Oxidative dimerization of 4-methoxynaphthylamines in the presence of semiconductors

Article abstract of DOI:10.3987/COM-09-S(S)107

Three types of 4-methoxynaphthylamines 4a-c were oxidized by treatment with metal oxides under molecular oxygen (O₂). 4-Methoxy-1-naphthylamine 4a and 4,6-dimethoxy-1-naphthylamine 4b, on treatment with TiO₂ under O₂, gave mainly 2-amino-1,4-naphthoquinone derivatives 5a and 5b, respectively whereas 4,8-dimethoxy-1-naphthylamine 4c afforded an unique carbazole 6c as the major product.

Full text of DOI:10.3987/COM-09-S(S)107

HETEROCYCLES, Vol. 80, No. 2, 2010
1479
HETEROCYCLES, Vol. 80, No. 2, 2010, pp. 1479 - 1488. © The Japan Institute of Heterocyclic Chemistry
Received, 6th August, 2009, Accepted, 11th September, 2009, Published online, 15th September, 2009
DOI: 10.3987/COM-09-S(S)107
OXIDATIVE DIMERIZATION OF 4-METHOXYNAPHTHYLAMINES IN
§
THE PRESENCE OF SEMICONDUCTORS
Tetsuya Takeya,* Yosuke Takahashi, Iwao Okamoto, and Osamu Tamura*
Showa Pharmaceutical University, 3-3165 Higashi-tamagawagakuen, Machida,
Tokyo 194-8543, Japan
E-mail: tamura@ac.shoyaku.ac.jp
Abstract – Three types of 4-methoxynaphthylamines 4a-c were oxidized by
treatment
-Methoxy-1-naphthylamine 4a and 4,6-dimethoxy-1-naphthylamine 4b, on
treatment with TiO under O , gave mainly 2-amino-1,4-naphthoquinone
with
metal
oxides
under
molecular
oxygen
(O2).
4
2
2
derivatives 5a and 5b, respectively whereas 4,8-dimethoxy-1-naphthylamine 4c
afforded an unique carbazole 6c as the major product.
Most of semiconductor-mediated transformation of organic molecules are initiated by
1
-10
photo-irradiation, namely photo-catalytic reaction as well as electochemistry using semiconductors as
1
1,12
electrodes.
In stark contrast, we recently reported that oxidative dimerization of naphthols and
1
3-15
phenols mediated by semiconductors and molecular oxꢀgen (O2).
In this context, we would like to
report herein reactions of 4-methoxynaphthylamines by treatment with semiconductor and O2.
Preparation of the starting 4-methoxynaphthylamines is outlined in Scheme 1. O-Methylation of
1
-naphthols 1a-c by Me SO or MeI gave 1-methoxynaphthalenes 2a-c, which were treated with nitric
2 4
acid and acetic anhydride to provide 4-methoxy-1-nitronaphthalenes 3a-c. Finally, reduction of nitro
groups in 3a-c by hydrogenation afforded 4-methoxynaphthylamines 4a-c.
§
This paper is dedicated to Professor Emeritus Akira Suzuki, with respect and admiration, on the
occasion of his 80th birthday.

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HETEROCYCLES, Vol. 80, No. 2, 2010
Scheme 1
R1
R1
R1 NO2
R1 NH2
a) or b)
c)
d)
R2
R2
R2
R2
OH
OMe
OMe
OMe
1
2
1
2
1
2
1
2
1
1
1
a: R = R = H
2a: R = R = H
3a: R = R = H
4a: R = R = H
1
2
1
2
1
2
1
2
b: R = H, R = OH
2b: R = H, R = OMe
3b: R = H, R = OMe
4b: R = H, R = OMe
1
2
1
2
1
2
1
2
c: R = OH, R = H
2c: R = OMe, R = H
3c: R = OMe, R = H
4c: R = OMe, R = H
Conditions: a) Me SO , KOH, Bu NBr for 1a and 1b; b) MeI, K CO for 1c; c) cHNO , Ac O; d) H , Pd/C.
