Synthesis of benzo[b]naphtho[2,3-d]thiophene-6,11-diones via palladium(II) acetate-mediated cyclization of 3-arylthio-1,4-naphthoquinone

Article abstract of DOI:10.3987/COM-05-10341

Palladium(II)-mediated oxidative cyclization of 3-arylthio-1,4- naphthoquinone (4) giving biologically important benzo[b]naphtho-[2,3-d] thiophene-6,11-diones (2) has been performed with a stoichiometric amount of palladium(II) acetate in distillated acet

Full text of DOI:10.3987/COM-05-10341

HETEROCYCLES, Vol. 65, No. 5, 2005
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HETEROCYCLES, Vol. 65, No. 5, 2005, pp. 1205 - 1214
Received, 18th January, 2005, Accepted, 24th February, 2005, Published online, 1st March, 2005
SYNTHESIS OF BENZO[b]NAPHTHO[2,3-d]THIOPHENE-6,11-DIONES
VIA PALLADIUM(II) ACETATE-MEDIATED CYCLIZATION OF
3-ARYLTHIO-1,4-NAPHTHOQUINONE
Chung-Kyu Ryu,* Ik Hwa Choi, Jung Yoon Lee, and Seong Hee Jung
College of Pharmacy, Ewha Womans University, 11-1 Daehyun-dong,
Seodaemun-ku, Seoul 120-750, Korea; E-mail: ckryu@ewha.ac.kr
Abstract – Palladium(II)-mediated oxidative cyclization of 3-arylthio-
1,4-naphthoquinone (4) giving biologically important benzo[b]naphtho-
[2,3-d]thiophene-6,11-diones (2) has been performed with a stoichiometric
amount of palladium(II) acetate in distillated acetic acid.
INTRODUCTION
Palladium-mediated annulation methodology has been effectively employed for the preparation of new
heterocyclic systems.1 Compounds containing the quinone group represent an important class of
biologically active molecules that are widespread in nature.2-3 The heterocyclic
benzo[b]naphtho[2,3-d]furan-6,11-dione derivatives (1) have received attention due to their potential
biological activities (Figure 1).4
O
O
O
R
R
Bioisostere
O
S
O
R = H, OCH3 or OH
R = H, OCH3, F, ...
1
2
Figure 1
This fact prompted us to consider an bioisosteric substitution of the 5'-oxygen (O) by sulfur (S). The
quinone analogues containing a sulfur such as benzo[b]naphtho[2,3-d]thiophene-6,11-diones (2) could
have similar activity as compounds (1) because sulfur is isoelectronic with oxygen. Therefore, we

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HETEROCYCLES, Vol. 65, No. 5, 2005
synthesized benzo[b]naphtho[2,3-d]thiophene-6,11-diones (2) as a bioisostere of the compounds (1)
(Figure 1).
As shown in Scheme 1, compounds (2) could be synthesized by either one-pot (Path B) or two step
synthesis (Path A) from 1,4-naphthoquinone (4) and appropriate arylthiols (6). Although one-pot
synthesis of compounds (2) seem to be much more attractive, the two step synthesis is much easier than
one-pot synthesis as a result of the difficulty in both the substitution reaction and the C-C coupling.
Herein, we report efficient two-step synthesis of compounds (2) via quantitative palladium(II)
acetate-mediated cyclization of 3-arylthio-1,4-naphthoquinones (7).
O
O
R1
R2
R3
S
b
7
a
Path A
R2
R1
S
O
O
O
O
R1
R2
R3
R3
b
+
HS
Path B
R1, R2, R3 = H, CH3,Cl,..
6
4
2
Reagents and conditions
a) 0.05 equiv. Pd(OAc)2, C2H5OH, rt, 4~6 h
b) 1 equiv. Pd(OAc)2, HOAc, reflux, argon, 2~40 h
Scheme 1
RESULTS AND DISCUSSION
The first step in Path A synthesis was preparation of 3-arylthio-1,4-naphthoquinones (7) according to
known process5 with modification (Scheme 1). For example, the substitution of 4-methylbenzenethiol
(6a) to the quinone (4) in the presence of 0.05 equivalent palladium(II) acetate as a catalyst in air at room
temperature for 5 h afforded 3-(4-methylphenylthio)-1,4-naphthoquinone (7a) in moderate yield (Scheme
2).

