Thermal reactions of N-Alkyl-2-benzylaniline and N-Alkyl-N′-phenyl-o- phenylenediamine: An unusual route to 2-phenylindole and 2-phenylbenzimidazole

Article abstract of DOI:10.1002/jhet.5570450331

(Chemical Equation Presented) Thermal cyclization reactions of N-alkyl-2-benzylaniline 1a-d and N-alkyl-N′-phenyl-o-phenylenediamine 2a-b were carried out expecting to get seven-membered heterocyclic compounds. However, the results show that aside from th

Full text of DOI:10.1002/jhet.5570450331

May-Jun 2008
837
Thermal Reactions of N-Alkyl-2-benzylaniline and
N-Alkyl-N'-phenyl-o-phenylenediamine: An Unusual Route to
2-Phenylindole and 2-Phenylbenzimidazole
Evelyn Cuevas Creencia*1, Kei Taguchi2 and Takaaki Horaguchi*2
1Department of Chemistry, College of Science and Mathematics,
MSU-Iligan Institute of Technology, Iligan City 9200, Philippines
csm-ecc@sulat.msuiit.edu.ph
2Department of Chemistry, Faculty of Science, Niigata University,
Ikarashi, Niigata 950-2181, Japan
hora@chem.sc.niigata-u.ac.jp
Received October 9, 2007
CH2R1
R2
N
H
H
N
N
N
CaO
+
+
+
6
1a-d
3
4
5
CH2R1
R2
H
N
N
N
N
CaO
+
+
N
N
N
H
5
7
8
2a-b
Thermal cyclization reactions of N-alkyl-2-benzylaniline 1a-d and N-alkyl-N'-phenyl-o-
phenylenediamine 2a-b were carried out expecting to get seven-membered heterocyclic compounds.
However, the results show that aside from the formation of the normally expected six-membered ring
products of acridine 5, anthracene 6, and phenazine 8, thermal cyclization of N-alkyl-2-benzylaniline and
N-alkyl-N'-phenyl-o-phenylenediamine also resulted to the unexpected formation of 2-phenylindole 3 and
2,3-diphenylindole 4, and 2-phenylbenzimidazole 7, respectively.
J. Heterocyclic Chem., 45, 837 (2008).
INTRODUCTION
RESULTS AND DISCUSSION
Thermal decomposition reactions of N-alkyl-2-amino-
biphenyls were investigated by passing vapors of the
aromatic amines over calcium oxide at 450°C – 600°C.
The procedure afforded a method for the preparation of
carbazole (69%) and phenanthridine (92%) [1]. Hence,
thermal decomposition reactions may also be utilized for
the syntheses of other N-containing heterocycles which
are of great importance in the field of medicine [2] and
some areas in material science [3].
A survey of the literature showed many improved
methods for the syntheses of indoles and benzimidazoles
[4,5] but none describes a method for the synthesis via
thermal cyclization of N-alkyl-2-benzylaniline and N-
alkyl-N'-phenyl-o-phenylenediamine in the presence of
calcium oxide catalyst.
The different substrates (1a-d and 2a-b) for the thermal
reactions were synthesized either by methylation or
benzylation of 2-benzylaniline and N-phenyl-o-phenyl-
enediamine. The thermal reactions were carried out at
450°C, 500°C, and 560°C.
The thermally-induced reaction of N-methyl-2-benzyl-
aniline 1a yielded 45% of 2-phenylindole 3 at 450°C
(Table 1, Entry1) but decreased as the temperature of the
reaction was raised. The reaction also produced acridine
5 and anthracene 6 whose yields remained practically
unaffected by the changes in the reaction temperatures
(Entry 1, 2, 3). When subjected to very high
temperatures, N,N-dimethyl-2-benzylaniline 1b also gave
2-phenylindole 3 together with the expected acridine 5
and anthracene 6 (Entry 4, 5, 6). However, the yield of 2-
phenylindole 3 is lower compared to that from N-methyl-
2-benzylaniline 1a at the same temperature. This can be
explained by proposing an imine intermediate in the
formation of 2-phenylindole from 1a and 1b (Scheme 2).
