Synthesis of 1-aryl-1H-indole derivatives by iodine-mediated cyclization of 2-(arylamino)styrene derivatives

Article abstract of DOI:10.1246/bcsj.79.1580

A convenient synthetic method for 1-aryl-1H-indole derivatives has been developed. 2-(Arylamino)-α-methylstyrene derivatives were treated with iodine in the presence of sodium hydrogencarbonate to give 1-aryl-3-methyl-1H- indole derivatives in fair to goo

Full text of DOI:10.1246/bcsj.79.1580

1580 Bull. Chem. Soc. Jpn. Vol. 79, No. 10, 1580–1584 (2006)
Ó 2006 The Chemical Society of Japan
Synthesis of 1-Aryl-1H-indole Derivatives by Iodine-Mediated
Cyclization of 2-(Arylamino)styrene Derivatives
ꢀ
Osamu Morikawa, and Hisatoshi Konishi
Kazuhiro Kobayashi, Kazuna Miyamoto, Tohru Yamase, Daizo Nakamura,
Department of Materials Science, Faculty of Engineering, Tottori University,
4-101 Koyama-minami, Tottori 680-8552
Received April 12, 2006; E-mail: kkoba@chem.tottori-u.ac.jp
A convenient synthetic method for 1-aryl-1H-indole derivatives has been developed. 2-(Arylamino)-ꢀ-methylsty-
rene derivatives were treated with iodine in the presence of sodium hydrogencarbonate to give 1-aryl-3-methyl-1H-
indole derivatives in fair to good yields. 3-Ethyl-2-methyl-1-phenyl-1H-indole and 3,30-dimethyl-1,10-(p-phenylene)-
diindole were also prepared from the respective 2-(phenylamino)styrene derivatives under the same conditions in
reasonable yields.
R3
R3
The intramolecular haloamination reaction has been one of
the most useful methodologies for the construction of nitrogen
R1
R1
I2, NaHCO3
heterocycles.1 Nishida and his colleagues described that 2-
MeCN, 0 °C
R2
N
R2
NHAr
acetylamino-ꢀ-methylstyrene derivatives react with N-bromo-
(or iodo)succinimide to give 3-halo-3-methyl-2,3-dihydro-1H-
indole derivatives.1a On the other hand, we previously showed
that 2-(acylamino)styrene derivatives react with iodine in the
presence of sodium hydrogencarbonate to give 1-acyl-2-(iodo-
methyl)benzazetine (7-acyl-8-iodomethylbicyclo[4.2.0]-7-aza-
octa-1,3,5-triene) derivatives.1f Accordingly, we became inter-
ested in investigating reactions of 2-(arylamino)styrene deriv-
atives under similar conditions, and found that the reactions
gave 1-aryl-1H-indole derivatives. Undoubtedly, 1H-indoles
are one of the most important families of heterocyclic com-
pounds, and so, numerous methods for their preparation have
been reported.2 However, only a few methods have been
reported for the synthesis of 1-aryl derivatives involving con-
struction of the pyrrole moiety.3 Most of the syntheses of 1-
aryl-1H-indoles have been based on the metal-mediated N-
arylation of 1H-indoles with halobenzenes.4 Herein, we wish
to report a new synthesis of 1-aryl-1H-indole derivatives.
Ar
1a R1 = R2 = H, R3 = Me, Ar = Ph
1b R1 = R2 = H, R3 = Me, Ar = p-Tol
1c R1 = R2 = H, R3 = Me, Ar = p-MeOC6H4
1d R1 = R2 = H, R3 = Me, Ar = p-ClC6H4
1e R1 = R2 = OMe, R3 = Me, Ar = Ph
1f R1 = Cl, R2 = H, R3 = Me, Ar = Ph
1g R1 = H, R2 = Cl, R3 = Me, Ar = Ph
1h R1 = R2 = H, R3 = Ar = Ph
2
Scheme 1.
Table 1. Preparation of 1-Aryl-1H-indoles 2, 4, and 6
Reaction
time
Product
(Yield/%)a)
Entry
2-(Arylamino)styrene
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
1g
1h
3
1 h
2 h
1 h
15 min
10 min
30 min
10 min
1 h
2a (84)
2b (81)
2c (76)
2d (90)
2e (69)
2f (74)
2g (77)
2h (0)b)
Results and Discussion
The conversion of 2-(arylamino)-ꢀ-methylstyrene deriva-
tives 1, readily prepared from 1-[2-(arylamino)phenyl]etha-
nones or 2-(arylamino)benzoates by treatment with methyl-
magnesium bromide followed by dehydration, into 1-aryl-3-
methyl-1H-indoles 2 was conducted as illustrated in Scheme 1.
The endo-cyclization of derivatives 1 proceeded smoothly on
treatment with three molar amounts of iodine and sodium
hydrogencarbonate in acetonitrile at 0 ꢁC to yield, after usual
workup followed by purification by preparative TLC on silica
gel, the corresponding desired indoles 2 in fair to good yields,
as summarized in Table 1 (Entries 1–7). However, it should be
noted that the treatment of ꢀ-phenyl-2-(phenylamino)styrene
(1h) with iodine under the same reaction conditions resulted
in the formation of an intractable mixture of products, from
9
10
3 h
2 h
4
6
(43)
(40)
5
a) Isolated yields. b) An intractable mixture was obtained.
which no more than a trace amount of the desired 1,3-diphen-
yl-1H-indole was isolated (Entry 8). However, we have no
explanation for this.
We next examined the iodine-mediated reaction of 2-(1-eth-
ylpropen-1-yl)-N-phenylbenzenamine (3). When compound 3
was treated with iodine under the same conditions as described
for the preparation of derivative 2, a similar cyclization pro-
Published on the web October 10, 2006; doi:10.1246/bcsj.79.1580

K. Kobayashi et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 10 (2006) 1581
ucts, probably due to oxidation by the iodine.
Et
Et
In conclusion, a convenient route for the preparation of 1-
aryl-1H-indole derivatives using iodine-mediated endo-cycli-
zation reactions of ꢀ-substituted 2-(arylamino)styrene deriva-
tives under very mild conditions has been developed. The pres-
ent method is valuable for organic synthesis because it is a rel-
atively simple procedure and the starting materials are readily
available. Work to prepare related heterocycles, such as benzo-
furans and benzo[b]thiophenes, are currently underway in our
laboratory.
