Oxidant effect of H2O2 for the syntheses of quinoline derivatives via one-pot reaction of aniline and aldehyde

Article abstract of DOI:10.1080/00397911.2011.563022

(Chemical Equation Presented) A convenient one-pot method for the synthesis of substituted quinolines via the reaction of aniline and aldehyde in the presence of a Lewis acid (AlCl₃) and an oxidant (H₂O ₂) has been developed. Hydrogen peroxide was found to promote the reaction by its function as a hydrogen hunter, hindering the formation of by-product N-alkylaniline. The effect of the oxidant on the yield and selectivity was studied. When the molar ratio of aniline, n-butyraldehyde, and H₂O₂ was 1:3:0.5 at 25°C, the yield of 3-ethyl-2-propylquinoline was improved from 64% (reaction without H ₂O₂) to 84% (with H₂O₂), and the quinoline selectivity was improved to almost 100%. Moreover, the reaction time was obviously reduced. The substituent effect was also investigated in this work. Copyright Taylor & Francis Group, LLC.

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Oxidant Effect of H2O2 for the Syntheses
of Quinoline Derivatives via One-Pot
Reaction of Aniline and Aldehyde
Qiaoxia Guo a , Wennian Wang a , Weiling Teng a , Liwei Chen a
Yanqing Wang a & Baojian Shen a
,
a State Key Laboratory of Heavy Oil Processing, College of Science,
China University of Petroleum, Beijing, China
Accepted author version posted online: 02 Jan 2012.Published
online: 29 May 2012.
To cite this article: Qiaoxia Guo , Wennian Wang , Weiling Teng , Liwei Chen , Yanqing Wang &
Baojian Shen (2012): Oxidant Effect of H2O2 for the Syntheses of Quinoline Derivatives via One-Pot
Reaction of Aniline and Aldehyde, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 42:17, 2574-2584
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Synthetic Communications1, 42: 2574–2584, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.563022
OXIDANT EFFECT OF H2O2 FOR THE SYNTHESES OF
QUINOLINE DERIVATIVES VIA ONE-POT REACTION OF
ANILINE AND ALDEHYDE
Qiaoxia Guo, Wennian Wang, Weiling Teng, Liwei Chen,
Yanqing Wang, and Baojian Shen
State Key Laboratory of Heavy Oil Processing, College of Science, China
University of Petroleum, Beijing, China
GRAPHICAL ABSTRACT
Abstract A convenient one-pot method for the synthesis of substituted quinolines via the
reaction of aniline and aldehyde in the presence of a Lewis acid (AlCl3) and an oxidant
(H2O2) has been developed. Hydrogen peroxide was found to promote the reaction by
its function as a hydrogen hunter, hindering the formation of by-product N-alkylaniline.
The effect of the oxidant on the yield and selectivity was studied. When the molar ratio
of aniline, n-butyraldehyde, and H2O2 was 1:3:0.5 at 25 ꢀC, the yield of 3-ethyl-2-propyl-
quinoline was improved from 64% (reaction without H2O2) to 84% (with H2O2), and
the quinoline selectivity was improved to almost 100%. Moreover, the reaction time was
obviously reduced. The substituent effect was also investigated in this work.
Keywords Aldehyde; aniline; hydrogen peroxide; oxidation; quinoline derivatives
INTRODUCTION
Quinolines and their derivatives are very important chemicals in the medical
industry and have been explored for more than one hundred years. The quinoline
ring system exists in various natural products, especially in alkaloids. Recently, qui-
nolines have been applied as antioxidants in rubber synthesis and in some biological
systems.[1] Furthermore, they play important roles in metal ion detection in the
Received August 18, 2010.
Address correspondence to Qiaoxia Guo, State Key Laboratory of Heavy Oil Processing, College
of Science, China University of Petroleum, Beijing 102249, China. E-mail: qxguo@cup.edu.cn
2574

