Efficient nucleophilic substitution reactions of quinolyl and isoquinolyl halides with nucleophiles under focused microwave irradiation

Article abstract of DOI:10.1016/S0040-4020(01)01225-X

Nucleophilic substitution reactions of 2-chloroquinoline, 3-bromoquinoline and 4-bromoisoquinoline with thiolate, alkoxy ions and aniline were completed within several minutes under microwave irradiation. This method gives the desired products with yields up to 99% in a short reaction time, and is superior to the classical heating process.

Full text of DOI:10.1016/S0040-4020(01)01225-X

TETRAHEDRON
Pergamon
Tetrahedron 58 72002) 1125±1129
Ef®cient nucleophilic substitution reactions of quinolyl
and isoquinolyl halides with nucleophiles under
focused microwave irradiation
p
Yie-Jia Cherng
Department of Medical Technology, Chung-Tai Institute of Health Science and Technology, Taichung 40605, Taiwan, ROC
Received 11 September 2001; revised 12 November 2001; accepted 6 December 2001
AbstractÐNucleophilic substitution reactions of 2-chloroquinoline, 3-bromoquinoline and 4-bromoisoquinoline with thiolate, alkoxy ions
and aniline were completed within several minutes under microwave irradiation. This method gives the desired products with yields up to
9
9% in a short reaction time, and is superior to the classical heating process. q 2002 Elsevier Science Ltd. All rights reserved.
1
. Introduction
a monomode microwave reactor. The reactions were
complete in 35 s to give high yields of 2-phenylthioquino-
line after column chromatography 7Table 1). On the other
hand, the conventionalheating method requires 2 days at
Severalderivatives of quino li nes have been found to possess
biological activities. The displacement reactions of the
1
2
halogen atoms in aryl halides have been studied. The
5
1008C.
reactions by conventionalheating process may encounter
dif®culty in reaching completion due to several factors
which include the ring substituents. Application of micro-
wave irradiation to decrease reaction time has recently
It appeared that 1.8 equiv. of PhSNa was essentialto
achieve the optimalyie dl 799%) by microwave irradiation
at 908C for 35 s 7Table 1, entry 2). By comparison, the
conventionalheating process 7Tab el 1, entry 4) was very
inef®cient, giving merely 4% of the desired product at the
same reaction temperature for the same reaction time. The
microwave effect besides giving heating ef®cacy could be
attributable to the high yielding displacement reaction of
2-chloroquinoline.
3
received much attention. However, only a few examples
of nucleophilic substitution of aromatic halides by using
4
microwave irradiation have been demonstrated. We report
herein an extension of this study toward the substitution
reactions of heteroaromatic compounds such as 2-chloro-
quinoline, 3-bromoquinoline and 4-bromoisoquinoline.
Because the reaction conditions cause a dramatic effect on
the reaction ef®ciency, we examined the solvent effect in the
substitution reactions. The sodium benzenethiolate was
used as a model nucleophile in the substitution reaction
7Table 2). The experiments indicated that the substitution
2
. Results and discussion
We carried out the substitution reactions of 2-chloroquino-
line with sodium thiophenoxide in HMPA by heating in
Table 1. Reaction of 2-chloroquinoline with sodium thiophenoxide
Entry
Molar proportions of PhSNa
Temperature 78C)
Time 7s)
Yield 7%)
1
2
3
4
1.5
1.8
1.8
1.8
90
90
80
90
35
35
35
35
83
99
95
a
4
a
Heating in an oilbath.
Keywords: nucleophilic substitution reaction.
Tel.: 1886-4-2239164ꢀxꢀ001; fax: 1886-4-22393305; e-mail: yjcherng@chtai.ctc.edu.tw
p
0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020701)01225-X

1126
Y.-J. Cherng / Tetrahedron 58 )2002ꢀ 1125±1129
Table 2. Solvent effects in the substitution reaction
give the corresponding 2-substituted quinolines 7Table 3).