The nitrogen proton of N-methyl-2-benzylaniline 1a is
more readily abstracted (more acidic) by calcium oxide
Thus, this paper reports the unusual behavior of N-
alkyl-2-benzylaniline 1a-d and N-alkyl-N'-phenyl-o-phen-
ylenediamine 2a-b when subjected to very high
temperatures in the presence of calcium oxide catalyst.
The mechanism for the indole and benzimidazole
formation by thermal cyclization is also discussed here.

838
E. C. Creencia, K. Taguchi and T. Horaguchi
Vol 45
Scheme 1
CH2R1
R2
N
H
N
H
N
N
CaO
+
+
+
1a-d
3
4
5
6
1
R1
R2
a
b
c
H
H
Ph
H
CH3
H
CH2Ph
d
Ph
Table 1
Thermal cyclization[a] of N-alkyl-2-benzylaniline 1a-d
Starting
Reaction
temperature
(°C)
Reaction
time[c]
(minutes)
Conversion
(%)
Product Yield[d] (%)
Entry
material[b]
R1
R2
3
4
5
6
1
2
1a
1a
1a
1b
1b
1b
1c
1c
1c
1d
1d
1d
H
H
H
H
450
500
560
450
500
560
450
500
560
450
500
560
40
40
40
40
40
40
40
40
40
40
40
40
100
100
100
100
100
100
100
100
100
100
100
100
45
36
10
36
31
11
15
4
-
-
-
-
-
-
19
19
16
3
10
12
12
10
13
12
-
3
H
H
4
5
H
H
CH3
CH3
CH3
H
4
6
H
1
7
8
Ph
Ph
Ph
Ph
Ph
Ph
7
7
69
51
41
26
20
18
H
-
9
H
3
6
-
10
11
12
CH2Ph
CH2Ph
CH2Ph
47
26
5
18
22
14
-
-
-
[a] Nitrogen carrier gas at 19mL/minute; [b] 1.0 mmol; [c] The reaction time corresponds to the time in minutes for the traveling furnace to reach
the stationary furnace (see Experimental Section); [d] Based on reacted starting material.
than the methyl proton of N,N-dimethyl-2-benzylaniline
three reaction temperatures. It was also observed that N-
benzyl-2-benzylaniline 1c and N,N-dibenzyl-2-benzyl-
aniline 1d yielded 2,3-diphenylindole 4, with N,N-
dibenzyl-2-benzylaniline 1d giving a fair yield over N-
benzyl-2-benzylaniline 1c.
1b, hence
intermediate.
a more facile formation of the imine
When N-benzyl-2-benzylaniline 1c was heated in the
presence of calcium oxide, acridine 5 was produced as the
major product, with a yield of 69% at 450°C (Entry 7) but
decreased as the reaction temperature was raised due to
Thermal reactions of N,N-dimethyl-N'-phenyl-o-
phenylenediamine 2a gave fair yields of 2-phenylbenz-
imidazole 7 at 450°C and 500°C which decreased
radically at 560°C (Table 2, Entry 1, 2, 3). This is due to
the fact that although imidazoles are thermally stable, they
decompose at temperatures higher than 500°C [6]. The
formation of 2-phenylbenzimidazole 7 is rather unusual
and may be due to an imine intermediate followed by
rearrangement after ring closure reaction. The results for
N,N-dibenzyl-N'-phenyl-o-phenylenediamine 2b show
good yield for phenazine 8 at 450°C and fair yields for 2-
phenylbenzimidazole 7 at 450°C and 500°C (Entry 4, 5).
Again, decomposition at 560°C led to a decrease in the
yield of 2-phenylbenzimidazole 7 and phenazine 8 (Entry
6). Unexpectedly high yield of phenazine 8 is obtained
from N,N-dibenzyl-N'-phenyl-o-phenylenediamine 2b as
decomposition.
The yield of 2-phenylindole 3 is
relatively low at all temperatures (Entry 7, 8, 9).
