Synthesis of quinolines and fused pyridocoumarins from N-propargylanilines or propargylaminocoumarins by catalysis with gold nanoparticles supported on TiO2

Article abstract of DOI:10.1016/j.tet.2013.04.026

[5,6]-Fused pyridocoumarins are prepared under mild conditions in excellent yields through the activation of the triple bond of 6-propargylaminocoumarins by gold nanoparticles supported on TiO₂. The analogous reaction of N-propargylanilines with Au/TiO₂ or Au/Al₂O₃ resulted in the formation of quinolines.

Full text of DOI:10.1016/j.tet.2013.04.026

Tetrahedron 69 (2013) 4612e4616
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Synthesis of quinolines and fused pyridocoumarins from
N-propargylanilines or propargylaminocoumarins by catalysis with
q
gold nanoparticles supported on TiO2
*
Theodoros S. Symeonidis, Ioannis N. Lykakis, Konstantinos E. Litinas
Laboratory of Organic Chemistry, Department of Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece
a r t i c l e i n f o
a b s t r a c t
Article history:
[5,6]-Fused pyridocoumarins are prepared under mild conditions in excellent yields through the acti-
vation of the triple bond of 6-propargylaminocoumarins by gold nanoparticles supported on TiO2. The
analogous reaction of N-propargylanilines with Au/TiO2 or Au/Al2O3 resulted in the formation of
quinolines.
Received 8 October 2012
Received in revised form 21 March 2013
Accepted 4 April 2013
Available online 10 April 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Gold nanoparticles
Heterogeneous catalysis
Pyrido[5,6]coumarins
Quinolines
Fused dipyridocoumarins
N-Propargylanilines
6-Propargylaminocoumarins
1. Introduction
It is known that the coumarin ring also exists in a variety of
natural and synthetic biologically active compounds.7 Fused cou-
Quinoline derivatives represent an interesting class of hetero-
cyclic systems, since the quinoline ring is an essential core moiety
in many natural (particularly in alkaloids) and synthetic products
with important biological activities, such as antibiotic, antimalarial,
marin derivatives, among them pyridocoumarins, have been re-
ported to possess antiallergic,8 antidiabetic,9 analgesic,10,11 anti-
inflammatory11 and antimicrobial11 properties. The synthesis of
pyridocoumarins was achieved either by formation of the
pyridine7g,10,12e15 or the pyranone7g,16e18 moieties. The construc-
tion of the pyridine moiety generally follows the syntheses referred
above for quinolines,10,12 but recently some other methods have
been developed including DielseAlder reactions of the O-methyl
imine of 2-oxo-2H-chromene-4-carboxaldehyde with dien-
ophiles13 and the treatment of propargylaminocoumarins with
BF3$Et2O under microwave irradiation14 or with AgSbF6 in DMSO at
110 ꢀC.15 The formation of the pyranone moiety is realized from the
quinolinols by Pechmann condensation16 or reactions17 with
DMAD and PPh3 and from the quinolinequinones by Wittig re-
actions17 or condensation with diethyl aminofumarate.18
antibacterial, antileishmanial, anti-inflammatory, insecticidal.1
A
variety of methods have been applied in the literature for their
preparation including Skraup, Friedlander, Combes, DoebnereMil-
ler, Camps, Knorr, and Pfitzinger syntheses.1,2 Most of the above
reactions require harsh reaction conditions with strong acids, toxic
compounds, high temperatures, and low yields. However, quino-
lines have been synthesized under mild reaction conditions by
electrophilic cyclization of N-propargylanilines using mercury
salts3 or under environmentally eco-friendly conditions, such as the
Friedlander modification with propylphosphonic anhydride,4 the
reactions of anilines and aldehydes under oxygen upon catalysis by
5
gold nanoparticles supported on SiO2 and the three component
Gold nanoparticles19 are selective and efficient green catalysts
with important applications in biomedicine,20 organic synthesis21
and analysis.22 Despite the extensive development of Au-
catalyzed addition reactions in alkynes under homogeneous con-
ditions, only a few examples concern the heterogeneous protocol
using Au NPs supported on metal oxide surfaces.21a,b,23,24 Among
them, Au/TiO2 was found to be an efficient catalyst for the trans-
formation of a series of aryl propargylethers into the corresponding
domino reaction from anilines, aldehydes and phenylacetylenes
under microwaves and montmorillonite K-10.6
q
Preliminary communication presented at International Conference on Chem-
istry for Health, September 9e14, 2012, Athens, Greece, Book of Abstrs., p. 100.
