2,4-Diarylquinolines: Synthesis, absorption and emission properties

Article abstract of DOI:10.3184/174751914X13945617338344

The absorption and emission spectra of series of 2,4-diarylquinolines prepared via palladium catalysed Suzuki-Miyaura cross-coupling of 2-aryl-4-chloroquinolines with arylboronic acids were measured in solution to understand the influence of substituents

Full text of DOI:10.3184/174751914X13945617338344

254 RESEARCH PAPER
VOL. 38 APRIL, 254–259
JOURNAL OF CHEMICAL RESEARCH 2014
2,4-Diarylquinolines: synthesis, absorption and emission properties
Adewale O. Adeloye and Malose J. Mphahlele*
Department of Chemistry, College of Science, Engineering and Technology, University of South Africa, PO Box 392, Pretoria 0003, South Africa
The absorption and emission spectra of series of 2,4-diarylquinolines prepared via palladium catalysed Suzuki–Miyaura
cross-coupling of 2-aryl-4-chloroquinolines with arylboronic acids were measured in solution to understand the influence of
substituents on intramolecular charge transfer.
Keywords: 2‑aryl‑4‑chloroquinolines, Suzuki–Miyaura cross‑coupling, 2,4‑diarylquinolines, photophysical properties
Polysubstituted quinolines in which the quinoline framework
is linked to an aryl substituent directly or via a π-conjugated
spacer to comprise a donor-π-acceptor system continue to attract
considerable attention as fluorophores. Polyarylquinolines
serve as emitting chromophores due to their inherent fluorescent
properties,1,2 and this scaffold serves as an electron‑acceptor
unit in carbazole–quinoline and phenothiazine–quinoline
copolymers and oligomers found to exhibit intramolecular
charge transfer (ICT).3 Moreover, polyarylquinoline–based
compoundsconstituteanimportantcomponentinoptoelectronic
materials4,5 and this moiety also constitutes a π-conjugated
bridge in nonlinear optical polymers.6 Similarly, quinolines are
also interesting ligands for transition metal complexes for the
development of organic electroluminescent diodes (OLEDs).7,8
Morethermallystableandmechanicallyrobustnonlinearoptical
polymers with donor‑acceptor architectures incorporating
quinoline units as a π-conjugated bridge have been prepared
previously and their photophysical properties investigated.3,7
Preliminary absorption and photoluminescence properties
of 5,7‑diphenylquinoline and 2,5,7‑triphenylquinolines in
chloroform (2.5 mol L–1) have previously been reported.8 The
absorption spectra of a series of 2‑(hetero)aryl‑substituted
4‑phenylquinolines in dichloromethane have revealed that
2‑substitution of the quinoline core only exerts a bathochromic
effect if the donor capacity is strong enough to generate
co‑planarity to comprise a push–pull system.1 We required
quinoline derivatives substituted with aryl substituents at the
2- and 4-positions to comprise the requisite donor-π-acceptor
systemandtoprobetheirabsorptionandfluorescenceproperties
in solvents of different polarities. Arylated quinolines were
previously prepared by classic reactions, such as the Skraup,
Doebner–Miller, Conrad–Limpach, Friedländer, and Pfitzinger
syntheses.9 Moreover, a three‑component approach involving
a coupling‑cycloisomerisation reaction of aldehydes, terminal
alkynes and amines to afford aryl‑substituted quinolines has
been reported.10,11 Treatment of 4‑chloro‑2‑arylquinolines with
arylmagnesium halides in the presence of nickel(II) chloride as a
catalyst in 2‑methyltetrahydrofuran afforded the corresponding
cross‑coupling products in good yields.12 Our approach to
the 2,4‑diarylquinolines involves the use of the 2‑aryl‑4‑
chloroquinolines as substrates for palladium‑catalysed Suzuki
cross‑coupling with arylboronic acids as coupling partners.
The 2,4‑diarylquinolines 2 used in this investigation as models
for the absorption and emission property studies were prepared
by subjecting substrates 1a–d to arylboronic acids (1.2 equiv.)
in the presence of the Pd(PPh3)4–PCy3 catalyst complex as the
Pd(0) source and potassium carbonate as a base in dioxane–
water mixture (3:1, v/v) under reflux, based on the literature
precedent (Table 1).13 The 18‑electron, Pd(0)(PPh3)4 dissociates
Table 1 Suzuki cross-coupling of the 2-aryl-4-chloroquinolines with
arylboronic acids.
