Novel formation of 2-arylquinolines and 1,3-benzoxazines from 2-(1-alkenyl)acylanilides and active halogens

Article abstract of DOI:10.1246/bcsj.80.1824

2-Arylquinolines 1 were obtained in good yields by reacting iodine or NIS with 2-aminochalcones 2, which were easily synthesized by the Claisen-Schmidt reaction from 2-nitrobenzaldehyde and acetophenones. The reaction of iodine with 2-isopropenylacetanili

Full text of DOI:10.1246/bcsj.80.1824

1824 Bull. Chem. Soc. Jpn. Vol. 80, No. 9, 1824–1827 (2007)
Ó 2007 The Chemical Society of Japan
Novel Formation of 2-Arylquinolines and 1,3-Benzoxazines
from 2-(1-Alkenyl)acylanilides and Active Halogens
ꢀ1
Kentaro Okuma, Takumi Yasuda,1 Kosei Shioji,1 and Yoshinobu Yokomori2
1Department of Chemistry, Faculty of Science, Fukuoka University, Jonan-ku, Fukuoka 814-0180
2National Defense Academy, Hashirimizu, Yokosuka 239-8686
Received March 8, 2007; E-mail: kokuma@fukuoka-u.ac.jp
2-Arylquinolines 1 were obtained in good yields by reacting iodine or NIS with 2-aminochalcones 2, which were
easily synthesized by the Claisen–Schmidt reaction from 2-nitrobenzaldehyde and acetophenones. The reaction of iodine
with 2-isopropenylacetanilide (3a), followed by the addition of aq. NaHCO3, afforded 4-iodomethyl-2,4-dimethyl-4H-
3,1-benzoxazine (6a), of which the structure has previously been reported to be 1-acetyl-2-iodomethyl-2-methyl-1,2-
dihydrobenzazete (4a) or 1-acetyl-3-iodo-3-methylindoline (5a). The reaction mechanism is discussed.
Quinolines 1 are widely occurring natural alkaloids that
display a variety of pharmacological activities, including anes-
thetic, tumoricidal, antihypertensive, and antibacterial.1 The
development of new synthetic methods for quinoline deriva-
tives is in great demand, because of the increased resistance
of malarial parasites to chloroquine, a hitherto used malarial
drug.2 One of the important methods is the photoisomerization
of 2-aminochalcones 2 to afford 2-substituted quinolines.3 If
cis–trans isomerization occurs by halogen activation of 2, 2-
substituted quinolines 1 will form. Recently, iodine- or N-iodo-
succinimide (NIS)-activated intramolecular cyclizations of 2-
(1-alkenyl)acylanilides 3 have been achieved by Kobayashi
et al. and Arisawa et al., but with different results, namely, for-
mation of 1,2-dihydrobenzazetes 4 by Kobayashi et al.4 and
indolines 5 by Arisawa et al.,5 has been observed. These results
prompted us to investigate the correct structures of the prod-
ucts obtained from the reaction of 2-(1-alkenyl)acylanilides 3
with active halogen compounds. Herein, we report the novel
synthesis of 2-arylquinolines 1 and 3,1-benzoxazines 6 from
2-alkenylanilides and 2-aminochalcones.
and 5,5 we applied it to the synthesis of quinolines 1 via intra-
molecular cyclization of 2-aminochalcone 2. The synthesis of
2-aminochalcones 2 was carried out by reacting acetophenones
with 2-nitrobenzaldehyde according to the reported proce-
dure.7 When 2-aminochalcone (2a) was treated with NIS
(equimolar amount) at rt followed by the addition of aq.
NaHCO3, 2-phenylquinoline (1a) was obtained in 80% yield
(Scheme 1).
To improve the yield of 1a, the reaction conditions, in-
cluding solvent, temperature, and reaction time, were varied
(Table 1). Treatment of 2a with iodine (1.2 molar amount)
in the presence of solid NaHCO3 at rt for 1 h resulted in
the formation of the same compound 1a in 85% yield. When
the reaction with NIS (1.2 molar amount) at 0 ꢁC was carried
out, 1a was obtained in 88% yield (Entry 3). In contrast,
quinoline 1a was not obtained when N-chlorosuccinimide
O
1) NIS or I2, rt, 2h
2) base
N
NH2
R
R
Results and Discussion
1a: R=H
2a: R= H
1b: R=Me
1c: R=Cl
1d: R=OMe
2b: R=Me
2c: R=Cl
Synthesis of 2-Arylquinolines. Since the intramolecular
cyclization that uses iodine and 2-alkenylanilide 3 has been
proven to be a good procedure for the synthesis of indoles6
2d: R= OMe
Scheme 1.