Here, acidity of the nitrogen proton coupled with the
facile cleavage of the N-C bond of the benzylamino group
at high temperatures made cyclization to form acridine 5 a
favored reaction over the formation of the imine
intermediate. N,N-Dibenzyl-2-benzylaniline 1d, on the
other hand, produced a good yield of 2-phenylindole 3 at
450°C (47%, Entry 10), which decreased as the
temperature of the reaction was raised. Abstraction of the
methylene proton of one benzyl group followed by facile
cleavage of the N-C bond of the second benzyl group led
to the formation of an imine intermediate (Scheme 3). The
reaction also produced a fair amount of acridine 5 at the

May-Jun 2008
Thermal Reactions of N-Alkyl-2-benzylaniline and N-Alkyl-N'-phenyl-o-phenylenediamine
839
Scheme 3
Scheme 2
PhH2C
H3C
CH3
NH
CH2Ph
CH3
CH2Ph
N
N
N
H
1a
1b
1c
1d
-H+
-H+
-H+
-H+
PhH2C
H3C
CH2Ph
N
CH3
N
CHPh
CH2
N
N
-H
-CH2Ph
-CH3
-H
CHPh
N
CH2
N
9
9
-H+
-H+
CHPh
N
CH2
N
C
H
C
H
cyclization
cyclization
N
Ph
H
H
Ph
-H
-Ph
N
H
H
N
N
H
Ph
H
-H
rearrangement
H
H
rearrangement
tautomeric equilibrium
H
N
H
N
H
N
3
3
4
Scheme 4
H
N
N
N
2a
CH2R1
+
+
+
R1 = H
R2 = CH3
N
R2
N
N
8
CaO
7
5
H
N
N
H
N
2b
2a-b
R1 = Ph
N
N
R2 = CH2Ph
7
8
Scheme 3
Scheme 2
compared with N,N-dimethyl-N'-phenyl-o-phenylene-
diamine 2a, due to the facile cleavage of the N-C bond of
the benzylamino group which favored the cyclization
reaction over the formation of the imine intermediate
(Scheme 5) [7].
In another experiment, the proposition that the indole
and benzimidazole were formed through an imine
intermediate was investigated. N-Benzylidene-2-benzyl-
aniline 9 and N-benzylidene-N'-phenyl-o-phenylenedi-
amine were synthesized from 2-benzylaniline and

840
E. C. Creencia, K. Taguchi and T. Horaguchi
Vol 45
Table 2
Thermal cyclization[a] of N-alky-N'-phenyl-o-phenylenediamine 2a-b
Starting
material[b]
Reaction
temperature ( °C)
Reaction time[c]
(minutes)
Conversion
(%)
Product Yield[d] (%)
Entry
R1
R2
7
8
5
1
2
3
4
5
6
2a
2a
2a
2b
2b
2b
H
H
H
Ph
Ph
Ph
CH3
CH3
CH3
CH2Ph
CH2Ph
CH2Ph
450
500
560
450
500
560
40
40
40
40
40
40
100
100
100
100
100
100
31
32
14
33
37
21
9
6
5
52
37
20
11
11
6
-
-
-
[a] Nitrogen carrier gas at 19mL/minute; [b] 1.0 mmol; [c] The reaction time corresponds to the time in minutes for the traveling furnace to reach
the stationary furnace (see Experimental Section); [d] Based on 1H nmr data.
The results show that a good yield of 2-phenylindole 3
and 2,3-diphenylindole 4 (Table 3, Entry 1, 2) were
obtained from N-benzylidene-2-benzylaniline 9. This
proved that the unusual formation of 2-phenylindole 3
occurs via an imine intermediate. On the other hand, the
mechanism for the formation of benzimidazole via an
imine intermediate cannot be validated due to the
instability of N-benzylidene-N'-phenyl-o-phenylenedi-
amine that was synthesized. Fair amounts of acridine 5
and fluorene 10 were also obtained from the thermal
reactions of N-benzylidene-2-benzylaniline 9 at the three
temperatures (Entry 1, 2, 3).
