Synthesis of substituted quinolines from arylamines and aldehydes via tandem reaction promoted by chlorotrimethylsilane

Article abstract of DOI:10.3184/030823409X401835

Substituted quinolines were effectively synthesised by utilising chlorotrimethylsilane (TMSCI) as an efficient catalyst in the cyclisation condensation of aromatic amines and enolisable aldehydes via a tandem process in air and DMSO. The clean, mild reaction conditions, operational simplicity and high yields were attractive features of the reaction which enables a facile preparative procedure for building the quinoline ring.

Full text of DOI:10.3184/030823409X401835

JOURNAL OF CHEMICAL RESEARCH 2009
FEBRUARY, 81–83
RESEARCH PAPER 81
Synthesis of substituted quinolines from arylamines and aldehydes
via tandem reaction promoted by chlorotrimethylsilane
Xiaoqin Biana,b, Lanhai Liua, Xin Genga, Zengyang Xiea, Shuangshuang Lia and Cunde Wanga*
aSchool of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225002, P. R. China
bDepartment of Environmental and Chemical Engineering, Taizhou Polytechnic College, Taizhou 225300, P. R. China
Substituted quinolines were effectively synthesised by utilising chlorotrimethylsilane (TMSCl) as an efficient catalyst
in the cyclisation condensation of aromatic amines and enolisable aldehydes via a tandem process in air and DMSO.
The clean, mild reaction conditions, operational simplicity and high yields were attractive features of the reaction
which enables a facile preparative procedure for building the quinoline ring.
Keywords: substituted quinolines, TMSCl, enolisable aldehydes, cyclisation reaction
Substitutedquinolinesandtheirderivativesareaveryimportant
class of heterocyclic compounds which have been used widely
DVꢀ DQWLLQÀDPPDWRU\ꢀ DJHQWVꢁꢀ DQWLPDODULDOꢁꢀ DQWLK\SHUWHQVLYHꢁꢀ
antibacterial, antiasthamatic, antiprotozoan, antituberculosis,
tyrosine kinase inhibiting agents, liverꢀ uꢀ receptor agonists,
anti-HIV, and anticancer activity.1-8 Furthermore they had
important roles as versatile building blocks for the synthesis
of natural products and nano and mesostructures with
enhanced electronic and photonic properties.9 In addition
to the medicinal applications, substituted quinolines have
been employed in the bioorganic and bioorganometallic
research.10 Studies of their properties and synthesis have
attracted considerable attention from medicinal and synthetic
organic chemists.
Many substituted quinolines have been synthesised by
various conventional named routes such as Skraup, Döbner-
YRQꢀ 0LOOHUꢁꢀ &RQUDGꢂ/LPSDFKꢁꢀ )ULHGODHQGHUꢀ DQGꢀ 3¿W]LQJHUꢀ
syntheses.11,12 They are still considered as the most useful
methods for preparing quinolines and related bicyclic
azaaromatic compounds, although they require harsh reaction
conditions and the yields are unsatisfactory in most cases.
Recently, in conjunction with the conventional syntheses,
more and more new methods of simple and elegant syntheses
of substituted quinolines have also been attempted because of
IDFLOLW\ꢁꢀHI¿FLHQF\ꢀDQGꢀFRQYHQLHQFHꢀRIꢀIRUPDWLRQꢀRIꢀTXLQROLQHꢀ
ring system.13,14 In view of the remarkable importance
from pharmacological, industrial and synthetic point, the
development of new synthetic approaches using mild reaction
conditions remains an active research area.
Trimethylchlorosilane (TMSCl) has been used as a mild and
HI¿FLHQWꢀSURPRWHUꢀIRUꢀYDULRXVꢀRUJDQLFꢀWUDQVIRUPDWLRQVꢃ15 It has
also been reported as a mild, useful and inexpensive Lewis
acid catalyst for one-pot chemoselective multicomponent
Biginellireactions,16 thebiguanideformationwithbenzylamine
and dicyandiamide,17 and direct cross aldol additions
and the related Claisen condensation using TiCl4/Bu3N.18
In continuation of our efforts to develop new synthetic routes
of substituted quinolines, we report here a TMSCl-promoted
one-pot synthesis of substituted quinolines from aromatic
amines and enolisable aldehydes via Tandem reaction under
an air atmosphere (Scheme 1).