Me
I2, NaHCO3
Me
MeCN, 0 °C
N
NHPh
Ph
3
4
Scheme 2.
Me
NH
Me
N
N
Experimental
I2, NaHCO3
General. The melting points were determined on a Laboratory
Devices MEL-TEMP II melting-point apparatus and are uncor-
rected. The IR spectra were recorded on a Shimadzu FTIR-8300
spectrometer. The 1H NMR spectra were determined using SiMe4
as an internal reference in CDCl3 with a JEOL JNM-GX270 FT
NMR spectrometer operating at 270 MHz, or a JEOL ECP500
FT NMR spectrometer operating at 500 MHz. Low-resolution
mass spectra were recorded on a JEOL AUTOMASS 20 spec-
trometer (Center for Joint Research and Development, this Uni-
versity). Thin-layer chromatography (TLC) was carried out on
Merck Kieselgel 60 PF254. All of the solvents used were dried
over appropriate drying agents and distilled under argon prior
to use.
Starting Materials. 2-[2-(Phenylamino)phenyl]propan-2-ol,5
1-[2-(4-methylphenylamino)phenyl]ethanone,6 1-[2-(4-methoxy-
phenylamino)phenyl]ethanone,6 methyl 2-(phenylamino)benzoate,6
ethyl 2-amino-5-chlorobenzoate,7 ethyl 2-amino-4-chloroben-
zoate,8 1-[2-(phenylamino)phenyl]ethanone,6 and 2-(2-{4-[2-(1-
hydroxy-1-methylethyl)phenylamino]phenylamino}phenyl)propan-
2-ol6 were prepared by the reported methods. All other chemicals
used in this study were commercially available.
MeCN, 0 °C
NH
Me
Me
5
6
Scheme 3.
Me
Me
I+
I
R1
R2
R1
R2
I2
HI
2
1
N
NHAr
Ar
7
8
Scheme 4.
I
Me
I2, NaHCO3
Me
N
MeCN, 0 °C
COBut
NHCOBut
2-(1-Methylethenyl)-N-phenylbenzenamine (1a). 2-[2-(Phen-
ylamino)phenyl]propan-2-ol5 (neat, 0.23 g, 1.0 mmol) was heated
at 250 ꢁC for 3 h. After removing water under reduced pressure,
the residue was subjected to column chromatography on silica
gel to give compound 1a (0.15 g, 74%) as a colorless viscous oil;
9
10
Scheme 5.
ceeded successfully to afford the desired product 3-ethyl-2-
methyl-1-phenyl-1H-indole (4) in moderate yield (Table 1,
Entry 9), as depicted in Scheme 2.
Subsequently, we investigated the possibility of preparing
a 1,10-(p-phenylene)diindole derivative. N,N0-Bis[2-(1-methyl-
ethenyl)phenyl]benzene-1,4-diamine (5) afforded 3,30-dimeth-
yl-1,10-(p-phenylene)diindole (6), in satisfactory yield (Table 1,
Entry 10), as shown in Scheme 3.
The probable pathway which leads to derivatives 2 from
derivatives 1 is illustrated in Scheme 4. Thus, treatment of
1 with iodine generates the iodonium ion intermediate 7. This
undergoes 5-endo-cyclization to give the 3-iodoindoline inter-
mediate 8, from which the loss of hydrogen iodide gives 2. The
selectivity of cyclization may be ascribed to the bulkiness of
N-substituents of derivatives 1 compared to those of 2-(acyl-
amino)styrenes.1f Thus, the reaction of 2-(pivaloylamino)-ꢀ-
methylstyrene (9) with iodine under the same conditions was
performed, and only 2-iodomethyl-2-methyl-1-pivaloylbenz-
azetine (10) was obtained (75% yield), as shown in Scheme 5.
Therefore, 5-endo-cyclization of derivatives 1 is attributed to
the higher nucleophilicity of the nitrogens of derivatives 1 com-
pared to those of 2-(acylamino)styrenes. 2-(Methylamino)-ꢀ-
methylstyrene, however, gave an intractable mixture of prod-
Rf 0.77 (1:3 EtOAc–hexane); IR (neat) 3404 and 1637 cmꢂ1
;
1H NMR (270 MHz) ꢁ 2.06 (3H, dd, J ¼ 1:6 and 1.0 Hz), 5.06 (1H,
q, J ¼ 1:0 Hz), 5.29 (1H, q, J ¼ 1:6 Hz), 5.85 (1H, br s), 6.85–6.95
(2H, m), 7.06 (2H, dd, J ¼ 7:6 and 1.0 Hz), 7.1–7.35 (4H, m), and
7.49 (1H, dd, J ¼ 7:6 and 1.3 Hz). Found: C, 85.91; H, 7.18; N,
6.81%. Calcd for C15H15N: C, 86.08; H, 7.22; N, 6.69%.
2-[2-(4-Methylphenylamino)phenyl]propan-2-ol: To a stir-
red solution of 1-[2-(4-methylphenylamino)phenyl]ethanone6
(2.0 g, 9.1 mmol) in Et2O (47 mL) at 0 ꢁC was added MeMgBr
(3 M in Et2O, 23 mmol) dropwise (1 M = 1 mol dmꢂ3). After
30 min, aqueous saturated NH4Cl (30 mL) was added to quench
the reaction. The layers were separated, and the aqueous layer
was extracted with Et2O twice (30 mL each). The combined organ-
ic layers were washed brine, and dried over anhydrous Na2SO4,
and the Et2O was evaporated. The residue was chromatographed
on silica gel to give the title compound (1.1 g, 52%) as a brown-
ish-yellow oil; Rf 0.51 (1:3 EtOAc–hexane); IR (neat) 3533, 3364,
and 1616 cmꢂ1; 1H NMR (500 MHz) ꢁ 1.69 (6H, s), 2.12 (1H, br s),
2.30 (3H, s), 6.82 (1H, ddd, J ¼ 8:2, 7.3, and 1.4 Hz), 6.99 (2H, d,
J ¼ 8:8 Hz), 7.07 (2H, d, J ¼ 8:8 Hz), 7.14 (1H, ddd, J ¼ 8:2, 7.3,
and 0.9 Hz), 7.25 (1H, dd, J ¼ 8:2 and 1.4 Hz), 7.30 (1H, dd, J ¼
8:2 and 0.9 Hz), and 7.70 (1H, br s). Found: C, 79.64; H, 7.93; N,
5.78%. Calcd for C16H19NO: C, 79.63; H, 7.94; N, 5.80%.