N-phenyl-o-phenylenediamine, respectively. However,
the synthesized N-benzylidene-N'-phenyl-o-phenylenedi-
amine reverted back to the original amine during column
chromatography. Only N-benzylidene-2-benzylaniline 9
was subjected to thermal reactions and the results are
given in Table 3.
Scheme 5
H3C
PhH2C
CH2R
CH2R
N
N
N
H
2a
N
H
2b
EXPERIMENTAL
-H+
Melting points are uncorrected. Column chromatography was
performed on silica gel (Wakogel C-200). Unless otherwise
stated, anhydrous sodium sulfate was employed as the drying
agent. Ether refers to diethyl ether. The ir spectra were
determined on a Hitachi Model 270-30 IR Spectrophotometer.
-H+
H3C
PhH2C
CHR
CHR
N
N
1
The H and 13C nmr spectra were determined at 500 MHz and
N
H
N
H
125 MHz, respectively, on a Varian Unity plus-500W NMR
Spectrophotometer, using tetramethylsilane as the internal
standard.
-CH2Ph
-CH3
CHR
N
General Procedure for Thermolysis Reaction [8] of N-
Alkyl-2-benzylaniline 1a-d and N-Alkyl-N'-phenyl-o-phenyl-
enediamine 2a-b. Elemental analysis apparatus (Micro
Elemental Analyzer, Mitamura Riken Kogyo Inc.) was used for
the thermolysis reaction. Granules of calcium oxide were
obtained by grinding large pieces of calcium oxide (Nakalai
Tesque, Inc.) and collecting particles which passed through the 5
mm sieve and retained by the 2 mm sieve. A quartz tube (66 cm
in length, 12 mm i.d.) was packed to a length of 28 cm with the
calcium oxide granules (18.0 g). The tube was positioned in the
horizontal stationary furnace with heating coils (38 cm in
length). The column was then purged with N2 gas at a rate of
about 19 mL/min and kept at this condition throughout the
experiment. The stationary furnace was kept at the reaction
temperatureꢀ (450-600 °C). Starting material (1.0 mmole) was
weighed into a quartz boat and placed inside the reaction tube at
3 cm from the stationary furnace and vaporized by the traveling
furnace under N2 carrier gas. When the reaction temperature
was 450°C or 500°C, the stationary furnace was kept at 450 °C
or 500 °C while the traveling furnace was kept at 560°C. When
the reaction temperatures were 560°C and higher (temperature
of the stationary furnace), the traveling furnace was raised to
reaction temperature plus 50°C. The traveling furnace was set to
R
N
H
H
2a
2b
-H+
Ph
CHR
N
N
cyclization
N
R
H
N
Ph
-R
rearrangement
H
N
N
7

May-Jun 2008
Thermal Reactions of N-Alkyl-2-benzylaniline and N-Alkyl-N'-phenyl-o-phenylenediamine
841
Scheme 6
CHPh
H
N
H
N
N
N
CaO
+
+
+
9
3
4
10
5
Table 3
Thermal cyclization[a] of N-benzylidene-2-benzylaniline 9
Reaction
temperature
(°C)
Reaction
time[c]
(minutes)
Conversion
(%)
Product Yield[d] (%)
Entry
Starting material[b]
3
4
5
10
16
23
16
1
2
3
9
9
9
450
500
560
40
40
40
100
100
100
18
21
10
39
15
0
20
13
3
[a] Nitrogen carrier gas at 19mL/minute; [b] 1.0 mmol; [c] The reaction time corresponds to the time in minutes for the traveling furnace
to reach the stationary furnace (see Experimental Section); [d] Based on reacted starting material.
