Synthesis of 2,4-diarylquinolines: Nickel-catalysed ligand-free cross-couplings of 4-chloro-2-arylquinolines with arylmagnesium halides in 2-methyltetrahydrofuran

Article abstract of DOI:10.3184/174751911X13026226423986

A ligand-free and room temperature protocol for the synthesis of 2,4-diarylquinolines is described. Treatment of 4-chloro-2-arylquinolines with arylmagnesium halides in the presence of a catalytic amount of nickel(II) chloride without ligands in 2-methylt

Full text of DOI:10.3184/174751911X13026226423986

240 RESEARCH PAPER
APRIL, 240–242
JOURNAL OF CHEMICAL RESEARCH 2011
Synthesis of 2,4-diarylquinolines: nickel-catalysed ligand-free
cross-couplings of 4-chloro-2-arylquinolines with arylmagnesium halides
in 2-methyltetrahydrofuran
Zhenhua Li, Lingmin Xu and Weike Su*
Key Laboratory of Pharmaceutical Engineering of Ministry of Education, College of Pharmaceutical Sciences, Zhejiang University of
Technology, Hangzhou 310014, P. R.China
A ligand-free and room temperature protocol for the synthesis of 2,4-diarylquinolines is described. Treatment of
4-chloro-2-arylquinolines with arylmagnesium halides in the presence of a catalytic amount of nickel(II) chloride
without ligands in 2-methyltetrahydrofuran (2-MeTHF) afforded the corresponding cross-coupling products in good
yields.
Keywords: nickel-catalysis, cross-coupling, Grignard reagents, organomagnesium reagents, 2,4-diarylquinolines
Compounds containing the quinoline scaffold in the structural
framework are expected to have wide-spectrum biological
activity. Among their various applications,1–3 functionalised
quinolines are in widespread use as a result of their anti-
malarial,4–6 anti-inflammatory,7,8 anti-asthmatic,9,10 anti-
bacterial11,12 and anti-hypersensitive activities.13,14
Firstly, the starting materials, 4-chloro-2-arylquinolines 1,
were prepared by treatment of the 2p-aminochalcones with the
novelVilsmeier–typereagentderivedfrombis(trichloromethyl)
carbonate (BTC) and DMF, followed by oxidative defor-
mylation with FeCl3.6H2O in refluxing methanol (Scheme 2).22
We initially chose 4-chloro-2-phenylquinoline 1a as a
model to test this reaction. Treatment of 1a (1.0 mmol) with
p-tolylmagnesium chloride (4.0 mmol) in 2-MeTHF in the
presence of nickel(II) chloride (0.1 mmol) for 1 h at room
temperature afforded 2-phenyl-4-(p-tolyl)quinoline 2a in 81%
yield. We re-examined the reaction conditions in order to
improve the yield, and the results are summarised in Table 1. It
was found that inexpensive NiCl2 was a good coupling catalyst
to give 2-phenyl-4-(p-tolyl)quinoline 2a in good yield at room
temperature (entry 1). Other metal salts such as CoCl2, FeCl3
and MnCl2 (entries 2-4) also catalysed the reaction, but the
yields were lower under the same conditions. When 0.05 mmol
catalyst was used, the reaction gave 71% yield of 2a (entry 5).
Under the catalyst-free conditions, the yield of 2a was sharply
reduced to 15% (entry 6). Parallel experiments using 3.0, 4.0
and 5.0 mmol of p-tolylmagnesium chloride indicated that 4.0
mmol of Grignard reagent was optimal for the conversion of
1a into 2a and that more Grignard reagent did not afford the
product in significantly increased yield (entries 1, 7 and 8).
Neither lower nor higher temperatures improved the yield of
2a (entries 9–11).
Transition metal-catalysed cross-coupling has proved to be
efficient in forming new C–C bonds. This methodology plays
an important role in the synthesis of 4-substituted quinolines.
Usually, palladium-15, iron-16,17 or cobalt-18 catalysed cross-
coupling required the use of phosphine or other ligands.