HETEROCYCLES, Vol. 65, No. 5, 2005
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O
O
O
O
CH3
Pd(OAc)2, C2H5OH
+
CH3
HS
air, rt, 5 h
S
6a
4
7a (85%)
Scheme 2 Substitution of 4-methylbenzenethiol (6a) to 1,4-naphthoquinone (4)
Otherwise, reactions in absence of the palladium(II) acetate provided the compound (7a) with poor yields
(15%) along with 2,3-bis(4-methylphenylthio)-1,4-naphthoquinone (8a) as a by-product (67%). The
desired product (7a) and the by-product (8a) were separated by column chromatography on silica gel
using CHCl3 as eluent.
O
S
S
CH3
O
8a
CH3
Ethanol for the reaction seems to be the best solvent. Acetic acid and THF were also tried, and in the
solvents the product (7a) were observed with lower yield than in ethanol (Table 1).
Table 1 Substitution of 4-methylbenzenethiol (6a) to 1,4-naphthoquinone (4)
entry
reaction condition
7 (%)a)
52
8 (%) 7/8 ratio
1
2
3
4
3
C2H5OH/ air/ reflux/ 5 h
34
23
0
6 : 4
HHOAc/ air/ reflux/ 5 h
41
2 : 1
0.05 equiv. Pd(OAc)2/ C2H5OH/ air/ reflux/ 5 h
0.05 equiv. Pd(OAc)2/ HOAc/ air/ reflux/ 5 h
0.05 equiv. Pd(OAc)2/ THF/ air/ reflux/ 5 h
85
-
-
-
6
0
70
0
a) isolated yield
A number of 3-arylthio-1,4-naphthoquinones (7) synthesized by employing the optimized reaction
condition (Scheme 1 and Table 1). The various 3-arylthio-1,4-naphthoquinones (7) were prepared by the
substitution of appropriate arylthiols (6) to the quinone (4) in the presence of 0.05 equivalent
palladium(II) acetate as a catalyst in air at room temperature for 5 h in moderate yield, respectively (Table
2).

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Table 2 Structure of afforded 3-arylthio-1,4-naphthoquinones (7)
O
R1
R2
R3
S
O
7
compounds
R1
H
Cl
H
H
CH3
H
R2
CH3
H
H
Cl
H
R3
H
H
H
H
CH3
H
H
yield (%)
7a
7b
7c
7d
7e
7f
85
55
62
65
74
65
56
F
H
7g
F
Reaction condition: 1.0 mmol quinone (4)/ 0.05 mmol Pd(OAc)2/ C2H5OH/ air/ rt/ 6 h
The second step in Path A synthesis was palladium(II)-mediated oxidative cyclization of compounds (7)
in acetic acid provided the desired products (2) (Scheme 1). For example, we refluxed the
3-(4-methylphenylthio)-1,4-naphthoquinone (7a) with stoichiometric amounts of palladium(II) acetate in
the distilled acetic acid under an argon atmosphere for about 40 h to afford 2-methyl-
benzo[b]naphtho[2,3-d]thiophene-6,11-dione (2a) (Scheme 3). The acetic acid seems to be the best
solvent for the oxidative cyclization. The purity of acetic acid is of primary importance for the
cyclization,5 but the reason for this is not known. Ethanol and THF were also tried, but in these solvents
no cyclization was observed (Table 3).
CH3
O
O
CH3
1 equiv. Pd(OAc)2, HOAc
argon, reflux, 40 h
S
S
O
O
7a
2a (55%)
Scheme 3 Oxidative cyclization of 3-(4-methylphenylthio)-1,4-naphthoquinone (7a)
Furukawa described the first palladium(II)-mediated oxidative cyclization of 3-phenylamino-
1,4-benzoquinones to carbazole-1,4-quinones.6 In the synthesis of benzo[b]carbarzole-6,11-diones,
Knölker demonstrated that this reaction becomes catalytic in palladium by reoxidation of Pd(0) to Pd(II)
with Cu(II).7-8 We also tried, but the catalytic condition by reoxidation with cupper(II) acetate was not
useful for getting the cyclized product (2a) (Table 3).

