Friedl?nder synthesis of poly-substituted quinolines in the presence of dodecylphosphonic acid (DPA) as a highly efficient, recyclable and novel catalyst in aqueous media and solvent-free conditions

Article abstract of DOI:10.1016/j.tetlet.2008.09.097

Poly-substituted quinolines were synthesized in the presence of a catalytic amount of dodecylphosphonic acid (DPA) in aqueous media and solvent- free conditions. The reactions proceed very well under relatively mild conditions, and DPA can be recycled.

Full text of DOI:10.1016/j.tetlet.2008.09.097

Tetrahedron Letters 50 (2009) 514–519
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Tetrahedron Letters
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Friedländer synthesis of poly-substituted quinolines in the presence of
dodecylphosphonic acid (DPA) as a highly efficient, recyclable and novel
catalyst in aqueous media and solvent-free conditions
*
S. Ghassamipour, A. R. Sardarian
Chemistry Department, College of Science, Shiraz University, Shiraz 71454, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 June 2008
Revised 29 August 2008
Accepted 17 September 2008
Available online 20 September 2008
Poly-substituted quinolines were synthesized in the presence of a catalytic amount of dodecylphosphonic
acid (DPA) in aqueous media and solvent- free conditions. The reactions proceed very well under rela-
tively mild conditions, and DPA can be recycled.
Ó 2008 Published by Elsevier Ltd.
1. Introduction
the products, long reaction times, and harsh reaction conditions.
Moreover, this reaction is usually carried out in polar and in aprotic
Quinolines and their derivatives are very important biological
compounds that occur widely in natural products. Some members
of this family have displayed interesting physiological activities
and found attractive applications in medicinal chemistry, being
used as antimalarial,1 antibacterial,2 anti-inflammatory,3 antihy-
pertensive,4 and antiplatelet agents, and as tyrosine kinase inhibit-
ing agents.5,3a,6,7 In addition, quinolines are valuable synthons used
in a variety of nano-structures and meso-structures with enhanced
electronic and photonic functions.8 Also, quinolines have been
employed in the study of bioorganic and bioorganometallic
processes.9 There has been tremendous interest in developing effi-
cient methods for quinoline synthesis.10,11 Among these methods,
the Friedländer annulation is still one of the most simple and
straightforward procedures for the synthesis of poly-substituted
quinolines.
solvents such as acetonitrile, THF, DMSO, and DMF leading to
tedious work-up procedures. The main disadvantage of almost all
existing methods is that the catalysts cannot be recovered during
the work-up procedure. Thus, the development of simple, conve-
nient, and environmentally benign methods for the synthesis of
quinolines is still required. For these reasons, the use of solid and
heterogeneous catalysts in organic reactions in aqueous media
and solvent-free conditions, have drawn the attention of chemists
for the Friedländer quinoline synthesis. A review of the literature
showed that there is only one report on the use of a Brønsted acid
as a catalyst in the Friedländer reaction in pure water.20 The
Brønsted acid, in this report, was hydrochloric acid (1N, pH 1),
which is a strong, volatile, and corrosive acid. Also, it was found
that sulfamic acid21 and p-toluenesulfonic acid18b are the only
Brønsted acids that have been used for the synthesis of quinolines
via the Friedländer protocol under solvent-free conditions.
To overcome the problems associated with hydrochloric acid,
herein, we describe the utility of dodecylphosphonic acid (Fig. 1),
which is a mild, non-volatile and non-corrosive organic acid, as
an efficient solid surfactant-type Brønsted acid catalyst in pure
water and solvent-free conditions for the Friedländer reaction.