Korn et al.19 and Rueping and Teawsuwan20 later independently
discovered that Kumada-type coupling also could generate
4-substituted quinolines by cobalt and manganese catalysis
without any ligands. However, the majority of the reactions
required low temperatures and, after reactions were quenched,
a large amount of toluene or other solvent was needed to extract
the products. With 2-MeTHF, which provides very clean
organic-water phase separations, the product can be conve-
niently isolated without adding another solvent. Furthermore,
2-MeTHF has proved to be a greener and more environmen-
tally friendly solvent due to its specific characteristics such as
high temperature for the preparation of chloro-Grignard
reagents, ready availability from renewable resources, and
being readily recoverable.21 We now report a practical, ligand-
free arylation of 4-chloro-2-arylquinolines by treatment with
organomagnesium reagents and catalytic amounts of nickel(II)
chloride in 2-MeTHF with convenient extraction at room
temperature in good to excellent yields (Scheme 1).
To extend the scope of this reaction, a wide range of
substituted and structurally diverse 4-chloro-2-arylquinolines
were subjected to this reaction and the corresponding
substituted 2,4-diarylquinolines were obtained. The results are
summarised in Table 2.
As can be seen from Table 2, with some variations in detail
this method was successful in all cases except 4-chloro-2-
(4-nitrophenyl)quinoline (entry 1m). To our delight, we found
that using 9-chloro-1,2,3,4-tetrahydroacridine 1n also afforded
the corresponding product in 65% yield (Scheme 3). The
electronic effect of substituted groups in the 4-chloro-2-
arylquinolines was obvious and the substrates with electron-
donating groups (entries 1c–f, 1j) were more active and
Scheme 1
Scheme 2
* Correspondent. E-mail: pharmlab@zjut.edu.cn

JOURNAL OF CHEMICAL RESEARCH 2011 241
Table 1 Addition of p-tolylMgCl to 4-chloro-2-phenylquinoline
1a to afford 2-phenyl-4-(p-tolyl)quinoline 2a
Entry Cat. /mol%
Ratio :
1a:p-tolylMgCl
Temp.
/°C
Yielda
/%
1
2
NiCl2(10)
CoCl2(10)
FeCl3(10)
MnCl2(10)
NiCl2(5)
1:4
1:4
1:4
1:4
1:4
1:4
1:3
1:5
1:4
1:4
1:4
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
0
81
73
35
76
71
15
68
82
43
39
68
3
4
5
6
NiCl2(0)
7
NiCl2(10)
NiCl2(10)
NiCl2(10)
NiCl2(10)
NiCl2(10)
8
Scheme 3
9
10
11
–10
40
aIsolated yields based on 4-chloro-2-phenylquinoline 1a
Preparation of 2,4-diarylquinolines
A 25-mL Schlenk tube, equipped with a magnetic stirring bar and a
septum, was charged with the appropriate 4-chloro-2-arylquinoline
(1.0 mmol), NiCl2 (0.10 mmol) and 2-MeTHF (5.0 mL). The corre-
sponding arylmagnesium halide (4.0 mmol) was added dropwise at
room temperature. The reaction mixture was stirred at the temperature
stated in each experiment until the cross-coupling reaction was
complete (0.5–1 h, monitored by TLC). The suspension was quenched
with HCl (5.0 mL) and the organic phase was dried with anhydrous
Na2SO4, filtered, and concentrated under reduced pressure to yield
the corresponding crude product, which was purified by silica gel
chromatography using 2% ethyl acetate/petroleum ether as eluent.
2,4-Diphenylquinoline (2a): White solid; m.p. 113–114 °C (lit.23
111–112 °C); 1H NMR δ: 8.23 (1H, d, J = 8.4 Hz), 8.19–8.14 (2H, m),
7.89 (1H, d, J = 8.4 Hz), 7.80 (1H, s), 7.72 (1H, td, J = 8.4, 1.4 Hz),
7.58–7.44 (9H, m); 13C NMR δ: 119.3, 124.5, 125.5, 125.6, 126.2,
127.5 (2C), 128.3, 128.5 (2C), 128.7 (2C), 129.2, 129.4 (2C), 129.9,
138.2, 139.5, 148.6, 149.0, 156.7; MS (EI): m/z (%) = 281 (M+, 75),
204 (30), 77 (20).
