Quinolines by three-component reaction: Synthesis and photophysical studies

Article abstract of DOI:10.5935/0103-5053.20150011

The synthesis of five quinolines 8-octyloxy-4-[4-(octyloxy)phenyl]quinoline and 6-alkoxy- 2-(4-alkoxyphenyl)-4-[(4-octyloxy)aryl]quinolines are described by three-component coupling reaction mediated by Lewis acid FeCl₃ and Yb(OTf)₃. 4-n-octyloxybenzaldehyde, anisaldehyde, 4-n-octyloxyaniline p-anisidine, and 1-ethynyl-4-heptyloxybenzene, 1-ethynyl-4-octyloxybenzene and 2-ethynyl-6-heptyloxynaphthalene are the reagents in this protocol. A Yb³⁺ catalyst resulted in higher yields of quinolines than Fe³⁺. Polarizing optical microscopy (POM) revealed that none of the quinolines were liquid crystals, even the more anisotropic. UV-Vis measurements of one of the quinolines in polar solvent show two absorption bands at 280 and 350 nm related to π,π?and n,π?transitions. No changes were observed to lower-energy absorption band (ε < 10⁴ mol L^-1 cm^-1) related to n,π?transition. A laser flash photolysis study for one of the quinolines relates a main transient band at 450 nm with a lifetime of 2.6 μs in ethanol, which is completely quenched in the presence of oxygen. This transient band was assigned to triplet-triplet absorption of one of the quinolines, which is semi-oxidised in the presence of phenol. Radiative rate constants have been determined along singlet and triplet excited state energies (3.39 and 3.10 eV, respectively). The chemical structure of one of the quinolines was also unequivocally confirmed by single-crystal X-ray analysis.

Full text of DOI:10.5935/0103-5053.20150011

http://dx.doi.org/10.5935/0103-5053.20150011
J. Braz. Chem. Soc., Vol. 26, No. 3, 562-571, 2015.
Printed in Brazil - ©2015 Sociedade Brasileira de Química
0
103 - 5053 $6.00+0.00
Article
A
Quinolines by Three-Component Reaction: Synthesis and Photophysical Studies
a
a
a
b
Eric S. Sales, Juliana M. F. M. Schneider, Marcos J. L. Santos, Adailton J. Bortoluzzi,
c
,c
,a
Daniel R. Cardoso, Willy G. Santos* and Aloir A. Merlo*
a
Instituto de Química, Universidade Federal do Rio Grande do Sul (UFRGS),
0040-060 Porto Alegre-RS, Brazil
9
b
Departamento de Química, Universidade Federal de Santa Catarina(UFSC),
8040-900 Florianópolis-SC, Brazil
8
c
Chemistry Institute of São Carlos, Universidade de São Paulo (USP),
3566-590 São Carlos-SP, Brazil
1
The synthesis of five quinolines 8-octyloxy-4-[4-(octyloxy)phenyl]quinoline and 6-alkoxy-
-(4-alkoxyphenyl)-4-[(4-octyloxy)aryl]quinolines are described by three-component coupling
2
reaction mediated by Lewis acid FeCl and Yb(OTf) . 4-n-octyloxybenzaldehyde, anisaldehyde,
3
3
4
-n-octyloxyaniline p-anisidine, and 1-ethynyl-4-heptyloxybenzene, 1-ethynyl-4-octyloxybenzene
3+
and 2-ethynyl-6-heptyloxynaphthalene are the reagents in this protocol. A Yb catalyst resulted
3
+
in higher yields of quinolines than Fe . Polarizing optical microscopy (POM) revealed that none
of the quinolines were liquid crystals, even the more anisotropic. UV-Vis measurements of one of
the quinolines in polar solvent show two absorption bands at 280 and 350 nm related to π,π* and
4
-1
-1
n,π* transitions. No changes were observed to lower-energy absorption band (e < 10 mol L cm )
related to n,π* transition. A laser flash photolysis study for one of the quinolines relates a main
transient band at 450 nm with a lifetime of 2.6 ms in ethanol, which is completely quenched in
the presence of oxygen. This transient band was assigned to triplet-triplet absorption of one of the
quinolines, which is semi-oxidised in the presence of phenol. Radiative rate constants have been
determined along singlet and triplet excited state energies (3.39 and 3.10 eV, respectively). The
chemical structure of one of the quinolines was also unequivocally confirmed by single-crystal
X-ray analysis.
Keywords: quinolines, three-component synthesis, single-crystal resolution, photophysics,
flash photolysis
Introduction
drug used in the treatment of malaria, should not be used
during pregnancy.
6
Quinolines are present in many pharmacologically
active natural compounds. The simplest structure is the
The biological activity of chloroquine was evaluated
through fluorescence quenching studies developed by
Naal et al. Their findings provide information about the
7
1
-azanaphthalene named quinoline itself, which was
prepared by Friedländer in 1882 through the condensation
chloroquine-micellar surface interactions in water and
their ability to cross biological membranes in order to
accumulate inside lysosomes.
of o-aminobenzaldehyde with acetaldehyde in the presence
1
of sodium hydroxide. Quinolines display a broad spectrum
of application in medicine, such as antiseptic, antimalarial,
and as fungicides and antibiotics. Chloroquine is the most
well-known drug, and has been applied for the control and
The combination of quinoline ring and styryl moiety
resulted in a small and powerful luminescent molecular
material, which presents pronounced fluorescence
and noticeable nonlinear responses to be exploited in
2-4
treatment of malaria for many decades. Some quinolines
such as chloroquine, amodiaquine and quinine can be safely
8
protochromic ON-OFF-ON effects. In addition, small
5
used during pregnancy. Primaquine, however, another
fluorescent molecules can be applied for the detection of
fibrillar aggregates by binding to the fibril and changing
its fluorescence properties by absorbing and emitting light
*
e-mail: aloir.merlo@ufrgs.br, willy_glen@yahoo.com.br

Vol. 26, No. 3, 2015
Sales et al.