Despite the applications of dodecylphosphonic acid (DPA) as a
fire proofing agent,22 an activator of 5-lipoxygenase,23 an adjuvant
for positive electrostatic developers,24 germicides,25 and glycolysis
inhibitors,26 there is no report on its application in organic
The Friedländer quinoline synthesis involves a condensation
reaction between an aromatic ortho-aminoaryl ketone or aldehyde
with an aldehyde or ketone containing an a-methylene group, and
then a cyclodehydration.12 This reaction is generally carried out by
refluxing either an aqueous or an alcoholic solution of reactants in
the presence of a base at high temperature, 150–220 °C, in the
absence of a catalyst.13 However, under basic- or thermal-catalysis
conditions, ortho-aminobenzophenone does not react with simple
ketones, such as cyclohexanone and b-keto esters.14 Brønsted acid
catalysts such as hydrochloric acid, sulfuric acid, p-toluenesulfonic
acid, and polyphosphoric acid have been widely used.15 Also,
modified methods, employing Lewis acid16 and inorganic salt
catalysts,15 ionic liquids,17 microwave conditions,18 and molecular
iodine,19 have been reported for this reaction. Many of these
procedures have significant drawbacks such as low yields of
O
P
OH
OH
* Corresponding author. Tel.: +98 711 2284822; fax: +98 711 2286008.
E-mail address: sardarian@susc.ac.ir (A. R. Sardarian).
Figure 1.
0040-4039/$ - see front matter Ó 2008 Published by Elsevier Ltd.
doi:10.1016/j.tetlet.2008.09.097

S. Ghassamipour, A. R. Sardarian / Tetrahedron Letters 50 (2009) 514–519
515
reactions. So, due to its amphipathic structure and low acidity, we
decided to apply DPA as a mild solid surfactant-type Brønsted acid
catalyst in the Friedländer synthesis of quinolines in pure water
(method A) and solvent-free conditions (method B). In order to
optimize the reaction conditions in aqueous media, the effect of
temperature and amount of the Brønsted acid (5 mol %, 10 mol %,
and 20 mol %, respectively) were investigated on the reaction of
2-aminobenzophenone and ethyl acetoacetate in the presence of
DPA (Scheme 1).
5-chloro-2-aminobenzophenone with cyclopentanone, cyclohexa-
none, and 1-phenyl-butan-1,3-dione, better results. However, in
most of the examples, the use of DPA under solvent-free conditions
produced better yields.
In summary, we have reported the first application of DPA in
organic synthesis, and introduced two new mild and efficient
methods, A and B, for the synthesis of quinolines and polycyclic
quinolines via Friedländer condensation of 2-aminoarylketones
with
a-methylene ketones using DPA as a recyclable catalyst in
These studies showed (a) the reaction did not occur at all at a
temperature lower than 90 °C, and (b) the reaction did not proceed
in the absence of catalyst and gave the best results in 10 mol % of
DPA. A lower amount of DPA, 5 mol %, led to smaller yield and a
higher amount, 20 mol %, did not show any improvement in the
yield or reaction time.
pure water and in solvent-free procedures. The easy preparation
of DPA, (it is also commercially available) along with the simple
experimental procedure, and the ease of recovery and reuse of this
novel catalyst makes these methods simple and convenient for the
synthesis of quinolines and their derivatives.
With optimized conditions, we next studied the generality and
efficiency of DPA in pure water and solvent-free conditions in
several example reactions (Scheme 2).
2. General procedure
2.1. Preparation of dodecylphosphonic acid (DPA)
Various 1,3-diketones such as 1,3-cyclohexadione, 1,3-cyclo-
pentadione, 2,4-pentadione, acetoacetophenone, and cyclic ke-
tones including cyclohexanone and cyclopentanone reacted with
2-aminobenzophenone to produce, efficiently, the corresponding
substituted quinolines (Table 1).
A mixture of 5 ml (0.02 mol) of 1-bromododecane and 3.9 ml
(0.02 mol) of triethylphosphite was heated for 4 h at 160–190 °C
with continuous removal of the ethyl bromide formed. Then
21 ml of HBr (40%) was added at room temperature, and the mix-
ture was refluxed with stirring for 3 h. Next, HBr and water were
removed by simple distillation to afford DPA as a yellow solid,
which was washed with pentane and recrystallised from hexane
to give the pure product as colorless crystals. Mp 98 °C (Lit.