2-Phenyl-4-(p-tolyl)quinoline (2b): White solid; m.p. 101–102 °C
(lit.24 100–100.5 °C); 1H NMR δ: 8.21 (1H, d, J = 8.4 Hz), 8.16 (2H,
d, J = 7.2 Hz), 7.90 (1H, d, J = 8.4 Hz), 7.77 (1H, s), 7.69 (1H, t,
J = 7.6 Hz), 7.49 (2H, t, J = 6.8 Hz), 7.43 (4H, d, J = 8.0 Hz), 7.32
(2H, d, J = 7.6 Hz), 2.46 (3H, s); 13C NMR δ: 21.8, 119.6, 125.9,
126.0, 126.4, 127.8 (2C), 129.0 (2C), 129.5 (3C), 129.6 (3C), 130.2,
135.6, 138.5, 139.8, 148.8, 149.4, 157.0; MS (EI): m/z (%) = 295 (M+,
35), 280 (20), 205 (100).
efficient in providing the products in higher yields than those
with the electron-withdrawing groups (entries 1g, 1m). On
the other hand, while the use of electron-rich substituted
aryl magnesium halides (entry 1) was successful, the use of
electron deficient substituents or of heterocyclic magnesium
halides gave the corresponding desired products in rather
diminished yields (entries 1k, 1l).
In summary, ligand-free nickel catalysed cross-coupling
of 4-chloro-2-arylquinolines with arylmagnesium halides to
prepare a range of 2,4-diarylquinolines in 2-MeTHF was
developed. Furthermore, the reaction products can be
directly extracted and no additional solvents were needed.
We believe that this protocol will be a useful alternative for
the synthesis of 2,4-disubstituted quinolines from readily
available precursors.
Experimental
1H NMR and 13C NMR spectra were recorded on a Varian 400 MHz or
Bruker Avance III (500 MHz) instrument in CDCl3 as the solvent, and
chemical shifts were expressed in parts per million (ppm) using TMS
as an internal standard. IR spectra (KBr) were recorded on an
AVATAR-370 instrument. Mass spectra were measured with a Trace
Finnigan DSQ instrument. Melting points were measured on a Büchi
B-540 apparatus and are uncorrected.
2,4-Di-p-tolylquinoline (2c): Pale yellow solid; m.p. 107–108 °C;
1
IR: νmax 2920, 1592, 1543, 1497, 1357, 818, 764 cm−1; H NMR δ:
8.22 (1H, d, J = 8.2 Hz), 8.08 (2H, d, J = 8.0 Hz), 7.90 (1H, dd,
J = 8.4, 0.8 Hz), 7.77 (1H, s), 7.70 (1H, td, J = 8.2, 1.2 Hz), 7.45–7.41
(3H, m), 7.35–7.30 (4H, m), 2.47 (3H, s), 2.42 (3H, s); 13C NMR δ:
19.8, 20.1, 119.2, 124.9, 125.5, 125.6, 125.9, 128.6, 129.1 (3C), 129.3
(3C), 129.7, 130.0, 135.4, 136.9, 138.0, 138.1, 148.4, 149.0, 156.8;
HRMS (ESI): Calcd for C23H20N 310.1596 (M+H) found 310.1582.
2-(4-Methoxyphenyl)-4-(p-tolyl)quinoline (2d): Pale yellow solid;
m.p. 108–109 °C (lit.25 108 °C); 1H NMR δ: 8.21 (1H, d, J = 8.6 Hz),
8.14 (2H, d, J = 8.8 Hz), 7.88 (1H, dd, J = 8.4, 0.8 Hz), 7.74 (1H, s),
Preparation of 4-methylphenylmagnesium chloride
A solution of 4-chlorotoluene (4.0 mmol) in 2-MeTHF (5.0 mL) was
added dropwise to a three-necked flask, charged with activated
magnesium (4.8 mmol), 2-MeTHF (1.0 mL) and nitrogen atmosphere.
The mixtures were refluxed for 6 h. The flask was then cooled to
room temperature and the Grignard reagent was used directly in the
following experiment.