563
CHO
CHO
in the far red/near-infrared (NIR) region (ca. 600-800 nm).
Under this circumstance, tissue scattering and absorption is
lowest. Most particularly, they are able to cross the blood-
C H17Br, KOH
8
CH CN, heat
3
(99%)
HO
C8H17O
H2N
1
2a
9,10
brain barrier due to their small molecular size.
NO2
1
. RBr, KOH
CH CN (70%)
Industrial applications of quinolines include use as
dyes, preservatives and ligands to metal complexes, and
3
HO
2. H2 (10bar)
Pd/C, MeOH (90%)
OR
1
1
R = CnH2n+1
have strong impact in luminescence chemistry. Multi-
component reactions are a useful tool to synthesize
molecules from simple to complex architectures in a way
that their chemical and pharmaceutical properties can be
explored, making quinolines important in pharmacology
3
a p-nitro
b o-nitro
3
4a p-amine n = 9
b o-amine n = 8
4
1
. RBr, KOH
CH CN (95-97%)
Br
3
2. Mebynol (6), PdCl2(PPh3)2,
CuI, PPh ,THF/TEA (65%)
3
RO
HO
12
3
. NaOH, Toluene
R = C H
n 2n+1
and functional material chemistry.
5
7
a n = 7 (70%)
Quinolines are fluorescent molecules with good
electron acceptance in biological media and in devices.
The potential redox of simple quinolines is a reversible
process. However, the potential redox, and the absorption
and spectral emission properties of quinoline derivatives
can be tailored by appropriate substitution in the quinoline
7
b n = 8 (85%)
OHC
H N
2
C H15O
7
OCH3
CH2O
OCH3
2c
2b
4c
7c
13
ring or/and in the peripheral aryl groups.
Scheme 1. Preparation of key intermediates 2a, 4a and 7a-b.
We here report our results involving the synthesis
and characterisation of new quinolines synthesised by
three-component reaction between aldehyde, amine and
alkyne under Lewis catalyst FeCl andYb(OTf) . Ground-
4
coupling was performed as outlined in Scheme 2. Two
Lewis acids were tested: FeCl and Yb(OTf) as a catalyst
of three-component coupling. FeCl was chosen due to
3
3
3
3
3
state and excited-stated dynamics analysis are discussed
for one quinoline synthesised in this work along with
electrochemical data. These results will be exploited in
the future, in the preparation and utilisation of new iridium
complexes in the field of organic-light emitting diodes
its low price, non-toxicity, and environmental friendly
18
characteristics. Despite the attributes mentioned above,
the approach using a three-component reaction with
Fe(III) resulted in poor yield and reproducibility. Very
low yields were obtained for 8a (12%), 8b (15%) and 8c
13
(OLEDs) and metal-complex liquid crystals (MCLC).
(13%) using FeCl . When the catalyst ratio was increased
3
to 20 mol%, the yield of 8b rose to 40%. Previous work
1
9
Results and Discussion
by Furukawa showed that the Yb(III) triflate is an
effective catalyst to prepare 2-arylquinolines. Following
19
Synthesis
the procedure described by Furukawa, quinolines 8c and
d were obtained in 40% and 60%, by usingYb(III) triflate
8
The preparation of key intermediates for the three-
component reaction of the quinolines 8a-e is described
in Scheme 1. Aldehyde 2a was obtained by alkylation
as a catalyst. The ratio of catalyst (mol%), yields (%) and
melting point (°C) for quinolines 8a-e are shown in Table 1.
The mechanism for the formation of the quinoline
derivatives is generally accepted as activation on both
processes of imine addition and cyclization. The double
and triple bond of both imine group and alkyne could be
14
reaction of 1, in nearly quantitative yield. Amines 4a-b
were prepared in two steps: alkylation reaction followed by
reduction of the nitro group to the amine group by means of
15
20
21
hydrogenolysis reaction (H /Pd/C in MeOH). Aldehydes
activated by a Lewis acid such as Au(III), Fe(III) and
2
22
2
b and 2c and amine 4c are commercial chemicals.
Yb(III). The complexation effect promotes the formation
23
Alternatively, they can be prepared using the condition
of propargylamine intermediate A, which undergoes an
1
6
16
24
reaction described by Vogel and Markiewicz et al.
Alkynes 7a-b were synthesised in three steps, starting with
by alkylation reaction, followed by Sonogashira cross-
coupling reaction and acetone release in the basic medium
intramolecular hydroarylation to give another intermediate
dihydroquinoline B. PropargylamineA is generally isolated
when aliphatic amines are used. In the present study, no
attempt to detect or to isolate intermediate A was made.
5
17
17
25
to give 7a and 7b in good yields. Alkyne 7c was made
similarly to 7a-b from 6-bromo-2-napthol.
Dihydroquinolines could then be further oxidized by O2
to afford quinoline products 8a-e. In summary, this one-
pot reaction undergoes domino imine formation, imine
addition, cyclization and an oxidation process.
Since the preparation of the intermediates 2a, 4a, 7a-b
was accomplished, metal-catalysed three-component

5
64
Quinolines by Three-Component Reaction: Synthesis and Photophysical Studies
J. Braz. Chem. Soc.
Table 1. Lewis acid and yields (%) of quinolines 8a-e
aryl group or lengthening the flexible alkyl chain were
not enough for the generation of liquid crystal properties
as exemplified by the more anisotropic quinoline 8e one.