98–99 °C).27
In addition, substituted 2-aminoaryl ketones such as 2-amino-
acetophenone and 2-amino-5-chlorobenzophenone reacted
smoothly with
a-methylene ketones, Table 1, to produce a range
of quinoline derivatives. In all cases, the products were isolated
by simple extraction with DCM. The crude products were purified
and recrystallized from a mixture of diethyl ether/n-hexane or by
silica gel column chromatography. In the case of reactions in aque-
ous media, the catalyst was separated by evaporation of water, and
reused directly without any activation. For example, the reaction of
2-aminobenzophenone and ethyl acetoacetate afforded the corre-
sponding quinoline in 85%, 83%, and 80% yields over three runs.
Furthermore, both methods A and B were clean, free of side
reactions, and thus provided easy access to substituted quinolines
with good to excellent yields in relatively short times. Also, these
methods had simple, experimental, and work-up procedures.
For comparison of these methods with the aqueous hydrochlo-
ric acid method,20 we ran several reactions with the same sub-
strates, the corresponding data are shown in Table 2. This study
showed, in general, that DPA gives comparable and in some of
the cases, including the reactions of 2-aminobenzophenone and
2.2. Preparation of quinolines and polyheterocycles under
aqueous media (method A)
A mixture of 2-amino-substituted ketone (1a, 1b, 1c, 1 mol) and
ketone (2, 1.5 mol) was added to 0.1 mol of dodecylphosphonic
acid (DPA) in 10 ml of water. The reaction mixture was heated at
90 °C with stirring for the appropriate time mentioned in Table 1.
The extent of reaction was monitored by TLC. The crude mixture
was extracted with dichloromethane (2 Â 10 ml) and the com-
bined organic layer was dried over anhydrous calcium chloride
and filtered. Evaporation of the solvent gave a crude product,
which was purified by silica gel column chromatography with
petroleum ether (bp 60 °C) and ethyl acetate (4:1) to give the pure
product. Distillation of the aqueous layer allowed the DPA to be
recovered and used again.
O
O
Ph
N
O
O
DPA (0.1 mmol)
Ph
OEt
CH3
OEt
H2O
NH2
Scheme 1.
R1
N
O
O
R2
R3
R
R
R1
DPA (0.1 mmol)
R3
H2O or neat
90 ºC
R2
NH2
1a; R=H, R1=Ph
1b; R=Cl, R1=Ph
1c; R=H, R1=CH3
3a-o
2
Scheme 2.

516
S. Ghassamipour, A. R. Sardarian / Tetrahedron Letters 50 (2009) 514–519
Table 1
DPA-catalyzed Friedländer reaction between 2-aminoaryl ketones and various
a-methylene ketones
Entry
2-Aminoketone 1a–c
Ketone 2
Quinoline 3a–o
Mp (°C)
Found (Lit.)
Yielda (%) (A/B)
78/95
Time (min) (A/B)
60/43
O
O
Ph
3a
3b
1a
138–141
Ph
1
NH2
N
O
Ph
O
1a
1a
O
O
O
Ph
2
3
4
93
85/90
65/70
73/90
140/30
90/33
54/45
OEt
(97)17
OEt
NH2
N
CH3
Ph
O
3c
Ph
133–135
(135)28
NH2
O
N
O
Ph
1a
3d
O
O
O
O
O
Ph
NH2
112–115
(114)29
CH3
Ph
N
CH3
O
Ph
O
1a
3e
3f
Ph
5
6
7
133–134
90–93
69/89
70/75
52/95
41/46
70/20
75/16
Ph
NH2
N
CH3
O
Ph
O
1a
O
O
Ph
OCH2Ph
CH3
OCH2Ph
NH2
O
N
O
Ph
1a
1a
3g
Ph
151–153
171–175
NH2
O
N
O
Ph
O
O
3h
Ph
NH2
8
9
53/85
72/97
120/14
35/10
N
O
O
Ph
O
1b
3i
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Ph
159
(163)14
NH2
N
Ph
O
3j
1b
Ph
O
O
O
10
11
12
100
70/91
82/98
58/93
162/25
96/20
45/14
(105)14
NH2
N
O
Ph
3k
O
1b
O
O
Ph
102–104
(108)14
OEt
CH3
OEt
NH2
N
CH3
O
Ph
1b
O
3l
Cl
Ph
NH2
154
(151)14
N
CH3

S. Ghassamipour, A. R. Sardarian / Tetrahedron Letters 50 (2009) 514–519
517
Table 1 (continued)
Entry
2-Aminoketone 1a–c
Ketone 2
Quinoline 3a–o
Mp (°C)
Found (Lit.)