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Table 3 Oxidative cyclization of the quinone (7a) for getting the cyclized product (2a)
entry
solvent
HOAc
HOAc
HOAc
HOAc
C2H5OH
C2H5OH
THF
Cu(OAc)2
time
24 h
40 h
40 h
40 h
40 h
40 h
40 h
atmosphere
argon
argon
air
yield (%)
30%
55%
0
1
2
3
4
5
6
7
-
-
-
2.5 equiv.
argon
argon
argon
argon
trace
0
2.5 equiv.
-
-
0
trace
We refluxed the 0.2 mmol quinone (7a) with 0.2 mmol of Pd(OAc)2 in various conditions
In order to determine the versatility of this intramolecular C-C coupling process on a quinone system, a
number of benzo[b]naphtho[2,3-d]thiophene-6,11-diones (2) were synthesized by employing the
optimized
reaction
condition
(Scheme
1
and
Table
3).
The
various
benzo[b]naphtho[2,3-d]thiophene-6,11-diones (2) was obtained by clyclization of 3-arylthio-
1,4-naphthoquinones (7) with stoichiometric amounts of palladium(II) acetate in refluxed acetic acid
under an argon atmosphere for about 40 h (Table 4).
Table 4 Structure of benzo[b]naphtho[2,3-d]thiophene-6,11-diones (2)
R2
R1
O
R3
S
O
2
compounds
R1
H
Cl
H
H
CH3
H
R2
CH3
H
H
Cl
H
R3
H
H
H
H
CH3
H
H
yield (%)
2a
2b
2c
2d
2e
2f
47
25
30
41
55
26
38
F
H
2g
F
Reaction condition: 1 equiv. Pd(OAc)2/ HOAc/ argon/ reflux/ 40 h.

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As shown in Scheme 1, compounds (2) could be also synthesized by one pot synthesis of
1,4-naphthoquinone (4) with arylthiols (6) in both substitution reaction and the C-C coupling (Path B).
For example of one pot synthesis, the quinone (4) was reacted with 4-methylthiophenol (6a) and
stoichiometric amounts of palladium(II) acetate in refluxed acetic acid under an argon atmosphere for
about 2 h. As a result of unexpected discovery, the one-pot synthesis provided 2-(4-methylphenyl)-
1,4-naphthoquinone (9a) in major along with the desired product (2a) in low yields (Scheme 4). Although
the one-pot synthesis seems to be much more attractive than the two step route synthesis, the latter is
more favorable for getting the cyclized product (2a) than one-pot synthesis occurring both intra- and
intermolecular coupling all at once (Schemes 4 and 5).
CH3
CH3
O
O
O
O
1 equiv. Pd(OAc)2
+
CH3
HS
+
HOAc, argon, reflux, 2 h
S
O
O
6a
4
9a (45%)
2a (15%)
Scheme 4 One-pot synthesis
In
conclusion,
we
achieved
an
efficient
palladium
mediated
synthesis
of
benzo[b]naphtho[2,3-d]thiophene-6,11-diones (2). And we suggest that the palladium-mediated coupling
has potential for even wider application to the quinone series or sulfur chemistry especially as shown in
our study than described in the present work.
EXPERIMENTAL
All melting points were measured in open capillary tubes with a Büchi melting point B-545 and were
uncorrected. The TLC was performed on precoated silica gel (60G 254, Merck) using chloroform as a solvent.
The compounds were detected under UV light (254 nm) or by heating to 110 oC after spraying with a 30%
H2SO4-vanillin solution. Column chromatography was performed on silica gel G60 (70-230 mesh, ASTM,
Merck). 1H-NMR spectra were recorded on Unity Varian INOVA 400 MHz FT-NMR spectrometer using
CDCl3 as a solvent, and chemical shifts were given in ppm with TMS as a standard. High-resolution mass
(HRMS EI) spectra were taken from Jeol JMS AX505 WA. 1,4-Naphthoquinone, arylthiols, palladium(II)
acetate, CDCl3 and other reagents were purchased from Aldrich Chemical Co. Acetic acid was used after
purification by the distillation.