A particularly interesting feature of the single-crystal
X-ray structure of 8e is related to the pendant naphthyl
group. It is twisted 65.2° from the plane of the quinoline
unit. A flexible alkyl chain linked to this pendant aryl
group is also randomly coiled, which indicates non-longer
planarity of the molecule and a non-favourable molecular
package. In fact, the absence of a mesophase for the
quinolines 8a-e can be attributed to the planarity and
package structure. Although our efforts in preparation of
the mono- and disubstituted arylquinolines liquid crystals
as exemplified by 8a and 8b-e failed, we performed
a photophysical study of donor-acceptor luminescent
molecules derived from quinolines in this work.
Ar
+
3
Yb
.
.
N
H
N
NH
Ar
H
Ar
Ar
H
Ar
H
Ar
Alkyne addition
activated
by Lewis acid
Dihydroquinoline B
Propargylamine A
Lewis acid /
mol%)
Melting
point / °C
Quinoline
Yield / %
12
(
8
8
a
FeCl (12)
68-70
3
b
FeCl (10)
15
40
85-86
3
FeCl (20)
3
8
c
FeCl (10)
13
60
75-76
3
Yb(OTf) (10)
3
8
8
d
e
Yb(OTf) (10)
40
36
87-88
67-68
3
Yb(OTf) (10)
3
The single crystal X-ray diffraction studies
The three-component protocol applied in this study
allows us to prepare new quinolines, which are, of course,
naturally anisotropic. The choice of amines, aldehydes and
alkynes are crucial in order to reach the final anisometric-
shape molecules. However, concerning phase transition,
these new quinolines are not liquid crystals. According to
polarising optical microscopy (POM) studies, no evidence
of mesophases was observed. Upon heating or cooling,
the quinolines pass directly from solid state to isotropic
state or vice versa. Upon cooling, quinolines 8a-e display
a large hysteresis range and they recrystallize well below
their melting point, while when left for a long time at room
temperature, they recrystallize very slowly.A homeotropic
film was also observed over a large area of the sample from
the POM texture. Unfortunately, neither enantiotropic
nor monotropic behaviour can be seen in those samples.
Starting from simple quinoline 8a and adding a second
The structural characterization of quinolines obtained
by three component reaction was also established
unequivocally by single crystal X-ray structure analysis
of quinoline 8e (Figure 1, top). The single crystal X-ray
diffraction studies for 8e were accomplished successfully,
showing distinct conformation behaviour of alkylaryl
groups linked to the quinoline moiety. The structure
of 8e shows that the phenyl group is almost coplanar,
whereas the pendant naphthyl group is twisted compared
to the plane of the quinoline unit. The torsion angle for
N1-C1-C10-C11 is 7.30(17)° and for C4-C3-C24-C33 is
65.22(15)°. From this point of view, the electron migration
is more pronounced through the phenyl-quinolinyl system
than the naphtyl-quinolinyl system. The preference for
non-coplanarity of the naphtyl group is due to a hydrogen
atom at the C5 carbon atom where the free rotation around
7 15
OC H
OC
8
H
17
8 17
OC H
8a
8b
8c
3
H CO
3
H CO
N
N
N
Aldehydes
a-c
Amines
a-c
Alkynes
OC
8
H
17
8 17
OC H
2
7a-c
OCH
3
4
7 15
OC H
Lewis acid
10-20 mol %)
toluene, heat
7 15
OC H
(
8d
Quinolines
a-e
8e
8
9 19
C H O
3
H CO
N
N
8 17
OC H
8 17
OC H
Scheme 2. Three-component synthesis of quinolines 8a-e.

Vol. 26, No. 3, 2015
Sales et al.
565
C3-C24 bond is hindered by a steric effect hydrogen atom.
The conformational issue observed in this study has been
also observed in kinetics studies of hydrolysis of acetoxy
(Figure 1, bottom). The single crystal structure of quinoline
8e provides a basis for elucidating the effect of solid-state
morphology on their photophysics and liquid-crystalline
properties. The absence of a mesophase, the glass-like
appearance of the samples after heating/cooling cycles
and UV-Vis absorption spectra profile are related to the
molecular packing, as revealed by crystal structure of 8e.
26
naphthoic acids. To overcome this geometrical constraint,
the bond length of the aryl group attached at the bay of the
quinoline ring are slightly different. For instance, the bond
length of C1-C10 is 1.4868(16) Å, while for C3-C24, the
bond length value is longer by 0.0057 Å (1.4925(14) Å).
Although the arrangement of the aryl groups at the bay
of quinoline ring is quite different, the torsion angles
to the three set of atoms namely C7-C6-O3-C41,
C14-C13-O1-C16 and C30-C29-O2-C34 are 179.38(10)°,
Ground-state and excited singlet-state: dependence on
solvent and temperature
The UV-Vis absorption and fluorescence emission
spectra of the quinolines 8a-e are shown in Figures 2 and 3.
The substitution of an aryl group affects the two absorption
bands in different ways; in fact, the p-alcoxyaryl group
177.72(11)° and 178.13(11)°, respectively. Thus, the first
carbon atom of the alkyl chains is located on the same
plane as the aryl and quinolinyl groups. The alkoxy chain
connected to the C6 and C13 aromatic carbon atoms have
an antiperiplanar arrangement for most carbon atoms
including O1 and O3 oxygen atoms. However, the third
alkoxy group connected to C29 aromatic carbon atom does
not have an antiperiplanar arrangement for all saturated
carbon atoms. They probably lost their conformational
memory due to the twisted disposition of the naphthyl group
to which they are bonded. The flexible alkyl chain linked
to the pendant naphthyl group is randomly coiled. The
disordered pendant group in 8e aligns itself in an opposite
direction, exhibiting alternate dispositions such as head-tail.