1582 Bull. Chem. Soc. Jpn. Vol. 79, No. 10 (2006)
Synthesis of 1-Aryl-1H-indoles
2-(1-Methylethenyl)-N-(4-methylphenyl)benzenamine (1b):
Compound 1b was prepared from 2-[2-(4-methylphenylamino)-
phenyl]propan-2-ol as described for the preparation of compound
1a in 83% yield; a pale-yellow oil; Rf 0.69 (1:7 EtOAc–hexane);
IR (neat) 3408, 1633, and 1614 cmꢂ1; 1H NMR (500 MHz) ꢁ 2.07
(3H, d, J ¼ 1:4 Hz), 2.30 (3H, s), 5.06 (1H, d, J ¼ 0:9 Hz), 5.30
(1H, q, J ¼ 1:4 Hz), 5.79 (1H, br s), 6.86 (1H, ddd, J ¼ 7:8, 7.3,
and 1.4 Hz), 6.99 (2H, d, J ¼ 8:2 Hz), 7.08 (2H, d, J ¼ 8:2 Hz),
7.11–7.15 (2H, m), and 7.22 (1H, dd, J ¼ 7:8 and 0.9 Hz). Found:
C, 86.15; H, 7.63; N, 6.19%. Calcd for C16H17N: C, 86.05; H,
7.67; N, 6.27%.
benzoate and iodobenzene according to the procedure reported
by Hellwinkel and Ittermann6 in 80% yield; mp 125–127 ꢁC
(hexane–CH2Cl2); IR (KBr disk) 3288, 3256, and 1668 cmꢂ1
;
1H NMR (500 MHz) ꢁ 3.79 (3H, s), 3.87 (3H, s), 3.89 (3H, s),
6.81 (1H, s), 7.06 (1H, t, J ¼ 7:8 Hz), 7.25 (2H, d, J ¼ 7:8 Hz),
7.34 (2H, t, J ¼ 7:8 Hz), 7.41 (1H, s), and 9.40 (1H, s). Found:
C, 66.71; H, 5.99; N, 4.81%. Calcd for C16H17NO4: C, 66.89;
H, 5.96; N, 4.88%.
2-[4,5-Dimethoxy-2-(phenylamino)phenyl]propan-2-ol: This
compound was prepared from methyl 4,5-dimethoxy-2-(phenyl-
amino)benzoate and MeMgBr (3.5 molar amounts) as described
for the preparation of 2-(2-phenylaminophenyl)propan-2-ol in
62% yield; a pale-yellow solid; mp 110–113 ꢁC (hexane–Et2O–
2-[2-(4-Methoxyphenylamino)phenyl]propan-2-ol:
This
compound was prepared from 1-[2-(4-methoxyphenylamino)-
phenyl]ethanone6 as described for the preparation of 2-[2-(4-meth-
ylphenylamino)phenyl]propan-2-ol in 80% yield; a yellow viscous
CH2Cl2); IR (KBr disk) 3452, 3348, and 1612 cmꢂ1 1H NMR
;
(500 MHz) ꢁ 1.64 (6H, s), 2.17 (1H, s), 3.78 (3H, s), 3.87 (3H, s),
6.72 (1H, br s), 6.84 (1H, s), 6.85 (1H, t, J ¼ 7:8 Hz), 6.92 (1H, s),
6.97 (2H, d, J ¼ 7:8 Hz), and 7.23 (2H, t, J ¼ 7:8 Hz). Found: C,
71.08; H, 7.15; N, 4.85%. Calcd for C17H21NO3: C, 71.06; H,
7.37; N, 4.88%.
4,5-Dimethoxy-2-(1-methylethenyl)-N-phenylbenzenamine
(1e): Compound 1e was prepared from 2-[4,5-dimethoxy-2-
(phenylamino)phenyl]propan-2-ol as described for the preparation
1
oil; Rf 0.49 (1:3 EtOAc–hexane); IR (neat) 3360 cmꢂ1; H NMR
(500 MHz) ꢁ 1.71 (6H, s), 2.05 (1H, s), 3.80 (3H, s), 6.78 (1H, td,
J ¼ 7:8 and 1.4 Hz), 6.85 (2H, d, J ¼ 8:7 Hz), 7.05 (2H, d, J ¼
8:7 Hz), 7.11 (1H, td, J ¼ 7:8 and 1.4 Hz), 7.15 (1H, dd, J ¼ 7:8
and 1.4 Hz), 7.23 (1H, dd, J ¼ 7:8 and 1.4 Hz), and 7.26 (1H,
br s). Found: C, 74.68; H, 7.48; N, 5.29%. Calcd for C16H19NO2:
C, 74.68; H, 7.44; N, 5.44%.
N-(4-Methoxyphenyl)-2-(1-methylethenyl)benzenamine (1c):
Compound 1c was prepared from 2-[2-(4-methoxyphenylamino)-
phenyl]propan-2-ol as described for the preparation of compound
1a in 83% yield; a colorless viscous oil; Rf 0.56 (1:5 EtOAc–hex-
of compound 1a in 58% yield; a colorless oil; Rf 0.50 (1:2
EtOAc–hexane); IR (neat) 3368 and 1639 cmꢂ1 1H NMR (500
;
MHz) ꢁ 2.02 (3H, s), 3.81 (3H, s), 3.87 (3H, s), 5.00 (1H, s), 5.22
(1H, s), 5.56 (1H, br s), 6.72 (1H, s), 6.85 (1H, t, J ¼ 7:8 Hz), 6.87
(1H, s), 6.93 (2H, d, J ¼ 7:8 Hz), and 7.23 (2H, t, J ¼ 7:8 Hz).
Found: C, 75.61; H, 7.16; N, 5.12%. Calcd for C17H19NO2: C,
75.81; H, 7.11; N, 5.20%.
1
ane); IR (neat) 3393 and 1639 cmꢂ1; H NMR (500 MHz) ꢁ 2.09
(3H, d, J ¼ 1:4 Hz), 3.80 (3H, s), 5.09 (1H, s), 5.32 (1H, q, J ¼
1:4 Hz), 5.75 (1H, br s), 6.81 (1H, td, J ¼ 8:2 and 1.4 Hz), 6.86
(2H, d, J ¼ 9:2 Hz), and 7.04–7.12 (5H, m). Found: C, 80.16; H,
7.45; N, 5.76%. Calcd for C16H17NO: C, 80.30; H, 7.16; N, 5.85%.