Yielda (%) (A/B)
71/90
Time (min) (A/B)
O
O
1b
Ph
Ph
3m
Ph
CH3
O
O
O
Cl
Cl
13
209–211
60/49
Cl
Cl
Ph
NH2
N
O
Ph
O
1b
Ph
NH2
3n
OCH2Ph
O
O
14
121–123
70/89
50/88
39/
OCH2Ph
N
CH3
3o
CH3
O
1c
CH3
NH2
15
78
127/34
(78)14
N
a
Isolated yields.
2.3. Preparation of quinolines and polyheterocycles under
solvent-free conditions (method B)
126.87, 128.10, 128.12, 128.24, 128.31, 128.37, 128.66, 129.14,
130.07, 134.59, 135.28, 145.98, 147.51, 154.29, 168.11. EIMS: m/z
(%): 353 (M+, 25), 308 (13), 246 (18), 218 (10), 149 (20), 107 (2),
91 (66), 77 (5), 57 (100). Anal. Calcd for C24H19NO2: C, 81.58; H,
5.38; N, 3.96. Found: C, 81.34; H, 5.51; N, 3.89.
A mixture of 2- amino-substituted ketone (1a, 1b, 1c, 1 mol),
ketone (2, 1.5 mol), and dodecylphosphonic acid (DPA) (0.1 mol)
was heated at 90 °C with stirring for the appropriate time men-
tioned in Table 1. The extent of reaction was monitored by TLC.
The crude mixture was extracted with dichloromethane (10 ml),
and the combined organic layer was dried over anhydrous calcium
chloride and then filtered. Evaporation of the solvent gave the
crude product, which was purified by silica gel column chromatog-
raphy with n-hexane and ethyl acetate (4:1) to give the pure
product.
2.3.4. 9-Phenyl-3,4-dihydroacridin-1(2H)-one (3g)
Pale yellow solid, mp 151–153 °C. IR (KBr): 3039, 2974, 1689,
1550, 1481, 771, 702 cmÀ1 1H NMR (250 MHz, CDCl3): d 2.19 (m,
.
2H), 2.62 (t, J = 6.32 Hz, 2H), 3.29 (t, J = 6.17 Hz, 2H), 7.10 (m,
2H), 7.36 (m, 5H), 7.67 (m, 1H), 7.99 (d, J = 8.45 Hz, 1H). 13C NMR
(63 MHz, CDCl3): d 21.35, 34.59, 40.57, 123.63, 126.20, 127.32,
127.80, 127.88, 128.00, 128.30, 131.50, 137.42, 148.43, 151.15,
161.97, 197.64. EIMS: m/z (%): 273 (M+, 87), 272 (98), 245 (39),
244 (100), 217 (36), 189 (19), 176 (9), 137 (21), 127 (11), 120
(22), 108 (26), 94 (22), 77 (4), 51 (4), 43 (4).
Known products were characterized by comparison of their
melting point and spectra with authentic samples. New com-
pounds were characterized by melting point, IR, 1H NMR, 13C
NMR, CHN, and mass spectral analysis as follows.
2.3.5. 9-Phenyl-2,3-dihydrocyclopenta[b]quinolin-1-one (3h)
Pale yellow solid, mp 171–175 °C. IR (KBr): 2931, 1712, 1566,
2.3.1. 9-Phenyl-2,3-dihydro-1H-cyclopenta[b]quinoline (3a)
Pale yellow solid, mp 138–141 °C. IR (KBr): 3068, 2931, 2862,
833, 771 cmÀ1 1H NMR (250 MHz, CDCl3): d 2.74 (m, 2H), 3.36
.