We suggest that the conformational behaviour observed
in the crystal state may have an influence on the mesogenic
behaviour as well as on the photophysical properties. The
packing analysis shows neighbouring quinoline units are
almost coplanar with respect to each other, with an average
distance of 3.8 Å, exhibiting face-to-face π-stacking
in C position of quinoline ring does not seem to greatly
4
disturb the electronic UV-Vis spectrum of 8a, while the
p-alkoxyphenyl group in C position induces the rise of
2
the band at 290 nm, as observed for 8b-e in Figure 2.
The comparison between the UV-Vis spectra of quinoline
and 8a reveals similar patterns (optical behaviour) in the
27
interval of wavelength of 270-330 nm. Quinoline itself
and quinoline 8a have similar spectra, indicating that the
aryl group in C position does not change the chromophore
4
characteristics. However, when an alkoxyaryl group is
present in C position, the quinolines 8b-e absorption shows
2
an intense band around 290 nm, which is not observed
to 8a. The quinolines 8a-e have similar absorption at the
230-320 nm range, which is assigned to π,π transition that
shifts to red in polar solvent (acetonitrile and ethanol) and
is characterized by a large molar absorption coefficient.
The n,π* transitions are observed as a shoulder in the
Figure 1. ORTEP plot of compound 8e (top) and a view of partial packing of 8e showing face-to-face π-stacking between neighbouring quinoline units
bottom, centroids are shown in magenta, see Supplementary Information (SI)).
(

5
66
Quinolines by Three-Component Reaction: Synthesis and Photophysical Studies
J. Braz. Chem. Soc.
3
-1
-1
3
20-450 nm range (e ca. 10 mol L cm ), which is not
is estimated from the intersection of the normalised
absorption and emission spectra, is observed in Table 3.
No significant changes are observed on the Stokes shifts
shifted in polar solvent, as shown in Figure 2.
8
c
1
0
0
0
0
0
.0
.8
.6
.4
.2
.0
when replacing acetonitrile with ethanol. E is independent
(a)
S1
8
b
of the solvent, with energy of 3.39 eV, discarding a
hydrogen-bond interaction in the excited single-state. The
compounds studied exhibit an overall increase of Stokes
shift from non-polar to polar solvents mainly due to the
combined effect of increasing the polarity of the medium
and intramolecular charge transfer state (ICT). Other
researchers relate the presence of the ICT state in quinoline
molecules to the density functional theory and experimental
8
e
8
d
8a
2
75
300
325
350
375
400
425
1
00
(b)
8
6
4
2
0
0
0
0
0
28,29
studies. The absorption spectrum of 8d has an extinction
8
d
4
-1
−1
coefficient of 1.4 × 10 mol L cm at 350 nm in ethanol.
The fluorescence of quinoline 8d in ethanol at 298 K and
8b
7
7 K is shown in Figure 4, which is more intense at low
8
e
8
a
temperature (77 K) with a maximum of 400 nm, indicating a
relevant and competitive non-radiative process to deactivate
the excited single-state.
8
c
3
00
350
400
450
500
550
600
Wavelength / nm
1
600
1
500
τP = 950 ms
1500
1000
500
0
Figure 2. Absorption (a) and fluorescence (b) spectra of quinolines 8a-e
in dichloromethane (DCM); lexc = 350 nm.
1400
1200
1
000
8
6
00
00
1
00
1000
Acetonitrile
Ethanol
400
200
0
8
6
4
2
0
0
0
0
0
Cyclohexane
0
1
2
3
4
5
time / s
500
Fluorescence at 293 K
Fluo. + phos. at 77K
Phosphorescence at 77K
0
3
50
375
400
425
450
475
500
350
400
450
500
550
600
650
700
Wavelength / nm
λ / nm
Figure 4. Fluorescence and phosphorescence emission (total emission)
of 8d in ethanol at 77 K (blue dots) and fluorescence emission at 293 K
(black dots). Insert demonstrates the phosphorescence time decay at 77 K.
Figure 3. Emission spectra recorded to the quinoline 8b in acetonitrile
(), ethanol () and cyclohexane (). lexc = 350 nm.
In contrast with absorption, the solvent polarity affects
The quinoline derivatives 8a-e present an emission band
around 400 nm in polar solvent. The maximum absorption
and emission wavelength and other photophysical
properties of quinoline derivatives are shown in Table 2.
Quinoline 8d displays a phosphorescence emission at 77 K
the fluorescence properties of quinolines. The Stokes
shift data, given by the difference between the maximum
peak of normalised absorption and emission spectra, and
the energy of the lowest singlet excited state, E , which
S1
Table 2. Photophysical properties of quinolines 8a-e in DCM
abs
MAX
a
em
a
e × 10 / (mol L cm-1)
3
-1
a
l
/ nm
l
/ nm
DE / eV
MAX
b
Quinolines
lST / nm
FFX
π-π*
n-π*
330
350
350
347
350
n-π*
411
398
399
409
407
π-π*
-
n-π*
1.9
1.7
18
π-π*
2.64
3.02
3.00
3.08
3.07
n-π*
-
8
8
8
8
a
b
c
245
288
290
282
285
81
48
49
62
57
0.24
0.22
0.27
0.25
0.30
51
66
41
44
2.49
2.49
2.51
2.49
d
e
14
8
14
a
Optical measurements condition: DCM, 298 K; quinine sulphate 1 mol L was used as fluorescent standard (Fo = 0.546, lexc = 337 nm).
b
-1
F

Vol. 26, No. 3, 2015
Sales et al.