Results and discussion
The more classical and convenient synthesis of substituted
quinolines was carried out11-14 by a one-step condensation
reaction from the available and inexpensive starting material
aromatic amines and enolisable aldehydes in the presence of
Lewis acid. Although the role of TMSCl is not completely
understood, it may be explained in terms of Lewis acid,
which activates the carbonyl group. We thought that it could
be applied in the one-step condensation reaction of aromatic
amine and enolisable aldehyde. Thus we initiated our
studies in a model reaction by subjecting 4-methoxyaniline
(1a) and isopentanal (2a) to TMSCl in DMSO under an air
atmosphere at 90°C, which gave 2-isobutyl-3-isopropyl-6-
methoxyquinoline (3a) (Table 1).
R2
R3
TMSCl, 3 h
R1
R1
+
O
N
R1
R2
DMSO, 90oC
R3
H
82-92 %
R3
R1
3a–j
NH2
1a–j
2a–j
Entry ArNH2(R1/R2)(1)
Aldehydes(R3)(2)
Quinolines (3)(%)
a
b
c
d
e
f
H / CH3O
CH3O / H
H / Ph
(CH3)2CH
(CH3)2CH
(CH3)2CH
CH3(CH2)3CH2
CH3(CH2)3CH2
PhCH2
PhCH2
PhCH2
CH3(CH2)3CH2
CH3CH2
92
86
88
89
86
84
82
86
86
83
H / Ph
CH3O / H
H / CH3O
CH3O / H
H / Ph
H / CH3O
H / H
g
h
i
j
Scheme1
* Correspondent. E-mail: cundeyz@hotmail.com

82 JOURNAL OF CHEMICAL RESEARCH 2009
Table 1 Effect of the ratio of 1a/2a/TMSCla
Table 3 Effect of the reaction timea
Entry
1a/2a/TMSCl /mol/mol/mol
Quinoline (3a)/%
Entry
Time/h
Quinoline 3a/%
1
2
3
4
5
6
7
8
1/2/0.01
1/3/0.01
1/4/0.01
1/5/0.01
1/4/0.02
1/5/0.02
1/4/0.03
1/4/0.05
67
74
81
81
87
88
92
92
1
2
3
4
1.5
2.0
3.0
3.5
67
78
92
92
aConditions: 1a/2a/TMSCl: 1/4/0.03 (mol/mol/mol), DMSO,
90°C, air.
IR spectrometer, 1H NMR and 13C NMR spectra were recorded on a
JNM-90Q spectrometer by using TMS as an internal standard (CDCl3
as solvent).
aConditions: DMSO (5 mL), reaction temperature 90°C, air, 3 h.
The results (Table 1) showed that the best results were
obtained using 3.0 mol% catalyst in the ratio of 1/4 and
excessive TMSCl was not necessary.
General procedure for one-pot synthesis of substituted quinolines
from arylamines and aldehydes via Tandem reaction promoted by
chlorotrimethylsilane.
In order to optimise other reaction conditions, reaction
temperature, solvents and reaction time were measured. As
shown in Table 2 and Table 3, the reaction gave a satisfactory
yield in DMSO under an air atmosphere at 90°C for 3 h.
Thus, with these results in hand, we synthesised substituted
quinolines (3a–j) by one-pot condensation reaction of
aromatic amines and enolisable aldehydes under the optimum
reaction conditions (Scheme 1).
TMSCl (0.1303 g, 1.2 mmol) was added to a mixture of aldehyde
(16 mmol) and substituted aniline (4 mmol) in DMSO (5 mL) at room
temperature. The resulting mixture was stirred at 90°C for 3 h under
an air atmosphere. After the mixture was cooled to room temperature,
it was poured to 10% sodium carbonate and was extracted with ethyl
acetate (3 u 15 mL), then the organic phase was washed with water
and brine, dried over Na2SO4. Removal of solvent, the residue was
SXUL¿HGꢀE\ꢀFROXPQꢀFKURPDWRJUDSK\ꢀꢄVLOLFDꢀJHOꢁꢀ(W2$Fꢅ&+2Cl2: 1/20)
to yield product (3a–i).
The mechanism for the conversion of imine and enolisable
aldehyde to a quinoline can be explained tentatively as in
Scheme 2. A E-amino aldehyde is preformed by direct-
Mannich reaction of silyl enol ether and imine, followed
by subsequent cyclisation and aromatisation under air.19
Oxygen in the air apparently acts as an effective oxidant for
aromatisation of hydroquinoline.20
,Qꢀ VXPPDU\ꢁꢀ ZHꢀ KDYHꢀ GHYHORSHGꢀ Dꢀ QHZꢀ DQGꢀ HI¿FLHQWꢀ
procedure to substituted quinolines from available aromatic
amines and enolisable aldehydes under an air atmosphere
in DMSO at 90°C for 3 h. A catalytic amount of TMSCl
(3.0 mol%) effectively initiates the reaction in a one-
pot tandem process to yield the products in 82–92%.