* Corresponding author. Tel.: þ30 2310997864; fax: þ30 2310997679; e-mail
address: klitinas@chem.auth.gr (K.E. Litinas).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.04.026

T.S. Symeonidis et al. / Tetrahedron 69 (2013) 4612e4616
4613
Table 1
(2H)-chromenes, through alkyne activation by gold cationic species
stabilized on titania.24c Due to our interest in the synthesis13,14,17 of
fused pyridocoumarin derivatives, we focused on the novel appli-
cation of Au NPs as a heterogeneous catalyst in the synthesis of
pyridocoumarins and quinolines starting from propargylamino
derivatives through alkyne activation.
Synthesis of fused pyridocoumarins and quinolines from N-propargyl-
aminocoumarins or -anilines catalyzed by Au NPS supported on TiO2 or Al2O3
Entry N-Propargylamino- Conditions
Products (yields %)
compound
1
1a
A: Au/TiO2 (2) (1.8 mol %),
3a (92)
DCE, 70 ꢀC, 48 h
2
3
1b
1b
A
3b (96)
3b (91)
B: Au/Al2O3 (3 mol %),
DCE, 70 ꢀC, 48 h
2. Results and discussion
4
5
6
7
8
1c
1d
1e
1f
A
A
A
A
3c (94)
3d (91)
3e (92)
3f (98)
The gold catalyzed reactions studied herein are depicted in
Schemes 1 and 2. We were pleased to find that treatment of
6-propargylaminocoumarin (1a)14 in 1,2-dichloroethane (DCE) with
Au/TiO2 (2) (1.8 mol % added in two portions; first 1.2 mol % and
0.6 mol % after 24 h) at 70 ꢀC for 48 h resulted in the formation of 3H-
pyrano[3,2-f]quinoline-3-one (3a)12a,25 in 92% yield (Table 1, en-
try 1). The analogous reaction of 7-methyl-6-propargylaminocou-
marin (1b)14 gave the pyridocoumarin 3b14,26 in 96% yield (Table 1,
entry 2). It is worth noting that the yields measured for these re-
actions are higher compared to that found in our former synthesis of
pyridocoumarins14 through MW irradiation under BF3$Et2O.
4a
C: Au/TiO2 (2) (3.75 mol %), 5a (79), 6a27 (10)
DCE, 70 ꢀC, 3 days
D: Au/TiO2 (2) (1 mol %),
DCE, closed tube,
70 ꢀC, 24 h
9
4a
4a
5a (66), 7a34 (25)
10
E: Au/Al2O3 (4 mol %),
5a (90), 6a (8)
DCE, 70 ꢀC, 48 h
11
12
13
14
15
16
17
18
19
20
4b
4b
4b
4c
4c
4d
4d
4e
4f
C
D
E
C
D
C
D
D
C
5b28 (83), 6b (17)
5b (77), 7b34 (23)
5b (93), 6b (5)
5c29 (64)
5c (56), 7c35 (17)
5d30 (69)
5d (71), 7d35 (10)
5e31 (66), 7e36 (24)
5f (34)
R3
O
R3
O
N
HN
R1
Au/TiO2 (2)
4f
F: Au/TiO2 (2) (3.75 mol %), 8 (81)
DCE, closed tube, 70 ꢀC,
3 days
E
F
E
F
R1
O
O
(i)
R2
R2
21
22
23
24
4g
4g
4h
4h
5g32 (69)
5g (69)
1a-f
3a-f
5h33 (50)
5h (57)
1,3 a: R1=R2=R3=H
b: R1=CH3, R2=R3=H
of propargylaminocoumarins into pyridocoumarins. The gold
nanoparticles used for the catalytic reactions are commercially
available materials containing 1% w/w [Au].