567
in ethanol solution, showing clear vibrational resolution
with three main bands at 440, 505 and 540 nm, which have
the same time decay of 950 ms, close to that reported for
Quinoline 8d can form a semi-oxidised radical specie
·
+
(Q ) at 350-450 nm and a semi-reduced form of quinoline
·
-
(Q ) at 740 nm by reaction with electron acceptor and
electron donors molecules, respectively. Nedoloujko and
28
other quinolines (0.5-1.5 s). Phosphorescence properties
and others photophysical characterisation can be found
in Table 3. Figure 5 shows the transient species of 8d
obtained by laser pulse excitation at 355 nm in the absence
of oxygen. Quinoline 8d presents three transient absorption
bands centred at 250 nm, 450 nm and 900 nm with the same
time decay in ethanol. The lifetime decay of 2.6 ms was
observed in all spectra, suggesting T-T character absorption.
30
Kiwi relate the lifetime of semi-oxidized radical around
4 ms at 400 nm, comparable to 8d specie at the same spectral
range. No differences in the absorption spectra of 8d were
observed in methanol, ethanol, methylcyclohexane or
acetonitrile as solvent, however, in aired solution, the T-T
absorption of 8d was totally quenched in ethanol. In the
-4
-1
presence of a high concentration of phenol (× 10 mol L ),
the triplet of 8d is quenched, simultaneously with an
increase of the absorption in 280-500 nm range. These
absorptions can be ascribed to a semi-oxidized form of 8d,
formed by an electron transfer donation to phenol. Figure 6a
shows the effect of phenol in the 8d absorption spectra. In
photolysis experiments, the reaction of dye triplets with
phenols is very well-known and leads to the formation
Table 3. Photophysical properties of 8d
a
Photophysical properties
labs / nm
Quinoline 8d
355; 294; 280; 255; 225
397
lem / nm
lphos / nm
440; 503; 535
2.53
3
1-33
<tF> / ns
of the corresponding phenoxyl radicals,
which have
fF
kF / s-
0.22 (293 K); 0.40 (77 K)
strong absorption bands around 390nm. The kinetic
curve of decay of phenoxyl radical is easily differentiated
from the quinoline 8d species by the long lifetime decay
generated in ethanol. Scheme 3 shows the electron transfer
mechanism between quinoline 8d (Q) and phenol (PhOH),
1
7
8.69 × 10 (293 K)
fP (77K)
0.03
950
tP (77K) / ms
lT-T max / nm
tT-T / ms
450
·
·
2.60
3.39
3.10
where PhOH and PhO are the protonated and deprotonated
phenol radicals. Q(+H)· is the semi-oxidized quinoline
radical in protonated form.
+
ES1 / eV
ET1 / eV
a
The underlined values are the absorption band used for fluorescence
excitation and laser flash photolysis (LFP) excitation.
•+
•
1
hν
1
*
K
3
+Phenol
ISC
Q → Q   → Q   →Q + PhOH
o
s−ox
•
+
•
•
+
•
The shoulder observed in the absorption spectra in the
Qs−ox + PhOH  → Q(+H) + PhO
380 nm region with time decay of 6.8 ms is assigned to the
semioxidized radical of the 8d formed by self-quenching.
Scheme 3. Electron transfer mechanism between quinoline and phenol.
•
+
•−
3
Q+ Q →Q +Qs−red
Following the electron transfer process in the triplet
state of quinoline, the Rehm-Weller equation can be
written as:
o
s−ox
3
4
0
0
0
0
0
.20
.15
.10
.05
.00
0
0
0
.07
.06
.05
Quinoline 8d
λobs = 450 nm
τo = 2.60 µs
Time delay
Z1Z
2
0
1
4
.8 µs
.5 µs
.0 µs
0.04
∆G = E
− E
− E *+

D 
 D+ 
A 
 A− 




Dr12
0
0
0
0
.03
.02
.01
.00
7
0.0 µs
where E* is the energy of the triplet state (3.10 eV) and
the last term is the coulombic energy necessary to form an
ion pair with charges Z and Z in a medium of dielectric
0
20
40
60
80
100
time / µs
1
2
constant D at a distance r . The coulombic term can be
12
neglected in a medium of high dielectric constant. E(
(+1.65V from voltammetry) and E(A/A-) (+0.86V vs. NHE)
D/D+)
35
3
00
400
500
600
700
800
900
are the potential, in volts, for the oxidation of quinoline
and reduction of phenol, respectively. The negative free
λ / nm
-
1
energy (∆G = -242.20 kJ mol ) calculated by Rehm-
Figure 5. Transient spectra of 8d in ethanol at different time delay.
lexc = 355 nm at 12 mJ.
et
Weller equation connects a favourable electron transfer

5
68
Quinolines by Three-Component Reaction: Synthesis and Photophysical Studies
J. Braz. Chem. Soc.
process between triplet-state of quinoline 8d and phenol,
indicating a good alternative for compounds that can be
photo-activated, such as solar cells.
to the C2 and C4 carbon of the quinoline ring with torsion
angles of 7.30° and 65.2°, respectively. The flexible alkyl
located on the naphthyl group is randomly coiled. UV-Vis
absorbance measurements of the quinolines in different
dielectric constant media show two different bands at
280 and 350 nm, that were attributed to π,π* and n,π*
transitions, respectively. In polar solvents, the quinoline
0
0
0
0
.15
.10
.05
.00
(
a)
Time delay
0
1
3
3
7
.3 µs
.2 µs
.5 µs
1.5 µs
5.0 µs
8
d presents a progressive red shift of the lowest-energy
emission band at 400 nm and no change was observed to
4
-1
-1
the lower-energy absorption band (e < 10 mol L cm ),
which was characterised as n,π* transition. A laser flash
photolysis study for 8d connects a main transient band at
4
50 nm with a lifetime of 2.6 ms in ethanol that is totally
quenched in the presence of oxygen. The transient was
assigned to triplet-triplet absorption of quinoline 8d, which
is semi-oxidized in the presence of phenol by electron
transfer.