motion gradually, reached the stationary furnace in 35 minutes
and kept for 5 minutes at this state. Products which came from
the outlet (5 mm i.d.) of the quartz tube were collected in a
vessel cooled with ice-water. The products were extracted with
acetone. After removal of the acetone, the residue was
chromatographed on a silica gel column and eluted with
benzene, benzene-hexane or benzene-ethyl acetate to give a
variety of products. Structures of the products were determined
from their spectra. Compounds 3, 5, 6, 7, and 8 were identified
(d, J=7.5 Hz, 2H, 2 Ar-H), 7.25 (dd, J=7.5 Hz and 7.5 Hz, 2H, 2
Ar-H); 13C nmr (deuteriochloroform): δ 36.6 (t), 45.2 (q), 119.5
(d), 123.4 (d), 125.8 (d), 126.9 (d), 128.3 (d), 129.2 (d), 130.9
(d), 135.9 (s), 141.8 (s), 152.9 (s). Anal. Calcd for C15H17N: C,
85.26; H, 8.11; N, 6.63. Found: C, 85.14; H, 8.04; N, 6.72.
N-Benzyl-2-benzylaniline (1c). 2-Benzylaniline (1.632 g,
8.91 mmol), benzaldehyde (4.74 mL, 44.6 mmol), sodium
acetate trihydrate (3.80 g, 26.76 mmol) and acetic acid (7.5 mL,
128.4 mmol) were added to ethanol (20 mL). The mixture was
stirred for 30 minutes at room temperature. To the solution,
sodium borohydride (1.65 g, 44.6 mmol) was added under
cooling with ice-water and the solution was stirred for another
30 minutes. 2 M Sodium hydroxide solution was then added
until alkaline and the solution was extracted with ether. The
extract was washed, dried over sodium sulfate and evaporated.
The product was chromatographed on a silica gel column and
eluted with benzene:hexane (4:1) to give N-benzyl-2-benzyl-
aniline 1c (1.893 g, 78%, crystals) [10]. Recrystallization from
ethanol gave colorless crystals, mp 38-40°C; ir(KBr): 3432 cm-1
(NH); 1H nmr (deuteriochloroform): δ 3.90 (s, 2H, CH2), 4.23 (s,
2H, CH2-N), 6.61 (d, J=7.5 Hz, 1H, Ar-H), 6.71 (dd, J=7.5 Hz
1
by comparison of the ir, H nmr and 13C nmr spectra with those
of commercially available samples and compound
comparison of its spectral data with literature value.
4 by
N-Methyl-2-benzylaniline (1a) and N,N-Dimethyl-2-benz-
ylaniline (1b). 2 M Sodium hydroxide solution (5 mL) was
added to a mixture of 2-benzylaniline (0.71 g, 3.87 mmol) and
water (10 mL). To the mixture, dimethylsulfoxide (1.36 mL, 11
mmol) was added and the mixture was stirred for 3 hours at
room temperature. When the solution became acidic, 2 M
sodium hydroxide was added to keep it basic. After reaction, the
mixture was extracted with ether. The extract was washed, dried
over sodium sulfate and evaporated. The product was chromato-
graphed on a silica gel column and eluted with benzene:hexane
(4:1) to give N-methyl-2-benzylaniline 1a (0.159 g, 21%,
colorless crystals from ethanol, mp 39-40°C) and N,N-dimethyl-
2-benzylaniline 1b (0.397g, 49%, colorless oil) [9].
and 7.5 Hz, 1H, Ar-H), 7.06-7.28 (m, 13H, 12 Ar-H, 1 NH); 13
C
nmr (deuteriochloroform): δ 38.3 (t), 48.0 (t), 110.9 (d), 117.3
(d), 124.7 (s), 126.5 (d), 127.1 (d), 127.2 (d), 127.9 (d), 128.5
(d), 128.6 (d), 128.7 (d), 130.7 (d), 139.3 (s), 139.4 (s), 145.9
(s). Anal. Calcd for C20H19N: C, 87.87; H, 7.01; N, 5.12.
Found: C, 87.96; H, 7.02; N, 5.22.