R2
Cl
(i)
N
N
R1
R1
2a–l
1a–d
Compd
R1
R2
Yield 2/%
2a
2b
2c
2d
2e
2f
2g
2h
2i
H
F
Cl
OMe
H
F
Cl
OMe
H
F
H
H
H
H
F
F
F
F
OMe
OMe
OMe
OMe
40
74
53
62
52
48
51
63
47
54
61
48
2j
2k
2l
Cl
OMe
Reagents and conditions: (i) 4-R2C6H4B(OH)2 (1.2 equiv.), Pd(Ph3)4, PCy3,
dioxane–water (3:1, v/v), reflux, 18 h.
in solution to form a stable 16‑electron SPd(0)(PPh3)3 which,
in turn, produces the 14‑electron Pd(0)(PPh3)2 as follows:
Pd(0)(PPh3)4
SPd(0)(PPh3)2+PPh3, (K1/[PPh3]>>1);
where S is the solvent}.14 The extra PPh3 generated from this
dissociation has been found to inhibit the oxidative addition
step particularly when the palladium(0) complex is generated
from Pd(0)(PPh3)4.14 Tricyclohexylphosphine (PCy3) in this case
counteracts the inhibitory effect of PPh3 by coordinating to
palladium of either the 16‑ or 14‑electron Pd(0) species thereby
increasing the electron density of the metal and speeding up the
oxidative addition step. Some of the compounds prepared in this
investigation have been prepared previously via methods such
as the Friedlander synthesis15 or tandem addition–cyclisation–
oxidation reactions of imines with alkynes.11 However, the
compounds previously reported have either been described as
oils10,16 or with no melting point values included.15 Despite these
anomalies, the spectroscopic data of compounds 2a–l represent
a close fit that are fully consistent with the assigned structures.
Polysubstituted quinolines 2a–l comprise an electron‑
deficient quinoline framework as an electron‑acceptor linked
directly to the 4-substituted aryl ring to comprise a donor-π-
acceptor system. A quinoline moiety is known to act only as an
acceptor in the ICT,17 which occurs through space interaction or
orbital overlap between donor and acceptor groups.18,19 The lone
pair electrons of nitrogen are in an orbital which is orthogonal
* Correspondent. E‑mail: mphahmj@unisa.ac.za
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JOURNAL OF CHEMICAL RESEARCH 2014 255
to the π-ring system and this makes it is difficult for N-1 to
become a donor through a resonance effect. As a prelude to
compounds with photophysical properties, we determined the
absorption and fluorescence properties of compounds 2a–l in
solvents of medium (chloroform) and high polarity (methanol).
The electronic absorption spectra of compounds 2a–l were
acquired in chloroform (CHCl3) at room temperature (Fig. 1a–c
and Table 2). Both the absorption maxima and wavelength
within each series are influenced by the variation of
substituents on the para position of the 4‑aryl‑ and the 2‑aryl‑
groups. The high energy intense absorption maxima are located
in the UV region λ 260–284 nm with lower intensity and broad
bands observed in the near visible region λ 316–336 nm (ε in
the order of 103 dm3 mol–1 cm–1). The bands are assigned to the
π–π* transitions and the intermolecular donor-acceptor charge
transfer absorption20. For the 2‑aryl‑4‑phenylquinolines 2a–d,
the presence of a 4‑(halogenophenyl) ring at the 2‑position
leads to an increased molar extinction coefficient over those
for the 2‑phenyl‑ and 2‑(4‑methoxyphenyl)‑substituted
derivatives and the trend is as follows: 2c>2b>2a>2d
(Fig. 1a). Although the methoxyphenyl derivative 2d has the
lowest molar extinction coefficient, it absorbs at a relatively
higher wavelength (λ 277 nm) than the other compounds. The
reverse in trend for the molar extinction coefficient is observed
for the 4‑(4‑fluorophenyl) derivatives, 2e>2f>2g>2h, with the
methoxyphenyl derivative 2h absorbing at higher wavelength
at λ 275 nm (Fig. 1b). A combination of the 2-phenyl- and
4‑(4‑fluorophenyl)‑groups on the electron deficient quinoline
framework of 2e leads to the highest molar extinction coefficient
of all of the compounds. Increased broadening and molar
extinction coefficients compared to 2d and 2h are observed
for compound 2l bearing the 4‑methoxyphenyl‑group at both
positions 2‑ and 4‑ (Fig. 1c). The molar extinction coefficient
and the absorption wavelength are enhanced and red‑shifted by
λ ca 24 nm for 2l (Fig. 1c). This observation is consistent with a
recent study on the distinct photophysical properties observed
in 2,4‑diphenylquinoline.21 The increase in the wavelength for
2l clearly indicates that the methoxy substituent plays a role in
determining the gap between the highest occupied molecular
orbital (HOMO) and the lowest unoccupied molecular orbital
(LUMO).22
into the quinoline ring leading to increased emission maxima.