300
400
500
600
700
800
900
λ / nm
Experimental
0
.08
.06
.04
.02
.00
0
.2
(
b)
8
8
d
Spectral measurements
d + phenol
0
0.1
Absorption spectra, time-resolved fluorescence and
electrochemistry data as well as crystallographic analysis
are reported in the SI section.
0
.0
0
0
0
-
0.1
0
1
2
3
4
time / µs
Synthesis
All starting materials were purchased from commercial
suppliers (SigmaAldrich Chemical Co.,Acros Organics and
ABCR Chemicals) and used without further purification.
All reactions were carried out under a nitrogen atmosphere
in oven-dried glassware with magnetic stirring. Solvents
were dried, purified and degassed under classical methods.
Solvents used in extraction and purification were distilled
prior to use. Thin layer chromatography (TLC) was
performed using silica gel 60 F254 aluminum sheets and
the visualization of the spots has been done under UV
light (254 nm) or stained with iodine vapor. Products
were purified by flash chromatography on silica gel 60 M,
230-400 mesh. Melting point was measured using an
Olympus BX43 microscope equipped with a Mettler Toledo
0
10
20
time / µs
Figure 6. (a) Transient absorption spectrum for 8d in the presence of
30
40
-4
-1
phenol (1 × 10 mol L ) and (b) transient decay of 8d in the presence
and absence of phenol at 390 nm. Inset: growth and decay lifetime of
d + phenol solution monitored at 390 nm on a short timescale.
8
Conclusions
In summary, a three-component coupling reaction of
aldehydes 2, amines 4 and alkynes 7 mediated by Lewis
acid FeCl andYb(OTf) was applied to five new synthesised
3
3
quinolines 8a-e. 8a is 4-aryl-8-alkyl disubstituted and
b-e is 2,4-diaryl-6-alkyl trisubstituted quinolines. The
Yb catalyst rendered the quinolines in better yields than
Fe . None of quinolines 8a-e displayed LC behaviour,
even the more anisotropic 8e. The chemical structures
of the quinolines were fully characterised by H and C
nuclear magnetic resonance (NMR) and mass spectrometry
1
13
8
FP82HT Hot Stage FP90. H ( C) NMR spectra were
recorded at 300 (75) MHz on aVarian Inova and 400 (100)
3
+
3
+
1
MHz Bruker spectrometer using CDCl as solvent. The H
3
13
and C chemical shifts were reported in parts per million
(δ) referenced to residual solvent signals at δH/C 7.26/77.00
1
13
(CDCl ) relative to tetramethylsilane (TMS) as internal
3
(
MS) analysis. A single-crystal X-ray analysis was also
standard. Coupling constants J [Hz] were directly taken
from the spectra and are not averaged. Splitting patterns
are designated as s (singlet), d (doublet), t (triplet),
determined for 8e. From a single-crystal structure, 8e has
a phenyl group and a pendant naphthyl group connected

Vol. 26, No. 3, 2015
Sales et al.
569
q (quartet), m (multiplet) and br (broad). Attenuated
total reflection (ATR)/Fourier transform infrared (FTIR)
spectra were recorded on aVarian FT-IR-640 spectrometer.
Low-resolution mass spectra were obtained with a
Shimadzu GC-MS-QP5050 mass spectrometer interfaced
with a Shimadzu GC-17A gas chromatograph equipped
with a DB-17 MS capillary column. High resolution
mass spectrometry (HRMS) spectra were obtained from a
Fourier transform ion cyclotron resonance (FT-ICR) mass
spectrometer equipped with an Infinity™ cell, a 7.0 Tesla
superconducting magnet, an RF-only hexapole ion guide
and an external electrospray ion source (off axis spray)
and with ESI(+)-MS and tandem ESI(+)-MS/MS using a
hybrid high-resolution and high accuracy MicroTOF-Q II
mass spectrometer (Bruker Daltonics), or on a Micromass
Q-TOFmicro instrument.
3.80 (s, 3H, OCH ), 1.85 (m, 2H, CH CH O), 1.55-1.25 (m,
3
2
2
13
10H, (CH ) ), 0.90 (t, 3H, CH ); C NMR (75 MHz, CDCl )
2
5
3
3
δ 160.6, 159.5, 157.6, 154.5, 147.7, 145.0, 132.6, 131.5,
131.0, 130.7, 128.7, 126.7, 121.8, 119.4, 114.8, 114.3,
103.9, 68.4, 55.6, 55.5, 32.0, 29.6, 29.5, 29.4, 26.3, 22.9,
+
+
14.3; HRMS (ESI) m/z [M + H] calcd. for C H NO :
31
36
3
470.2690; found: 470.2695.
Data for 4-(4-heptyloxyphenyl)-6-methoxy-2-[4-
(octyloxy)phenyl]quinoline (8c): Yield 13% (10 mol%
FeCl ) and 60% (10 mol% Yb(OTf) ); yellow solid; m.p.