In many cases, the substitution reactions in NMP afforded
even higher yields than those conducted in HMPA. When
1
.2 equiv. of MeONa were used, 2-chloroquinoline was
converted to 2-methoxyquinoline in an excellent yield
96%), in HMPA or NMP, within 30 s at a relatively low
Entry Solvent Molar proportions Temperature Time Yield
of nucleophile
7
78C)
7s)
7%)
temperature ꢀ08C 7Table 3, entries 6 and ꢀ). However, the
yield of 2-methoxyquinoline decreased when greater
quantities of MeONa were applied 7Table 3, entries 8 and
9). Indeed, 2-hydroxyquinoline instead of 2-methoxyquino-
line was formed exclusively when 2-chloroquinoline was
treated with 4 equiv. of MeONa at 1108C for 4 min 7Table
1
2
3
4
HMPA
NMP
DMSO
DMF
1.8
100
120
120
120
35
99
81
ꢀ8
61
2.5
2.5
2.5
300
300
300
3, entry 10). These results indicated that 2-methoxy-
quinoline reacted further to give 2-hydroxyquinoline
under microwave irradiation. An application of this
method for the deprotection of methylethers might be
conceived. The substitution reaction of 2-chloroquinoline
with 3 equiv. of aniline required no solvent, and produced
reaction could be realized by using NMP 7N-methylpyrro-
lidone), DMSO and DMF as the solvent on microwave
irradiation. However, HMPA was still the solvent of choice
in terms of short reaction times and high yields of the
desired product.
6
a
2-7phenylamino)quinoline in 66% yield 7Table 3, entry 11).
When 2 equiv. of PhSNa was used in NMP by microwave
irradiation at 1208C for 3 min, 2-chloroquinoline was also
converted to 2-phenylthioquinoline in 99% yield 7Table 3,
entry 1). Under microwave irradiation, 2-chloroquinoline
also reacted with MeSNa, EtONa, MeONa and aniline to
Similar experiments were performed with another two
substrates, 3-bromoquinoline and 4-bromoisoquinoline
7Tables 4 and 5). The reaction of 3-bromoquinoline with
PhSNa in HMPA or NMP under microwave irradiation
Table 3. Reactions of 2-chloroquinoline with nucleophiles
Entry
Nucleophile
Solvent
Molar proportions
of nucleophile
Temperature
78C)
Time
7s)
Product, Rˆ
Yield
7%)
1
2
3
4
5
6
ꢀ
8
9
PhSNa
NMP
HMPA
NMP
HMPA
NMP
2.0
1.5
1.8
4.0
4.0
1.2
1.2
1.3
2.0
4.0
3.0
120
ꢀ0
90
110
110
ꢀ0
ꢀ0
ꢀ0
180
30
120
360
240
30
30
30
30
SPh
99
90
98
ꢀ0
93
96
96
81
ꢀ0
99
66
MeSNa
MeSNa
EtONa
EtONa
MeONa
MeONa
MeONa
MeONa
MeONa
SMe
SMe
OEt
OEt
HMPA
NMP
OMe
OMe
OMe
OMe
OH
HMPA
HMPA
HMPA
ꢀ0
110
110
1
1
0
1
240
360
a
PhNH
2
±
NHPh
a
No solvent was used.
Table 4. Reactions of 3-bromoquinoline with nucleophiles
Entry
Nucleophile
Solvent
Molar proportions
of nucleophile
Temperature
78C)
Time
7s)
Product, Rˆ
Yield
7%)
1
2
3
4
5
6
ꢀ
8
9
PhSNa
PhSNa
PhSNa
PhSNa
MeSNa
MeSNa
MeONa
MeONa
MeONa
MeONa
MeONa
HMPA
HMPA
HMPA
NMP
HMPA
NMP
HMPA
NMP
HMPA
HMPA
HMPA
1.8
1.8
1.8
3.0
2.0
2.0
1.3
1.3
1.5
2.0
4.0
100
100
100
120
90
100
90
90
90
40
40
40
240
35
120
35
35
35
35
240
SPh
SPh
SPh
SPh
SMe
SMe
OMe
OMe
OMe
OMe
OH
98
NR
98
a
b
98
83
91
ꢀ2
30
64
38
63
1
1
0
1
90
110
a
Heating in an oilbath. NR represents no reaction.