2
4
4
2
3
3
2
2
Before synthetic experiments, we measured cyclic voltammetry of 4a-c to examine their oxidation
ox
potentials (E s) (Table 1). The measurements showed low oxidation potentials, ca. 0.5 V for 4a and 4b
and 0.33 V for 4c in CH Cl . The oxidation potentials (0.37 V and 0.23 V for 4a and 4c, respectively) in
2
2
MeCN were further lower. These experiments implied that 4-methoxy-1-naphthylamines 4a-c readily
underwent single electron transfer (SET) reaction to give radical cation species.
a)
Table 1. Oxidative Potentials of 1-Naphthylamines
CH
2
Cl
2
MeCN
CH
2
Cl
2
MeCN
1
-Naphthylamine
1-Naphthylamine
OX b)
OX b)
OX b)
OX b)
E
E
E
E
NH2
MeO
NH2
0
.49 V
0.37 V
0.33 V
0.23 V
OMe
OMe
4a
4c
NH2
not
measured
0
.5 V
MeO
OMe
4b
a) Potentials (V) are versus Ag/AgCl; all substrates were measured in the range of about 0.0-2.0 V. The
oxidation potentials of anodic current (E) were obtained by cyclic voltammetry of 0.1 mM solutions of
the substrates in an argon-saturated solvent containing 0.1 M n-Bu NClO as a supporting electrolyte at a
4
4
-
1
ox
Pt electrode. The voltage scan rate in cyclic voltammetry was 100 mV s at 23 °C. b) E = the first
1
6
halfwave oxidation potential.
Oxidation of 4-methoxynaphthylamine 4a was first examined with various metal oxides, SnO , ZrO ,
2
2
NbO , and TiO in oxygen-saturated solvents (Table 2, entries 1-8). As a result, it was found that use of
5
2
TiO shortened reaction time both in CH Cl and in MeCN to give oxidative dimerized product,
2
2
2
aminoquinone 5a, as the major product along with small amount of another dimerized product, carbazole
a (entries 7 and 8). Next, oxidative dimerization of 4a with TiO in various solvents was conducted at
6
2

HETEROCYCLES, Vol. 80, No. 2, 2010
1481
room temperature (entries 9-14). The reaction did not proceed at room temperature in MeNO , DMF,
2
and dioxane probably due to reduced reactivity of TiO by coordination with the solvent (entries 10-12).
2
Use of aromatic solvents improved the reaction (entries 13-15). Thus, the reaction in benzene completed
even at room temperature within 3 h to afford 5a in 50% yield and a small amount (4%) of 6a (entry 13).
Considering toxicity of benzene, toluene was examined as the solvent (entries 14 and 15). Although the
reaction in toluene seemed to be slightly less efficient than that in benzene (entry 14), mild heating at
6
0°C accelerated the reaction to give 5a and 6a in comparable yield to that of entry 13 (entriy 15).
O
O
NH2
H
N
OMe
metal oxide/ O2
N
H
MeO
OMe
OMe
4
a
5a
6a
Table 2. Oxidative dimerization of 4a with various metal oxides
a)
Entry
Catalyst
Solvent
Temp. Time
Product (%)
Recovered 4a
(
°C)
(h)
96
53
96
48
96
30
3
5a
6a
(%)
36
1
2
3
4
5
6
7
8
9
SnO
SnO
2
2
CH
MeCN
CH Cl
MeCN
CH Cl
MeCN
CH Cl
2
Cl
2
rt
trace
–
70
rt
complex mixture
ZrO
ZrO
2
2
2
17
trace
12
12
2
70
rt
complex mixture
Nb
Nb
2
O
5
5
2
2
34
trace
2
O
70
rt
complex mixture
TiO
TiO
TiO
TiO
TiO
TiO
TiO
TiO
TiO
2
2
2
2
2
2
2
2
2
2
2
34
55
43
8
–
–
MeCN
MeCN
70
rt
3
trace
3
trace
10
11
12
13
14
15
MeNO
DMF
2
rt
3
no reaction
–
–
–
–
–
–
rt
3
no reaction
dioxane
benzene
toluene
toluene
rt
3
no reaction
rt
3
50
19
48
4
2
6
rt
3
60
0.5
a)
Isolated yield.