Reduced intensity and the blue shift for the emission band of
compound 2d in methanol (see 2d′ in Fig. 2a) are presumably
the result of additional hydrogen bonding between the solvent
and the methoxy group, which would, in our view, diminish its
propensity for electron donation to the aromatic ring.
Compounds 2e–h with a moderately electron donating
4‑fluorophenyl‑group at the 4‑position of the quinoline moiety
exhibited increased emission intensities in chloroform and
the emission wavelengths are influenced by the substituent
on the para position of the 2‑aryl‑group (Fig. 2b). However,
compound 2e emits at a shorter wavelength compared to the
other compounds, with reduced emission intensity resulting
from the envisioned methanol–quinoline interaction (see 2e′
in Fig. 2b). The 2‑(4‑chlorophenyl)‑group in compound 2g is
expected to reduce the electron density of the quinoline ring
and presumably its capacity to participate in hydrogen bonding
with methanol. This, in turn, would cause the moderately
donating 4‑(4‑fluorophenyl)‑group to release electrons
through the resonance effect, hence exhibiting increased
intensity in both solvents. The presence of the electron
releasing 4‑fluorophenyl‑ unit at the 2‑ or the 4‑positions in
2f or 2‑(4‑fluorophenyl)‑ and 4‑(4‑methoxyphenyl)‑groups in
2h leads to an increased π–π* transition in both solvents and
then shifts the emission wavelength in methanol to the red.
All the 4‑(4‑methoxyphenyl)‑substituted derivatives 2i–k
exhibit increased emission intensities due to an increased π–π*
transition, however, their emission wavelengths seem to be
influenced by the substituent on the 2‑aryl‑group (Fig. 2c). As
in the case of 2e in methanol above (see 2e′ in Fig. 2b), the
2‑phenyl‑derivative 2i emits at relatively lower wavelength (λem.
ca 410 nm) in methanol presumably due to hydrogen bonding
between the solvent and N‑1 (see 2i′ in Fig. 2c). Increased
emission intensity in this case is due to the propensity of the
4-(4-methoxyphenyl)-group for π-electron donation into the
quinoline ring, which leads to an increased π–π* transition. The
emission band for the 2‑(4‑chlorophenyl)‑substituted derivative
in methanol (see 2k′), on the other hand, is shifted to relatively
longer emission wavelength. The additional undesired red‑
shifted emission band of reduced intensity exhibited for 2l
in methanol is presumably due to the re‑absorption of light
emitted and/or molecular excited state interaction with a
ground state molecule, leading to a partial transfer of charge
in the molecule.24
The fluorescence emission spectra of compounds 2a–l in less
polar chloroform (dashed lines) and more polar protic methanol
(solid lines) at excitation wavelength, λex =370 nm, show similar
patterns and are characterised by single intense emission bands
(Fig. 2a–c). These compounds yield blue to green emission and
the maximal emission peaks are mainly located in the region
The absorption and fluorescent properties of compounds 2a–l
showed a strong correlation with the substituent on the para
position of the 2‑ and 4‑phenyl groups. The solvent‑dependent
emission characteristics of compounds 2a–l may result from
λ
em =410–520 nm. Intense emission maxima are observed for
all the compounds in chloroform and methanol; however, within
each series the emission wavelengths are influenced by the
variation of substituents on the para position of the 4‑aryl‑ and
the 2-aryl-groups. Since the π,π* state is much more polarisable
than the ground state, a change in polarity of the medium has
been previously found to cause measurable displacements
of the π–π* transition towards the red bands.23 Methanol is
expected to form strong solute–solvent interaction through
intermolecular hydrogen bonds with N‑1 and, in turn, make the
quinoline framework more electron‑deficient. A combination
of such interaction and the strongly electron withdrawing
effect of the 2‑(4‑chlorophenyl)‑group in compound 2c (see 2c′
in Fig. 2a) would result in a less pronounced ICT due to the
π–π* transition and therefore reduced emission intensity. The
moderately and strongly donating 4‑fluoro‑ and 4‑methoxy‑
groups, respectively, in compounds 2b and 2d, on the other
hand, are expected to increase the π-electron delocalisation
Table 2 The absorption and emission data for compounds 2a–l
Molar extinction
coefficient
Emission
Emission
2
λmax (nm)
wavelength,
wavelength,
(ε)×103 dm3 mol–1 cm–1 λem/nm CHCl3 λem/nm CH3OH
2a
2b
2c
2d
2e
2f
2g
2h
2i
261; 327
261; 327
266; 327
277; 336
260; 316
262; 316
268; 313
275; 336
260; 316
260; 316
265; 316
284; 334
47.52; 9.24
477
439
430
459
437
452
478
463
459
438
447
455
499
459
458
438
419
520
439
491
409
453
494
449
54.36; 11.10
60.38; 13.78
30.47; 10.09
81.85; 17.69
57.94; 12.25
53.38; 14.01
43.24; 14.76
52.76; 16.58
44.62; 14.39
51.22; 16.71
46.05; 18.61
2j
2k
2l
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256 JOURNAL OF CHEMICAL RESEARCH 2014
Fig. 1 UV-Vis spectra of 2-aryl-4-phenylquinolines in CHCl3 (1.0×10–3 mol L–1). (a) 2a–d; (b) 2e–h; and (c) 2i–l.