Table 1. Reaction of 2-Aminochalcones 2 with Active Halogens
Entry
R
Halogen Mol.
Amt.
Solvent Time/h Temp Product Yield/%
1
2
3
4
5
6
7
8
9
2a
2a
2a
2a
2a
2a
2b
2c
H
H
H
H
H
H
Me
Cl
NIS
I2
NIS
NBS
NCS
I2
I2
I2
I2
1
CH2Cl2
CH2Cl2
CH3CN
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
2
2
2
rt
rt
0 ꢁC
rt
1a
1a
1a
1a
1a
1a
1b
1c
1d
80
85
88
0
1.2
1.2
1.2
2
5
12
12
rt
rt
rt
rt
0
2
0 ꢁC
0 ꢁC
0 ꢁC
0 ꢁC
88
83
82
93
1.2
1.2
1.2
2d OMe
Published on the web September 13, 2007; doi:10.1246/bcsj.80.1824

K. Okuma et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007) 1825
H3C
H3C
O
I
I2
I
I
Ar
I2 or NIS
Ar
N
2
NH
Ac
Ac
4a
O
Kobayashi et al.
NH2
NH2
H3C
I
a
b
3a
I
X
NIS or NBS
I
- H2O
- I+
N
Arisawa et al.
1
Ac
OH
Ar
5a
5b
X = I
N
X = Br
H
c
Scheme 3.
Scheme 2.
X
H3C
H3C
H3C
CH3
NH
CH3
H3C
X
O
O
N
O
CH3
CH3
N
Ph
N
O
CH3
4a: X = I
4d: X = SCH3
6a: X = I
6d: X = SCH3
7
8
Chart 1.
(NCS) or N-bromosuccinimide (NBS) was used (Entries 4
and 5). Thus, the intramolecular cyclization of 2 by using
active iodine was achieved.
The reaction might proceed through iodonium ion inter-
mediate a. Owing to the co-existence of cation a and benzyl
cation b, a conformational change should result in the forma-
tion of intramolecular cyclization adduct c, from which quino-
line 1 is afforded after iodonium ion abstraction and dehydra-
tion (Scheme 2).
spectral data of which were identical with those of 4a, reported
by Kobayashi et al. These results clearly showed the need to
reinvestigate the exact structures of these products. Three
possible structures were examined: dihydrobenzazete 4a, pro-
posed by Kobayashi et al.; indoline 5a or 5b, suggested by
Arisawa et al.; and 4-iodomethyl-2,4-dimethyl-4H-3,1-benz-
oxazine (6a). We first examined 2,3-dihydroindole 5b. The
1H NMR spectrum of 5b showed methylene doublet signals
at 3.50 and 3.67 ppm, and methyl signals at 1.80 and 2.17 ppm.
The methylene carbon signal at 40.2 ppm in the 13C NMR
spectrum of 5b resonated at a higher field than the methylene
signal of 1-benzoyl-3-(1-hydroxy-1-methylethyl)indoline (52.4
ppm).8 Additionally, the amide carbonyl carbon signal at
159.5 ppm resonated at a higher field than normal amide sig-
nals (165–175 ppm), suggesting that the structure of 5 is in-
correct. Then, we analyzed the structure of dihydrobenzazetes
The present method has a number of advantages over photo-
isomerization,3 because workup was very simple. The reaction
mixture could be filtered, followed by evaporation of the
solvent to give almost pure 1 (see experimental section).
Synthesis of 3,1-Benzoxazines. The reaction of 2-isopro-
penylacetanilide (3a) with iodine or NIS has been reported by
Kobayashi et al.4 and Arisawa et al.,5 respectively. The reac-
tion of 3a with iodine gave 1-acetyl-2-iodomethyl-2-methyl-
1,2-dihydrobenzazete (4a),4 whereas the reaction with NIS or
NBS gave 1-acetyl-3-iodo-3-methylindoline (5a) or 1-acetyl-
3-bromo-3-methylindoline (5b), respectively (Scheme 3).5
We were interested in the difference in reactivity between
iodine and NIS (or NBS) toward 2-isopropenylacetanilide 3a.