We next examined oxidation reaction of 4b by using TiO and O (Table 3). In the case of 4b, both
2
2
MeCN and toluene could be used for oxidation reaction. Thus, mild heating 4b with TiO in
2
oxygen-saturated solvents, MeCN and toluene afforded aminoquinone 5b in 36% and 38% yields,
respectively along with small amount of carbazole 6b (entries 2 and 4).

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HETEROCYCLES, Vol. 80, No. 2, 2010
O
NH2
H
N
MeO
OMe MeO
OMe
TiO / O2
2
N
H
MeO
O
MeO
OMe
OMe
OMe
4b
5b
6b
Table 3. Oxidative dimerization of 4b with TiO2
a)
Entry
Solvent
Temp.
Time
(h)
3
Product (%)
(°C)
5b
33
36
25
38
17
6b
6
1
MeCN
MeCN
toluene
toluene
toluene
rt
2
70
rt
0.5
2.5
0.5
0.5
6
3
6
4
60
2
5
100
-
a)
Isolated yield.
4
,8-Dimethoxynaphthyl-1-amine (4c) having the lowest oxidation potential indicated different
distribution of the products (Table 4). Naphthylamine 4c reacted with TiO in oxygen-saturated MeCN
2
at room temperature to give equal amount (23% yield, each) of aminoquinone 5c and carbazole 6c (entry
1
). Use of higher reaction temperature led to increase of aminoquinone 5c (entry 2). Oxidation
reaction of 4c in toluene showed reversal of distribution of product (entry 3). Thus, reaction of 4c at
room temperature in toluene for 1.5 h provided carbazole 6c in 63% yield accompanied by aminoquinone
5
c in 27% yield.
OMe MeO
O
OMe NH2
H
N
OMe
TiO / O
2
2
N
H
OMe O
MeO
OMe
OMe
MeO
4c
5c
6c
Table 4. Oxidative dimerization of 4c with TiO2
a)
Entry
Solvent
Temp.
Time
(h)
3
Product (%)
(°C)
5c
23
40
27
6c
23
17
63
1
MeCN
MeCN
toluene
rt
2
70
rt
4
3
1.5
a)
Isolated yield.

HETEROCYCLES, Vol. 80, No. 2, 2010
1483
Although the detailed mechanism for the formation of 5 and 6 remains unclear, it may involve radical
cation A (Scheme 2). Thus, the electron-rich 1-naphthylamine 4 causes SET reaction to generate radical
cation A, which subsequently looses a proton to lead radical B. SET reaction of radical B gives cation C,
which undergoes hydrolysis to provide quinone D. Finally, nucleophilic addition of 4 to quinone D
followed by oxidation affords aminoquinone 5. On the other hand, long-lived radical cation A can react
with another 4 to give intermediate E, which causes cyclization to yield 6 via intermediates F and G.
Accordingly, electron-rich 4c tends to afford carbazole 6c. Use of toluene, a non-polar solvent, might
stabilize A by suppressing SET reaction of B into C leading to quinone 5, and hence carbazole 6c became
the main product (Table 4, entry 3).
Scheme 2
NH2
NH
NH2
NH
O
–H+
–
e•
–e•
hydrolysis
4
5
OMe
OMe
nucleophlic
addition
and oxidation
OMe
OMe
O
4
C
D
etc
etc
A
B
4
NH2
NH2
NH2
NH
H
N
H
–H+
e•
H
NH
2
H
–
–NH
3
6
H
MeO
OMe
OMe
OMe
OMe
OMe
E
F
G
EXPERIMENTAL
All melting points are uncorrected. Infrared (IR) spectra were recorded with a JASCO IR-700
1
13
spectrometer, and H- and C-NMR spectra with JEOL JNM-AL300 with tetramethylsilane as an internal
standard. Mass spectra were recorded on a JEOL JMS-D300 or Shimadzu QP-5000 spectrometer.
Merck Kieselgel 60 (230–400 mesh), Wako silica gel C-200 were used for column chromatography.
1
7
Although compounds 3a and 3c are known, their preparation and characterization are presented here.