The procedure offers several advantages including mild
reaction conditions, operational simplicity, inexpensive
reagents, short reaction time and high yields of products.
2-Isobutyl-3-isopropyl-6-methoxyquinoline (3a): White solid; m.p.
58–60°C (EtOAc/Hexanes); IR (KBr, cm-1) 1624, 1599, 1567, 1492,
1465, 1383, 1226, 1032, 830; 1H NMR (CDCl3, 300 MHz, ppm) G
7.90 (d, J = 9.3 Hz, 1H), 7.85 (s, 1H), 7.28 (dd, J = 2.7 Hz and 0.6
Hz, 1H), 7.02 (d, J = 3.0 Hz, 1H), 3.90 (s, 3H), 3.30 (m, 1H), 2.88
(d, J = 7.5 Hz, 2H), 2.23 (m, 1H), 1.32 (d, J = 6.9 Hz, 6H), 0.98 (d,
J = 6.6 Hz, 6H); 13C NMR (CDCl3, 75 MHz, ppm) G 157.7, 156.9,
142.2, 140.7, 130.3, 129.7, 127.9, 120.7, 104.4, 55.1, 43.7, 29.1,
28.5, 23.6(2C), 22.4(2C). Anal. Calcd for C17H23NO: C, 79.33; H,
9.01; N, 5.44. Found: C, 79.13; H, 8.82; N, 5.40%.
2-Isobutyl-3-isopropyl-5,7-dimethoxyquinoline (3b): White solid;
m.p. 64–65°C (EtOAc/Hexanes); IR (KBr, cm-1) 1622, 1598, 1576,
1492, 1454, 1382, 1258, 1205, 1056, 831; 1H NMR (CDCl3, 300
MHz, ppm) G 8.25 (s, 1H), 6.96 (d, J = 1.8 Hz, 1H), 6.43 (d, J = 2.1
Hz, 1H), 3.95 (s, 3H), 3.92 (s, 3H), 3.29 (m, 1H), 2.88 (d, J = 7.5
Hz, 2H), 2.23 (m, 1H), 1.32 (d, J = 6.9 Hz, 6H), 0.99 (d, J = 6.6 Hz,
6H); 13C NMR (CDCl3, 75 MHz, ppm) G 161.0, 160.4, 155.6, 148.1,
137.5, 126.2, 115.4, 99.1, 97.1, 55.5, 55.4, 44.1, 29.4, 28.7, 24.0(2C),
22.5(2C). Anal. Calcd for C18H25NO2: C, 75.22; H, 8.77; N, 4.87.
Found: C, 75.16; H, 8.82; N, 4.61%.
Experimental
2-Isobutyl-3-isopropyl-6-phenylquinoline (3c): Oil; IR (neat, cm-1)
1597, 1578, 1482, 1463, 1382, 1053, 837; 1H NMR (CDCl3, 300 MHz,
ppm) G 8.18 (d, J = 9.0 Hz, 1H), 7.98 (s, 1H), 7.92 (d, J = 2.1 Hz, 1H),
7.86 (dd, J = 6.4 Hz and 1.8 Hz, 1H), 7.68 (d, J = 7.2 Hz, 2H), 7.45
(t, J = 7.5 Hz, 2H), 7.34 (t, J = 7.5 Hz, 1H), 3.33 (m, 1H), 2.94 (d,
J = 6.9 Hz, 2H), 2.30 (m, 1H), 1.33 (d, J = 6.9 Hz, 6H), 1.01 (d,
J = 6.6 Hz, 6H); 13C NMR (CDCl3, 75 MHz, ppm) G 160.7, 145.5, 141.1,
140.7, 138.2, 131.6, 128.9 128.8(2C), 128.0, 127.4, 127.3, 127.2(2C),
124.8, 44.1, 29.2, 28.7, 23.8(2C), 22.6(2C). Anal. Calcd for C22H25N:
C, 87.08; H, 8.30; N, 4.62. Found: C, 87.16; H, 8.02; N, 4.60%.