Benzoquinone 710 mol%) was added to the reaction.
b

Y.-J. Cherng / Tetrahedron 58 )2002ꢀ 1125±1129
Table 5. Reactions of 4-bromoisoquinoline with nucleophiles
112ꢀ
Entry
Nucleophile
Solvent
Molar proportions
of nucleophiles
Temperature
78C)
Time
7s)
Product, Rˆ
Yield
7%)
1
2
3
4
5
6
PhSNa
PhSNa
PhSNa
MeSNa
MeSNa
MeONa
HMPA
HMPA
NMP
HMPA
NMP
HMPA
2.4
2.4
3.0
2.5
2.5
1.6
110
110
120
100
100
90
60
60
600
90
180
35
SPh
SPh
SPh
SMe
SMe
OMe
98
NR
8ꢀ
53
85
56
a
a
Heating in an oilbath. NR represents no reaction.
afforded 3-phenylthioquinoline in 98% yield 7Table 4,
entries 1 and 4). The similar reactions of 4-bromoisoquino-
line 7Table 5, entries 1 and 3) also gave 4-phenylthioiso-
quinoline in very high yield 798%). In a sharp contrast, such
substitution reactions did not occur by heating at 100±
heating at 1658C for ꢀ.5 h gave a low yield 718%) of
6b
3-phenylthioquinoline, whereas the reaction was pro-
moted signi®cantly by microwave irradiation at 1008C for
40 s to give a very high yield 798%) of the desired product
7Table 4, entry 1). Our results also indicated that the relative
aptitude for the nucleophilic substitution reactions appeared
to be 2-chloroquinoline.3-bromoquinoline.4-bromo-
isoquinoline. For example, the substitution reaction of
2-chloroquinoline with MeSNa occurred at ꢀ08C in 30 s
7Table 3, entry 2), the reaction of 3-bromoquinoline
occurred at 908C in 35 s 7Table 4, entry 5), and the corre-
sponding reaction of 4-bromoisoquinoline occurred at
1
3
108C 7Table 4, entry 2 and Table 5, entry 2). When
-bromoquinoline was heated at a higher temperature
7
1658C) for a prolonged period 7ꢀ.5 h), 3-phenylthioquino-
6b
line was obtained only in a low yield 718%). The micro-
wave effect in promoting nucleophilic aromatic substitution
reactions was remarkable in comparison with heating
processes.
1008C in 90 s 7Table 5, entry 4). NMP was found to be an
3
-Bromoquinoline also reacted with MeSNa in HMPA to
give 3-methylthioquinoline 783% yield) at 908C within 35 s
Table 4, entry 5). The yield was increased to 91% in NMP
by microwave irradiation at 1008C for 120 s 7Table 4, entry
). Longer microwave irradiation at a higher temperature
up to 1108C) did not further improve the yield. The micro-
appropriate solvent to replace HMPA in the aromatic
nucleophilic substitution reactions under microwave
irradiation. Such substitution reactions of quinolyl and
isoquinolyl halides probably proceed via an SNAr
mechanism.