1
-Methoxynaphthalene (2a)
Dimethyl sulfate (420 mL, 4.5 mol) was added dropwise to a stirred mixture of 1-naphthol (1a, 400 g, 2.8
mol), tetra-n-butylammonium bromide (116 g, 0.36 mol) in THF (760 mL) and a solution of KOH (500 g,
8
.9 mol) in water (300 mL) at 0 °C, and the mixture was further stirred for 1.5 h at the same temperature.

1484
HETEROCYCLES, Vol. 80, No. 2, 2010
To the mixture was added a 10% aqueous solution of NaOH (500 mL). The whole was extracted with
AcOEt (1.5 L x 3), and organic layer was washed with water and brine, dried (MgSO ), and concentrated
4
in vacuo. The crude product was purified by column chromatography on silica gel (CH Cl ) to give 2a
2
2
-
1
1
(
420 g, 95%) as an oil. IR (KBr) cm : 1580. H-NMR (300 MHz, CDCl ) ꢀ: 4.00 (3H, s), 6.81 (1H, dd,
3
1
3
J = 1.5, 7.0 Hz), 7.35-7.51 (4H, m), 7.79 (1H, m), 8.26 (1H). C-NMR (75 MHz, CDCl ) ꢀ: 55.2, 103.7,
3
+
1
20.1, 121.9, 125.1, 125.5, 125.8, 126.3, 127.4, 134.4, 155.3. LR-MS m/z: 158 (M ). HR-MS m/z:
1
58.0734 (Calcd for C H O: 158.0732).
1
1
10
1
-Methoxy-4-nitronaphthalene (3a)
A mixture of nitric acid (51 mL, 0.56 mol) in acetic anhydride (100 mL, 0.98 mol) was added dropwise to
a solution of 2a (92 g, 0.63 mol) in acetic anhydride (280 mL, 2.7 mol) at 0 °C, and the resulting mixture
was stirred at the same temperature for 4 h. To the mixture was added ice-cold water, and the mixture
was stirred for 5 h. The precipitates were collected by filtration and purified by column chromatography
on silica gel (n-hexane-AcOEt, 1:20) to give 3a (64 g, 50%) as yellow needles. mp 85.0-87.0 °C
-
1
1
(
CH Cl -hexane). IR (KBr) cm : 1625. H-NMR (300 MHz, CDCl ) ꢀ: 4.11 (3H, s), 6.83 (1H, d, J = 8.8
2
2
3
Hz), 7.60 (1H, m, 6 or 7-H), 7.74 (1H, m, 6 or 7-H), 8.38 (1H, dd, J = 0.7, 1.0, 8.5 Hz, 5 or 8-H), 8.41
1
3
(
1H, d, J = 8.6 Hz, 3-H), 8.79 (1H, dd, J = 0.7, 0.9, 8.7 Hz). C NMR (75 MHz, CDCl ) ꢀ: 56.0, 101.6,
3
+
1
2
22.5, 123.0, 125.1, 126.2, 126.4, 127.0, 129.7, 138.6, 160.3. LR-MS m/z: 203 (M ). HR-MS m/z:
03.0599 (Calcd for C H NO : 203.0582).
1
1
9
3
4
-Methoxy-1-naphthylamine (4a)
A mixture of 3a (1.00 g, 4.9 mmol) and 10% Pd-C (200 mg) in THF was stirred at room temperature for 3
h under an atmosphere of hydrogen. The mixture was filtered through a pad of Celite, and the filtrate
was concentrated in vacuo. The crude product was purified by column chromatography on silica gel
(n-hexane-AcOEt, 2:1) to give 4a (721 mg, 85%) as crystals. mp 38.0-40.0 °C (Et O-n-hexane). IR
2
-
1
1
(
KBr) cm : 3360, 3185. H NMR (300 MHz, CDCl ) ꢀ: 3.94 (3H, s), 6.67 (1H, d, J = 8.1 Hz), 6.72 (1H, d,
3
1
3
J = 8.1 Hz), 7.49 (2H, m), 7.82 (1H, m), 8.24 (1H, m). C-NMR (75 MHz, CDCl ) ꢀ: 55.8, 104.4, 109.6,
3
+
1
20.9, 122.5, 125.2, 125.2, 125.6, 126.1, 135.2, 149.2. LR-MS m/z: 173 (M ). HR-MS m/z: 173.0855
(
Calcd for C H NO: 173.0841).