Table 2 Nickel(II)-catalysed cross-coupling between 4-chloro-2-arylquinolines and aryl magnesium halides
Entry 1
Quinoline 2-substituent (R)
Arylmagnesium halide (Ar)
Product 2
Time /h
Yield/%a
1a
1b
1c
1d
1e
1f
Phenyl
p-Tolyl
2a
2b
2c
2d
2e
2f
1
81
77
Phenyl
Phenyl
1
p-Tolyl
p-Tolyl
0.5
0.5
0.5
0.5
1
1
1
0.5
1
1
1
85
4-Methoxyphenyl
3,4-Dimethylphenyl
3,4-Dimethoxyphenyl
4-Chlorophenyl
2-Furyl
p-Tolyl
93
p-Tolyl
88
p-Tolyl
95
1g
1h
1i
p-Tolyl
2g
2h
2i
50b
65
Phenyl
2-Thiophenyl
p-Tolyl
Phenyl
Phenyl
4-Nitrophenyl
p-Tolyl
70
1j
1-Naphthyl
3,4,5-Trifluorophenyl
1-Thiophenyl
p-Tolyl
2j
80
1k
1l
2k
2l
42
Trace
None
1m
2m
aIsolated yields based on heteroaryl chloride.
bRatio of 1g : p-tolylMgCl = 1 : 2.5

242 JOURNAL OF CHEMICAL RESEARCH 2011
7.69 (1H, td, J = 8.4, 1.2 Hz), 7.46–7.39 (3H, m), 7.34 (2H, d, J =
8.0 Hz), 7.03 (2H, d, J = 8.6 Hz), 3.88 (3H, s), 2.48 (3H, s); 13C NMR
δ: 21.4, 55.4, 114.1, 118.8, 125.5, 125.6, 125.8, 128.8, 129.1, 129.3,
129.6, 129.8, 131.9, 135.3, 138.2, 148.4, 149.0, 156.2, 160.6; MS
(EI): m/z (%) = 325 (M+, 100), 310 (41), 281 (22).
NMR δ: 8.29 (1H, s), 8.17 (2H, d, J = 7.2 Hz), 7.83–7.71 (3H, m),
7.58–7.42 (4H, m), 7.23–7.15 (2H, m); 13C NMR δ: 114.1 (J =
6.0 Hz), 114.2 (J = 6.0 Hz), 119.4, 124.9, 125.1, 127.2, 127.7 (2C),
129.1 (2C), 129.9, 130.2, 130.5, 134.4 (J = 6.0 Hz), 139.2 (J =
35 Hz), 141.5 (J = 35 Hz), 146.1, 148.8, 150.1 (J = 6.0 Hz), 152.6
(J = 6.0 Hz), 156.9; HRMS (ESI): Calcd for C21H13F3N 336.1000
(M+H)+ found 336.0990.
9-(p-Tolyl)-1,2,3,4-tetrahydroacridine (2n): Yellow solid; m.p.
135–136 °C (lit.27 145–146 °C); 1H NMR δ: 8.01 (1H, d, J = 8.4 Hz),
7.62–7.55 (1H, m), 7.36–7.26 (4H, m), 7.10 (2H, d, J = 8.0 Hz), 3.20
(2H, t, J = 6.6 Hz), 2.61 (2 H, t, J = 6.4 Hz), 2.46 (3H, s), 2.00–1.92
(2H, m), 1.79 (2H, m). 13C NMR δ: 21.2, 22.7, 22.9, 27.9, 33.9, 125.0,
125.5, 126.5, 127.7, 128.0, 128.2, 128.6 (2C), 128.9 (2C), 133.6,
137.1, 145.5, 146.6, 158.5; MS (ESI): m/z = 274.4 (M+1)+.
2-(3,4-Dimethylphenyl)-4-(p-tolyl)quinoline (2e): Pale yellow
solid; m.p. 115–116 °C; IR: νmax 2917, 1589, 1543, 1494, 823, 761
1
cm−1; H NMR δ: 8.23 (1H, d, J = 8.4 Hz), 7.98 (1H, s), 7.88 (2H,
t, J = 8.4 Hz), 7.77 (1H, s), 7.69(1H, td, J = 8.4, 1.2 Hz), 7.48–7.39
(3H, m), 7.34 (2H, d, J = 7.6 Hz), 7.25 (1H, t, J = 7.6 Hz), 2.47 (3H,
s), 2.38 (3H, s), 2.33 (3H, s); 13C NMR δ: 19.8, 20.1, 21.4, 29.8, 119.2,
124.9, 125.5, 125.6, 125.9, 128.6, 129.1 (2C), 129.3 (3C), 129.7,
130.0, 135.3, 136.9, 138.0, 138.1, 148.4, 149.0, 156.8; HRMS (ESI):
Calcd for C24H22N 324.1752 (M+H) found 324.1740.