7
6
7
wave irradiation of 3-bromoquinoline with 1.3 equiv. of
MeONa gave a ꢀ2% of 3-methoxyquinoline in HMPA
4. Experimental
7
Table 4, entry ꢀ). The yields of 3-methoxyquinoline
deteriorated when 1.5 and 2.0 equiv. of MeONa were used
Table 4, entries 9 and 10). Only 3-hydroxyquinoline was
obtained in 63% yield when 4.0 equiv. of MeONa was used
Table 4, entry 11), presumably due to a further cleavage of
1
H NMR spectra were measured in deuterochloroform
solutions on a Varian Mercury 400 spectrometer using
Me Si as the internalstandard. Reactions were monitored
4
7
7
by analytical thin-layer chromatography using silica gel 60
F-254 70.2 mm layer thickness). Flash chromatography was
carried out by utilizing silica gel 60 7ꢀ0±230 mesh ASTM).
The Synthewave 402e monomode microwave reactor was
purchased from Prolabo Company.
the methylether il nkage.
We examined the substitution reaction of 3-bromoquinoline
with PhSNa in the presence of benzoquinone as a radical
scavenger 7Table 4, entry 3). This experiment also provided
a high yield 798%) of 3-phenylthioquinoline without the
4.1. General procedure for reaction of hetaryl halides
with nucleophile
inhibition of benzoquinone. Involvement of an SRN
1
mechanism was thus excluded. As the substitution reactions
of 3-bromoquinoline and 4-bromoisoquinoline were regio-
speci®c, the elimination±addition mechanism via quinoline
or isoquinoline intermediates was unlikely. Thus, the substi-
In a quartz reaction vessel712 mL) were p al ced hetero-
aromatic halide 70.3 mmol) and nucleophile in an appro-
priate solvent 71 mL). The reaction vessel was then placed
into the cavity of a focused monomode microwave reactor
7Synthewave 402), and irradiated for the period indicated in
the tables. The reaction temperature was maintained by
modulating the power level of the reactor. The crude
reaction mixture was then absorbed directly onto silica
gel, and puri®ed using silica gel chromatography by elution
with a mixture of hexane and ethylacetate.
tution reactions under microwave irradiation probably
proceeded via an ionic S Ar mechanism.
ꢀ
N
3. Conclusion
According to our present study, microwave irradiation did
exert a bene®cial effect to accelerate the nucleophilic substi-
tution reactions of heteroaromatic halides. For example, the
8
5b
4.1.1. 2-Phenylthioquinoline. White solid, mpˆ46±4ꢀ8C
5
b
1
substitution reaction of 3-bromoquinoline with PhSNa by
7lit mpˆ48±498C). H NMR 7400 MHz) d ꢀ.96 7d,

1128
Y.-J. Cherng / Tetrahedron 58 )2002ꢀ 1125±1129
6
a
Jˆ8.4 Hz, 1H), ꢀ.89 7d, Jˆ8.4 Hz, 1H), ꢀ.ꢀ1±ꢀ.64 7m, 1H),
4.1.13. 4-Methoxyisoquinoline. Colorless crystals, mpˆ
6
a
1
ꢀ
.4ꢀ±ꢀ.43 7m, 4H), 6.98 7dd, Jˆ8.4, 1.2 Hz, 1H).
68±698C 7lit mpˆꢀ1±ꢀ58C). H NMR 7400 MHz) d 8.91
7
s, 1H), 8.21 7d, Jˆ8.4 Hz, 1H), 8.08 7s, 1H), ꢀ.95 7d, Jˆ
9
.1.2. 2-Methylthioquinoline. Yellow oil, H NMR 7400
1
4
8.0 Hz, 1H), ꢀ.ꢀ3±ꢀ.69 7m, 1H), ꢀ.66±ꢀ.26 7m, 1H), 4.08 7s,
3H).
MHz) d ꢀ.9ꢀ 7d, Jˆ8.2 Hz, 1H), ꢀ.88 7d, Jˆ8.8 Hz, 1H),
ꢀ
1
.ꢀ1 7d, Jˆ8.2 Hz, 1H), ꢀ.6ꢀ±ꢀ.63 7m, 1H), ꢀ.44±ꢀ.41 7m,
H), ꢀ.31 7d, Jˆ8.8 Hz, 1H), 2.ꢀ1 7s, 3H).