OXIDANT EFFECT OF H2O2
2575
environment and lots of fine chemicals.[2] The synthesis of quinoline derivatives has
always been one of the hot areas of organic chemistry research.
To date, various methods of quinoline synthesis have been explored, inclu-
ding Doebner–Miller,[3] Skraup,[4] and Friedla¨nder[5] syntheses and some
modifications.[6–9] These methods show great power to synthesize versatile quino-
lines. However, most of them suffer from harsh reaction conditions or multiple steps.
Moreover, the products are always in poor yield and low selectivity because the
by-product (N-alkylaniline) competes with quinolines, which leads to laborious
product isolation and material waste.
Previous mechanism studies[9a,10] suggest the possibility of quinoline formation
via a tetrahydroquinoline intermediate. After dehydration and dehydrogenation,[10b]
the intermediate can be oxidized to quinoline and secondary amines. Nakajima
et al. reported that the yield of substituted quinolines was promoted by using
[IrCl2H(cod)]2 as a catalyst under an O2 atmosphere.[9a] Leardini et al. reported that
FeCl3 could catalyze the transformation from imines to quinoline in good yield.[9c]
Shindoh et al. described the formation of quinolines from imines with the assistance
of an expensive oxidant, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.[11] Tanaka et al.
found that aerobic conditions prevent the reduction of imines effectively.[12] In the
classical Skraup method, nitrobenzene was used as an oxidizing agent.[4a,10b,13]
It is known that hydrogen peroxide (H2O2) is used as an oxidant in the
epoxidation of olefin and selective oxidations of aldehyde, ketone, and alkane.[14]
Most important, it is an environmentally friendly reagent.[15] However, to the best
of our knowledge, no literature was found on the syntheses of quinolines using
hydrogen peroxide as an oxidant.
Therefore, in the course of our study on the oxidative reagent effect on the for-
mation of quinoline derivatives, the widely available hydrogen peroxide was selected
to introduce as an oxidant into the reaction mixture to trap hydrogens from dihydro-
quinoline in order to prevent the reduction of imines. We expected to enhance quino-
line yield and selectivity under mild conditions instead of the previous harsh
conditions. AlCl3 was selected as catalyst, which is usually used as a traditional
Lewis acid to mediate or catalyze organic transformations.[16] Our target is to
improve quinoline yield and selectivity.
EXPERIMENTAL
Unless noted otherwise, all starting materials were obtained from commercial
supplies and used without further purification. All reactions were performed under
anhydrous conditions and a dry nitrogen atmosphere. The crude products were pur-
ified by column chromatography over silica gel (300–400 mesh) using Et2O=hexane=
petroleum ether (1:10:20) as eluent. The yield was analyzed on a Shimadzu gas
chromatograph (GC-14B, Shimadzu) equipped with a fused silica capillary column
(CBP1-M25-025, Shimadzu) and a chromatopacy integrator (C-R8A, Shimadzu).
The detection temperature was set from 60 ꢀC to 270 ꢀC through temperature
programming. Dodecane was used as an internal standard. Proton (300 MHz) and
carbon (75 MHz) NMR spectroscopy were performed in CDCl3 with tetramethylsi-
lane (TMS) as an internal standard at 25 ꢀC on a JNM-LA300 FT-NMR (Jeol Ltd.)
spectrometer.