3
3
1
75-76 °C; H NMR (300 MHz, CDCl ) δ 8.10 (m, 3H, Ar-
3
H), 7.70 (s, 1H, Ar-H), 7.49 (d, J 6.0 Hz, 2H, Ar-H), 7.36
(dd, J 9.0 Hz, J 2.9 Hz, 1H, Ar-H), 7.21 (d, J 2.8 Hz, 1H,
Ar-H), 7.06 (d, J 6.0 Hz, 2H, Ar-H), 7.02 (d, J 9.0 Hz, 2H,
Ar-H), 4.04 (m, 4H, (CH O) ), 3.80 (s, 3H, OCH ), 1.83
2
2
3
(
m, 4H, (CH CH O) ), 1.53-1.30 (m, 18H), 0.90 (m, 6H,
2 2 2
13
General procedure for the synthesis of quinolines
(CH ) ); C NMR (75 MHz, CDCl ) δ 160.1, 159.3, 157.4,
3 2 3
8
a-e: A solution of aldehyde (1 mmol or 1.5 mmol for
154.4, 147.4, 144.9, 132.2, 131.3, 130.9, 130.6, 128.5,
126.5, 121.6, 119.7, 114.7, 114.6, 103.8, 68.2, 68.1, 55.4,
31.9, 31.8, 29.5, 29.4, 29.3, 29.2, 26.1, 22.7 (2C), 14.2.
paraformaldehyde), aniline (1 mmol) and catalyst (FeCl3
or Yb(OTf) 10 mol%) in 5 mL of dry toluene was stirred
3
for 10 min, subsequently, 1 equivalent of alkyne was added
to this mixture. The solution was heated at azeotropic
reflux under an air atmosphere until the reactants are
consumed (ca. 48 h). When the procedure was realized
Data for 4-[(6-heptyloxynaphthalen)-2-yl]-6-methoxy-2-
[4-(octyloxy)phenyl] quinoline (8d):Yield 40%; yellow solid;
1
m.p. 87-88 °C; H NMR (300 MHz, CDCl ) δ 8.13 (m, 3H,
3
o
using Yb(OTf) , the mixture was heated for 36 h at 80 C.
Ar-H), 7.96 (d, J 1.3 Hz, 1H, Ar-H), 7.88 (d, J 8.4 Hz, 1H,
Ar-H), 7.81 (m, 2H, Ar-H), 7.64 (dd, J 8.4 Hz, 1.8 Hz, 1H,
Ar-H), 7.38 (dd, J 9.2 Hz, 2.9 Hz, 1H, Ar-H), 7.23 (m, 3H,
3
The dark reaction mixture was cooled and filtered through
a celite plug covered with thin activated charcoal. After
evaporation of the solvent, the crude product was purified
by silica gel chromatography (95:5 hexane:CH Cl ).
Ar-H), 7.02 (d, 2H, J 8.4 Hz, Ar-H), 4.13 (t, 2H, CH O),
2
4.03 (t, J 6.8 Hz, 2H, CH O), 3.75 (s, 3H, OCH ), 1.89 (m,
2
2
2
3
2
H, CH CH O), 1.82 (m, 2H, CH CH O), 1.55-1.34 (m,
2 2 2 2
13
Data for 8-octyloxy-4-[4-(octyloxy)phenyl]quinoline
18H, (CH ) ); 0.91 (m, 6H, (CH ) ); C NMR (75 MHz,
2 9 3 2
1
(
8a): Yield 12%; yellow solid; m.p. 68-70 °C; H NMR
CDCl ) δ 160.1, 157.8, 157.5, 154.4, 147.8, 144.9, 134.3,
3
(
(
300 MHz, CDCl ) δ 8.97 (d, J 4.3 Hz, 1H, Ar-H), 7.52
dd, J 8.6 Hz, J 3.0 Hz, 1H, Ar-H), 7.45 (d, J 9.0 Hz, 2H,
133.9, 132.2, 131.4, 129.6, 128.8, 128.5, 128.3, 127.7,
127.0, 126.9, 126.6, 121.7, 119.8, 119.4, 114.8, 106.5,
103.8, 68.2, 68.1, 55.4, 31.8, 29.4, 29.3, 29,2, 29.1, 26.1,
3
Ar-H), 7.41 (m, 1H, Ar-H), 7.34 (d, J 4.5 Hz, 1H, Ar-H),
.08 (m, 1H, Ar-H), 7.05 (d, J 6.0 Hz, 2H, Ar-H), 4.28 (t,
J 6.5 Hz, 2H, CH O), 4.06 (t, J 7 Hz, 2H, CH O), 2.07 (m,
+
7
26.0, 22.7, 22.6, 14.1; HRMS (ESI) m/z [M + H] calcd.
+
3
for C H NO : 604.3785; found: 604.3793.