Acknowledgements
1
0
1
.1.3. 2-Ethoxyquinoline. Colorless oil, H NMR 7400
4
MHz) d ꢀ.9ꢀ 7d, Jˆ8.6 Hz, 1H), ꢀ.83 7d, Jˆ8.8 Hz, 1H),
We thank the ®nancialsupport of the Chung-Tai Institute of
Health Science and Technology, and the facility support
of the Department of Chemistry, NationalChung-Hsing
University.
ꢀ
.ꢀ0 7d, Jˆ8.0 Hz, 1H), ꢀ.61±ꢀ.59 7m, 1H), ꢀ.38±ꢀ.34 7m,
H), 6.88 7d, Jˆ8.8 Hz, 1H), 4.54 7q, Jˆꢀ.2 Hz, 2H), 1.45
1
7
t, Jˆꢀ.2 Hz, 3H).
1
.1.4. 2-Methoxyquinoline. Colorless oil, H NMR 7400
0
1
4
MHz) d ꢀ.98 7d, Jˆ8.8 Hz, 1H), ꢀ.88 7d, Jˆ8.4 Hz, 1H),
References
ꢀ
.ꢀ2 7d, Jˆ8.0 Hz, 1H), ꢀ.64±ꢀ.61 7m, 1H), ꢀ.40±ꢀ.38 7m,
H), 6.91 7d, Jˆ8.8 Hz, 1H), 4.09 7s, 3H).
1
1. 7a) Raymond, J. B.; Wiegand, J.; Weimar, J. R. J. Med. Chem.
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999, 42, 95. 7b) Wanda, P. C.; Francois, P.; Lukasz, K.;
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1
4
7
9
1
9
.1.5. 2-Hydroxyquinoline. White solid, mpˆ198±1998C
1
1
1
lit mpˆ1998C). H NMR 7400 MHz) d ꢀ.85 7d, Jˆ
.2 Hz, 1H), ꢀ.58 7d, Jˆ8.0 Hz, 1H), ꢀ.54 7d, Jˆ8.4 Hz,
H), ꢀ.52±ꢀ.46 7m, 1H), ꢀ.26±ꢀ.22 7m, 1H), 6.ꢀ5 7d, Jˆ
.2 Hz, 1H), 2.14 7br, ±OH).
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2
4
.1.6. 2-*Phenylamino)quinoline.
Colorless crystals,
1
2
1
mpˆ101±1028C 7lit mpˆ103±1048C). H NMR 7400
MHz) d ꢀ.94 7d, Jˆ9.0 Hz, 1H), ꢀ.ꢀ9 7d, Jˆ8.4 Hz, 1H),
ꢀ
1
.6ꢀ±ꢀ.55 7m, 4H), ꢀ.40±ꢀ.29 7m, 3H), ꢀ.12 7t, Jˆꢀ.4 Hz,
H), ꢀ.00 7d, Jˆ8.4, 1.2 Hz, 1H).
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b) Strauss, C. R. Aust. J. Chem. 1999, 52, 83. 7c) Strauss,
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b
4
7
.1.7. 3-Phenylthioquinoline. White solid, mpˆꢀ9±808C
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6
b
1
lit mpˆꢀ8.5±80.58C). H NMR 7400 MHz) d 8.82 7d,
Jˆ2.4 Hz, 1H), 8.11±8.09 7m, 2H), ꢀ.ꢀ3±ꢀ.68 7m, 2H),
ꢀ
.5ꢀ±ꢀ.54 7m, 1H), ꢀ.42±ꢀ.31 7m, 5H), 6.98 7dd, Jˆ8.4,
1
.2 Hz, 1H).