1-[2-(4-Chlorophenylamino)phenyl]ethanone: This com-
pound was prepared from 1-(2-aminophenyl)ethanone and 1-
chloro-2-iodobenzene according to the procedure reported by
Hellwinkel and Ittermann6 in 84% yield; a yellow solid; mp
Ethyl 5-Chloro-2-(phenylamino)benzoate: The benzoate de-
rivative was prepared from ethyl 2-amino-5-chlorobenzoate7 and
iodobenzene according to the procedure reported by Hellwinkel
and Ittermann6 in 63% yield; a yellow oil; Rf 0.76 (1:3 EtOAc–
hexane); IR (neat) 3317 and 1688 cmꢂ1 1H NMR (500 MHz) ꢁ
;
1.42 (3H, t, J ¼ 7:3 Hz), 4.36 (2H, q, J ¼ 7:3 Hz), 7.11 (1H, tt,
J ¼ 7:3 and 1.4 Hz), 7.17 (2H, d, J ¼ 8:2 Hz), 7.20–7.25 (2H, m),
7.35 (2H, dd, J ¼ 8:2 and 7.3 Hz), 7.93 (1H, d, J ¼ 2:7 Hz), and
9.44 (1H, br s). Found: C, 65.35; H, 5.07; N, 4.85%. Calcd for
C15H14ClNO2: C, 65.34; H, 5.12; N, 5.08%.
47–49 ꢁC (hexane–Et2O); IR (KBr disk) 3242 and 1631 cmꢂ1
;
1H NMR (500 MHz) ꢁ 2.65 (3H, s), 6.76 (1H, td, J ¼ 7:8 and
0.9 Hz), 7.17–7.21 (3H, m), 7.29–7.34 (3H, m), 7.83 (1H, dd, J ¼
7:8 and 1.4 Hz), and 10.50 (1H, br s). Found: C, 68.32; H, 4.94; N,
5.67%. Calcd for C14H12ClNO: C, 68.44; H, 4.92; N, 5.70%.
2-[2-(4-Chlorophenylamino)phenyl]propan-2-ol: This com-
pound was prepared from 1-[2-(4-chlorophenylamino)phenyl]-
ethanone as described for the preparation of 2-[2-(4-methylphen-
ylamino)phenyl]propan-2-ol in 65% yield; a yellow viscous oil;
2-[5-Chloro-2-(phenylamino)phenyl]propan-2-ol: This com-
pound was prepared from ethyl 5-chloro-2-(phenylamino)ben-
zoate and MeMgBr (3.5 molar amounts) as described for the prep-
aration of 2-(2-phenylaminophenyl)propan-2-ol in 80% yield; a
pale-yellow oil; Rf 0.35 (1:5 EtOAc–hexane); IR (neat) 3543
Rf 0.48 (1:3 EtOAc–hexane); IR (neat) 3358 cmꢂ1
;
1H NMR
and 3364 cmꢂ1 1H NMR (500 MHz) ꢁ 1.68 (6H, s), 2.08 (1H,
;
(500 MHz) ꢁ 1.68 (6H, s), 2.05 (1H, br s), 6.89 (1H, td, J ¼ 7:8
and 1.4 Hz), 6.99 (2H, d, J ¼ 8:7 Hz), 7.16–7.21 (3H, m), 7.27
(1H, dd, J ¼ 7:8 and 1.4 Hz), 7.32 (1H, dd, J ¼ 7:8 and 1.4 Hz),
and 7.85 (1H, br s). Found: C, 68.83; H, 6.20; N, 5.31%. Calcd
for C15H16ClNO: C, 68.83; H, 6.16; N, 5.35%.
br s), 6.91 (1H, tt, J ¼ 7:8 and 0.9 Hz), 7.05 (2H, dd, J ¼ 7:8
and 0.9 Hz), 7.11 (1H, dd, J ¼ 8:7 and 2.3 Hz), 7.21 (1H, d,
J ¼ 2:3 Hz), 7.25 (1H, d, J ¼ 8:7 Hz), 7.27 (2H, t, J ¼ 7:8 Hz),
and 7.77 (1H, br s). Found: C, 68.75; H, 6.34; N, 5.09%. Calcd
for C15H16ClNO: C, 68.83; H, 6.16; N, 5.35%.
N-(4-Chlorophenyl)-2-(1-methylethenyl)benzenamine (1d):
Compound 1d was prepared from 2-[2-(4-chlorophenylamino)-
phenyl]propan-2-ol as described for the preparation of compound
1a in 78% yield; a pale-yellow solid; mp 61–64 ꢁC (hexane–
4-Chloro-2-(1-methylethenyl)-N-phenylbenzenamine (1f):
Compound 1f was prepared from 2-[5-chloro-2-(phenylamino)-
phenyl]propan-2-ol as described for the preparation of compound
1
1a in 80% yield; IR (neat) 3406, 1634, and 1603 cmꢂ1; H NMR
1
Et2O); IR (KBr disk) 3393 and 1635 cmꢂ1; H NMR (500 MHz)
(500 MHz) ꢁ 2.04 (3H, d, J ¼ 1:3 Hz), 5.07 (1H, d, J ¼ 1:3 Hz),
5.31 (1H, quint, J ¼ 1:3 Hz), 5.77 (1H, br s), 6.94 (1H, tt, J ¼
7:8 and 1.4 Hz), 7.03 (2H, dd, J ¼ 7:8 and 0.9 Hz), 7.09–7.12
(2H, m), 7.21 (1H, dd, J ¼ 7:8 and 1.4 Hz), and 7.25–7.29 (2H,
m). Found: C, 73.75; H, 6.05; N, 5.75%. Calcd for C15H14ClN:
C, 73.92; H, 5.79; N, 5.75%.
ꢁ 2.04 (3H, dd, J ¼ 1:4 and 0.9 Hz), 5.04 (1H, q, J ¼ 0:9 Hz), 5.29
(1H, q, J ¼ 1:4 Hz), 5.81 (1H, br s), 6.94 (1H, td, J ¼ 7:8 and
1.4 Hz), 6.97 (2H, d, J ¼ 9:2 Hz), 7.14–7.18 (2H, m), 7.20 (2H, d,
J ¼ 9:2 Hz), 7.24 (1H, d, J ¼ 7:8 Hz). Found: C, 73.88; H, 5.80;
N, 5.72%. Calcd for C15H14ClN: C, 73.92; H, 5.79; N, 5.75%.