2-(3,4-Dimethoxyphenyl)-4-(p-tolyl)quinoline (2f): Pale yellow
solid; m.p. 120–121 °C; IR: νmax 2930, 1590, 1517, 1498, 1263, 1024,
765 cm−1; 1H NMR δ: 8.22 (1H, d, J = 8.4 Hz), 7.88 (2H, m), 7.75 (1H,
s), 7.73–7.65 (2H, m), 7.46–7.41 (3H, m), 7.35 (2H, d, J = 8.0 Hz),
We are grateful to the National Natural Science Foundation of
China (No. 20876147) for financial support.
6.97 (1H, d, J = 8.4 Hz), 4.04 (3H, s), 3.95 (3H, s), 2.48 (3H, s); 13
C
Received 16 February 2011; 31 March 2011
Paper 1100576 doi: 10.3184/174751911X13026226423986
Published online: 3 May 2011
NMR δ: 21.4, 56.0, 56.1, 110.3, 110.9, 118.8, 120.2, 125.5, 125.8,
129.1 (2C), 129.3 (2C), 129.5, 129.6, 132.2, 135.3, 136.5, 138.2,
148.4, 149.0, 149.1, 150.1, 156.1; HRMS(ESI): Calcd for C24H22NO2
356.1651 (M+H) found 356.1644.
2-(4-Chlorophenyl)-4-(p-tolyl)quinoline (2g): white solid; m.p.
91–92 °C; IR: νmax 2917, 1592, 1491, 1091, 814, 756 cm−1; 1H NMR δ:
8.19 (1H, dd, J = 8.4, 0.4 Hz), 8.13–8.07 (2H, m), 7.89 (1H, dd,
J = 8.4, 0.8 Hz), 7.72 (1H, s), 7.69 (1H, td, J = 8.4, 1.6 Hz), 7.47–7.38
(5H, m), 7.32 (2H, d, J = 8.0 Hz), 2.46 (3H, s); 13C NMR δ: 30.1,
119.1, 125.9, 126.1, 126.6, 129.0 (2C), 129.2 (2C), 129.5 (2C), 129.6
(2C), 129.8, 130.2, 135.4, 135.7, 138.2, 138.6, 148.9, 149.6, 155.6;
HRMS (ESI): Calcd for C22H1735ClN 330.1050 (M+H) found
330.1033.
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2-(Thiophen-2-yl)-4-(p-tolyl)quinoline (2i): White solid; m.p.
95–96 °C; IR: νmax 2923, 1592, 1547, 1498, 1428, 1082, 821 cm−1; 1H
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(3H, m), 7.57–7.28 (5H, m), 7.13 (1H, dd, J = 4.8, 3.6 Hz), 2.47 (3H,
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128.9 (2C), 129.0 (2C), 129.1, 129.2, 134.8, 137.9, 145.0, 148.2,
148.7, 151.4. HRMS (ESI): Calcd for C20H16NS 302.1003 (M+H)+
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4-(Naphthalen-1-yl)-2-(p-tolyl)quinoline (2j): White solid; m.p.
1
135–136 °C; IR: νmax 2919, 1594, 1542, 782, 767 cm−1; H NMR δ:
8.33 (1H, s), 8.11 (2H, d, J = 8.0 Hz), 7.98 (2H, dd, J =15.6, 8.0 Hz),
7.90 (1H, s), 7.71 (1H, t, J = 7.6 Hz), 7.62 (1H, t, J = 7.2 Hz), 7.54–
7.46 (2H, m), 7.45–7.37 (2H, m), 7.33–7.26(4H, m), 2.43 (3H, s); 13
C
NMR δ: 21.5, 120.3, 125.2, 125.9, 126.0 (2C), 126.1, 126.4, 126.8,
127.3, 127.4 (2C), 128.2, 128.6, 129.5 (4C), 129.6, 131.8, 133.3,
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346.1596 (M+H)+ found 346.1596.
2-Phenyl-4-(3,4,5-trifluorophenyl)quinoline (2k): Pale yellow
solid; m.p. 146–147 °C; IR: νmax 3060, 1527, 1405, 1043, 772 cm−1; 1H
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