As the reported spectral data of 4a and 5b were quite similar,
we performed these reactions under conditions similar to those
reported by Kobayashi et al.4 and Arisawa et al.5 Unfortunate-
ly, the spectral data of 5a was not reported by Arisawa et al.
Treatment of 3a with iodine (3 molar amounts) and NaHCO3
in acetonitrile at 0 ꢁC resulted in the formation of pale yellow
crystals, the spectral data of which were identical with those of
4a, reported by Kobayashi et al. The reaction of 3a with NBS
in dichloromethane, followed by the addition of sat. NaHCO3,
gave colorless crystals, the mp and spectral data of which were
identical with those of 5b, reported by Arisawa et al. On the
other hand, the reaction of 3a with NIS, followed by the addi-
tion of sat. NaHCO3, according to the procedure by Arisawa et
al., afforded pale yellow crystals (5a by Arisawa et al.), the
1
4a by comparing the IR and H NMR data of 4a and 6a with
those of N-1-methyl-1-phenylethylacetamide (7)9 and 2-phen-
yl-4,4-dimethyl-4H-3,1-benzoxazine (8) (Chart 1).10
The IR spectra of 4a, 7, and 2-methyl-4,5-dihydrooxazole
showed strong absorptions at 1645 (C=O), 1650 (C=O), and
1665 cmꢂ1 (C=N), which cannot be used to differentiate three
structures. The 1H NMR spectrum of 4a showed methylene
doublet signals at 3.39 and 3.58 ppm, and methyl signals at
1.81 and 2.17 ppm. The 1H NMR spectrum of 8 showed 4-
methyl signal at 1.71 ppm, while that of 7 showed an acetyl
group at 1.95 ppm. These data again showed the difficulty in
determining the exact structure. However, the signal at 159.4
ppm for 4a in the 13C NMR spectrum would be too high for
an acetamide carbonyl carbon (168.8 ppm for 7). In compari-
son, the signal assigned to the iminyl carbon at the 2-position
of 3,1-benzoxazine 8 resonated at ꢀ 156.7, which was compa-
rable to the value for 4a. More definitive information was
given by the chemical shift of the signal due to the quaternary
carbon at the 4-position of 4a, which resonated at ꢀ 77.3, sim-
ilar to that of the corresponding carbon of 2-phenyl-2-propanol

1826 Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007)
Synthesis of Arylquinoline and Benzoxazine
H3C
I
H3C
X
R
H3C
I2 or NBS
rt, 2h
aq. NaHCO3
O
NH
H
Ac
N
I
N
H3C
I
O
I2
R
3a
6a: R = CH3, X = I
6b: R = Ph, X = I
6c: R = CH3, X = Br
N
3a: R = CH3
3b: R = Ph
H3C
Ac
I
4a
H3C
O
C
Scheme 4.
O
N
CH3
Table 2. Reaction of 3 with Active Halogens
H
CH3
N
d
6a
Substrate Halogen equiv Solvent Product Yield/%
Scheme 5.
3a
3a
3b
3b
I2
NIS
I2
1.5
1.1
1.2
1.2
CH3CN
CH2Cl2
CH2Cl2
CH2Cl2
6a
6a
6b
6c
86
91
92
88
In summary, we developed a simple method for the synthe-
sis of 2-phenylquinolines and 4H-3,1-benzoxazines, using
iodine or NIS as double-bond activating reagents, which
resulted in the intramolecular cyclization of 2-alkenylanilides.
Thus, the regioselective and chemoselective syntheses of 3,1-
benzoxazines 6 and quinolines 1 were achieved by the use of
2-alkenylanilides and active halogen compounds.
NBS
Experimental
General. Flash chromatography was carried out using Merck
Kieselgel 60 (230–400 mesh). Thin layer chromatography (TLC)
was performed on commercially available pre-coated aluminum
plates (Merck silica Kieselgel 60F254). All solvents were distilled
before use, and no further treatment was carried out. NMR spectra
were measured on a Varian Innova-400 (400 MHz for 1H, 100
MHz for 13C). The melting points were not corrected.