N,N-Dibenzyl-2-benzylaniline (1d). 2-Benzylaniline (0.30
g, 1.64 mmol), benzyl bromide (0.40 mL, 3.36 mmol) and
potassium carbonate (0.464g, 3.36 mmol) were added to
dimethylsulfoxide (10 mL). The mixture was stirred for 2.5
hours at room temperature. The mixture was then extracted with
ether. The extract was washed, dried over sodium sulfate and
evaporated. The product was chromatographed on a silica gel
column and eluted with benzene:hexane (4:1) to give N,N-
dibenzyl-2-benzylaniline 1d (0.551g, 91%, colorless oil) [11];
1H nmr (deuteriochloroform): δ 4.05 (s, 4H, 2 NH2Ph), 4.18 (s,
2H, CH2Ph), 6.96 (d, J=7.5 Hz, 1H, Ar-H), 7.05-7.28 (m, 18H,
18 Ar-H); 13C nmr (deuteriochloroform): δ 36.5 (t), 57.9 (t),
N-Methyl-2-benzylaniline (1a). ir(KBr): 3436 cm-1 (NH); 1H
nmr (deuteriochloroform): δ 2.75 (s, 3H, CH3), 3.52 (broad s,
1H, NH), 3.86 (s, 2H, CH2), 6.64 (d, J=7.5 Hz, 1H, Ar-H), 6.72
(dd, J=7.5 Hz and 7.5 Hz, 1H, Ar-H), 7.02 (d, J=7.5 Hz, 1H, Ar-
H), 7.16 (d, J=7.5 Hz, 2H, 2 Ar-H), 7.18-7.22 (m, 2H, 2 Ar-H),
7.27 (dd, J=7.5 Hz and 7.5 Hz, 2H, 2 Ar-H); 13C nmr (deuterio-
chloroform): δ 30.8 (q), 38.0 (t), 110.1 (d), 117.1 (d), 124.6 (d),
126.4 (s), 127.9 (d), 128.5 (d), 128.7 (d), 130.5 (d), 139.4 (s),
147.3 (s). Anal. Calcd for C14H15N: C, 85.24; H, 7.66; N, 7.10.
Found: C, 85.30; H, 7.62; N, 7.22.
N,N-Dimethyl-2-benzylaniline (1b):
1H nmr (deuterio-
chloroform): δ 2.66 (s, 6H, 2 CH3), 4.10 (s, 2H, CH2), 6.96 (dd,
J=7.5 Hz and 7.5 Hz, 1H, Ar-H), 7.02 (d, J=7.5 Hz, 1H, Ar-H),
7.13 (d, J=7.5 Hz, 1H, Ar-H), 7.15-7.19 (m, 4H, 4 Ar-H), 7.18

842
E. C. Creencia, K. Taguchi and T. Horaguchi
Vol 45
123.3 (d), 124.2 (d), 125.8 (d), 126.5 (d), 126.9 (d), 128.1 (d),
128.3 (d), 128.9 (d), 129.2 (d), 130.9 (d), 137.4 (s), 138.3 (s),
141.5 (s), 149.6 (s). Anal. Calcd for C27H25N: C, 89.21; H, 6.93;
N, 3.85. Found: C, 89.34; H, 6.82; N, 3.94.
(d, J=7.5 Hz, 1H, 1 Ar-H), 8.23 (s, 1H, NH); 13C nmr
(deuteriochloroform) [13]: δ 110.9 (d), 115.0 (s), 119.7 (d),
120.4 (d), 122.7 (d), 126.2 (d), 127.7 (d), 128.2 (s), 128.5 (d),
128.7 (d), 128.7 (d), 130.1 (d), 132.7 (s), 134.1 (s), 135.0 (s),
135.9 (s). Spectral properties are identical with those in the
literature [14].
N,N-Dimethyl-N'-phenyl-o-phenylenediamine (2a). N-
Phenyl-o-phenylenediamine (1.14 g, 6.19 mmol), methyl iodide
(1.20 mL, 18.57 mmol) and tripotassium phosphate (0.03 g, 0.14
mmol) were added to dimethylsulfoxide (20 mL). The mixture
was kept at 60°C for 1 hour with constant stirring. When the
mixture became acidic, tripotassium phosphate (0.01g, 0.05
mmol) was added. The product was extracted with ether. The
extract was washed, dried over sodium sulfate and evaporated.