c: R1-R2= CH2CH2CH2CH2, R3=H
d: R1-R2= CH2CH2CH2CH2, R3=CO2Me
e: R1-R2= CH=CH-CH=CH, R3=CO2Me
From the reactions of the fused propargylaminocoumarin de-
rivatives 1c, d,14 e,14 f with Au/TiO2 under the conditions described
above the fused pyridocoumarins 3cef were obtained in very good
to excellent yields (Scheme 1, Table 1, entries 4e7). In the case of 1d
(R3¼ester) cyclization, only the cyclized product 3d was observed,
with the ester group unaffected. However, using MW irradiation in
the presence of BF3$Et2O, the decarboxylated product 3c14 was
formed. The ester group is also retained in the preparation of the
fused pyridocoumarins 3e, f catalyzed by Au/TiO2.
For further investigation of the Au/TiO2 catalyzed cyclization
reaction of propargylaminocoumarins, we applied this method to
the reactions of simple molecules, such as N-propargylanilines
4aed, f with 4.8 mol % Au/TiO2 (1.6 mol % at initially time, 1.6 mol %
f: R1-R2= CH=CH-CH=N, R3=CO2Me
Scheme 1. (i) Au/TiO2 (2) (1.8 mol %), DCE, 70 ꢀC, 24 h.
When we performed the same reaction of 1b in H2O, the yield
was found to be 33% for product 3b, with 66% of the starting ma-
terial recovered. In addition, 3 mol % Au/Al2O3 have been also used
as catalyst in DCE (70 ꢀC, 48 h) for this cyclization process, leading
to pyridocoumarin 3b in 91% yield (Table 1, entry 3), with 9% of the
starting compound. For comparison, gold nanoparticles supported
on ZnO have been used for the same reaction, but only 4% of the
expected product was observed. Therefore, Au/TiO2 in refluxing
DCE was found to be a more efficient catalyst for the transformation
N
N
HN
HN
N
N
Au/TiO2 (2)
N
+
(i)
R
R
R
R
R
7a-e
6a,b
4a-h
8f
5a-h
e: R=Cl
4,5,6,7 a: R=H
b: R=CH3
CH
f: R=NHCH2C
g: CO2CH2CH3
h: R=NO2
c: R=OCH3
d: R=Br
Scheme 2. (i) Au/TiO2 (2) (4.8 mol %), DCE, 70 ꢀC, 3 days (for 4aef); Au/TiO2 (2) (1.8 mol %), DCE, sealed tube, 70 ꢀC, 24 h (for 4aee); Au/TiO2 (2) (4.8 mol %), DCE, sealed tube, 70 ꢀC,
3 days (for 4f,g,h); Au/Al2O3 (4 mol %), DCE, 70 ꢀC, 48 h (for 4a,b,h).

4614
T.S. Symeonidis et al. / Tetrahedron 69 (2013) 4612e4616
after 24 h and 1.6 mol % after 48 h) in refluxing DCE for a total of 3
days (Scheme 2). The expected quinoline derivatives 5aed, f were
observed in moderate to high yields (Table 1, entries 8, 11, 14, 16, 19)
accompanied with significant amounts of the dimerization prod-
ucts 6a and 6b. In the case of the N-propargylanilines 4g and 4h
cyclization processes, starting materials with electron withdrawing
substituents (COOEt and NO2), no reaction products were observed.
In an effort to increase the yield of the reactions a sealed tube with
1.8 mol % Au/TiO2 in DCE at 70 ꢀC for 24 h was used (Table 1, entries
9, 12, 15, 17, 18). In these cases no dimerization products (6) were
found, but the reduced products N-allylanilines 7aee were isolated.