1575, 1485, 761, 705 cmÀ1
.
1H NMR (250 MHz, CDCl3): d 1.72 (m,
(m, 2H), 7.27 (m, 2H), 7.44 (m, 4H), 7.73 (m, 2H), 8.04 (d,
J = 8.42 Hz, 1H). 13C NMR (63 MHz, CDCl3): d 28.43, 36.53, 123.59,
126.34, 126.42, 127.87, 128.17, 128.61, 128.79, 129.15, 130.65,
131.91, 132.96, 148.74, 151.0, 170.72, 203.28. EIMS: m/z (%): 259
(M+, 85), 258 (100), 230 (38), 189 (3), 176 (19), 129 (19), 114
(32), 100 (19), 84 (16), 77 (4), 51 (3). Anal. Calcd for C18H13NO:
C, 83.39; H, 5.02; N, 5.40. Found: C, 82.88; H, 5.08; N, 5.11.
2H), 1.84 (m, 2H), 2.52 (t, J = 6.3 Hz, 2H), 3.12 (t, J = 6.59 Hz, 2H),
7.16 (m, 1H), 7.23 (m, 1H), 7.40 (m, 6H), 7.93 (d, J = 8.3 Hz, 1H).
13C NMR (63 MHz, CDCl3): d 22.8, 22.9, 27.9, 34.1, 125.1, 125.5,
126.4, 127.5, 128.1, 128.4, 128.8, 136.9, 146.2, 146.5, 158.8. EIMS:
m/z (%): 259 (M+, 100), 230 (13.1), 203 (1.3), 182 (13.0), 149 (4.6),
121 (10.6), 77 (8.2), 57 (17.2).
2.3.2. (2-Methyl-4-phenylquinoline-3-yl)(phenyl)methanone
(3e)
2.3.6. (6-Chloro-2-methyl-4-phenylquinolin-3-yl)(phenyl)
methanone (3m)
Pale yellow solid, mp 133–134 °C. IR (KBr): 3058, 2912, 1674,
White solid, mp 209–211 °C. IR (KBr): 2923, 2846, 1674, 1234,
1577, 767, 702 cmÀ1
.
1H NMR (250 MHz, CDCl3): d 2.56 (s, 3H),
786, 702 cmÀ1 1H NMR (250 MHz, CDCl3): d 2.54 (s, 3H), 7.18
.
7.18 (m, 7H), 7.35 (m, 2H), 7.54 (m, 3H), 7.68 (m, 1H), 8.09 (d,
J = 8.4 Hz, 1H). 13C NMR (63 MHz, CDCl3): d 24.03, 125.08, 126.04,
126.30, 127.81, 128.06, 128.24, 128.71, 129.04, 129.80, 129.89,
132.24, 133.31, 134.61, 136.95, 145.34, 147.59, 154.40, 197.48.
EIMS: m/z (%): 323 (M+, 19), 322 (100), 306 (9), 246 (48), 218
(26), 217 (40), 189 (6), 176 (27), 105 (38), 77 (66), 51 (13).
(m, 7H), 7.38 (m, 1H), 7.48 (m, 3H), 7.62 (d, J = 2.28 Hz, 1H), 7.99
(d, J = 8.9 Hz, 1H). 13C NMR (63 MHz, CDCl3): d 23.96, 124.80,
125.91, 128.03, 128.30, 128.38, 129.01, 129.69, 130.36, 130.78,
132.24, 133.00, 133.48, 133.91, 136.67, 144.56, 145.96, 154.84,
199.95. EIMS: m/z (%): 357 (M+, 58), 280 (24), 217 (25), 176 (18),
149 (49), 105 (43), 77 (45), 71 (52), 57 (75), 43 (100). Anal. Calcd
for C23H16ClNO: C, 77.20; H, 4.47; N, 3.91. Found: C, 77.68; H,
4.76; N, 3.48.