The product was chromatographed on a silica gel column and
eluted with benzene:hexane (4:1) to give N,N-dimethyl-N'-
phenyl-o-phenylenediamine 2a (1.093 g, 83%, colorless oil)
2-Phenylbenzimidazole (7).
mp (benzene) 290-291°C;
ir(KBr): 3050 cm-1 (NH); H nmr (deuteriochloroform): δ 7.26-
7.30 (m, 2H, 2 Ar-H), 7.46-7.50 (m,, 3H, 3 Ar-H), 7.65 (broad s,
1H, NH), 7.65-7.67 (m, 2H, 2 Ar-H), 8.07 (d, J=9.0 Hz, 1H, Ar-
H); 13C nmr (deuteriodimethylsulfoxide): δ 111.3 (d), 118.9 (d),
122.1 (d), 122.1 (d) 126.6 (d), 128.6 (d), 129.7 (d), 130.2 (s),
135.1 (s), 143.7 (s), 151.2 (s).
1
N-Benzylidene-2-benzylaniline (9). 2-Benzylaniline (0.366g,
2 mmol) and benzaldehyde (0.106g, 1 mmol) were added to
benzene (20 mL). The mixture was heated to 40°C for 2 hours
under constant stirring. The mixture was then extracted with
ether. The extract was washed, dried over anhydrous sodium
sulfate and evaporated. The product was chromatographed on a
silica gel column and eluted with hexane:ethyl acetate (5:1) to
give 55% N-benzylidene-2-benzyl-aniline 9 as a colorless oil.
1
[12]; ir(neat): 3368 cm-1 (NH); H nmr (deuteriochloroform): δ
2.66 (s, 6H, 2 CH3), 6.56 (s, 1H, NH), 6.84 (dd, J= 7.5 Hz and
7.5 Hz, 1H, Ar-H), 6.90 (dd, J=7.5 Hz and 7.5 Hz, 1H, Ar-H),
6.97 (dd, J=7.5 Hz and 7.5 Hz, 1H, Ar-H), 7.08 (d, J= 7.5 Hz,
1H, Ar-H), 7.14 (d, J=7.5 Hz, 2H, 2 Ar-H), 7.26 (dd, J=7.5 Hz
and 7.5 Hz, 2H, 2 Ar-H), 7.31 (d, J=7.5 Hz, 1H, Ar-H); 13C nmr
(deuteriochloroform): δ 44.0 (q), 114.3 (d), 118.1 (d), 119.7 (d),
119.9 (d), 120.8 (d), 124.0 (d), 129.1 (d), 137.9 (s), 142.3 (s),
142.8 (s). Anal. Calcd for C14H16N2: C, 79.21; H, 7.60; N, 13.20.
Found: C, 79.12; H, 7.72; N, 13.34.
1
ir(neat): 1620 cm-1 (C=N); H nmr (deuteriochloroform): δ 4.15
(s, 2H, CH2), 6.97 (d, J=7.5 Hz, 1H, Ar-H), 7.12-7.26 (m, 8H, 8
Ar-H), 7.46-7.49 (m, 3H, 3 Ar-H), 7.88-7.90 (m, 2H, 2 Ar-H),
8.32 (s, 1H, N=C-H); 13C nmr (deuteriochloroform): δ 37.4 (t),
117.8 (d), 125.7 (d), 125.9 (d), 127.3 (d), 128.2 (d), 128.7 (d),
128.7 (d), 129.0 (d), 129.9 (d), 131.2 (d), 135.1 (s), 136.4 (s),
141.4 (s), 150.5 (s), 159.7 (d).