2576
Q. GUO ET AL.
Representative Experimental Procedure
CH2Cl2 (20 mL) was added to a dried Schlenk tube with Teflon-coated mag-
netic stir bar under an N2 atmosphere. While stirring, aluminium trichloride (AlCl3,
0.1333 g, 1 mmol), aniline (0.09 mL, 1 mmol), n-butyraldehyde (0.26 mL, 3 mmol),
and H2O2 (0.10 mL, 30% in H2O, 1 mmol) were added sequentially to the solution
at room temperature. Dodecane was added as an internal standard. The resulting
mixture was stirred at room temperature and monitored by gas chromatographic
(GC) analysis until the reaction finished. Then it was quenched with 3 M ammonia
solution (in H2O), and the mixture was extracted with Et2O (30 mL ꢁ 3). The com-
bined organic layers were washed with H2O, NaHCO3 (20%, aq.), H2O, and brine in
sequential order, dried over anhydrous Na2SO4, filtered, and concentrated in vacuo.
The residue was purified by silica-gel chromatography using (Et2O–hexane–
petroleum ether ¼ 1:10:30) as eluent to give pure product 3-ethyl-2-propylquinoline.
The products were characterized by gas chromatography (GC), GC–mass spec-
trometry (MS), and NMR.
3-Ethyl-2-propylquinoline (3a)
1H NMR (CDCl3, Me4Si): d 1.07(t, J ¼ 7.5 Hz, 3H), 1.33(t, J ¼ 7.5Hz, 3H),
1.77–1.87 (m, 2H), 2.83 (q, J ¼ 7.4 Hz, 2H), 2.96 (t, J ¼ 7.8 Hz, 2H), 7.43 (t, J ¼
7.4 Hz, 1H), 7.60 (t, J ¼ 7.7 Hz, 1H), 7.71 (d, J ¼ 8.1 Hz, 1H), 7.85 (s, 1H), 8.02 (d,
J ¼ 8.4 Hz, 1H). 13C NMR (CDCl3, Me4Si): d 14.3, 14.4, 22.8, 25.1, 37.7, 125.5,
126.9, 127.3, 128.3, 128.4, 133.9, 135.3, 146.3, 162.0.
N-Butylaniline (4a)
1H NMR (CDCl3, Me4Si): d 0.95 (t, J ¼ 7.4 Hz, 3H), 1.36–1.48 (m, 2H), 1.55–
1.64 (m, 2H), 3.10 (t, J ¼ 7.1 Hz, 2H), 3.32 (s, 1H), 6.58–6.70 (m, 3H), 7.13–7.23 (m,
2H). 13C NMR (CDCl3, Me4Si): d 13.8, 20.2, 31.7, 43.6, 112.7, 117.1, 129.2, 148.5.
3-Ethyl-6-methyl-2-propylquinoline (3b)
1H NMR (CDCl3, Me4Si): d 1.07( t, J ¼ 7.4 Hz, 3H), 1.33 ( t, J ¼ 7.6 Hz, 3H),
1.78–1.85 (m, 2H), 2.50 (s, 3H), 2.82 (q, J ¼ 7.6 Hz, 2H), 2.94 (t, J ¼ 7.9 Hz, 2H),
7.44 (d, J ¼ 8.3 Hz, 1H), 7.48 (s, 1H), 7.76 (s, 1H), 7.90 (d, J ¼ 8.2 Hz, 1H). 13C
NMR (CDCl3, Me4Si): d 14.5, 14.6, 21.6, 23.0, 25.3, 37.8, 125.9, 127.3, 128.2,
130.6, 133.4, 135.3, 135.4, 145.1, 161.1.
6-Chloro-3-ethyl-2-propylquinoline (3c)
1H NMR (CDCl3, Me4Si): d 1.06 (t, J ¼ 7.4 Hz, 3H), 1.33 (t, J ¼ 7.6 Hz, 3H),
1.80–1.86 (m, 2H), 2.82 (q, J ¼ 7.5 Hz, 2H), 2.94 (t, J ¼ 7.8 Hz, 2H), 7.54 (d,
J ¼ 8.8 Hz, 1H), 7.70 (s, 1H), 7.76 (s, 1H), 7.93 (d, J ¼ 8.8 Hz, 1H). 13C NMR
(CDCl3, Me4Si): d 14.3, 14.4, 22.8, 25.2, 37.8, 125.7 128.0, 129.2, 130.2, 131.2,
132.9, 136.5, 144.8, 162.4.