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Fig. 2 Fluorescence emission spectra (λex =370 nm) in CHCl3 (dashed lines) and MeOH (solid lines) at room temperature (conc. =1.0×10–3 mol L–1). (a) of
2a–d; (b) 2e–h; and (c) 2i–l.
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258 JOURNAL OF CHEMICAL RESEARCH 2014
(d, 4JCF =3.2 Hz), 138.3, 148.7, 149.3, 155.8, 163.8 (d, 1JCF =247 Hz); m/z
300 (100 MH+); HRMS (ES): MH+, found 300.1191. C21H15NF+ requires
300.1189.
the dipolar interaction with the polar solvent thus suggesting the
ICT character of the emission state, in which the HOMOs and
LUMOs are localised on the aryl rings and the quinoline‑based
moiety, respectively. The 2,4‑diarylquinolines 2a–l are suitable
candidates for potential application as organic light‑emitting
diode materials, either as a single component or as ligands
for further synthesis of metal complexes (e.g., with iridium,
palladium, platinum, etc.). This is because polyarylsubstituted
quinolines have been metallated with iridium to form
cyclometallated iridium complexes with potential application
in OLEDs,4,5,7 or novel red‑emitting electrophosphorescent
devices.2
2-(4-Chlorophenyl)-4-phenylquinoline (2c): A mixture of 1c (0.50 g,
1.82 mmol), phenylboronic acid (0.27 g, 2.19 mmol), Pd(PPh3)4 (0.11 g,
0.09 mmol), PCy3 (0.05 g, 0.19 mmol) and K2CO3 (0.50 g, 3.64 mmol) in
dioxane–water (15 mL) afforded 2c as a white solid (0.30 g, 53%), m.p.
101–103 °C (lit.1 103 °C); Rf (CHCl3) 0.30; νmax/cm–1 (ATR): 485, 539,
602, 742, 756, 963, 1093, 1355, 1415, 1485, 1544, 1590; δH (300 MHz,
CDCl3): 7.45 (m, 8H), 7.72 (d, J=7.5 Hz, 1H), 7.77 (s, 1H), 7.90 (d,
J=7.5 Hz, 1H), 8.15 (d, J=7.5 Hz, 2H), 8.21 (d, J=7.5 Hz, 1H); δC
(75 MHz, CDCl3): 118.9, 125.7, 125.8, 126.5, 128.5, 128.6, 128.8, 129.0,
129.5, 129.7, 130.1, 135.6, 138.0, 138.2, 148.7, 149.4, 155.5; m/z 316
(100 MH+); HRMS (ES): MH+, found 316.0897. C21H15N35Cl+ requires
316.0893.