Methyl 4,5-Dimethoxy-2-(phenylamino)benzoate: This
compound was prepared from methyl 2-amino-4,5-dimethoxy-
Ethyl 4-Chloro-2-(phenylamino)benzoate: This compound
was prepared from ethyl 2-amino-4-chlorobenzoate8 and iodoben-

K. Kobayashi et al.
Bull. Chem. Soc. Jpn. Vol. 79, No. 10 (2006) 1583
zene according to the procedure reported by Hellwinkel and
Ittermann6 in 63% yield; a pale-yellow solid; mp 73–75 ꢁC (hex-
ol as described for the preparation of compound 1a in 60% yield;
a pale-yellow liquid; a mixture of stereoisomers (E:Z = ca. 1:3);
Rf 0.54 (1:10 THF–hexane); IR (neat) 3404 and 1593 cmꢂ1
;
1
ane–Et2O); IR (KBr disk) 3294, 3250, and 1692 cmꢂ1; H NMR
(500 MHz) ꢁ 1.40 (3H, t, J ¼ 7:3 Hz), 4.35 (2H, q, J ¼ 7:3 Hz),
6.67 (1H, dd, J ¼ 8:7 and 2.3 Hz), 7.15 (1H, t, J ¼ 7:3 Hz), 7.17
(1H, d, J ¼ 2:3 Hz), 7.24 (2H, d, J ¼ 8:2 Hz), 7.38 (2H, dd, J ¼
8:2 and 7.3 Hz), 7.90 (1H, d, J ¼ 8:7 Hz), and 9.57 (1H, br s).
Found: C, 65.30; H, 4.98; N, 5.08%. Calcd for C15H14ClNO2:
C, 65.34; H, 5.12; N, 5.08%.
1H NMR (500 MHz) ꢁ 0.91 (0.75H, t, J ¼ 7:3 Hz), 0.98 (2.25H,
t, J ¼ 7:3 Hz), 1.48 (2.25H, dt, J ¼ 6:4 and 1.4 Hz), 1.79 (0.75H,
d, J ¼ 6:9 Hz), 2.28 (1.5H, qt, J ¼ 7:3 and 1.4 Hz), 2.37 (0.5H, q,
J ¼ 7:3 Hz), 5.49 (0.25H, q, J ¼ 6:4 Hz), 5.69–5.74 (1.75H, m),
and 6.85–7.32 (9H, m). Found: C, 85.92; H, 8.10; N, 5.64%. Calcd
for C17H19N: C, 86.03; H, 8.07; N, 5.90%.
2-[4-Chloro-2-(phenylamino)phenyl]propan-2-ol: This com-
pound was prepared from ethyl 4-chloro-2-(phenylamino)ben-
zoate and MeMgBr (3.5 molar amounts) as described for the prep-
aration of 2-(2-phenylaminophenyl)propan-2-ol in 71% yield; a
brownish-yellow solid; mp 95–97 ꢁC (hexane–Et2O); IR (KBr
N,N0-Bis[2-(1-methylethenyl)phenyl]benzene-1,4-diamine (5):
Compound 5 was prepared from 2-(2-{4-[2-(1-hydroxy-1-methyl-
ethyl)phenylamino]phenylamino}phenyl)propan-2-ol6 as describ-
ed for the preparation of compound 1a in 41% yield; a white solid;
mp 77–78 ꢁC (hexane–CH2Cl2); IR (KBr disk) 3404 and 1634
disk) 3416 and 3350 cmꢂ1
;
1H NMR (500 MHz) ꢁ 1.68 (6H, s),
cmꢂ1; H NMR (500 MHz) ꢁ 2.09 (6H, d, J ¼ 1:4 Hz), 5.09 (2H,
1
1.95 (1H, br s), 6.77 (1H, dd, J ¼ 8:7 and 2.3 Hz), 6.97 (1H, t, J ¼
7:3 Hz), 7.10 (2H, d, J ¼ 7:3 Hz), 7.14 (1H, d, J ¼ 8:7 Hz), 7.27–
7.32 (3H, m), and 7.98 (1H, br s). Found: C, 68.68; H, 6.40; N,
5.48%. Calcd for C15H16ClNO: C, 68.83; H, 6.16; N, 5.35%.
5-Chloro-2-(1-methylethenyl)-N-phenylbenzenamine (1g):
Compound 1g was prepared from 2-[4-chloro-2-(phenylamino)-
phenyl]propan-2-ol as described for the preparation of compound
1a in 74% yield; a colorless oil; Rf 0.74 (1:8 EtOAc–hexane); IR
dq, J ¼ 2:3 and 0.9 Hz), 5.32 (2H, dq, J ¼ 2:3 and 1.4 Hz), 5.80
(2H, br s), 6.84 (2H, td, J ¼ 7:3 and 1.4 Hz), 7.04 (4H, s), 7.09–
7.19 (6H, m). Found: C, 84.67; H, 6.98; N, 8.25%. Calcd for
C24H24N2: C, 84.67; H, 7.11; N, 8.23%.
A Typical Procedure for the Preparation of Indoles 2, 4,
and 6. 3-Methyl-1-phenyl-1H-indole (2a).9 To a stirred solution
of compound 1a (0.11 g, 0.54 mmol) in MeCN (10 mL) containing
NaHCO3 (0.14 g, 1.6 mmol) at 0 ꢁC was added I2 (0.41 g, 1.6
mmol) in small portions. After 1 h, 10% aqueous Na2SO3 was
added until the color of I2 disappeared. Most of MeCN was evapo-
rated, and the resulting mixture was extracted with Et2O three
times (10 mL each). The combined extracts were washed with
brine, and dried over anhydrous K2CO3, and the Et2O was evapo-
rated. The residue was purified by preparative TLC on silica gel to
give compound 2a (94 mg, 84%) as a pale-yellow viscous oil; Rf
0.58 (1:10 EtOAc–hexane). The spectral data for this product were
identical to those reported previously.9
(neat) 3404, 1634, and 1603 cmꢂ1 1H NMR (500 MHz) ꢁ 2.05
;
(3H, d, J ¼ 1:4 Hz), 5.07 (1H, d, J ¼ 1:4 Hz), 5.33 (1H, quint,
J ¼ 1:4 Hz), 5.90 (1H, br s), 6.83 (1H, dd, J ¼ 8:2 and 2.3 Hz),
7.00 (1H, t, J ¼ 7:3 Hz), 7.03 (1H, d, J ¼ 8:2 Hz), 7.10 (2H, d,
J ¼ 7:3 Hz), 7.23 (1H, d, J ¼ 2:3 Hz), 7.31 (2H, t, J ¼ 7:3 Hz).