HETEROCYCLES, Vol. 65, No. 5, 2005
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General procedure for synthesis of 3-arylthio-1,4-naphthoquinones (7a-g)
A solution of 1,4-naphthoquinone (4) (158 mg, 1.0 mmol) and palladium(II) acetate (112 mg, 0.05 mmol)
in 20 mL of 95% ethanol was added to a solution of arylthiols (6) (1.1 mmol) in 10 mL of 95% ethanol
and then the mixture was stirred at rt for 4~6 h. After the reaction, the precipitate was
collected by the filtration. The crude product was purified by silica gel column chromatography with
EtOAc/n-hexane (1:2) or crystallized from 95% ethanol (Table 2).
2-(4-Methylphenylthio)-1,4-naphthoquinone (7a): Yellow powder (85%). mp 118℃ (lit.,5 mp
118-120℃). 1H-NMR (CDCl3) δ 8.12 (d, J=7.5 Hz, 1H, benzene), 7.99 (d, J=7.5 Hz, 1H, Ph-H), 7.70 (m,
1H, Ph-H), 7.38 (m, 2H, Ph-H), 7.26 (m, 2H, Ph-H), 6.09 (s, 1H, quinone), 2.48 (s, 3H, CH3). MS (m/z)
280 (M+). HRMS Calcd for C17H12O2S, 280.0558, Found: 280.0559.
2-(3-Chlorophenylthio)-1,4-naphthoquinone (7b): Yellow powder (55%). mp 155℃. 1H-NMR
(CDCl3) δ 8.11 (d, J= 7.7 Hz, 1H, benzene), 8.00 (d, J=7.7 Hz, 1H, benzene), 7.70 (m, 1H, Ph-H), 7.60 (m,
2H, Ph-H), 7.57 (m, 1H, Ph-H), 7.45 (t, J=7.7 Hz, 1H, benzene), 7.36 (m, 1H, Ph-H) ), 6.22 (s, 1H,
quinone). MS (m/z) 300 (M+). HRMS Calcd for C16H9O2ClS, 300.0012, Found: 300.0012.
1
2-Phenylthio-1,4-naphthoquinone (7c): Yellow powder (62%). mp 159℃ (lit.,5 mp 159℃). H-NMR
(CDCl3) δ 8.15 (m, 1H, Ph-H), 8.03 (m, 1H, Ph-H), 7.73 (m, 1H, Ph-H), 7.54 (m, 5H, Ph-H), 6.12 (s, 1H,
quinone). MS (m/z) 266 (M+). HRMS Calcd for C16H10O2S, 266.0401, Found: 266.0403.
2-(4-Chlorophenylthio)-1,4-naphthoquinone (7d): Yellow powder (65%). mp 149℃ (lit.,5 mp
149-50℃). 1H-NMR (CDCl3) δ 8.15 (d, J=7.3 Hz, 1H, Ph-H), 8.03 (d, J=7.3 Hz, 1H, Ph-H), 7.74 (m, 2H,
Ph-H), 7.46 (m, 4H, benzene), 6.08 (s, 1H, quinone). MS (m/z) 300 (M+). HRMS Calcd for C16H9O2ClS,
300.0012, Found: 300.0013.
1
2-(3,5-Dimethylphenylthio)-1,4-naphthoquinone (7e): Yellow powder (74%). mp 115℃. H-NMR
(CDCl3) δ 8.11 (m, 1H, Ph-H), 8.00 (m, 1H, Ph-H), 7.70 (m, 1H, Ph-H), 7.12 (s, 1H, benzene), 7.10 (s,
2H, benzene), 6.13 (s, 1H, quinone), 2.78 (s, 6H, CH3). MS (m/z) 294 (M+). HRMS Calcd for C18H14O2S,
294.0715, Found: 294.0714.
2-(4-Fluorophenylthio)-1,4-naphthoquinone (7f): Yellow powder (65%). mp 121℃. 1H-NMR (CDCl3)
δ 8.11 (m, 1H, Ph-H), 8.02 (m, 1H, Ph-H), 7.71 (m, 1H, Ph-H), 7.51 (d, J=7.2Hz, 2H, Ph-H), 7.18 (d,
J=7.2Hz, 2H, Ph-H), 6.06 (s, 1H, quinone). MS (m/z) 284 (M+). HRMS Calcd for C16H9O2FS, 284.0307,
Found: 284.0308.
2-(3-Fluorophenylthio)-1,4-naphthoquinone (7g): Yellow powder (56%). mp 125℃. 1H-NMR (CDCl3)
δ 8.15 (m, 1H, Ph-H), 8.05 (m, 1H, Ph-H), 7.73 (m, 2H, Ph-H), 7.50 (m, 1H, Ph-H), 7.36 (m, 1H, Ph-H),
7.30 (m, 1H, Ph-H), 7.23 (m, 1H, benzene), 6.14 (s, 1H, quinone). MS (m/z) 284 (M+). HRMS Calcd for
C16H9O2FS, 284.0307, Found: 284.0306.