1
3
1
.1.8. 3-Methylthioquinoline. Yellow oil, H NMR 7400
4
MHz) d 8.81 7d, Jˆ2.2 Hz, 1H), 8.08 7d, Jˆ8.4 Hz, 1H),
ꢀ
.91 7d, Jˆ2.2 Hz, 1H), ꢀ.ꢀ4 7d, Jˆ8.4 Hz, 1H), ꢀ.6ꢀ±ꢀ.63
7
m, 1H), ꢀ.56±ꢀ.53 7m, 1H), 2.61 7s, 3H).
1
.1.9. 3-Methoxyquinoline. Colorless oil, H NMR 7400
4
1
4
MHz) d 8.68 7d, Jˆ2.8 Hz, 1H), 8.06 7d, Jˆ8.4 Hz, 1H),
ꢀ
.ꢀ4 7d, Jˆ8.0 Hz, 1H), ꢀ.59±ꢀ.39 7m, 2H), ꢀ.40 7d,
Jˆ2.8 Hz, 1H), 3.96 7s, 3H).
7
n) Gedye, R.; Smith, F.; Westaway, H.; Baldisera, L.;
1
5
4
1
1
.1.10. 3-Hdroxyquinoline. Colorless crystals, mpˆ198±
Laberge, L.; Rousell, J. Tetrahedron Lett. 1986, 27, 2ꢀ9.
7o) Giguere, R. J.; Bray, T. L.; Duncan, S. M.; Majetich, G.
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1
5
1
998C 7lit mpˆ1988C). H NMR 7400 MHz) d 8.90 7s,
H), 8.15 7d, Jˆ8.4 Hz, 1H), ꢀ.ꢀ5 7d, Jˆ8.0 Hz, 1H), ꢀ.ꢀ3
7
s, 1H), ꢀ.63±ꢀ.54 7m, 2H), 3.31 7br, ±OH).
4. Cherng, Y.-J. Tetrahedron 2000, 56, 828ꢀ.
5
. 7a) Brooker, L. G. S.; Keyes, G. H.; Sparague, R. H.; Vandyke,
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3349.
2
a
4
5
1
1
5
.1.11. 4-Phenylthioisoquinoline. White solid, mpˆ5ꢀ±
2
a
1
88C 7lit mpˆ60±618C). H NMR 7400 MHz) d 9.24 7s,
H), 8.63 7s, 1H), 8.28 7d, Jˆ8.0 Hz, 1H), 8.03 d, Jˆ8.0 Hz,
H), ꢀ.ꢀꢀ±ꢀ.ꢀ3 7m, 1H), ꢀ.68±ꢀ.66 7m, 1H), ꢀ.26±ꢀ.19 7m,
H).
6. 7a) Zoltewicz, J. A.; Oestreich, T. M.; Sale, A. A. J. Am. Chem.
Soc. 1975, 97, 5889. 7b) Zoltewicz, J. A.; Locko, G. A. J. Org.
Chem. 1983, 48, 4214.
2
.1.12. 4-Methylthioisoquinoline. Colorless crystals,
a
4
ꢀ. 7a) Buck, P. Angew. Chem., Int. Ed. Engl. 1969, 8, 120.
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8. Berlan, J. Radiat. Phys. Chem. 1995, 45, 581.
2
a
1
mpˆ61±628C 7lit mpˆ65±668C). H NMR 7400 MHz)
d 9.09 7s, 1H), 8.43 7s, 1H), 8.23 7d, Jˆ8.4 Hz, 1H), 8.00
7
2
d, Jˆ8.4 Hz, 1H), ꢀ.81±ꢀ.ꢀꢀ 7m, 1H), ꢀ.69±ꢀ.26 7m, 1H),
.62 7s, 3H).

Y.-J. Cherng / Tetrahedron 58 )2002ꢀ 1125±1129
1129
9
. Testafeni, L.; Tingoli, M.; Tiecco, M.; Chianelli, D.;
12. Molina, P.; Alajarin, M.; Vidal, A. J. Org. Chem. 1992, 57,
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