In the presence of 4.8 mol % amount of catalyst (added in three
portions, 1.6 mol % in each 24 h) and after heating for 3 days,
N-propargylanilines 4g and 4h, led to the expected quinolines 5g
and 5h in good yields (Table 1, entries 22, 24). Under the same
conditions, the Au/TiO2 cyclization reaction of di-N-propargyl
p-phenylenediamine (4f) gave the 4,7-phenanthroline37 (8) in 81%
isolated yield (Table 1, entry 20).
For comparison, the cyclization reactions of N-propargylanilines
4a, b, g, h were studied, using Au/Al2O3 as catalyst (4 mol % in two
portions, 2 mol % at initial time and 2 mol % after 24 h) under the
same conditions. In the case of 4a and 4b cyclizations, the corre-
sponding quinolines 5a and 5b were formed in higher yields
compared to that observed in the case of Au/TiO2 (Table 1, entries
10, 13), while smaller amounts of the dimerization products 6a and
6b were isolated. Also, the yields were quite similar for the case of
N-propargylanilines 4g and 4h, with electron withdrawing group,
compared with that of Au/TiO2 (Table 1, entries 21, 23).
E. The formation of N-allylanilines 7aee in the sealed tubes could
be attributed to the reduction of N-propargylanilines by the hy-
drogen abstracted during the latter step. In accordance with the
mechanism, the electron-donating substituents facilitate the pro-
cess, while with the electron acceptors more catalyst is necessary
for the reaction in a sealed tube.
The formation of biquinoline derivatives 6a and 6b could be
explained by the AuIII catalysis.24c (Scheme 3). The vinyl-Au in-
termediate C acted as an electrophilic center and cyclized a second
N-propargylaniline A under abstraction of Hþ to give the dio-
rganogold intermediate F. The latter with intermolecular CeC
coupling resulted in tetrahydrobiquinoline derivatives G with
elimination of AuI species. Air oxidation of G led to the dimeric
products H, while the AuI was oxidized to AuIII species.
3. Conclusion
Herein, N-propargyl-anilines and coumarins were efficiently
transformed into the corresponding quinolines and fused pyr-
idocoumarins catalyzed by gold nanoparticles supported on TiO2
and Al2O3 under mild conditions. In all cases, pyridocoumarins and
quinolines were obtained in high yields, via a synthetically useful
procedure.
4. Experimental section
4.1. General remarks
A mechanistic scenario for the transformation of N-prop-
argylanilines into fused pyridocoumarins or quinolines by analogy
to the FriedeleCrafts hydroarylation of alkynes24c,38 catalyzed
by cationic AuI or AuIII species present in Au/TiO2 is shown in
Scheme 3. Electrophilic aromatic substitution of the activated al-
Melting points were determined on a Kofler hot-stage appara-
tus. IR spectra were obtained with a PerkineElmer 1310 spectro-
photometer as Nujol mulls. NMR spectra were recorded on a Bruker
AM 300 (300 MHz and 75 MHz for 1H and 13C, respectively) using
CDCl3 as solvent and TMS as an internal standard. J values are re-
ported in Hertz. Mass spectra were determined on an LCMS-2010
EV Instrument (Shimadzu) under Electrospray Ionization (ESI)
conditions. Microanalyses were performed on a PerkineElmer
2400-II Element analyzer. Silica gel No 60, Merck A.G. was used for
kyne-Au-p complex B by the electron-rich arene resulted in the
vinyl-Au intermediate C through a 6-endo-dig cyclization. 1,3-H
shift gave the dihydroquinoline derivative D under re-generation
of the catalyst. Air-oxidation of D led to the isolated products
H
[Au](n-1)+
R
R
R
[Au]n+
[1,3-H shift]
- [Au]n+
[Au]n+
N
H
N
H
N
H
A
B
C
R
R
Air Oxidation
N
H
N
E
D
[Au]III
R
-H+
R
R
R
C + A
for [Au]III
- [Au]I
R
N
N
H
N
H
N
H
H
G
F
R
Air Oxidation
N
N
H
Scheme 3. Proposed mechanism for the transformation of N-propargylanilines into quinolines or biquinolines.