Experimental
Melting points were recorded on a thermocouple digital melting point
apparatus and are uncorrected. IR spectra were recorded as powders
using a Bruker VERTEX 70 FT‑IR spectrometer with a diamond
ATR (attenuated total reflectance) accessory by using the thin‑
film method. The UV‑Vis spectra were recorded on a Cecil CE 9500
(9000 Series) UV‑Vis spectrometer while emission spectra were taken
using a PerkinElmer LS 55 fluorescence spectrometer. For column
chromatography, Merck kieselgel 60 (0.063–0.200 mm) was used as
stationary phase. NMR spectra were obtained as CDCl3 solutions using
Varian Mercury 300 MHz NMR spectrometer and the chemical shifts
are quoted relative to the solvent peaks. Low‑ and high‑resolution
mass spectra were recorded at an ionisation potential of 70 eV
using Micromass Autospec‑TOF (double focusing high resolution)
instrument. The synthesis and analytical data of compounds 1a–d have
been described previously.25
2-(4-Methoxyphenyl)-4-phenylquinoline (2d): A mixture of 1d
(0.30 g, 1.09 mmol), phenylboronic acid (0.16 g, 1.31 mmol), Pd(PPh3)4
(0.06 g, 0.06 mmol), PCy3 (0.03 g, 0.11 mmol) and K2CO3 (0.30 g,
2.19 mmol) in dioxane–water (15 mL) afforded 2d as a white solid
(0.21 g, 62%), m.p. 73–75 °C (lit. 76 °C,1 oil10); Rf (CHCl3) 0.60; νmax
/
cm–1 (ATR): 543, 750, 823, 1025, 1171, 1250, 1518, 1575; δH (300 MHz,
CDCl3): 3.87 (s, 3H), 7.05 (d, J=9.3 Hz, 2H), 7.44 (t, J=7.5 Hz,
1H), 7.52–7.58 (m, 5H), 7.72 (t, J=7.5 Hz, 1H), 7.78 (s, 1H), 7.89 (d,
J=7.8 Hz, 1H), 8.10–8.25 (m, 3H); δC (75 MHz, CDCl3): 55.3, 114.1,
114.2, 118.8, 125.5, 125.9, 128.3, 128.5, 128.8, 129.4, 129.5, 129.8, 132.1,
138.4, 148.7, 148.9, 156.3, 160.7; m/z 312 (100 MH+); HRMS (ES): MH+,
found 312.1397. C22H16NO+ requires 312.1388.
4-(4-Fluorophenyl)-2-phenylquinoline (2e): A mixture of 1a (0.50 g,
2.09 mmol), 4‑fluorophenylboronic acid (0.35 g, 2.51 mmol), Pd(PPh3)4
(0.12 g, 0.10 mmol), PCy3 (0.06 g, 0.21 mmol) and K2CO3 (0.58 g,
4.17 mmol) in dioxane–water (15 mL) afforded 2e as a white solid
(0.13 g, 52%), m.p. 82–83 °C; Rf (CHCl3) 0.29; νmax/cm–1 (ATR): 696,
763, 838, 1156, 1222, 1491, 1542, 1607; δH (300 MHz, CDCl3): 7.25 (t,
J=7.5 Hz, 2H), 7.47–7.56 (m, 6H), 7.74 (t, J=7.5 Hz, 1H), 7.79 (s, 1H),
7.86 (d, J=7.5 Hz, 1H), 8.19 (d, J=7.5 Hz, 2H), 8.25 (d, J=7.5 Hz, 1H),
Suzuki-Miyaura cross-coupling of 1 with arylboronic acids; general
procedure
2‑Aryl‑4‑chloroquinoline 1 (1 equiv.), arylboronic acid (1.2 equiv.),
Pd(PPh3)4 (5 mol% of 1), PCy3 (10 mol% of 1), K2CO3 (2 equiv.) and
3:1 dioxane–water (ca 5 mL mmol–1 of 1) were added to a two‑necked
flask equipped with a stirrer bar, rubber septum and a condenser.
The mixture was flushed for 20 minutes with argon gas and a balloon
filled with argon gas was connected to the top of the condenser. The
mixture was heated with stirring at 80–90 °C under argon atmosphere
for 18 h and then allowed to cool to room temperature. The cooled
mixture was poured into ice‑cold water and the product was taken‑up
into chloroform. The combined organic extracts were washed with
brine, dried over anhydrous MgSO4, filtered and then evaporated
under reduced pressure. The residue was purified by column
chromatography over silica gel to afford the 2,4‑diarylquinoline 2. The
following products were prepared in this fashion:
2,4-Diphenylquinoline (2a): A mixture of 1a (0.50 g, 2.09 mmol),
phenylboronic acid (0.31 g, 2.50 mmol), Pd(PPh3)4 (0.12 g, 0.10 mmol),
PCy3 (0.06 g, 0.21 mmol) and K2CO3 (0.58 g, 4.17 mmol) in dioxane–
water (15 mL) afforded 2a as a white solid (0.23 g, 40%), m.p. 107–
109 °C (lit. 109 °C,1 99–101 °C10); Rf (CHCl3) 0.38; νmax/cm–1 (ATR):
588, 699, 765, 872, 1356, 1405, 1444, 1488, 1544, 1588; δH (300 MHz,
CDCl3): 7.46–7.55 (m, 9H), 7.73 (t, J=7.2 Hz, 1H), 7.82 (s, 1H), 7.91
(d, J=8.4 Hz, 1H), 8.19 (d, J=7.5 Hz, 2H), 8.25 (d, J=8.4 Hz, 1H);
δC (75 MHz, CDCl3): 119.4, 125.6, 125.8, 126.3, 127.6, 128.4, 128.6,
128.8, 129.3, 129.5, 129.6, 130.1, 138.4, 139.7, 148.8, 149.2, 156.9; m/z
282 (100 MH+); HRMS (ES): MH+, found 282.1289. C21H16N+ requires
282.1283.