N,N-Dibenzyl-N'-phenyl-o-phenylenediamine (2b). N-
Phenyl-o-phenylenediamine (0.10 g, 0.55 mmol), benzyl
bromide (0.13 mL, 1.1 mmol) and potassium carbonate (0.152 g,
1.1 mmol) were added to dimethylsulfoxide (10 mL). The
mixture was stirred for 2.5 hours at room temperature. The
mixture was then extracted with ether. The extract was washed,
dried over sodium sulfate and evaporated. The product was
chromatographed on a silica gel column and eluted with
hexane:ethyl acetate (3:1) to give N, N-dibenzyl-N'-phenyl-o-
phenylenediamine 2b (0.082 g, 41%, colorless oil) [13]; ir(neat):
Acknowledgement. ECC would like to thank the Japan
Society for the Promotion of Science (JSPS) for the research
grant at Niigata University, Japan. We thank Mr. Yoshiaki
Matsuda for the elemental analyses.
REFERENCES AND NOTES
1
3380 cm-1 (NH); H nmr (deuteriochloroform): δ 4.05 (s, 4H, 2
[1] Creencia, E.C.; Horaguchi, T. J. Heterocycl. Chem. 2006,
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PhCH2), 6.76 (dd, J=7.5 Hz and 7.5 Hz, 1H, A-H), 6.84 (s, 1H,
NH), 6.92 (dd, J=7.5 Hz and 7.5 Hz, 1H, Ar-H), 6.97 (dd, J=7.5
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Hz and 7.5 Hz, 1H, Ar-H), 7.03 (d, J=7.5 Hz, 1H, Ar-H), 7.06
13
(d, J=7.5 Hz, 2H, 2 Ar-H), 7.18-7.28 (m, 13H, 13 Ar-H);
C
nmr (deuteriochloroform): δ 57.3 (t), 114.3 (d), 118.7 (d), 119.4
(d), 121.1 (d), 123.6 (d), 124.9 (d), 127.1 (d), 128.2 (d), 128.9
(d), 129.2 (d), 137.9 (s), 138.7 (s), 139.3 (s), 142.8 (s). Anal.
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85.54; H, 6.68; N, 7.80.
2-Phenylindole (3). mp (ethanol) 187-188 °C; ir(KBr): 3444
1
cm-1 (NH); H nmr (deuteriochloroform): δ 6.83 (s, 1H, indole
C-H), 7.12 (dd, J=8.0 Hz and 8.0 Hz, 1H, Ar-H), 7.20 (dd, J=8.0
Hz and 8.0 Hz, 1H, Ar-H), 7.32 (dd, J=8.0 Hz and 8.0 Hz, 1H,
Ar-H), 7.40 (d, J=8.0 Hz, 1H, Ar-H), 7.45 (dd, J=8.0 Hz and 8.0
Hz, 2H, 2 Ar-H), 7.63 (d, J=8.0 Hz, 1H, Ar-H), 7.67 (d, J=8.0
Hz, 2H,
2
Ar-H), 8.33 (broad s, 1H, NH); 13C nmr
(deuteriochloroform): δ 100.0 (d), 110.9 (d), 120.2 (d), 120.6
(d), 122.3 (d), 125.1 (d), 127.7 (d), 129.0 (d), 129.2 (s), 132.3
(s), 136.8 (s), 137.9 (s).
2,3-Diphenylindole (4). mp (ethanol) 120-123°C (lit. [13]
1
mp 122-124°C); ir(KBr): 3400 cm-1 (NH); H nmr (deuterio-
chloroform): δ 7.15 (dd, J=7.5 Hz and 7.5 Hz, 1H, 1 Ar-H), 7.25
(dd, J=7.5 Hz and 7.5 Hz, 1H, 1 Ar-H), 7.29 (dd, J=7.5 Hz and
7.5 Hz, 1H, 1 Ar-H), 7.31 (dd, J=7.5 Hz and 7.5 Hz, 1H, 1 Ar-
H), 7.33 (dd, J=7.5 Hz and 7.5 Hz, 2H, 2 Ar-H), 7.38 (dd, J=7.5
Hz and 7.5 Hz, 2H, 2 Ar-H), 7.42 – 7.46 (m, 5H, 5 Ar-H), 7.68

May-Jun 2008
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