2.3.3. Benzyl 2-methyl-4-phenylquinoline-3-carboxylate (3f)
White solid, mp 90–93 °C. IR (KBr): 3070, 2916, 1720, 1566,
1488, 887, 763 cmÀ1
5.03 (s, 2H), 7.08 (m, 2H), 7.36 (m, 3H), 7.41 (m, 2H), 7.42 (m,
4H), 7.44 (d, J = 10.3 Hz, 1H), 7.71 (m, 1H), 8.09 (d, J = 8.4 Hz, 1H).
13C NMR (63 MHz, CDCl3): d 23.8, 67.28, 124.87, 126.22, 126.27,
.
1H NMR (250 MHz, CDCl3): d 2.76 (s, 3 H),
2.3.7. Benzyl 6-chloro-2-methyl-4-phenylquinoline-3-
carboxylate (3n)
White solid, mp 121–123 °C. IR (KBr): 3078, 3039, 1720, 1581,
1481, 1226, 833, 740, 709 cmÀ1 1H NMR (250 MHz, CDCl3): d
.

518
S. Ghassamipour, A. R. Sardarian / Tetrahedron Letters 50 (2009) 514–519
Table 2
Comparison of the isolated yields obtained in the presence of DPA in water and solvent-free conditions, and HCl (1 N)
Entry
1
2-Aminoketone
Ketone
Quinoline
HCl (aq)a yield (%)
DPA(aq)b yield (%)
70
DPAc yield (%)
91
O
Ph
O
—
Ph
NH2
N
Ph
O
O
O
Ph
2
3
10
95
65
52
70
95
NH2
N
O
O
Ph
Ph
NH2
O
N
O
Ph
O
O
Ph
4
5
90
30
53
70
85
91
NH2
N
O
Ph
O
O
O
Cl
Cl
Cl
Ph
Ph
NH2
N
O
Ph
O
O
Cl
6
40
71
90
Ph
CH3
Ph
NH2
N
a
HCl (1 N), H2O, 60 °C.
DPA (0.1 mmol), H2O, 90 °C.
DPA (0.1 mmol), solvent-free, 90 °C.
b
c
Chem. 1996, 61, 3398; (b) Chen, Y. L.; Fang, K. C.; Sheu, J. Y. S.; Hsu, L.; Tzeng, C.
C. J. Med. Chem. 2001, 44, 2374.
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Brideau, C.; Chan, C.; Desmarais, S.; Eithier, D.; Fagueyret, J. P.; Friesen, R. W.;
Girad, M.; Girad, Y.; Guay, J.; Tagari, P.; Young, R. N. Bioorg. Med. Chem. Lett.
1998, 8, 1255.
7. (a) Ko, T.-C.; Hour, M.-J.; Lien, J.-C.; Teng, C.-M.; Lee, K.-H.; Kuo, S.-C.; Huang, L.-
J. Bioorg. Med. Chem. Lett. 2001, 11, 279; (b) Ferrarini, P. L.; Mori, C.; Badawneh,
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2.66 (s, 3H), 4.95 (s, 2H), 7.00 (m, 2H), 7.20-7.26 (m, 5H), 7.37 (m,
3H), 7.46 (m, 1H), 7.58 (m, 1H), 7.94 (d, J = 8.95 Hz, 1H). 13C NMR
(63 MHz, CDCl3): d 23.72, 67.42, 125.00, 125.68, 126.92, 127.04,
127.65, 128.21, 128.28, 128.32, 128.41, 128.63, 129.03, 130.32,
130.96, 132.16, 134.43, 134.55, 145.88, 154.68, 167.74. EIMS: m/z
(%): 387 (M+, 32), 342 (14), 310 (4), 296 (4), 280 (12), 252 (5),
217 (12), 189 (5), 176 (10), 107 (2), 91 (100), 77 (6), 65 (12), 51 (3).
8. (a) Agarwal, A. K.; Jenekhe, S. A. Macromolecules 1991, 24, 6806; (b) Zhang, X.;
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Alam, M. M. Macromolecules 2001, 34, 7315.
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Acknowledgment
We gratefully acknowledge the support of this work by Shiraz
University research council.
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