2
δC (75 MHz, CDCl3): δ 115.6 (d, JCF =21.3 Hz), 119.3, 125.3, 125.6,
126.4, 127.5, 128.8, 129.4, 129.6, 130.2, 131.2 (d, 3JCF =8.3 Hz), 134.3 (d,
4JCF =3.5 Hz), 139.5, 147.9, 148.8, 156.8, 162.8 (d, 1JCF =246.7 Hz); m/z
300 (100 MH+); HRMS (ES): MH+, found 300.1186. C21H15NF+ requires
300.1189.
2,4-Bis(4-fluorophenyl)quinoline (2f): A mixture of 1b (0.50 g,
1.94 mmol), 4‑fluorophenylboronic acid (0.33 g, 2.33 mmol), Pd(PPh3)4
(0.11 g, 0.09 mmol), PCy3 (0.05 g, 0.19 mmol) and K2CO3 (0.54 g,
3.88 mmol) in dioxane–water (15 mL) afforded 2f as a flaky yellow
solid (0.29 g, 48%), m.p. 103–105 °C; Rf (CHCl3) 0.62; νmax/cm–1
(ATR): 762, 838, 1157, 1223, 1354, 1493, 1599; δH (300 MHz, CDCl3):
7.19–7.29 (m, 4H), 7.48–7.57 (m, 3H), 7.75 (s, 1H), 7.76 (d, J=6.0 Hz,
1H), 7.86 (d, J=9.0 Hz, 1H), 8.18–8.25 (m, 3H); δC (75 MHz, CDCl3):
2
2
115.8 (d, JCF =21.3 Hz), 115.7 (d, JCF =21.6 Hz), 118.9, 125.3, 125.6,
126.5, 129.4 (d, 3JCF =8.3 Hz), 129.6, 130.1, 131.2 (d, 3JCF =8.0 Hz), 134.2
4
4
(d, JCF =3.1 Hz), 135.6 (d, JCF =3.1 Hz), 148.2, 148.7, 155.7, 162.9 (d,
1JCF =243.5 Hz), 163.8 (d, JCF =247.6 Hz); m/z 318 (100 MH+); HRMS
(ES): MH+, found 318.1096. C21H14NF2+ requires 318.1094.
1
2-(4-Chlorophenyl)-4-(4-fluorophenyl)quinoline (2g): A mixture of
1c (0.50 g, 1.82 mmol), 4‑fluorophenylboronic acid (0.31 g, 2.18 mmol),
Pd(PPh3)4 (0.11 g, 0.09 mmol), PCy3 (0.05 g, 0.18 mmol) and K2CO3
(0.50 g, 3.64 mmol) in dioxane–water (15 mL) afforded 2g as a white
solid (0.31 g, 51%), m.p. 96–98 °C; Rf (CHCl3) 0.47; νmax/cm–1 (ATR):
553, 718, 806, 829, 1013, 1090, 1156, 1221, 1501, 1597; δH (300 MHz,
CDCl3): 7.26 (t, J=8.4 Hz, Hz, 2H), 7.48–7.56 (m, 5H), 7.74 (s, 1H),
7.75 (d, J=7.8 Hz, 1H), 7.85 (d, J=8.4 Hz, 1H), 8.15 (d, J=8.4 Hz, 2H),
2-(4-Fluorophenyl)-4-phenylquinoline (2b): A mixture of 1b (0.50 g,
1.94 mmol), phenylboronic acid (0.28 g, 2.33 mmol), Pd(PPh3)4 (0.11 g,
0.09 mmol), PCy3 (0.05 g, 0.19 mmol) and K2CO3 (0.54 g, 3.88 mmol)
in dioxane–water (15 mL) afforded 2b as a white solid (0.43 g, 74%),
2
8.22 (d, J=9.3 Hz, 1H); δC (75 MHz, CDCl3): 115.7 (d, JCF =21.3 Hz),
10
m.p. 83–85 °C (lit. 68–69 °C); Rf (CHCl3) 0.44; νmax/cm–1 (ATR):