OXIDANT EFFECT OF H2O2
2577
6-Bromo-3-ethyl-2-propylquinoline (3d)
1H NMR (CDCl3, Me4Si): d 1.06 (t, J ¼ 7.4 Hz, 3H), 1.33 (t, J ¼ 7.4 Hz, 3H),
1.80–1.86 (m, 2H), 2.82 (q, J ¼ 7.5 Hz, 2H), 2.92 (t, J ¼ 7.8 Hz, 2H), 7.64–7.67 (m,
1H), 7.74 (s, 1H), 7.85–7.87 (m, 2H). 13C NMR (CDCl3, Me4Si): d 14.3, 14.4,
22.7, 25.2, 37.8, 119.3, 128.6, 129.0, 130.4, 131.7, 132.8, 136.5, 145.0, 162.6.
3-Ethyl-6-methoxy-2-propylquinoline (3e)
1H NMR(CDCl3, Me4Si): d 1.06 (t, J ¼ 7.2 Hz, 3H), 1.33 (t, J ¼ 7.4 Hz, 3H),
1.79–1.84 (m, 2H), 2.81 (q, J ¼ 7.5 Hz, 2H), 2.91 (t, J ¼ 8.0 Hz, 2H), 3.91 (s, 3H),
7.01 (s, 1H), 7.25–7.28 (m, 1H), 7.76 (s, 1H), 7.90 (d, J ¼ 9.2 Hz, 1H). 13C NMR
(CDCl3, Me4Si): d14.4, 14.6, 23.0, 25.3, 37.7, 55.5, 104.7, 120.8, 128.2, 130.0,
133.0, 135.7, 142.6, 157.2, 159.5.
2-Heptyl-3-hexylquinoline (3g)
1H NMR (CDCl3, Me4Si): d 0.89–0.91 (m, 6H), 1.30–1.50 (m, 14H),
1.65–1.70(m, 2H), 1.76–1.82 (m, 2H), 2.77 (t, J ¼ 7.9 Hz, 2H), 2.97 (t, J ¼ 8.3 Hz,
2H), 7.42 (t, J ¼ 7.2 Hz, 1H), 7.59 (t, J ¼ 8.1 Hz, 1H), 7.69 (d, J ¼ 8.3 Hz, 1H), 7.82
(s, 1H), 8.02 (d, J ¼ 8.3 Hz, 1H). 13C NMR (CDCl3, Me4Si): d 14.2, 22.7, 22.8,
29.3, 29.4, 29.9, 30.0, 30.6, 31.8, 31.9, 32.5, 36.0, 125.6, 126.9, 127.3, 128.3, 128.6,
134.2, 134.9, 146.6, 162.4.
N-Benzylideneaniline (i)
1H NMR (CDCl3, Me4Si): d 7.18–7.20 (m, 3H), 7.34–7.35 (m, 2H), 7.41–7.42
(m, 3H), 7.86–7.87 (m, 2H), 8.39 (s, 1H). 13C NMR (CDCl3, Me4Si): d 121.1,
126.1, 128.9, 129.0, 129.3, 131.5, 136.4, 152.3, 160.5.
3-Ethyl-6-nitryl -2-propylquinoline (3f)
1H NMR (CDCl3, Me4Si): d 1.09 (t, J ¼ 7.4 Hz, 3H), 1.38 (t, J ¼ 7.5 Hz, 3H),
1.82–1.94 (m, 2H), 2.89 (q, J ¼ 7.6 Hz, 2H), 3.00 (t, J ¼ 7.9 Hz, 2H), 8.02 (s, 1H),
8.11 (d, J ¼ 9.3 Hz, 1H), 8.37 (d, J ¼ 12.4 Hz, 1H), 8.71 (s, 1H). 13C NMR (CDCl3,
Me4Si): d 13.8, 14.1, 22.1, 24.9, 37.3, 121.8, 123.8, 126.0, 130.1, 135.0, 137.7,
144.9, 148.5, 166.4.
RESULTS AND DISCUSSION
The reaction scheme, and the results are shown in Scheme 1. First, the reaction
of aniline 1a and n-butyraldehyde 2a was run with AlCl3 in CH2Cl2 at 25 ꢀC for 6 h
without H2O2. The desired product, 3-ethyl-2-propylquinoline, was obtained in 64%
GC yield (isolated yield was 48%) with 10% of the by-product, 4a (N-butylaniline).
In contrast, when H2O2 (0.10 mL, 30% in H2O, 1 mmol) was added into the reaction
mixture, the reaction gave 3-ethyl-2-propylquinoline in 82% GC yield and 70% iso-
lated yield without the detectable formation of 4a (N-butylaniline) (Scheme 1).