Materials. 2-Nitrobenzaldehyde, acetophenones, and 2-iso-
propenylaniline were commercially available. Aminochalcones
2a–2d were synthesized by the reported procedure.7 2-Isopropenyl-
anilides 3a and 3b were synthesized by the reported procedure.13
Reaction of 2a with NIS. To a solution of 2a (112 mg, 0.50
mmol) in dichloromethane (5 mL) was added NIS (124 mg, 0.55
mmol) in one portion at rt. After stirring for 2 h, the reaction
mixture was washed with aq NaHCO3 (10%), separated, and dried
over magnesium sulfate, and the solvent was evaporated to give
pale brown crystals of 1a, which was chromatographed over silica
gel by eluting with dichloromethane–hexane (1:1) to afford color-
less crystals of 1a (82 mg, 0.40 mmol). Recrystallization from
dichloromethane–hexane gave pure 1a. mp 83–84 ꢁC: Spectral
data of 1a was identical with the commercially available sample
(mp 84–85 ꢁC).
Reaction of 2-Aminochalcone with Iodine. To a solution of
2a (56 mg, 0.25 mmol) in acetonitrile (3 mL) containing NaHCO3
(21 mg, 0.25 mmol) was added iodine (76 mg, 0.30 mmol) in one
portion. After stirring for 1 h at 0 ꢁC, the reaction mixture was
washed with 10% Na2S2O3 and extracted with dichloromethane
(5 mL ꢃ 3), separated, and dried over magnesium sulfate, and
the solvent was evaporated to give pale brown crystals of 2-phen-
ylquinoline (1a), which was recrystallized from dichloromethane–
hexane to afford pure 1a (43 mg, 0.21 mmol). 2-p-Tolylquinoline
(1b) was obtained in a similar manner by using 2b (95 mg, 0.40
mmol) and iodine (121 mg, 0.48 mmol). 1b (77 mg, 0.35 mmol):
mp 80–81 ꢁC (lit.14 81–82 ꢁC).
Fig. 1. ORTEP drawing of 3,1-benzoxazine 6a. Selected
˚
bond lengths and angles. Bond length: C6–N1 1.421(6) A,
˚
N1–C8 1.265(7) A, C8–O1 1.346(7) A, C7–O1 1.460(7) A,
˚
˚
˚
˚
C5–C6 1.392(7) A, C5–C7 1.523(8) A. Bond Angle:
O1–C7–C5 110.1(4)ꢁ, N1–C8–O1 126.3(5)ꢁ, C8–O1–C7
120.4(4)ꢁ, C5–C6–N1 121.3(5)ꢁ, C6–C5–C7 118.8(5)ꢁ,
C6–N1–C8 118.0(4)ꢁ.
(ꢀ 72.4). Additionally, as the C=N carbon of 2-phenyl-4H-3,1-
benzoxazine resonated at 157.4 ppm,11 we concluded that the
exact structure of this compound should not be 1,2-dihydro-
benzazete 4a but 4H-3,1-benzoxazine 6a. The reaction of
anilide 3a with NBS at rt, followed by the addition of aq.
NaHCO3, also gave colorless crystals of 6c (Scheme 4).
The results are shown in Table 2. Recently, we have report-
ed the reaction of 2-isopropenylacetanilide (3a) with dimethyl-
methylthiosulfonium trifluoromethanesulfonate to afford 1-ace-
tyl-2-methyl-2-methylthiomethyl-1,2-dihydrobenzazete (4d),
which should be corrected to 2,4-dimethyl-4-methylthiometh-
yl-4H-3,1-benzoxazine (6d).12
Since the recrystallization of 6a from hexane–dichlorometh-
ane (5:1) gave single crystals, X-ray crystallographic analysis
of 6a was carried out. Figure 1 shows an ORTEP drawing of
6a. The results clearly show that activated intermediate d is at-
tacked by acyl oxygen at the benzyl position, which is more
cationic than the ꢁ-position, to afford not 1,2-dihydrobenz-
azetes 4a but the less strained six-membered heterocycle,
4H-3,1-benzoxazine 6a (Scheme 5).