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Synthesis of 2,3-bis(4-methylphenylthio)-1,4-naphthoquinone (8a)
A solution of 1,4-naphthoquinone (4) (158 mg, 1.0 mmol) in 20 mL of 95% ethanol was added to a
solution of arylthiols (6a) (2.1 mmol) in 10 mL of 95% ethanol and then the mixture was stirred at rt
for 4~6 h. After the reaction, the precipitate was collected by the filtration. The filtrated
crude product was purified by silica gel column chromatography with CHCl3. The compound (7a) was
obtained with poor yields (15%) along with 2,3-bis(4-methylphenylthio)-1,4-naphthoquinone (8a) as a
by-product (67%).
2,3-Bis(4-mehylphenylthio)-1,4-naphthoquinone (8a): Deep red plate (67%). mp 173-175℃ (lit.,5 mp
173-174℃). 1H-NMR (CDCl3) δ 8.04 (s, 2H, Ph-H), 7.72 (d, J=7.1 Hz, 2H, benzene), 7.07 (d, J=7.1 Hz,
2H, benzene), 6.92 (m, 2H, Ph-H), 2.36 (s, 6H, CH3). MS (m/z) 402 (M+). HRMS Calcd for C24H18O2S2,
402.0748, Found: 402.0749.
General procedure for synthesis of benzo[b]naphtho[2,3-d]thiophene-6,11-diones (2a-g)
A mixture of compounds (7) (2.0 mmol) and Pd(OAc)2 (448 mg, 2.0 mmol) in 10 mL of acetic acid was
refluxed und an argon atmosphere for about 40 h. The insoluble matter was filtered off and washed with
acetic acid. The filtrate was evaporated in vacuum. The residue was purified by silica gel column
chromatography with CH3Cl/n-hexane or crystallized from 95% ethanol to give the compounds (2a-g)
(Table 4).
2-Methylbenzo[b]naphtho[2,3-d]thiophene-6,11-dione (2a): Yellow powder (35%). mp 201-203℃.
1H-NMR (CDCl3) δ 8.74 (s, 1H, Ph-H), 8.27 (m, 1H, Ph-H), 8.23 (m, 1H, Ph-H), 7.83 (m, 1H, Ph-H),
7.78 (m, 2H, Ph-H), 2.56 (s, 3H, CH3). MS (m/z) 278 (M+). HRMS Calcd for C17H10O2S, 278.0402,
Found: 278.0401. Anal. Calcd for C17H10O2S: C, 73.36; H, 3.62, Found: C, 73.31; H, 3.64.
3-Chlorobenzo[b]naphtho[2,3-d]thiophene-6,11-dione (2b): Yellow powder (25%). mp 249-251℃.
1H-NMR (CDCl3) δ 8.84 (m, 1H, Ph-H), 8.26 (m, 1H, Ph-H), 8.23 (m, 1H, Ph-H), 7.95 (m, 1H, Ph-H),
7.79 (m, 2H, Ph-H), 7.56 (m, 1H, Ph-H). MS (m/z) 298 (M+). HRMS Calcd for C16H7O2ClS, 297.9855,
Found: 297.9856. Anal. Calcd for C16H7O2ClS: C, 64.33; H, 2.36, Found: C, 64.29; H, 2.35.
Benzo[b]naphtho[2,3-d]thiophene-6,11-dione (2c): Pale brown powder (30%). mp 199-201℃. 1H-NMR
(CDCl3) δ 8.94 (m, 1H, Ph-H), 8.28 (m, 1H, Ph-H), 8.23 (m, 1H, Ph-H), 7.96 (m, 1H, Ph-H), 7.78 (m,
2H, Ph-H), 7.59 (m, 1H, Ph-H). MS (m/z) 264 (M+). HRMS Calcd for C16H8O2S, 264.0245, Found:
264.0244. Anal. Calcd for C16H8O2S: C, 72.71; H, 3.05, Found: C, 72.73; H, 3.08.
2-Chlorobenzo[b]naphtho[2,3-d]thiophene-6,11-dione (2d): Yellow powder (26%). mp 210-212℃.
1H-NMR (CDCl3) δ 8.86 (m, 1H, Ph-H), 8.20 (m, 1H, Ph-H), 8.17 (m, 2H, Ph-H), 7.80 (s, 1H, Ph-H),
7.72 (d, J=7.1 Hz, 1H, Ph-H), 7.45 (d, J=7.1 Hz, 1H, Ph-H ). MS (m/z) 298 (M+). HRMS Calcd for