2578
Q. GUO ET AL.
Scheme 1. Model reaction of aniline and n-butyraldehyde. (Figure is provided in color online.)
The effect of the H2O2 amount is shown in Table 1. The yield of 3-ethyl-2-
propylquinoline was sharply increased from 64% to 84% with the addition of 0.5
equiv H2O2. The yield was 82% with the addition of 1 equiv. and 1.5 equiv. of
H2O2. These results indicate that the oxidative effect is notable and that 0.5 equiv.
H2O2 is sufficient for the reaction.
Table 2 presents the effect of reaction temperature. The reactions occurred
rapidly at different temperatures with high oxidant efficiency. The yield of 3-ethyl-2-
propylquinoline 3a was increased by at least 14% under different temperatures, and a
temperature of 25 ꢀC was the most effective. At 0 ꢀC or 15 ꢀC, the product yield was
increased because of the presence of H2O2, but not as high as at 25 ꢀC. High
temperature (35 ꢀC) did not improve the quinoline yield noticeably. This may be
attributed to the decomposition of H2O2 at higher temperatures. Thus, a tempera-
ture of 25 ꢀC was finally selected. The reaction time was also reduced when H2O2
was used as an oxidant. Moreover, to our surprise, the yield of the by-product
(N-butylaniline) was greatly decreased.
The influence of the amounts of AlCl3 on quinoline yield is summarized in
Table 3. It didnot show big difference in quinoline yield when 0.2 equiv. of AlCl3
was used instead of 1 equiv. Treatment of 1 equiv. aniline and 3 equiv. aldehyde with
0.1 equiv of AlCl3 afforded quinoline in 72% GC yield and N-butylaniline in 27%
GC yield, which indicated that AlCl3 should be catalytic to the overall transform-
ation. In contrast, when 1 equiv. of FeCl3 was used instead of AlCl3, quinoline
was obtained only in 8% GC yield under the same conditions, and when 1 equiv.
ZnCl2 was used, almost no quinoline was formed. This difference, compared to
Table 1. Influence of different amounts of H2O2 on quinoline yielda
b
Entry
Equivalent of H2O2
Yield (%)
1
2
3
4
0.25
0.5
1.0
1.5
47c
84
82
82
aThe ratio of aniline–butyraldehyde–AlCl3 was 1:3:1 in CH2Cl2 at 25 ꢀC.
bThe equiv of H2O2 was based on aniline.
cThe yield of the by-product (N-butylaniline) was 7%.

OXIDANT EFFECT OF H2O2
2579
Table 2. Yield of quinoline 3a at different temperaturesa
H2O2 absentb
H2O2 presentb
Temperature
(ꢀC)
Complete reaction
time (h)
Complete reaction
time (h)
Entry
3a
4a
3a
4a
1
2
3
4
0
15
25
35
17
40
11
20
10
15
6
6
3
3
65
68
84
83
Trace
Trace
Trace
Trace
1
3
1
1
64 (48)
69
aThe ratio of aniline–butyraldehyde–AlCl3–H2O2 was 1:3:1:0.5 in CH2Cl2.
bGC yields; isolated yields are in parentheses.
the literature results,[3c,5d] may be ascribed to the poor solubility of FeCl3 and ZnCl2
in dichloromethane.
The scope of substrates was explored under optimized reaction conditions.
The substrates include p-tolylamine 1b, p-chloroaniline 1c, p-bromaniline 1d,
p-methoxyaniline 1e, p-nitroaniline 1f, caprylic aldehyde 2b, and benzaldehyde 2c.
For 1a–1e, 2a, and 2b (Table 4, entries 1–9), H2O2 showed a positive effect on yield
and selectivity, and the quinoline yields were obviously increased with the use of
H2O2. However, for 1c and 1d, although the quinoline yields were increased with
0.5 equiv H2O2, a small amount of N-butylaniline still occurred (Table 4, entries 3
and 5). Further, 1 equiv H2O2 was used in the cases of 1c and 1d, resulting in a slight
increase in quinoline yields and undetectable amount of the by-product (N-
butylaniline). It indicated that H2O2 plays an important role in preventing the
reduction of imine. Murahashi et al. reported the tungstate-catalyzed oxidation of
tetrahydroquinolines with H2O2 to synthesize cyclic hydroxamic acid, affording
small amounts of quinolines as by-product, which shows the capability of H2O2 to
dehydrogenize tetrahydroquinoline to quinoline.[17] The reaction was also carried
out under air ambience, and parallelling the condition of H2O2, the yield of 3-
ethyl-2-propylquinoline was increased from 64% to 70% (Table 4, entry 13), indicat-
ing that the oxidation could take place in the presence of air even if it is not good as
H2O2. This result was consistent with data in the literature.[12]
In contrast, H2O2 showed negative influence on the quinoline yield of 1f. In
fact, a greater yield of 1f was obtained when H2O2 was absence (Table 4, entries
11 and 12). This result may be due to the presence of the nitro group (NO2) of
1f.[4a,10b,13] Furthermore, the a-carbon hydrogen of the aldehyde is necessary for
Table 3. Influence of different amounts of AlCl3 on quinoline yielda
Entry
Amount of AlCl3 (eq)
Conditions
Quinoline yield (%)b
N-Butylaniline yield (%)b
1
2
3
1
25 ꢀC, 3 h
25 ꢀC, 1 h
25 ꢀC, 7 h
64 (48)
65
72
10
35
27
0.2
0.1
aThe ratio of aniline–butyraldehyde was 1:3 in CH2Cl2.
bGC yields; isolated yields are in parentheses.