11 11
1
,7-Dimethoxynaphthalene (2b)
Using a procedure similar to that for the preparation of 2a, treatment of 1,7-naphthalenediol 1b (15.0 g,
4 mmol) with dimethyl sulfate (97 mL, 1.0 mol), tetra-n-butylammonium bromide (3.90 g, 12 mmol),
and KOH (116 g, 2.1 mol) in THF-water (1:2, 150 mL) gave crude product, which was purified by
9

HETEROCYCLES, Vol. 80, No. 2, 2010
1485
column chromatography on silica gel (n-hexane-AcOEt, 1:10) to afford 2b (17 g, 95%) as an oil. IR
-
1
1
(
KBr) cm : 1630, 1605, 1510. H-NMR (300 MHz, CDCl ) ꢀ: 3.75 (3H, s), 3.85 (3H, s), 6.76 (1H, d, J =
3
7
.7 Hz), 7.00 (1H, dd, J = 2.6, 9.5 Hz), 7.10 (1H, br t, J = 7.9 Hz), 7.24 (1H, d, J = 8.1 Hz), 7.40 (1H, d, J
1
3
=
2.6 Hz), 7.60 (1H, d, J = 8.9 Hz). C-NMR (75 MHz, CDCl ) ꢀ: 55.7, 55.9, 101.3, 105.4, 119.8, 120.9,
3
+
1
24.5, 127.5, 130.1, 130.9, 155.5, 158.5. LR-MS m/z: 188 (M ). HR-MS m/z: 188.0813 (Carcd for
C H O : 188.0837).
1
2
12
2
1
,7-Dimethoxy-4-nitronaphthalene (3b)
Using a procedure similar to that for the preparation of 3a, treatment of 2b (5.00 g, 27 mmol) with nitric
acid (2.1 mL, 24 mmol) in acetic anhydride (16 mL) gave crude product, which was purified by column
-
1
chromatography on silica gel (n-hexane-AcOEt, 1:20) to afford 3b (2.1 g, 35%). IR (KBr) cm : 1605.
1
H-NMR (300 MHz, CDCl ) ꢀ: 3.95 (3H, s), 4.09 (3H, s), 6.77 (1H, d, J = 8.6 Hz), 7.35 (1H, dd, J = 2.7,
3
1
3
9
.5 Hz), 7.60 (1H, d, J = 2.8 Hz), 8.24 (1H, d, J = 8.8 Hz), 8.68 (1H, d, J = 9.5 Hz). C-NMR (75 MHz,
CDCl ) ꢀ: 55.4, 56.3, 101.1, 102.3, 122.0, 122.2, 124.5, 125.3, 127.1, 139.3, 158.0, 159.3. LR-MS m/z:
3
+
2
33 (M ). HR-MS m/z: 233.0684 (Carcd for C H NO : 233.0688).
1
2
11
4
4
,6-Dimethoxy-1-naphthylamine (4b)
Using a procedure similar to that for the preparation of 4a, treatment of 3b (1.50 g, 6.4 mmol) with 10%
Pd-C (300 mg) in THF (10 mL) under hydrogen gave crude product, which was purified by column
chromatography on silica gel (n-hexane-AcOEt, 1:10) to afford 4b (1.10 g, 88%). mp 77.0-79.0 °C
-
1
1
(
Et O-n-hexane). IR (KBr) cm : 3385, 3215. H-NMR (300 MHz, CDCl ) ꢀ: 3.94 (6H, br s), 6.57 (1H, d,
2 3
J = 8.1 Hz), 6.66 (1H, d, J = 8.1 Hz), 7.15 (1H, dd, J = 2.8, 9.2 Hz), 7.54 (1H, d, J = 2.6 Hz), 7.73 (1H, d,
1
3
J = 9.2 Hz). C-NMR (75 MHz, CDCl ) ꢀ: 55.3, 55.8, 100.9, 105.3, 107.6, 117.9, 120.4, 122.8, 127.2,
3
+
1
35.4, 148.3, 157.4. LR-MS m/z: 203 (M ). HR-MS m/z: 203.0947 (Carcd for C H NO : 203.0946).