Found: C, 74.00; H, 5.05; N, 5.55%. Calcd for C15H14ClN: C,
73.92; H, 5.79; N, 5.75%.
1-Phenyl-1-[2-(phenylamino)phenyl]ethanol:
This com-
pound was prepared from 1-[2-(phenylamino)phenyl]ethanone6
and PhMgBr as described for the preparation of 2-[2-(4-methyl-
phenylamino)phenyl]propan-2-ol in 71% yield; a pale-yellow oil;
3-Methyl-1-(4-methylphenyl)-1H-indole (2b): A pale-yel-
low oil; Rf 0.87 (1:4 EtOAc–hexane); IR (neat) 3036 and
Rf 0.39 (1:20 EtOAc–hexane); IR (neat) 3539 and 3382 cmꢂ1
;
1609 cmꢂ1; H NMR (270 MHz) ꢁ 2.39 (3H, d, J ¼ 0:9 Hz), 2.42
1
1H NMR (500 MHz) ꢁ 1.93 (3H, s), 3.60 (1H, s), 5.95 (1H, br s),
6.71 (2H, dd, J ¼ 8:7 and 0.9 Hz), 6.83 (1H, t, J ¼ 7:3 Hz), 7.02
(1H, ddd, J ¼ 7:8, 7.3, and 1.4 Hz), 7.13 (2H, dd, J ¼ 8:7 and
7.3 Hz), 7.17–7.28 (5H, m), 7.37 (2H, dd, J ¼ 8:2 and 1.4 Hz), and
7.52 (1H, dd, J ¼ 7:8 and 1.4 Hz). Found: C, 82.83; H, 6.71; N,
4.53%. Calcd for C20H19NO: C, 83.01; H, 6.62; N, 4.84%.
(3H, s), 7.11 (1H, q, J ¼ 0:9 Hz), 7.16 (1H, td, J ¼ 7:8 and 0.9
Hz), 7.21 (1H, ddd, J ¼ 8:2, 7.8, and 1.4 Hz), 7.29 (2H, d, J ¼
7:8 Hz), 7.36 (2H, d, J ¼ 7:8 Hz), 7.51 (1H, d, J ¼ 7:8 Hz), and
7.62 (1H, d, J ¼ 8:2 Hz); MS m=z (%) 221 (Mþ, 100). Found:
C, 86.50; H, 6.89; N, 6.33%. Calcd for C16H15N: C, 86.84; H,
6.83; N, 6.33%.
2-(1-Phenylethenyl)-N-phenylbenzenamine (1h):
Com-
1-(4-Methoxyphenyl)-3-methyl-1H-indole (2c): A colorless
solid; mp 58–60 ꢁC (hexane–Et2O); IR (KBr disk) 3047 and 1612
pound 1h was prepared from 1-phenyl-1-[2-(phenylamino)phen-
yl]ethanol as described for the preparation of compound 1a in
59% yield; a white solid; mp 73–75 ꢁC (MeOH); IR (KBr disk)
1
cmꢂ1; H NMR (500 MHz) ꢁ 2.39 (3H, d, J ¼ 1:4 Hz), 3.87 (3H,
s), 7.02 (2H, d, J ¼ 8:9 Hz), 7.07 (1H, q, J ¼ 1:4 Hz), 7.16 (1H,
td, J ¼ 7:8 and 1.4 Hz), 7.20 (1H, td, J ¼ 7:8 and 1.4 Hz), 7.39
(2H, d, J ¼ 8:9 Hz), 7.44 (1H, dd, J ¼ 7:8 and 1.4 Hz), and 7.62
(1H, dd, J ¼ 7:8 and 1.4 Hz); MS m=z (%) 237 (Mþ, 100). Found:
C, 80.90; H, 6.33; N, 5.87%. Calcd for C16H15NO: C, 80.98; H,
6.37; N, 5.90%.
1
3408 cmꢂ1; H NMR (500 MHz) ꢁ 5.39 (1H, s), 5.51 (1H, br s),
5.84 (1H, s), 6.87 (2H, d, J ¼ 8:7 Hz), 6.95 (1H, t, J ¼ 7:3 Hz),
7.18 (2H, dd, J ¼ 8:7 and 7.3 Hz), and 7.21–7.40 (9H, m). Found:
C, 88.53; H, 6.33; N, 4.98%. Calcd for C20H17N: C, 88.52; H,
6.31; N, 5.16%.
3-[2-(Phenylamino)phenyl]pentan-3-ol: This compound was
prepared from methyl 2-(phenylamino)benzoate6 and EtMgBr (3.5
molar amounts) as described for the preparation of 2-[2-(phenyl-
amino)phenyl]propan-2-ol in 82% yield; a pale-yellow oil; Rf 0.55
1-(4-Chlorophenyl)-3-methyl-1H-indole (2d): A pale-yel-
low viscous oil; Rf 0.74 (1:7 EtOAc–hexane); IR (neat) 3049 and
1
1595 cmꢂ1; H NMR (500 MHz) ꢁ 2.38 (3H, d, J ¼ 1:4 Hz), 7.09
(1H, q, J ¼ 1:4 Hz), 7.19 (1H, td, J ¼ 7:8 and 1.4 Hz), 7.24 (1H,
td, J ¼ 7:8 and 1.4 Hz), 7.42 (2H, d, J ¼ 8:7 Hz), 7.46 (2H, d, J ¼
8:7 Hz), 7.50 (1H, d, J ¼ 7:8 Hz), and 7.62 (1H, d, J ¼ 7:8 Hz);
MS m=z (%) 241 (Mþ, 100). Found: C, 74.27; H, 5.00; N, 5.79%.
Calcd for C15H12ClN: C, 74.53; H, 5.00; N, 5.79%.