2-Hexyl-3-pentyl-6-phenylquinoline (3d): Oil; IR (neat, cm-1) 3060,
3032, 2955, 2926, 2857, 1682, 1598, 1578, 1483, 1465, 1377, 1354,
910, 836, 760, 697; 1H NMR (CDCl3, 300 MHz, ppm) G 8.07. (d,
J = 9.3 Hz, 1H), 7.90–7.85(m, 3H), 7.72–7.70 (m, 2H), 7.50–7.45 (m,
2H), 7.39–7.37 (m, 1H), 2.98 (t, J = 8.1 Hz, 2H), 2.78 (t, J = 8.1 Hz,
2H), 1.83–1.68 (m, 4H), 1.48–1.33 (m, 10H), 0.96–0.88 (m, 6H); 13C
NMR (CDCl3, 75 MHz, ppm) G 162.3, 145.9, 140.7, 138.2, 134.9,
134.5, 128.9, 128.8(2C), 127.9, 127.4(2C), 127.3(2C), 124.6, 35.9,
32.3, 31.7(2C), 30.1, 29.6, 29.5, 22.6, 22.5, 14.0, 13.9; Anal. Calcd
for C26H33N: C, 86.85; H, 9.25; N, 3.90. Found: C, 86.73; H, 9.12;
N, 3.70%.
Elemental analytical data were obtained by using a model 240
elementary instrument, IR spectra were measured with a model 408
Table 2 Effect of the temperature and solventa
Entry
Solvent
Temperature/°C
Quinoline 3a/%
1
2
3
4
5
6
THF
70
80
78
85
83
86
92
91
C6H6
DMF
80
DMSO
DMSO
DMSO
80
90
100
aConditions: 1a/2a/TMSCl: 1/4/0.03 (mol/mol/mol), air, 3 h.
OTMS
O
O
TMSCl
R1
R
R
R
H
H
R1
R
N
R
2-Hexyl-3-pentyl-5,7-dimethoxyquinoline (3e): Oil; IR (neat, cm-1)
3000, 2924, 2857, 1623, 1578, 1493, 1452, 1390, 1360, 1203, 1152,
H
N
H+
1
1048, 830; H NMR (CDCl3, 300 MHz, ppm) G 8.12. (s, 1H), 6.96.
(d, J = 2.1 Hz, 1H), 6.43. (d, J = 2.1 Hz, 1H), 3.93 (s, 3H), 3.91 (s,
3H), 2.92 (t, J = 7.8 Hz, 2H), 2.73 (t, J = 7.8 Hz, 2H), 1.79–1.64 (m,
4H), 1.49–1.32 (m, 10H), 0.95–0.87 (m, 6H); 13C NMR (CDCl3, 75
MHz, ppm) G 162.3, 160.3, 155.5, 148.5, 130.9, 129.6, 115.3, 99.1,
97.2, 55.6, 55.5, 35.9, 32.3, 31.7, 30.6, 29.8, 29.6(2C), 22.6, 22.5,
14.0, 13.9; Anal. Calcd for C22H33NO2: C, 76.92; H, 9.68; N, 4.08.
Found: C, 76.73; H, 9.72; N, 3.90%.
R
R
O2
R1
R1
R
R
N
N
H
Scheme 2 Plausible reaction mechanism.

JOURNAL OF CHEMICAL RESEARCH 2009 83
3-Benzyl-6-methoxy-2-phenethylquinoline (3f): Needle solid;
m.p. 142–144°C (EtOAc/hexanes); IR (KBr, cm-1): 1624, 1606,
1493, 1467, 1451, 1363, 1226, 1187, 1123, 1030, 835, 702; 1H NMR
(CDCl3, 300 MHz, ppm) G 7.96 (d, J = 9.0 Hz, 1H), 7.63 (s, 1H),
7.33–7.09 (m, 11H), 6.97 (d, J = 2.1 Hz, 1H), 3.91 (s, 2H), 3.89 (s,
3H), 3.17 (m, 2H), 3.05 (m, 2H); 13C NMR (CDCl3, 75 MHz, ppm)
G 158.2, 157.1, 142.7, 141.9, 139.2, 135.0, 132.5, 129.8, 128.8(2C),
128.5(2C), 128.4(2C), 128.1(2C), 127.8, 126.3, 125.7, 121.2, 104.6,
55.2, 38.4, 37.2, 35.1; Anal. Calcd for C25H23NO: C, 84.95; H, 6.56;
N, 3.96. Found: C, 84.83; H, 6.42; N, 3.88%.