T.S. Symeonidis et al. / Tetrahedron 69 (2013) 4612e4616
4615
column chromatography. Gold 1% on TiO2 and Gold 1% on Al2O3
were purchased from Strem Chemicals (AUROliteÔ Au/TiO2 and
AUROliteÔ Au/Al2O3).
isolated as white solid (58 mg, 81% yield), mp 215e217 ꢀC (acetone),
(lit.37 mp 217e218 ꢀC).
4.2.1. Methyl 2-oxo-9,10,11,12-tetrahydro-2H-benzo[h]pyrano[3,2-f]
quinoline-4-carboxylate (3d). (Conditions A, 70.3 mg, 91% yield),
light yellow solid, mp 184e186 ꢀC (DCM), IR (KBr): 3038, 2925,
4.2. General procedures for the synthesis of pyridocoumarins
or quinolines from 6-propargylaminocoumarins or
N-propargylanilines
2854, 1734, 1723 cmꢁ1 1H NMR (300 MHz, CDCl3)
; d 1.92e2.02
(m, 4H), 3.01e3.11 (m, 2H), 3.37e3.47 (m, 2H), 4.04 (s, 3H), 6.57
(s, 1H), 7.43 (dd, 1H, J1¼4.2 Hz, J2¼8.6 Hz), 8.05 (dd, 1H, J1¼1.4 Hz,
J2¼8.6 Hz), 8.92 (dd, 1H, J1¼1.4 Hz, J2¼4.2 Hz); 13C NMR (75.5 MHz,
Conditions A: Au/TiO2 (60 mg of 1%, 0.6 mg Au, 0.003 mmol,
1.2 mol %) was added in the solution of propargylaminocoumarin
1a (50 mg, 0.25 mmol) in DCE (6 mL) and the mixture was heated at
70 ꢀC for 24 h. More Au/TiO2 (30 mg of 1%, 0.3 mg Au, 0.0015 mmol,
0.6 mol %, total 1.8 mol %) was then added and the mixture was
heated for 24 h more. After the filtration of the catalyst through
silica gel layer and evaporation of the solvent the 3H-pyrano[3,2-f]
quinoline-3-one (3a) was received as white solid (45 mg, 92%
yield), mp 123e125 ꢀC (DCM), (lit.25 mp 124e125 ꢀC).
Conditions B: Au/Al2O3 (20 mg of 1%, 0.2 mg Au, 0.001 mmol,
2 mol %) was added in the solution of propargylaminocoumarin 1b
(11 mg, 0.05 mmol) in DCE (3 mL) and the mixture was heated at
70 ꢀC for 24 h. More Au/Al2O3 (10 mg of 1%, 0.1 mg Au,
0.0005 mmol, 1 mol %, total 3 mol %) was then added and the
mixture was heated for 24 h more. After the filtration of the catalyst
through silica gel layer, evaporation of the solvent and separation
by column chromatography [silica gel, hexane/ethyl acetate (2:1)]
the 6-methyl-3H-pyrano[3,2-f]quinoline-3-one (3b) was received
as white solid (9.6 mg, 91% yield), mp 198e200 ꢀC (DCM), (lit.26 mp
200 ꢀC).
Conditions C: Au/TiO2 (50 mg of 1%, 0.5 mg Au, 0.0025 mmol,
1.25 mol %) was added in the solution of N-propargylaniline (4a)
(26 mg, 0.2 mmol) in DCE (3 mL) and the mixture was heated at
70 ꢀC for 24 h. More Au/TiO2 (after each 24 h, 50 mg of 1%, 0.5 mg
Au, 0.0025 mmol, 1.25 mol %, total 3.75 mol %) was then added and
the mixture was heated for 48 h more. After the filtration of the
catalyst through silica gel layer, evaporation of the solvent and
separation by column chromatography [silica gel, hexane/ethyl
acetate (4:1) the quinoline (5a) was received as light yellow oil
(20.5 mg, 79% yield) followed by the biquinoline 6a27 (2.5 mg, 10%
yield).