1
2
13
2
4
,8-Dimethoxy-1-naphthylamine (2c)
A mixture of 1,5-naphthalenediol (1c, 5.00 g, 31 mmol), methyl iodide (9.7 mL, 0.16 mol), and K CO in
2
3
DMF (50 mL) was stirred at room temperature for 2 h. The mixture was poured into ice-cold water (50
mL), and the resulting precipitates were collected by filtration to give sufficiently pure 2c (4.7 g, 80%) as
-
1
1
granules. mp 181.0-183.0 °C (CH Cl -n-hexane). IR (KBr) cm : 1595. H-NMR (300 MHz, CDCl ) ꢀ:
2
2
3
1
3
3
.99 (6H, s), 6.84 (2H, d, J = 7.7 Hz), 7.37 (2H, br t, J = 8.3 Hz), 7.83 (2H, d, J = 8.8 Hz). C-NMR (75
+
MHz, CDCl ) ꢀ: 55.5, 104.5, 114.2, 125.1, 126.6, 155.2. LR-MS m/z: 188 (M ). HR-MS m/z: 188.0826
3
(
Calcd for C H O : 188.0837).
12 12 2

1486
HETEROCYCLES, Vol. 80, No. 2, 2010
1
,5-Dimethoxy-4-nitronaphthalene (3c)
Using a procedure similar to that for the preparation of 3a, treatment of 2c (1.00 g, 5.3 mmol) with nitric
acid (0.4 mL, 4.7 mol) in acetic anhydride (8 mL) gave crude product, which was purified by column
chromatography on silica gel (n-hexane-AcOEt, 1:20) to afford 3c (540 mg, 43%) as granules. mp
-
1
1
1
66.0-168.0 °C (CH Cl -hexane). IR (KBr) cm : 1595, 1530, 1515. H-NMR (300 MHz, CDCl ) ꢀ: 3.92
2 2 3
(3H, s), 4.04 (3H, s), 6.75 (1H, d, J = 8.3 Hz, 2-H), 7.02 (1H, dd, J = 0.7, 7.8 Hz), 7.50 (1H, br t, J = 8.2
1
3
Hz), 7.50 (1H, d, J = 8.3 Hz, 3-H), 7.91 (1H, dd, J = 0.9, 8.6 Hz). C-NMR (75 MHz, CDCl ) ꢀ: 56.0,
3
+
5
6.1, 102.3, 108.4, 114.7, 117.2, 127.2, 132.4, 141.0, 153.7, 157.1. LR-MS m/z: 233 (M ). HR-MS m/z:
2
33.0701 (Calcd for C H NO : 233.0688).
1
2
11
4
4
,8-Dimethoxy-1-naphthylamine (4c)
Using a procedure similar to that for the preparation of 4a, treatment of 3c (1.00 g, 4.3 mmol) with 10%
Pd-C (200 mg) in THF (60 mL) under hydrogen gave crude product, which was purified by column
chromatography on silica gel (n-hexane-CH Cl , 1:1) to afford 4c (742 mg, 85%) as grnules. mp
2
2
-
1
1
1
58.0-160.0 °C (CH Cl -n-hexane). IR (KBr) cm : 3495, 3380. H-NMR (300 MHz, CDCl ) ꢀ: 3.91 (3H,
2 2 3
s), 3.96 (3H, s), 6.52 (1H, d, J = 8.3 Hz), 6.70 (1H, d, J = 8.3 Hz), 6.77 (1H, dd, J = 0.9, 7.7 Hz), 7.30 (1H,
1
3
br t, J = 8.1 Hz), 7.80 (1H, dd, J = 1.0, 8.5 Hz). C-NMR (75 MHz, CDCl ) ꢀ: 55.7, 55.1, 104.8, 106.5,
3
+
1
09.1, 115.0, 116.1, 125.2, 128.4, 138.1, 147.3, 157.4. LR-MS m/z: 203 (M ). HR-MS m/z: 203.0978
(
Calcd for C H NO : 203.0946).
