyl)-4-methylquinoline (3e).20 Yellow oil
(54.1 mg, 76%). 1H-NMR (500 MHz, CDCl3) d 8.18 (d, J ¼
10.5 Hz, 1H), 7.99 (d, J ¼ 10.5 Hz, 1H), 7.92–7.90 (m, 2H), 7.75–
7.71 (m, 1H), 7.67 (s, 1H), 7.58–7.54 (m, 1H), 7.50–7.45 (m, 1H),
7.17–7.13 (m, 1H), 2.76 (s, 3H); 13C-NMR (125 MHz, CDCl3)
d 163.8 (d, J ¼ 247.5 Hz), 155.9, 148.1, 145.0, 135.9 (d, J ¼ 2.5
Hz), 130.2, 129.4, 129.3 (d, J ¼ 7.5 Hz), 127.2, 126.1, 123.6, 119.4,
115.7 (d, J ¼ 22.5 Hz), 19.0.
6-Fluoro-2-phenylquinoline (3l).16 White solid (41.5 mg,
62%), mp 94–95 ꢀC. 1H-NMR (500 MHz, CDCl3) d 8.21–8.19 (m,
2H), 8.17–8.15 (m, 2H), 7.91 (d, J ¼ 10.5 Hz, 1H), 7.56–7.44 (m,
5H); 13C-NMR (125 MHz, CDCl3) d 160.4 (d, J ¼ 248.0 Hz), 156.7
(d, J ¼ 2.8 Hz), 145.3, 139.2, 136.2 (d, J ¼ 5.2 Hz), 132.1 (d, J ¼ 9.1
Hz), 129.5, 128.9, 127.7 (d, J ¼ 10.0 Hz), 127.5, 119.9 (d, J ¼ 25.7
Hz), 119.7, 110.5 (d, J ¼ 21.7 Hz).
7-Fluoro-2-phenylquinoline (3m).25 White solid (38.8 mg,
1
ꢀ
58%), mp 88–89 C. H-NMR (500 MHz, CDCl3) d 8.22 (d, J ¼
8.0 Hz, 1H), 8.16 (d, J ¼ 7.5 Hz, 2H), 7.86–7.80 (m, 3H), 7.56–7.53
(m, 2H), 7.50–7.47 (m, 1H), 7.34–7.30 (m, 1H); 13C-NMR (125
MHz, CDCl3) d 163.3 (d, J ¼ 249.6 Hz), 158.3, 149.3 (d, J ¼ 12.9
Hz), 139.3, 136.6, 129.6, 129.4 (d, J ¼ 10.0 Hz), 128.9, 127.6,
124.2, 118.3 (d, J ¼ 2.5 Hz), 116.7 (d, J ¼ 25.5 Hz), 113.3 (d, J ¼
20.2 Hz).
2-(3-Fluorophenyl)-4-methylquinoline (3f).21 Yellow oil
(44.8 mg, 63%). 1H-NMR (500 MHz, CDCl3) d 8.18 (m, 3H), 7.86–
7.85 (m, 1H), 7.61–7.50 (m, 2H), 7.43–7.42 (m, 1H), 7.09–7.07
(m, 2H), 2.62 (s, 3H); 13C-NMR (125 MHz, CDCl3) d 163.4 (d, J ¼
243.8 Hz), 155.5 (d, J ¼ 2.5 Hz), 148.0, 145.1, 142.1 (d, J ¼ 7.5
Hz), 130.4, 130.2 (d, J ¼ 8.8 Hz), 129.5, 127.4, 126.4, 123.6, 123.0
(d, J ¼ 3.8 Hz), 119.4, 116.0 (d, J ¼ 21.3 Hz), 114.4 (d, J ¼ 22.5
Hz), 19.0.
6-Chloro-2-phenylquinoline (3n).26 White solid (40.3 mg,
56%), mp 109–110 C. 11H-NMR (500 MHz, CDCl3) d 8.16–8.11
ꢀ
(m, 4H), 7.89 (d, J ¼ 9.0 Hz, 1H), 7.84–7.80 (m, 1H), 7.66 (d, J ¼
9.0 Hz, 1H), 7.55–7.52 (m, 2H), 7.49–7.47 (m, 1H); 13C-NMR (125
MHz, CDCl3) d 157.5, 146.6, 139.2, 135.8, 132.0, 131.3, 130.6,
129.6, 128.9, 127.7, 127.5, 126.1, 119.8.
8590 | RSC Adv., 2020, 10, 8586–8593
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6-Chloro-2-(p-methoxyphenyl)quinoline (3o).27 Pale yellow
RSC Advances
Acknowledgements
solid (18.6 mg, 23%), mp 156–158 ꢀC. 1H NMR (500 MHz,
CDCl3) d 8.14 (d, J ¼ 8.5 Hz, 2H), 8.08 (d, J ¼ 8.5 Hz, 2H), 7.85 (d, We thank the National Natural Science Foundation of China
J ¼ 8.5 Hz, 1H), 7.77 (s, 1H), 7.64 (d, J ¼ 9.0 Hz, 1H), 7.05 (d, J ¼ (No. 21572162) and the Natural Science Foundation of Zhejiang
8.5 Hz, 2H), 3.89 (s, 3H); 13C NMR (125 MHz, CDCl3) d 161.1, Province (No. LY20B020015) for nancial support.
157.1, 146.6, 135.7, 131.5, 131.0, 130.5, 128.9, 127.5, 126.1,
119.3, 114.3, 55.4.
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ˇ
´
´
´
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2-Phenylquinoline (3s).30 White solid (31.4 mg, 51%), mp 84–
85 ꢀC. 1H-NMR (500 MHz, CDCl3) d 8.24–8.17 (m, 4H), 7.89 (d, J
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7.56–7.52 (m, 3H), 7.49–7.46 (m, 1H); 13C-NMR (125 MHz,
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(m, 2H), 8.04 (d, J ¼ 10.5 Hz, 1H), 7.74–7.70 (m, 2H), 7.56–7.52
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ꢀ
104–105 C. H-NMR (500 MHz, CDCl3) d 8.28 (d, J ¼ 10.5 Hz,
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Conflicts of interest
There are no conicts of interest to declare.
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