Conditions D: Au/TiO2 (40 mg of 1%, 0.4 mg Au, 0.002 mmol,
1 mol %) was added in the solution of N-propargylaniline (4a)
(26 mg, 0.2 mmol) in DCE (3 mL) in a screw-cup tube and the
mixture was heated at 70 ꢀC for 24 h. After the filtration of the
catalyst through silica gel layer, evaporation of the solvent the and
separation by column chromatography [silica gel, hexane/ethyl
acetate (4:1) the N-allylaniline (7a)34 was isolated as light yellow
oil (6.6 mg, 25% yield) followed by the quinoline (5a) as light yellow
oil (17 mg, 66% yield).
CDCl3)
d 21.9, 22.1, 23.8, 25.9, 53.5, 107.4, 114.9, 121.1, 121.5, 129.5,
131.3, 143.5, 144.7, 145.5, 148.5, 153.7, 159.4, 167.7; MS (ESI): 310
[MþH]þ; HRMS (ESI): m/z [MþH]þ calcd for C18H16NO4: 310.1079;
found, 310.1074.
4.2.2. Methyl 2-oxo-2H-benzo[h]pyrano[3,2-f]quinoline-4-carboxylate
(3e). (Conditions A, 70 mg, 92% yield), yellow solid, mp 261e263 ꢀC
(DCM), IR (KBr): 3075, 2921, 2840, 1734, 1724 cmꢁ1 1H NMR
;
(300 MHz, CDCl3)
d
4.05 (s, 3H), 6.82 (s, 1H), 7.50 (dd, 1H, J1¼4.4 Hz,
J2¼8.5 Hz), 7.78e7.91 (m, 2H), 8.05 (dd, 1H, J1¼1.4 Hz, J2¼8.5 Hz),
8.60 (d, 1H, J¼8.4 Hz), 8.97 (dd, 1H, J1¼1.4 Hz, J2¼4.3 Hz), 9.30 (d, 1H,
J¼8.3 Hz); 13C NMR (75.5 MHz, CDCl3)
d 53.6, 107.1, 116.1, 121.1, 121.8,
123.0, 124.5, 125.1, 129.5, 130.7, 131.7, 133.7, 144.4, 145.9, 148.6, 153.0,
159.0, 167.4; MS (ESI): 306 [MþH]þ.; HRMS (ESI): m/z [MþH]þ calcd
for C18H12NO4: 306.0766; found, 306.0761.
4.2.3. Methyl11-oxo-11H-pyrano[3,2-f]-1,7-phenanthroline-9-carboxylate
(3f). (Conditions A, 75 mg, 98% yield), yellow solid, mp 247e249 ꢀC
(dec) (DCM), IR (KBr): 3027, 2924, 2840, 1734 cmꢁ1; 1H NMR (300 MHz,
CDCl3)
d
4.12 (s, 3H), 6.82 (s, 1H), 7.58 (dd, 1H, J1¼4.4 Hz, J2¼8.5 Hz), 7.81
(dd, 1H, J1¼4.3 Hz, J2¼8.3 Hz), 8.13 (dd, 1H, J1¼1.5 Hz, J2¼8.5 Hz), 9.02
(dd, 1H, J1¼1.5 Hz, J2¼4.4 Hz), 9.23 (dd, 1H, J1¼1.8 Hz, J2¼4.3 Hz), 9.61
(dd, 1H, J1¼1.8 Hz, J2¼8.3 Hz); 13C NMR (75.5 MHz, CDCl3)
d 53.7, 110.2,
118.2,121.2,122.4,124.9,129.7,131.9,133.3,140.1,143.6,145.2,149.1,151.8,
152.4, 158.3, 167.1; MS (ESI): 307 [MþH]þ, 329 [MþNa]þ; HRMS (ESI):
m/z [MþH]þ calcd for C17H11N2O4: 307.0719; found, 307.0713.