(1:3 EtOAc–hexane); IR (neat) 3533 and 3360 cmꢂ1 1H NMR
;
(500 MHz) ꢁ 0.86 (6H, t, J ¼ 7:3 Hz), 1.93–2.01 (4H, m), 2.39
(1H, br s), 6.85–6.90 (2H, m), 7.03 (2H, dd, J ¼ 7:8 and 1.4 Hz),
7.12–7.16 (2H, m), 7.24 (2H, dd, J ¼ 7:8 and 7.3 Hz), 7.34 (1H,
dd, J ¼ 7:8 and 1.4 Hz), and 7.82 (1H, br s). Found: C, 79.85; H,
8.50; N, 5.21%. Calcd for C17H21NO: C, 79.96; H, 8.29; N, 5.49%.
2-(1-Ethyl-1-propenyl)-N-phenylbenzenamine (3): Com-
pound 3 was prepared from 3-[2-(phenylamino)phenyl]pentan-3-
5,6-Dimethoxy-3-methyl-1-phenyl-1H-indole (2e): A pale-
yellow solid; mp 80–82 ꢁC (hexane–Et2O); IR (KBr disk) 3056
1
and 1600 cmꢂ1; H NMR (500 MHz) ꢁ 2.35 (3H, d, J ¼ 0:9 Hz),
3.87 (3H, s), 3.97 (3H, s), 7.02 (1H, q, J ¼ 0:9 Hz), 7.03 (1H, s),

1584 Bull. Chem. Soc. Jpn. Vol. 79, No. 10 (2006)
Synthesis of 1-Aryl-1H-indoles
7.06 (1H, s), 7.31 (1H, tt, J ¼ 7:3 and 1.4 Hz), and 7.46–7.53 (4H,
m); MS m=z (%) 267 (Mþ, 100). Found: C, 76.24; H, 6.39; N,
5.22%. Calcd for C17H17NO2: C, 76.38; H, 6.41; N, 5.24%.
5-Chloro-3-methyl-1-phenyl-1H-indole (2f): A pale-yellow
References
For recent reports: a) M. Arisawa, Y. Ando, M. Yamanaka,
1
M. Nakagawa, A. Nishida, Synlett 2002, 1514. b) M. Ajad, D. W.
Knight, Tetrahedron Lett. 2004, 45, 539. c) S. G. Davies, R. L.
Nicholson, P. D. Price, P. M. Roberts, A. D. Smith, Synlett
2004, 901. d) A. Lei, X. Lu, G. Liu, Tetrahedron Lett. 2004,
45, 1785. e) C. Fiorelli, C. Marchioro, G. Martelli, M. Monari,
D. Savoia, Eur. J. Org. Chem. 2005, 3987. f) K. Kobayashi, K.
Miyamoto, O. Morikawa, H. Konishi, Bull. Chem. Soc. Jpn.
2005, 78, 886. For earlier reports, see pertinent references cited
in these papers.
oil; Rf 0.59 (1:8 EtOAc–hexane); IR (neat) 3045 and 1601 cmꢂ1
;
1H NMR (500 MHz) ꢁ 2.35 (3H, d, J ¼ 0:9 Hz), 7.14–7.17 (2H,
m), 7.33 (1H, t, J ¼ 7:3 Hz), 7.42–7.46 (3H, m), 7.50 (2H, t, J ¼
7:3 Hz), and 7.57 (1H, d, J ¼ 1:8 Hz); MS m=z (%) 241 (Mþ,
100). Found: C, 74.66; H, 5.16; N, 5.76%. Calcd for C15H12ClN:
C, 74.53; H, 5.00; N, 5.79%.
6-Chloro-3-methyl-1-phenyl-1H-indole (2g): A white solid;
mp 69–70 ꢁC (hexane–Et2O); IR (KBr disk) 3061 and 1595 cmꢂ1
;
1H NMR (500 MHz) ꢁ 2.36 (3H, d, J ¼ 0:9 Hz), 7.12 (1H, q, J ¼
0:9 Hz), 7.13 (1H, dd, J ¼ 8:2 and 1.8 Hz), 7.35 (1H, tt, J ¼ 7:3
and 0.9 Hz), 7.44 (2H, dd, J ¼ 7:3 and 0.9 Hz), and 7.49–7.53
(4H, m); MS m=z (%) 241 (Mþ, 100). Found: C, 74.53; H, 5.12;
N, 5.79%. Calcd for C15H12ClN: C, 74.53; H, 5.00; N, 5.79%.
2
For recent indole syntheses: K. B. Hong, C. W. Lee,
E. K. Yum, Tetrahedron Lett. 2004, 45, 693; F. Gallou, N. Yee,
F. Qiu, C. Senanayake, G. Linz, J. Schnaubelt, R. Soyka, Synlett
2004, 883; K. Hiroya, S. Itoh, T. Sakamoto, J. Org. Chem.
2004, 69, 1126; Y.-K. Lim, C.-G. Cho, Tetrahedron Lett. 2004,
45, 1857; W. R. Bowman, A. J. Fletcher, P. J. Lovell, J. M.
Pedersen, Synlett 2004, 1905; M. Pal, V. Subramanian, V. R.
Batchu, I. Dager, Synlett 2004, 1965; S. Cacchi, G. Fabrizi,
L. M. Parisi, Synthesis 2004, 1889; L. Ackermann, L. T. Kasper,
3-Ethyl-2-methyl-1-phenyl-1H-indole (4):
A pale-yellow
oil; Rf 0.59 (1:10 THF–hexane); IR (neat) 3053 and 1597 cmꢂ1
;
1H NMR (500 MHz) ꢁ 1.28 (3H, t, J ¼ 7:3 Hz), 2.23 (3H, s), 2.80
(2H, q, J ¼ 7:3 Hz), 7.05–7.12 (3H, m), 7.34 (2H, dd, J ¼ 8:2 and
1.4 Hz), 7.42 (1H, tt, J ¼ 7:3 and 1.4 Hz), 7.52 (2H, dd, J ¼ 8:2
and 7.3 Hz), and 7.58 (1H, dd, J ¼ 7:3 and 1.4 Hz); MS m=z (%)
235 (Mþ, 100). Found: C, 86.52; H, 7.31; N, 5.72%. Calcd for
C17H17N: C, 86.77; H, 7.28; N, 5.95%.
´
C. J. Gschrei, Chem. Commun. 2004, 2824; M. Nazare, C.
Schneider, A. Lindenschmidt, D. W. Will, Angew. Chem., Int.