118.9, 125.4, 126.7, 128.6, 128.8, 128.9, 129.8, 130.1, 131.2 (d,
3JCF =8.0 Hz), 134.1 (d, 4JCF =3.5 Hz), 135.6, 137.8, 148.3, 148.7, 155.4,
162.9 (d, 1JCF =246.8 Hz); m/z 334 (100 MH+); HRMS (ES): MH+, found
334.0804. C21H14NF35Cl+ requires 334.0799.
4-(4-Fluorophenyl)-2-(4-methoxyphenyl)quinoline (2h): A mixture
of 1d (0.50 g, 1.85 mmol), 4‑fluorophenylboronic acid (0.31 g,
528, 701, 727, 755, 769, 806, 831, 999, 1098, 1355, 1419, 1488, 1547,
1585; δH (300 MHz, CDCl3): 7.20 (t, J=7.8 Hz, 2H), 7.45–7.54 (m,
6H), 7.72 (d, J=7.8 Hz, 1H), 7.76 (s, 1H), 7.90 (d, J=7.8 Hz, 1H), 8.17–
2
8.23 (m, 3H); δC (75 MHz, CDCl3): 115.8 (d, JCF =21.3), 118.9, 125.7,
3
126.4, 128.5, 128.6, 129.4, 129.5 (d, JCF =4.8 Hz), 129.6, 130.0, 135.8
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2.22 mmol), Pd(PPh3)4 (0.11 g, 0.09 mmol), PCy3 (0.05 g, 0.18 mmol)
and K2CO3 (0.51 g, 3.70 mmol) in dioxane–water (15 mL) afforded
2h as a cream white solid (0.38 g, 62%), m.p. 117–120 °C; Rf (CHCl3)
0.54; νmax/cm–1 (ATR): 713, 750, 823, 1025, 1326, 1544, 1575, 1604;
δH (300 MHz, CDCl3): 3.88 (s, 3H), 7.04 (d, J=9.3 Hz, 2H), 7.24 (t,
J=7.8 Hz, 2H), 7.45 (t, J=7.8 Hz, 2H), 7.53 (t, J=7.8 Hz, 1H), 7.70 (d,
J=7.8 Hz, 1H), 7.74 (s, 1H), 7.82 (d, J=7.8 Hz, 1H), 8.15 (d, J=9.0 Hz,
2H), 8.20 (d, J=9.0 Hz, 1H); δC (75 MHz, CDCl3): 55.4, 114.2, 115.6 (d,
2JCF =21.3 Hz), 118.9, 125.3, 125.4, 126.1, 128.9, 129.5, 129.9, 131.2 (d,
3JCF =8.3 Hz), 132.0, 134.4 (d, 4JCF =3.1 Hz), 147.9, 148.8, 156.4, 160.8,
162.9 (d, 1JCF =246.4 Hz); m/z 330 (100 MH+); HRMS (ES): MH+, found
330.1297. C22H17NOF+ requires 330.1294.
2,4-Bis(4-methoxyphenyl)quinoline (2l): A mixture of 1d (0.40 g,
1.48 mmol), phenylboronic acid (0.27 g, 1.78 mmol), Pd(PPh3)4 (0.09 g,
0.07 mmol), PCy3 (0.04 g, 0.15 mmol) and K2CO3 (0.41 g, 2.96 mmol)
in dioxane–water (15 mL) afforded 2l as a white solid (0.24 g, 48%),
m.p. 84–87 °C (lit.16 orange oil); Rf (CHCl3) 0.49; νmax/cm–1 (ATR):
782, 830, 1027, 1178, 1234, 1247, 1307, 1496, 1511, 1605; δH (300 MHz,
CDCl3): 3.86 (s, 3H), 3.89 (s, 3H), 6.72 (d, J=3.3 Hz, 1H), 7.09–7.06
(m, 3H), 7.43 (d, J=7.8 Hz, 1H), 7.49 (s, 1H), 7.51 (d, J=3.0 Hz, 1H),
7.70 (t, J=7.5 Hz, 1H), 7.76 (d, J=3.0 Hz, 1H), 7.93 (d, J=7.5 Hz, 1H),
8.15 (dd, J=3.0 Hz, 9.3 Hz, 2H), 8.24 (d, J=9.3 Hz, 1H); δC (75 MHz,
CDCl3): 55.2, 55.3, 113.9, 114.1, 114.6, 116.1, 118.9, 125.6, 125.8, 128.9,
129.4, 129.6, 130.7, 148.7, 148.8, 156.5, 159.7, 160.7; m/z 342 (100 MH+);
HRMS (ES): MH+, found 342.1494. C23H20NO2+ requires 342.1494.