4.2.4. N-Prop-2-yn-1-ylquinolin-6-amine (5f). (Conditions C, 12.4 mg,
34% yield), white solid, mp 78e80 ꢀC (ethyl acetate), IR (KBr): 3273,
3067, 2925, 2853, 1622 cmꢁ1; 1H NMR (300 MHz, CDCl3)
d 2.25 (t, 1H,
J¼2.3 Hz), 4.06 (d, 2H, J¼2.3 Hz), 4.18 (br s, 1H), 6.83 (d, 1H, J¼2.6 Hz),
7.14 (dd,1H, J1¼2.6 Hz, J2¼9.0 Hz), 7.29 (dd,1H, J1¼4.2 Hz, J2¼8.3 Hz),
7.92 (d, 1H, J¼9.0 Hz), 7.97 (dd, 1H, J1¼1.6 Hz, J2¼8.3 Hz), 8.66 (dd,1H,
J1¼1.6 Hz, J2¼4.2 Hz); 13C NMR (75.5 MHz, CDCl3)
d 33.7, 71.7, 80.6,
104.7,121.4,121.5,130.0,130.6,134.3,143.8,145.0,146.9; MS (ESI): 183
[MþH]þ; HRMS (ESI): m/z [MþH]þ calcd for C12H11N2: 183.0922;
found, 183.0916.
Conditions E: Au/Al2O3 (20 mg of 1%, 0.2 mg Au, 0.001 mmol,
2 mol %) was added in the solution of N-propargylaniline (4a)
(6.5 mg, 0.05 mmol) in DCE (1 mL) and the mixture was heated at
70 ꢀC for 24 h. More Au/Al2O3 (20 mg of 1%, 0.2 mg Au, 0.001 mmol,
2 mol %, total 4 mol %) was then added and the mixture was heated
for 24 h more. After the filtration of the catalyst through silica gel
layer, evaporation of the solvent and separation by column chro-
matography [silica gel, hexane/ethyl acetate (4:1) the quinoline
(5a) was received as light yellow oil (5.8 mg, 90% yield) followed by
the biquinoline 6a (0.45 mg, 8% yield).
4.2.5. 6,60-Dimethyl-3,30-biquinoline (6b). (Conditions C, 4.8 mg,
17% yield), white solid, mp 251e253 ꢀC (ethyl acetate), IR (KBr):
3031, 2924, 2852, 1637, 1508 cmꢁ1 1H NMR (300 MHz, CDCl3)
;
d
2.59 (s, 3H), 7.60 (dd, 1H, J1¼1.7 Hz, J2¼8.6 Hz), 7.70 (d, 1H,
J¼1.7 Hz), 8.07 (d, 1H, J¼8.6 Hz), 8.35 (d, 1H, J¼2.2 Hz), 9.20 (d,
1H, J¼2.2 Hz); 13C NMR (75.5 MHz, CDCl3)
d 21.7, 126.9, 128.1, 129.1,
131.0, 132.3, 133.2, 137.4, 146.4, 148.7; MS (ESI): 285 [MþH]þ;
HRMS (ESI): m/z [MþH]þ calcd for C20H17N2: 285.1392; found,
285.1387.
Conditions F: Au/TiO2 (100 mg of 1%, 1 mg Au, 0.005 mmol,
1.25 mol %) was added in the solution of di-N-propargyl-p-phe-
nylenediamine (4f) (70 mg, 0.4 mmol) in DCE (5 mL) in a screw-cup
tube and the mixture was heated at 70 ꢀC for 24 h. More Au/TiO2
(after each 24 h, 100 mg of 1%, 1 mg Au, 0.005 mmol, 1.25 mol %,
total 3.75 mol %) was then added and the mixture was heated for
48 h more. After the filtration of the catalyst through silica gel layer
and evaporation of the solvent the 4,7-phenanthroline (8) was
Acknowledgements
This research (T.S.) has been co-financed by the European Union
(European Social FunddESF) and Greek national funds through the
Operational Program ‘Education and Lifelong Learning’ of the Na-
tional Strategic Reference Framework (NSRF)dResearch Funding
Program: Heracleitus II. Investing in knowledge society through the
European Social Fund.

4616
T.S. Symeonidis et al. / Tetrahedron 69 (2013) 4612e4616
17. Galariniotou, E.; Fragos, V.; Makri, A.; Litinas, K. E.; Nicolaides, D. N. Tetrahedron
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