3-Benzyl-5,7-dimethoxy-2-phenethylquinoline (3g): Oil; IR (neat,
cm-1) 1623, 1600, 1577, 1494, 1452, 1389, 1361, 1204, 1153, 1127,
1047, 831; 1H NMR (CDCl3, 300 MHz, ppm) G 8.14. (s, 1H), 7.29–7.07
(m, 10H), 7.02 (s, 1H), 6.46 (m, 1H), 4.03 (s, 2H), 3.92 (s, 3H), 3.91
(s, 3H), 3.14 (m, 2H), 2.97 (m, 2H); 13C NMR (CDCl3, 75 MHz, ppm)
G 161.8, 160.8, 155.7, 149.0, 142.0, 140.0, 131.6, 128.96, 128.62(2C),
128.50(2C), 128.46(2C), 128.26(2C), 126.2, 125.8, 115.4, 99.1, 97.6,
55.6, 55.2, 38.7, 37.7, 35.5; Anal. Calcd for C26H25NO2: C, 81.43; H,
6.57; N, 3.65. Found: C, 81.73; H, 6.42; N, 3.90%.
3-Benzyl-2-phenethyl-6-phenylquinoline (3h): Needle solid; m.p.
171–172°C (EtOAc/Hexanes); IR (KBr, cm-1): 1599, 1578, 1495,
1485, 1451, 1429, 1355, 1178, 835, 755, 729; 1H NMR (CDCl3,
300 MHz, ppm) G 8.13 (d, J = 8.7 Hz, 1H), 7.90 (dd, J = 8.7 and
1.8 Hz, 1H), 7.85 (d, J = 1.5 Hz, 1H), 7.73 (s, 1H), 7.67 (d, J = 7.5 Hz,
2H), 7.44 (t, J = 7.2 Hz, 2H), 7.37–7.08 (m, 11H), 4.03 (s, 2H),
3.24–3.19 (m, 2H), 3.10–3.05 (m, 2H); 13C NMR (CDCl3, 75 MHz,
ppm) G 161.1, 146.3, 141.9, 140.5, 139.2, 138.5, 136.4, 132.9, 128.99,
128.90(3C), 128.82(2C), 128.65(2C), 128.52(2C), 128.40, 128.30(2C),
127.5, 127.3(2C), 126.5, 125.9, 124.8, 38.6, 37.6, 35.2; Anal. Calcd
for C30H25N: C, 90.19; H, 6.31; N, 3.51. Found: C, 90.01; H, 6.42;
N, 3.48%.
J = 6.9 Hz, 3H), 1.01 (t, J = 6.6 Hz, 3H). 13C NMR (CDCl3, 75 MHz,
ppm) G 160.8, 142.8, 134.0, 132.2, 129.2, 128.0, 127.0, 126.4, 126.0,
39.2, 30.6, 24.8, 15.0, 12.9. Anal. Calcd for C14H17N: C, 84.37; H,
8.60; N, 7.03. Found: C, 84.19; H, 8.62; N, 7.22%.
We are grateful to the Natural Science Foundation of
(GXFDWLRQꢀ 0LQLVWU\ꢀ RIꢀ -LDQJVXꢁꢀ &KLQDꢀ IRUꢀ ¿QDQFLDOꢀ VXSSRUWꢃꢀ
(Grant 07KJB150135)
Received 11 September 2008; accepted 12 December 2008
Paper 08/0165 doi: 10.3184/030823409X401835
Published online: 24 February 2009
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2-Hexyl-6-methoxy-3-pentylquinoline (3i): Oil; IR (neat, cm-1)
1625, 1604, 1567, 1492, 1464, 1380, 1360, 1226, 1164, 1034, 830;
1H NMR (CDCl3, 300 MHz, ppm) G 7.91. (d, J = 9.0 Hz, 1H), 7.71. (s,
1H), 7.26 (m, 1H), 6.96 (m, 1H), 3.85 (s, 3H), 2.92 (t, J = 7.8 Hz, 2H),
2.73 (t, J = 7.8 Hz, 2H), 1.82–1.61 (m, 4H), 1.46–1.32 (m, 10H), 0.94–
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134.2, 133.6, 129.9, 127.9, 120.6, 104.5, 55.2, 35.6, 32.3, 31.7(2C),
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3-Ethyl-2-propylquinoline (3j): White solid; m.p. 57–58°C
(hexanes); IR (KBr, cm-1) 1624, 1590, 1564, 1492, 1460, 1382,
1032, 790; 1H NMR (CDCl3, 300 MHz, ppm) G 8.00 (d, J = 9.3 Hz,
1H), 7.72 (s, 1H), 7.68 (d, J = 9.0 Hz, 1H), 7.64 (m, 1H), 7.50 (m,
1H), 2.88 (t, J = 7.5 Hz, 2H), 2.58 (m, 2H), 1.63 (m, 2H), 1.23 (t,
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