2-p-Chlorophenylquinoline (1c) was obtained in a similar
manner by using 2c (77 mg, 0.30 mmol) and iodine (91 mg, 0.36

K. Okuma et al.
Bull. Chem. Soc. Jpn. Vol. 80, No. 9 (2007) 1827
mmol). 1c (62 mg, 0.26 mmol): mp 110–111 ꢁC (lit.15 mp 112–
114 ꢁC).
2-p-Methoxyphenylquinoline (1d) was obtained in a similar
manner by using 2d (76 mg, 0.30 mmol) and iodine (91 mg, 0.36
mmol). 1d (64 mg, 0.27 mmol): mp 120–121 ꢁC (lit.14 mp 120–
122 ꢁC).
(CDCl3) ꢀ 21.62 (CH3), 25.35 (CH3), 40.23 (CH2), 77.95 (q-C),
123.12 (Ar), 124.59 (Ar), 126.42 (Ar), 126.78 (Ar), 129.72 (Ar),
138.67 (Ar), 159.80 (N=C).
X-ray crystallographic data for 6a: Crystal data for C11H12-
INO. Colorles plate. Crystallized from hexane–dichloromethane
˚
(5:1). Mo Kꢂ radiation. Mr ¼ 301:11, a ¼ 9:7558(8) A, b ¼
3
˚
˚
˚
Reaction of 2-Isopropenylacetanilide (3a) with Iodine. To a
solution of 3a (88 mg, 0.50 mmol) in acetonitrile (5 mL) contain-
ing NaHCO3 (126 mg, 1.5 mmol) was added iodine (381 mg,
1.50 mmol) in one portion. After stirring for 1 h at 0 ꢁC, the reac-
tion mixture was washed with aq. 10% Na2S2O3 and aq. 10%
NaHCO3 and extracted with dichloromethane (5 mL ꢃ 3), sepa-
rated, and dried over magnesium sulfate, and the solvent was
evaporated to give colorless crystals of 4-iodomethyl-2,4-dimeth-
yl-4H-3,1-benzoxazine (6a), which was chromatographed over
silica gel by eluting with dichloromethane to afford pure 6a
(129 mg, 0.43 mmol). Colorless plates; mp 67–69 ꢁC (dichloro-
methane–hexane 5:1) (lit.4 mp 70–72 ꢁC as 4a); IR (neat) 3004,
2945, 1638 (C=N), 1598, 1579, 1480, 1448, 1422, 1373, 1293,
11:6392(10) A, c ¼ 10:6851(8) A, V ¼ 1164:03(16) A , T ¼ 296
K, monoclinic, space group: P21=n, S ¼ 1:01, Z ¼ 4. 4225 in-
dependent reflections, R ¼ 0:0352 for 2241 reflections (I <
2ꢃðIÞ), wR ¼ 0:1073, S ¼ 1:01, Rint ¼ 0:0221. Crystallographic
data have been deposited with Cambridge Crystallographic
Data Centre: Deposition number CCDC-643239 for 6a. Copies
of the data can be obtained free of charge via http://www.ccdc.
cam.ac.uk/conts/reterieving.html (or from the Cambridge Crystal-
lographic Data Centre, 12, Union Road, Cambridge, CB2 1EZ,
UK; Fax +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
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1264, 1196, 1150, 1029, 978, 883, 767 cmꢂ1
;
1H NMR (CDCl3)
1
a) F. S. Yates, in Comprehensive Heterocyclic Chemistry,
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11:2 Hz, CH2), 3.58 (d, 1H, J ¼ 11:2 Hz, CH2), 7.08 (d, 1H, J ¼
8:0 Hz, Ar), 7.09–7.20 (m, 2H, Ar), 7.29 (dd, 1H, J ¼ 1:6 Hz and
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6
Reaction of 3a with NBS. To a solution of 3a (88 mg, 0.50
mmol) in dichloromethane (5 mL) was added NBS (97 mg, 0.55
mmol) in dichloromethane (5 mL) in one portion. After stirring
for 2 h at rt, the reaction mixture was washed with 10% NaHCO3
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methane–hexane to afford pure 6c (111 mg, 0.44 mmol). Colorless
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86–87 ꢁC as 5b); IR (neat) 3009, 2954, 1638 (C=N), 1598,
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7
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;
3H, CH3), 2.17 (s, 3H, CH3), 3.49 (d, 1H, J ¼ 11:2 Hz, CH2), 3.67
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