Photohydrodimerization of 6-methoxyflavone to 6,6″-dimethoxy-2, 2″-biflavanones

Article abstract of DOI:10.1002/jccs.200400203

6-Methoxyflavone (7) easily afforded two hydrodimers of rac-6,6″-dimethoxy-2,2″-biflavanone (8a) and meso-6,6″- dimethoxy-2,2″-biflavanone (8b) and one reductive product of 6-methoxyflavanone (9) by using photolysis with the electron-donating amines including triethylamine, 2-(N,N-dimethylamino)ethanol or N,N-dimethylaniline in solvents of acetonitrile, benzene or methylene dichloride. They were found to give higher yields of rac-6,6″-dimethoxy-2,2″-biflavanone (8a) and meso-6,6″-dimethoxy-2,2″-biflavanone (8b) (38.7% and 4.5%, 35.3% and 6.2%, respectively) in the reaction conditions of 1/10 molar ratio of 6-methoxyflavone (7) to triethylamine in a solvent of acetonitrile with irradiation of twenty-four hours by using 306 nm and 352 nm lamps.

Full text of DOI:10.1002/jccs.200400203

Journal of the Chinese Chemical Society, 2004, 51, 1389-1394
1389
Photohydrodimerization of 6-Methoxyflavone to
6,6²-Dimethoxy-2,2²-Biflavanones
Arh-Hwang Chen* (
Department of Chemistry, National Kaohsiung Normal University, Kaohsiung 802, Taiwan, R.O.C.
), Wei-Bao Kuo (
) and Chia-Wen Chen (
)
6-Methoxyflavone (7) easily afforded two hydrodimers of rac-6,6²-dimethoxy-2,2²-biflavanone (8a) and
meso-6,6²-dimethoxy-2,2²-biflavanone (8b) and one reductive product of 6-methoxyflavanone (9) by using
photolysis with the electron-donating amines including triethylamine, 2-(N,N-dimethylamino)ethanol or
N,N-dimethylaniline in solvents of acetonitrile, benzene or methylene dichloride. They were found to give
higher yields of rac-6,6²-dimethoxy-2,2²-biflavanone (8a) and meso-6,6²-dimethoxy-2,2²-biflavanone (8b)
(38.7% and 4.5%, 35.3% and 6.2%, respectively) in the reaction conditions of 1/10 molar ratio of 6-methoxy-
flavone (7) to triethylamine in a solvent of acetonitrile with irradiation of twenty-four hours by using 306 nm
and 352 nm lamps.
Keywords: 6-Methoxyflavone; 6,6²-Dimethoxy-2,2²-biflavanones; 6-Methoxyflavanone; Photolysis;
Photohydrodimerization.
INTRODUCTION
Biflavonoids, widely distributed in natural plants, were
zene (1) with acetic anhydride in the presence of sulfuric acid
gave 1,4-diacetoxybenzene (2) in 96.4% yield. 1,4-Diaceto-
xybenzene (2) was heated in the presence of aluminium chlo-
ride to give 2,5-dihydroxyacetophenone (3) with a yield of
54.9% via Fries rearrangement. Methylation of 2,5-dihy-
droxyacetophenone (3) at a 5-position with dimethyl sulfate
classified into biflavones and biflavanones via C-C or C-O-C
linkages of two molecules of flavonoids such as 2,2²-, 2,3²¢-,
3,3²-, 3,8²-, 4,8²-, 6,6²-, 6,8²-, 6,3²¢-, 8,3¢-, 8,2²¢- and 8,3²¢-
C-C linkages and 3²,4²¢-, 6,4²¢- and 7,4²¢-C-O-C linkages.1
Recently, some biflavonoids have been found to reveal sig-
nificant biological activities, e.g., antiviral activity, anti-HIV
activity, anti-inflammatory activity, anticomplementatory
activity, etc., leading to much attention.2 Synthetic attempts
have been successful for preparations of some biflavonoids
such as the Ullmann coupling route for 8,3²¢-biflavones,3 the
Baker-Venkataraman rearrangement route for 3,3²¢-bifla-
vones,4 and the oxidative coupling, the reductive coupling,
the Pd-cathode reduction and the photoinduced electron
transfer routes for 2,2²-biflavanones,5 etc. We have commu-
nicated that the preparation of 2,2²-biflavanones from fla-
vone was carried out via an electrolytic reductive coupling
and a photodimerization.6 In our continuous study on syn-
thetic application of biflavonoids, this paper reports herein
the synthesis of rac- and meso-6,6²-dimethoxy-2,2²-bifla-
vanones from 6-methoxyflavone via a photolysis.
Scheme I
OH
OCOCH3
OH
O
AlCl3
(AcO)2O, H2SO4
96.4%
54.9%
HO
OH
OCOCH3
1
2
3
OH
O
PhCOCl, pyridine
69.6%
Me2SO4, 90% aq. acetone
62.3%
H3CO
4
OCOPh
OH
KOH, pyridine
86.5%
Ph
H3CO
H3CO
O
O
O
6
5
H2SO4, acetic acid
62.2%
O
Ph
RESULTS AND DISCUSSION
H3CO
O
6-Methoxyflavone (7) was synthesized from p-dihy-
7
droxybenzene (1), as shown in Scheme I. p-Dihydroxyben-