2
2
41 50
2
2
H, CH CH O), 1.85 (m, 2H, CH CH O), 1.58-1.38 (m,
2 2 2 2
13
4H, (CH ) ), 0.91 (m, 6H, (CH ) ); C NMR (75 MHz,
Data for 4-[(6-heptyloxynaphthalen)-2-yl]-6-nonyloxy-2-
2
12
3 2
CDCl ) δ 159.3, 155.0, 148.8, 148.1, 140.9, 130.8, 130.5,
[4-(octyloxyphenyl] quinoline (8e):Yield 36%; yellow solid;
3
1
1
3
2
28.2, 126.3, 121.8, 117.5, 114.5, 108.3, 69.1, 68.1, 31.9,
1.8, 29.6, 29.4 (2C), 29.3, 29.2 (2C), 29.1, 28.9, 26.1,
2.7, 22.6, 14.1.
m.p. 67-68 °C; H NMR (300 MHz, CDCl ) δ 8.39 (m, 1H,
3
Ar-H), 8.18 (d, J 8.2 Hz, 2H, Ar-H), 7.97 (s, 1H, Ar-H),
7.91-7.82 (m, 3H, Ar-H), 7.63 (dd, J 8.2 Hz, J 1.8 Hz, 1H,
Ar-H), 7.42 (dd, J 9.4 Hz, 2.3 Hz, 1H,Ar-H), 7.27-7.22 (m,
3H, Ar-H), 7.05 (d, J 8.8 Hz, 2H, Ar-H), 4.14 (t, J 6.5 Hz,
2H, CH O), 4.04 (t, J 6.5 Hz, 2H, CH O), 3.89 (t, J 6.5 Hz,
Data for 6-methoxy-2-(4-methoxyphenyl)-4-[4-(octyloxy)
phenyl]quinoline (8b): Yield 40%; yellow solid; m.p.
2
2
1
8
5-86 °C; H NMR (300 MHz, CDCl ) δ 8.11 (m, 3H), 7.70
2H, CH O), 1.94-1.70 (m, 6H, (CH CH O) ), 1.60-1.22 (m,
2 2 2 3
3
13
(
s, 1H), 7.49 (d, J 8.8 Hz, 2H, Ar-H), 7.36 (dd, J 9.2 Hz,
J 2.8 Hz, 1H, Ar-H), 7.22 (d, J 2.6 Hz, 1H, Ar-H), 7.05 (m,
H,Ar-H), 4.05 (t, J 7 Hz, 2H, CH O), 3.87 (s, 3H, OCH ),
30H, (CH ) ), 0.89 (m, 9H, (CH ) ); C NMR (75 MHz,
2 15 3 3
CDCl ) δ 160.1, 157.8, 157.0, 154.2, 147.7, 144.8, 134.3,
3
4
134.0, 132.2, 131.2, 129.6, 128.8, 128.5, 128.2, 127.7,
2
3

5
70
Quinolines by Three-Component Reaction: Synthesis and Photophysical Studies
J. Braz. Chem. Soc.
1
6
2
26.9, 126.5, 121.9, 119.8, 119.4, 114.7, 106.4, 104.6, 68.2,
13. Elangovan, A.; Chen, T-Y.; Chen, C-Y.; Ho, T-I.; Chem.
Commun. 2003, 2146; Elangovan, A.; Yang, S-W.; Lin, J-H.;
Kao, K-M.; Ho, T-I.; Org. Biomol. Chem. 2004, 2, 1597; Si, G.;
Zhao, Y.; Leong, E. S. P.; Liu, Y. J.; Materials 2014, 7, 1296;
Gamba, M-G.;Yu, C. H.; Tang, B. J.; Welch, C.; Kohlmeier,A.;
Schubert, C. P.; Mehl, G. H.; Materials 2014, 7, 3494.
8.1, 55.4, 31.9, 31.8, 29.5, 29.4, 29.3, 29.2, 29.1 (2C),
+
6.1, 26.0 (2C), 22.4, 14.1; HRMS (ESI) m/z [M + H]
+
calcd. for C H NO : 716.6037; found: 716.5043.
4
9
66
3
Supplementary Information
1
4. Tavares, A.; Livotto, P. R.; Gonçalves, P. F. B.; Merlo, A. A.;
J. Braz. Chem. Soc. 2009, 20, 1742; Vasconcelos, U. B.;
Schrader, A.; Vilela, G. D.; Borges, A. C. A.; Merlo, A. A.;
Tetrahedron 2008, 64, 4619.
Supplementary data are available free of charge at
http://jbcs.sbq.org.br as PDF file.
Acknowledgments
15. Merlo, A. A.; Livotto, P. R.; Gallardo, H. A. O.; Taylor, T. R.;
Mol. Cryst. Liq. Cryst. 1998, 309, 111.
The authors gratefully acknowledge INCT-Catálise,
edital 01/12-PPG-Química-UFRGS, Fapergs-edital PqG
16. Vogel, A. I.; Vogel´s Textbook of Practical Organic Chemistry,
th
5
ed.; England Longman Scientific & Technical, 1991;
2
012, FINEP and FAPESP 12/19823-4 for financial
Markiewicz, J. T.; Wiest, O.; Helquist, P.; J. Org. Chem. 2010,
75, 4887.
support. Thanks to LDRX-DF/UFSC for X-ray diffraction
experiments. The authors are also grateful to Sidnei Moura
e Silva (Universidade de Caxias do Sul) for the HRMS
analysis. Eric S. Sales thanks PIBIC-UFRGS for his
fellowship.
17. Vasconcelos, U. B.; Dalmolin, E.; Merlo,A.A.; Org. Lett. 2005,
7, 1027;Vasconcelos, U. B.; Merlo,A.A.; Synthesis 2006, 1141.
18. Bolm, C.; Legros, J.; Paih, J. L.; Zani, L.; Chem. Rev. 2004,
104, 6217; Correa,A.; Mancheño, O. G.; Bolm, C.; Chem. Soc.
Rev. 2008, 37, 1108; Enthaler, S.; Junge, K.; Beller, M.; Angew.
Chem., Int. Ed. 2008, 47, 3317; Sherry, B. D.; Fürstner,A.; Acc.
Chem. Res. 2008, 4, 1500.
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FAPERGS and FAPESP have sponsored the publication of this article.