12 13 2
2
-(4-Methoxynaphthalen-1-ylamino)-1,4-naphthoquinone (5a) and 5,8-dimethoxy-13H-dibenzo[a,i]-
carbazole (6a)
Oxygen was sufficiently bubbled through a mixture of 4a (50 mg, 0.29 mmol) and TiO (1.00 g, 0.63
2
mmol) in toluene (15 mL). The mixture was heated under oxygen in a sealed tube at 60 °C for 0.5 h.
The mixture was filtered through a pad of Celite, and the filtrate was concentrated in vacuo. The crude
product was chromatographed on silica gel (n-hexane-CH Cl , 5:1) to give 5a (23.0 mg, 48%), 6a (2.8 mg,
2
2
6
%).
a: Red granules, mp 199.0-201.0 °C (CH Cl -n-hexane). IR (KBr) cm : 3375, 1630, 1600. H-NMR
-
1
1
5
2
2
(
300 MHz, CDCl ) ꢀ: 4.05 (3H, s), 6.83 (1H, d, J = 8.3 Hz), 7.38 (1H, t, J = 8.1 Hz), 7.54 (2H, m), 7.58
3
(1H, s), 7.67 (1H, dt, J = 1.5, 7.5 Hz), 7.75 (1H, dd, J = 1.5, 7.5 Hz), 7.80 (1H, m), 8.08 (1H, dd, J = 1.5,
1
3
7
1
1
6
.5 Hz), 8.12 (1H, dd, J = 1.5, 7.5 Hz), 8.33 (1H, m). C-NMR (75 MHz, CDCl ) ꢀ: 55.8, 103.2, 103.4,
3
21.8, 122.9, 123.9, 125.3, 126.0, 126.2, 126.3, 126.4, 127.5, 130.0, 130.6, 132.2, 133.5, 134.9, 147.5,
+
55.0, 182.3, 183.7. LR-MS m/z: 329 (M ). HR-MS m/z: 329.1029 (Calcd for C H NO : 329.1052).
2
1
15
3
-
1
1
a: Colorless sylup. IR (KBr) cm : 3315. H-NMR (DMSO-d ) ꢀ: 4.16 (6H, s), 7.60 (2H, t, J = 7.3 Hz),
6

HETEROCYCLES, Vol. 80, No. 2, 2010
1487
7
.76 (2H, t, J = 7.3 Hz), 7.81 (2H, s), 8.34 (2H, d, J = 7.3 Hz), 8.71 (2H, d, J = 7.3 Hz), 12.40 (1H, s).
+
LR-MS m/z: 327 (M ).
7
-Methoxy-2-(4,6-dimethoxynaphthalen-1-ylamino)-1,4-naphthoquinone (5b) and 3,5,8,10-tetra-
methoxy-13H-dibenzo[a,i]carbazole (6b)
a) Using a procedure similar to that for the preparation of 5a and 6a, treatment of 4b (50 mg, 0.25 mmol)
(
with TiO (1.00 g, 0.63 mmol) in MeCN (15 mL) at 70 °C under oxygen gave crude product, which was
2
purified by column chromatography on silica gel (n-hexane-CH Cl , 2:1) to afford 5b (17.5 mg, 36%) and
2
2
6
b (2.9 mg, 6%).
(
b) The same reaction in toluene at 60 °C afforded 5b (18.5 mg, 38%) and 6b (1.0 mg, 2%).
-
1
1
5
b: IR (KBr) cm : 3330, 1665, 1630. H-NMR (300 MHz, CDCl ) ꢀ: 3.950 (3H, s), 3.954 (3H, s), 4.04
3
(3H, s), 5.78 (1H, s), 6.81 (1H, d, J = 8.2 Hz), 7.11 (1H, dd, J = 2.6, 8.6 Hz), 7.19 (1H, dd, J = 2.6, 9.3
Hz), 7.22 (1H, d, J = 8.4 Hz), 7.55 (1H, d, J = 2.6 Hz), 7.60 (1H, d, J = 2.6 Hz), 7.65 (1H, s), 7.71 (1H, d,
1
3
J = 9.3 Hz), 8.10 (1H, d, J = 8.4 Hz). C-NMR (75 MHz, CDCl ) ꢀ: 55.4, 55.7, 55.9, 101.2, 102.7, 103.9,
3
1
1
6
09.8, 118.6, 119.9, 121.1, 123.6, 123.8, 125.1, 125.5, 127.4, 129.0, 136.2, 147.8, 153.8, 157.9, 165.1,
+
80.8, 183.3. LR-MS m/z: 389 (M ). HR-MS m/z: 389.1286 (Carcd for C H NO : 389.1263).