Ed. 2004, 43, 4526; T. Shimada, I. Nakamura, Y. Yamamoto,
J. Am. Chem. Soc. 2004, 126, 10546; L.-P. Sun, X.-H. Huang,
W.-M. Dai, Tetrahedron 2004, 60, 10983; K. Pchalek, A. W.
Jones, M. M. T. Wekking, D. S. C. Black, Tetrahedron 2005,
61, 77; J. Barluenga, M. A. Fernandez, F. Aznar, C. Valdes,
Chem. Eur. J. 2005, 11, 2276; C. Mukai, Y. Takahashi, Org. Lett.
2005, 7, 5793; A. V. Butin, S. K. Smirnov, Tetrahedron Lett.
2005, 46, 8443; C. Barberis, T. D. Gordon, C. Thomas, X. Zhang,
K. P. Cusack, Tetrahedron Lett. 2005, 46, 8877; C. A. Simoneau,
B. Ganem, Tetrahedron 2005, 61, 11374; V. Sridharan, S.
3,30-Dimethyl-1,10-(p-phenylene)diindole (6): A white solid;
mp 195–197 ꢁC (hexane–CH2Cl2); IR (KBr disk) 3059 and 1611
1
cmꢂ1; H NMR (500 MHz) ꢁ 2.42 (6H, d, J ¼ 1:4 Hz), 7.18 (2H,
q, J ¼ 1:4 Hz), 7.21 (2H, ddd, J ¼ 7:8, 7.3, and 0.9 Hz), 7.27 (2H,
ddd, J ¼ 8:2, 7.3, and 0.9 Hz), 7.608 (4H, s), 7.611 (2H, d, J ¼
8:2 Hz), 7.65 (2H, d, J ¼ 7:8 Hz); MS m=z (%) 336 (Mþ, 100).
Found: C, 85.40; H, 6.00; N, 8.33%. Calcd for C24H20N2: C,
85.68; H, 5.99; N, 8.33%.
N-[2-(1-Methylethenyl)phenyl]-2,2-dimethylpropanamide (9):
Compound 9 was prepared by the reaction of pivaloyl chloride
with 2-(1-methylethenyl)benzenamine in pyridine in 98% yield;
a white solid; mp 55–56 ꢁC (hexane); IR (KBr disk) 3321 and
1647 cmꢂ1; 1H NMR (500 MHz) ꢁ 1.28 (9H, s), 2.08 (3H, s), 5.03
(1H, d, J ¼ 0:9 Hz), 5.43 (1H, s), 7.06 (1H, dd, J ¼ 7:8 and 7.3
Hz), 7.13 (1H, dd, J ¼ 7:3 and 1.4 Hz), 7.26 (1H, td, J ¼ 7:3
and 1.4 Hz), 7.96 (1H, br s), and 8.34 (1H, d, J ¼ 7:8 Hz). Found:
C, 77.29; H, 8.88; N, 6.40%. Calcd for C14H19NO: C, 77.38; H,
8.81; N, 6.45%.
´
Perumal, C. Avendan˜o, J. C. Menendez, Synlett 2006, 91; K. O.
Hessian, R. L. Flynn, Org. Lett. 2006, 8, 243; N. Sakai, K.
Annaka, T. Konakahara, Tetrahedron Lett. 2006, 47, 631, and
references cited in these papers.
3
L. Ackermann, R. Born, Tetrahedron Lett. 2004, 45, 9541;
L. Ackermann, Org. Lett. 2005, 7, 439; M. C. Willis, G. N. Brace,
I. P. Holmes, Angew. Chem., Int. Ed. 2005, 44, 403; Y.-Q. Fang,
M. Lautens, Org. Lett. 2005, 7, 3549; L. T. Kasper, L.
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P. C. J. Kamer, P. W. N. M. van Leeuwen, G. P. F. van Strijdonck,
Tetrahedron Lett. 2005, 46, 2405.
7-(2,2-Dimethylpropanoyl)-8-iodomethyl-8-methyl-bicyclo-
[4.2.0]-7-azaocta-1,3,5-triene (10): Compound 10 was obtained
by treating N-[2-(1-methylethenyl)phenyl]-2,2-dimethylpropana-
mide with iodine under the same conditions as described for the
preparation of compound 2a in 75% yield: a white solid; mp 45 ꢁC
4
M. Abou-Ghabia, U. R. Patel, M. B. Webb, J. A. Moyer,
T. H. Andree, E. A. Muth, J. Med. Chem. 1987, 30, 1818;
W. J. Smith, III, J. S. Sawyer, Tetrahedron Lett. 1996, 37, 299;
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L. M. Alcazar-Roman, J. Org. Chem. 1999, 64, 5575; Q. Cai,
W. Zhu, H. Zhang, Y. Zhang, D. Ma, Synthesis 2005, 496.
1
(hexane); IR (KBr disk) 1634 cmꢂ1; H NMR (500 MHz) ꢁ 1.30
(9H, s), 1.78 (3H, s), 3.48 (1H, d, J ¼ 11:0 Hz), 3.55 (1H, d,
J ¼ 11:0 Hz), 7.06 (1H, dd, J ¼ 7:3 and 1.4 Hz), 7.15–7.19 (2H,
m), and 7.28 (1H, ddd, J ¼ 7:8, 7.3, and 1.4 Hz); MS m=z (%)
343 (Mþ, 8.1) and 202 (100). Found: C, 48.99; H, 5.52; N,
4.06%. Calcd for C14H18INO: C, 48.99; H, 5.29; N, 4.08%.
5
6
7
D. Hellwinkel, W. Schmidt, Chem. Ber. 1980, 113, 358.
D. Hellwinkel, P. Ittermann, Chem. Ber. 1986, 119, 3165.
K. Kobayashi, A. Takanohashi, K. Hashimoto, O.
We thank Mrs. Miyuki Tanmatsu of this Department for de-
termining mass spectra and for performing combustion analy-
ses. This work was partially supported by a Grant-in-Aid for
Scientific Research (C) No. 15550092 from Japan Society
for the Promotion of Science.
Morikawa, H. Konishi, Tetrahedron 2006, 62, 3158.
8
9
G. E. Keyser, N. J. Leonard, J. Org. Chem. 1976, 41, 3529.
G. P. Tokmakov, I. I. Grandberg, Tetrahedron 1995, 51,
2091.