2580
Q. GUO ET AL.
a
Table 4. Reaction of anilines, aldehyde, and H2O2
Yield (%)b
H2O2 H2O2
absent present
Amount of
H2O2
Entry
1
Aniline
Aldehyde
Product
n-C3H7CHO
2a
0.5
64 (48) 84
2
3
n-C3H7CHO
n-C3H7CHO
0.5
0.5
37
85
65 (53)
90
4
5
6
7
8
n-C3H7CHO
n-C3H7CHO
n-C3H7CHO
n-C3H7CHO
n-C3H7CHO
1.0
0.5
1.0
0.5
1.0
87 (85) 93 (90)
53 (50) 64
53 (50) 67 (60)
30
29
36
63 (56)
(Continued )

OXIDANT EFFECT OF H2O2
2581
Table 4. Continued
Yield (%)b
Amount of
H2O2
H2O2 H2O2
absent present
Entry
Aniline
Aldehyde
Product
n-C7H15CHO
2b
9
0.5
53
73 (68)
87 (80)
10c
0.5
0.5
100
11
n-C3H7CHO
70
29
55 (33)
12
13
n-C3H7CHO
2.0
12
n-C3H7CHO
2a
0
(in air)
64 (48) 70d
aAniline (1 mmol), aldehyde (3 mmol), and AlCl3(1 mmol) in CH2Cl2, at 25 ꢀC.
bGC yield; isolated yields are in parentheses.
cThe product was isolated by recrystallization by using methanol as solvent.
dAccompanied by 17% of N-butylaniline.
the formation of the quinoline product. For example, when benzaldehyde was
employed, only N-benzylideneaniline (Table 4, entry 10) was formed in a good yield.
Based on the results, a reaction mechanism is proposed here (Scheme 2). First,
the nucleophilic addition reaction of aniline with aldehyde occurs to give imine 5
after a H2O release. Then, the addition of another molecule of aldehyde (enol tauto-
mer of aldehyde) to imine produces a new aldehyde 6, which undergoes cyclization to
form tetrahydroquinoline 7. The resulting tetrahydroquinoline undergoes a dehy-
dration process to yield dihydroquinoline 8, followed by the dehydrogenation (oxi-
dizing) of 8, in which two hydrogen atoms were removed, afford quinoline 3. Thus, a
hydrogen hunter must be beneficial for the quinoline formation. If there is
no additional oxidant in the reaction system, imine 5 can be easily reduced by

2582
Q. GUO ET AL.
Scheme 2. Proposed mechanism for synthesis of quinolines promoted by H2O2. (Figure is provided in
color online.)
dihydroquinoline to form N-alkylaniline 4 (Scheme 2), and quinoline yield is
decreased consequently. When H2O2 was added in the reaction, it trapped the hydro-
gen from dihydroquinoline, which prevented the reduction of imine and oxidized
dihydroquinoline to quinoline. As a result, the imine was not reduced by dihydroqui-
noline, and the quinoline yield increased distinctly without N-butylaniline formation.
Jacob and Jones [18] the selective conversion of diallylanilines and arylimines to qui-
nolines. In their work, in order to eliminate the reduction product, the reaction was
performed in the presence of a 10-fold excess of tert-butylethylene to trap hydrogen
produced during the reaction.
In summary, a convenient one-pot H2O2-promoted procedure was developed
for the synthesis of 2,3-dialkylquinoline derivatives; the reaction was finished under
mild conditions and without by-product formation. The good yield and selectivity of
the target products make this reaction attractive, with potential for large-scale appli-
cations. Further exploration of other oxidants for quinoline synthesis is now under
investigation in our laboratory.
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OXIDANT EFFECT OF H2O2
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