2
3
19
5
-
1
1
b: Blue purple powder, mp 257.0-261.0 °C (CH Cl -n-hexane). IR (KBr) cm : 3400. H-NMR (300
2
2
MHz, CDCl ) ꢀ: 3.82 (6H, s), 4.00 (6H, s), 7.14 (2H, dd, J = 2.6, 9.0 Hz), 7.55 (2H, s), 7.61 (2H, d, J =
3
1
3
2
.6 Hz), 8.30 (2H, d, J = 9.0 Hz), 11.21 (1H, s). C-NMR (75 MHz, CD Cl ) ꢀ: 55.5, 55.9, 97.1, 103.0,
2 2
+
1
17.1, 117.3, 118.0, 121.8, 125.7, 128.7, 149.5, 157.0. LR-MS m/z: 387 (M ). HR-MS m/z: 387.1502
(
Carcd for C H NO : 387.1470).
24 21 4
8
-Methoxy-2-(4,8-dimethoxynaphthalen-1-ylamino)-1,4-naphthoquinone (5c) and 1,5,8,12-tetra-
methoxy-13H-dibenzo[a,i]carbazole (6c)
Using a procedure similar to that for the preparation of 5a and 6a, treatment of 4c (50 mg, 0.25 mmol)
with TiO (1.00 g, 0.63 mmol) in toluene (15 mL) at room temperature under oxygen gave crude product,
2
which was purified by column chromatography on silica gel (CH Cl ) to afford 5c (13.1 mg, 27%) and 6c
2
2
(
30.5 mg, 63%).
-
1
1
5
c: Purple granules, mp 209.0-211.0 °C (CH Cl -n-hexane). IR (KBr) cm : 3450, 1670, 1625. H-NMR
2 2
(
(
(
300 MHz, CDCl ) ꢀ: 4.01 (3H, s), 4.06 (3H, s), 4.09 (3H, s), 6.54 (1H, s), 6.83 (1H, d, J = 8.6 Hz), 6.94
3
1H, d, J = 7.7 Hz), 7.22 (1H, d, J = 8.3 Hz, 7-H), 7.407 (1H, t, J = 8.2), 7.409 (1H, d, J = 8.4 Hz), 7.68
1
3
1H, t, J = 8.1 Hz), 7.80 (1H, d, J = 8.1 Hz), 7.92 (1H, d, J = 8.4 Hz), 10.14 (1H, s). C-NMR (75 MHz,
CDCl ) ꢀ: 55.8, 56.2, 56.5, 100.0, 104.0, 107.0, 115.3, 115.9, 118.5, 118.8, 119.6, 119.7, 125.9, 127.4,
3
+
1
28.3, 135.9, 136.0, 146.0, 152.5, 156.1, 160.1, 180.9, 183.6. LR-MS m/z: 389 (M ). HR-MS m/z:

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HETEROCYCLES, Vol. 80, No. 2, 2010
3
89.1270 (Calcd for C H NO : 389.1263).
23 19 5
-
1
1
6
c: Colorless crysrtals, mp over 300 °C (CH Cl -n-hexane). IR (KBr) cm : 3490. H-NMR (300 MHz,
2 2
DMSO-d ) ꢀ: 4.10 (6H, s), 4.26 (6H, s), 7.25 (2H, d, J = 7.7 Hz), 7.49 (2H, t, J = 8.1 Hz), 7.85 (2H, s),
6
1
3
7
1
.90 (2H, d, J = 8.1 Hz), 11.27 (1H, s). C-NMR (75 MHz, DMSO-d ) ꢀ: 55.9, 56.2, 98.0, 106.0, 113.2,
6
+
15.0, 116.7, 124.6, 125.4, 126.1, 148.6, 155.1. LR-MS m/z: 387 (M ). HR-MS m/z: 387.1463 (Calcd for
C H NO : 387.1470).
2
4
21
4
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