4-(4-Methoxyphenyl)-2-phenylquinoline (2i):
A mixture of 1a
(0.25 g, 1.04 mmol), phenylboronic acid (0.19 g, 1.25 mmol), Pd(PPh3)4
(0.06 g, 0.05 mmol), PCy3 (0.03 g, 0.10 mmol) and K2CO3 (0.29 g,
2.09 mmol) in dioxane–water (15 mL) afforded 2i as a pale yellow
Received 31 October 2013; accepted 23 February 2014
Paper 1302260 doi: 10.3184/174751914X13945617338344
Published online: 2 April 2014
solid (0.15 g, 47%), m.p. 99–100 °C (lit.16,26 oil); Rf (CHCl3) 0.58; νmax
/
cm–1 (ATR): 584, 676, 686, 718, 767, 1026, 1169, 1181, 1286, 1490, 1502,
1592, 1607; δH (300 MHz, CDCl3): 3.90 (s, 3H), 7.07 (d, J=8.7 Hz,
2H), 7.56–7.44 (m, 6H), 7.73 (t, J=8.4 Hz, 1H), 7.80 (s, 1H), 7.96 (d,
J=8.4 Hz, 1H), 8.20 (d, J=8.7 Hz, 2H), 8.26 (d, J=8.7 Hz, 1H); δC
(75 MHz, CDCl3): 55.4, 114.0, 119.3, 125.6, 125.9, 126.2, 127.5, 128.8,
129.2, 129.4, 130.1, 130.6, 130.8, 139.7, 148.8, 148.9, 156.9, 159.8; m/z
312 (100 MH+); HRMS (ES): MH+, found 312.1385. C22H18NO+ requires
312.1388.
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2-(4-Fluorophenyl)-4-(4-methoxyphenyl)quinoline (2j): A mixture
of 1b (0.25 g, 0.97 mmol), phenylboronic acid (0.18 g, 1.16 mmol),
Pd(PPh3)4 (0.06 g, 0.05 mmol), PCy3 (0.03 g, 0.10 mmol) and K2CO3
(0.27 g, 1.94 mmol) in dioxane–water (15 mL) afforded 2j as a white
solid (0.19 g, 54%), m.p. 89–91 °C (lit.16 orange oil); Rf (CHCl3) 0.56;
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3.91 (s, 3H), 7.08 (d, J=9.0 Hz, 2H), 7.20 (t, J=9.0 Hz, 2H), 7.49 (d,
J=7.5 Hz, 3H), 7.71 (d, J=7.5 Hz, 1H), 7.74 (s, 1H), 7.95 (d, J=9.3 Hz,
1H), 8.16–8.24 (m, 3H), δC (75 MHz, CDCl3): 55.3, 114.0, 115.7 (d,
2JCF =21.4 Hz), 118.8, 125.6, 125.8, 126.2, 129.3, 129.4 (d, 3JCF =8.3 Hz),
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4
129.9, 130.5, 130.7, 135.8 (d, JCF =3.1 Hz), 148.8, 148.9, 155.7, 159.8,
163.7 (d, 1JCF =247.3 Hz); m/z 330 (100 MH+); HRMS (ES): MH+, found
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2-(4-Chlorophenyl)-4-(4-methoxyphenyl)quinoline (2k): A mixture
of 1c (0.25 g, 0.97 mmol), phenylboronic acid (0.17 g, 1.09 mmol),
Pd(PPh3)4 (0.05 g, 0.05 mmol), PCy3 (0.03 g, 0.09 mmol) and K2CO3
(0.25 g, 1.82 mmol) in dioxane–water (15 mL) afforded 2k as a white
solid (0.21 g, 61%), m.p. 94–97 °C; Rf (CHCl3) 0.49; νmax/cm–1 (ATR):
718, 823, 1090, 1177, 1244, 1488, 1589; δH (300 MHz, CDCl3): 3.90
(s, 3H), 7.07 (d, J=9.3 Hz, 2H), 7.45–7.51 (m, 5H), 7.71 (d, J=6.0 Hz,
1H), 7.74 (s, 1H), 7.94 (d, J=9.3 Hz, 1H), 8.13 (d, J=9.0 Hz, 2H), 8.20
(d, J=7.5 Hz, 1H); δC (75 MHz, CDCl3): 55.4, 114.1, 118.8, 125.7, 125.9,
126.4, 128.8, 129.0, 129.6, 130.0, 130.5, 130.8, 135.5, 138.1, 148.8, 149.1,
155.5, 159.9; m/z 346 (100 MH+); HRMS (ES): MH+, found 346.1000.
C22H17NO35Cl+ requires 346.0999.
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