HETEROCYCLES, Vol. 65, No. 5, 2005
1213
C16H7O2ClS, 297.9855, Found: 297.9857. Anal. Calcd for C16H7O2ClS: C, 64.33; H, 2.36, Found: C,
64.35; H, 2.39
1,3-Dimethylbenzo[b]naphtho[2,3-d]thiophene-6,11-dione (2e): Yellow powder (55%). mp 252-254℃.
1H-NMR (CDCl3) δ 8.21 (m, 1H, Ph-H), 8.18 (m, 1H, Ph-H), 7.78 (m, 2H, Ph-H), 7.73 (s, 1H, Ph-H),
7.58 (s, 1H, Ph-H), 7.19 (s, 1H, Ph-H), 2.90 (s, 3H, CH3), 2.40 (s, 3H, CH3). MS (m/z) 292 (M+). HRMS
Calcd for C18H12O2S, 292.0558, Found: 292.0557. Anal. Calcd for C18H12O2S: C, 73.95; H, 4.14, Found:
C, 73.94; H, 4.17.
2-Fluorobenzo[b]naphtho[2,3-d]thiophene-6,11-dione (2f): Yellow powder (26%). mp 194-196℃.
1H-NMR (CDCl3) δ 8.58 (m, 1H, Ph-H), 8.27 (m, 1H, Ph-H), 8.21 (m, 1H, Ph-H), 7.88 (s, 1H
benzothiophene), 7.77 (d, J=7.3 Hz, 1H, Ph-H), 7.32 (d, J=7.3 Hz, 1H, Ph-H). MS (m/z) 282 (M+). HRMS
Calcd for C16H7O2FS, 282.0151, Found: 282.0150. Anal. Calcd for C16H7O2FS: C, 68.08; H, 2.50, Found:
C, 68.07; H, 2.51
3-Fluorobenzo[b]naphtho[2,3-d]thiophene-6,11-dione (2g): Yellow powder (38%). mp 227-229℃.
1H-NMR (CDCl3 ) δ 8.91 (m, 1H, Ph-H), 8.26 (m, 1H, Ph-H), 8.24 (m, 1H, Ph-H), 7.79 (m, 2H, Ph-H),
7.64 (m, 1H, Ph-H), 7.35 (d, 1H, Ph-H). MS (m/z) 282 (M+). HRMS Calcd for C16H7O2FS, 282.0151,
Found: 282.0151, Anal. Calcd for C16H7O2FS: C, 68.08; H, 2.51, Found: C, 68.09; H, 2.50
General procedure for one pot synthesis of 2-methylbenzo[b]naphtho[2,3-d]thiophene-6,11-dione
(2a)
A mixture of compound (4) (316 mg, 2.0 mmol) and Pd(OAc)2 (448 mg, 2.0 mmol) in 10 mL of acetic
acid was added to a solution of the arylthiol (6a) (261 mg, 2.1 mmol) in 10 mL of acetic acid, and the
mixture was refluxed for about 2 h under an argon atmosphere. The filtrate was evaporated in vacuum.
After evaporation, compounds (2a) (15%) and (9a) (45%) were separated by silica gel column
chromatography with CH3Cl/n-hexane, and crystallized from 95% ethanol.
2-(4-Methylphenyl)-1,4-naphthoquinone (9a): Yellow powder (45%). mp 111-112℃ (lit.,9 mp
111-112℃). 1H-NMR (CDCl3) δ 8.25 (s, 1H, Ph-H), 8.07 (d, J=7.7 Hz, 2H, benzene), 7.70 (d, J=7.7 Hz,
2H, benzene), 7.32 (m, 1H, Ph-H), 7.05 (m, 2H, Ph-H), 2.21 (s, 3H, CH3). MS (m/z) 248 (M+). HRMS
Calcd for C17H12O2, 248.0837, Found: 248.0838.
ACKNOWLEDGEMENTS
This study was supported by a grant of the Korea Science and Engineering Foundation (KOSEF
R06-2002-011-01004-0).

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