1390 J. Chin. Chem. Soc., Vol. 51, No. 6, 2004
Chen et al.
in a solvent of 90% aqueous acetone gave 2-hydroxy-5-meth-
oxyacetophenone (4) in 62.3% yield. Esterification of 2-hy-
droxy-5-methoxyacetophenone (4) with benzoyl chloride in
the presence of pyridine afforded 2-benzoyloxy-5-methoxy-
acetophenone (5) in a yield of 69.6%. The base-catalyzed re-
arrangement of 2-benzoyloxy-5-methoxyacetophenone (5)
gave 2-hydroxy-5-methoxydibenzoylmethane (6) with a
yield of 86.5%. Finally, 6-methoxyflavone (7) was obtained
from cyclization of 2-hydroxy-5-methoxydibenzoylmethane
(6) in the presence of acid with a yield of 62.2%.
Blue Lamp. Photolysis of 6-methoxyflavone (7) with the
electron-donating amines including triethylamine, 2-(N,N-
dimethylamino)ethanol or N,N-dimethylaniline in solvents
of acetonitrile, benzene or methylene dichloride was found to
afford two hydrodimers of rac-6,6²-dimethoxy-2,2²-bifla-
vanone (8a) and meso-6,6²-dimethoxy 2,2²-biflavanone (8b)
and one reductive product of 6-methoxyflavanone (9), as
shown in Scheme II.
As shown in Table 1, their yields were affected by the
kinds of amines, the solvents used, and the irradiation sources.
They were found to afford higher yields of rac-6,6²-dimeth-
oxy-2,2²-biflavanone (8a), meso-6,6²-dimethoxy-2,2²-bi-
The photolysis was carried out in a quartz cell equipped
with a Sankyo 306 nm UV-B Lamp or 352 nm Blacklight
Scheme II
Ph
Ph
Ph Ph
O
O
Ph
O
O
O
O
O
O
hv
+
MeO
OMe
OMe
MeO
MeO
O
O
8a (rac)
8b (meso)
7
O
Ph
+
MeO
O
9
Table 1. The yields of products for photolysis of 6-methoxyflavone (7)
Reaction Conditions
Yields of Products (%)d
Molar ratios,a Amines,b Solvents,
Irradiation Time, Irradiation Sourcec
Conversion (%)
Entries
8a
8b
9
1
2
3
4
5
6
7
8
1/10, TEA, CH3CN, 24 hrs, A
1/10, TEA, CH3CN, 24 hrs, B
1/10, TEA, C6H6, 24 hrs, A
1/10, TEA, C6H6, 24 hrs, B
1/10, TEA, CH2Cl2, 28 hrs, A
1/10, TEA, CH2Cl2, 24 hrs, B
1/10, DMAE, 18 hrs, A
1/10, DMAE, CH3CN, 18 hrs, B
1/10, DMAE, C6H6, 18 hrs, A
1/10, DMAE, C6H6, 18 hrs, B
1/10, DMAE, CH2Cl2, 18 hrs, A
1/10, DMAE, CH2Cl2, 18 hrs, B
1/10, DMA, CH3CN, 20 hrs, A
1/10, DMA, CH3CN, 20 hrs, B
1/10, DMA, C6H6, 20 hrs, A
1/10, DMA, C6H6, 20 hrs, B
100.0
98.0
90.3
92.0
61.5
67.3
65.7
77.4
70.8
72.3
90.3
93.7
95.6
97.5
92.0
95.4
38.7
35.3
41.7
42.3
4.2
4.5
6.2
12.9
10.7
15.2
14.7
10.3
7.3
17.4
8.6
2.3
2.7
1.9
2.1
28.7
22.5
1.2
0.8
3.2
2.5
6.4
19.0
13.5
22.3
18.4
4.7
8.5
9.6
9
11.4
7.2
18.2
11.3
6.9
3.4
10.3
8.5
10
11
12
13
14
15
16
3.1
22.4
17.7
10.2
9.7
a Molar ratio of substrate to amine.
b Amine: TEA: triethylamine, DMAE: 2-(N,N-dimethylamino)ethanol, DMA: N,N-dimethyl
aniline.
c Irradiation Source:
A: Sankyo 306nm UV-B Lamp.
B: Sankyo 352nm Blacklight Blue Lamp.
d Yield based on consumed 6-methoxyflavone (7).

Photohydrodimerization of Flavones
J. Chin. Chem. Soc., Vol. 51, No. 6, 2004 1391
flavanone (8b) and 6-methoxyflavanone (9) (38.7%, 4.5%,
12.9% and 35.3%, 6.2%, 10.7%, respectively) in the reaction
conditions of 1/10 molar ratio of 6-methoxyflavone (7) to
triethylamine in a solvent of acetonitrile with irradiation of
twenty-four hours by using 306 nm and 352 nm lamps (En-
tries 1 and 2, respectively). However, the reaction conditions
of 1/10 molar ratio of 6-methoxyflavone (7) to triethylamine
in a solvent of benzene with irradiation of twenty-four hours
by using 306 nm and 352 nm lamps (Entries 3 and 4, respec-
tively) afforded only the yields of rac-6,6²-dimethoxy-2,2²-
biflavanone (8a) and 6-methoxyflavanone (9) (41.7%, 15.2%
and 42.3%, 14.7%, respectively). The maximal absorptions
of flavone and 6-methoxyflavone (7) at 255 nm and at 297
nm, respectively, resulted in photolysis of flavone to afford
rac-2,2²-biflavanone and meso-2,2²-biflavanone (30.0% and
20.9%, 22.3% and 22.0%, respectively) in the reaction condi-
tions of 1/2 molar ratio of substrate to triethylamine in aceto-
nitrile or benzene with irradiation of fourteen or twenty-five
hours by using a 254 nm lamp,6b but photolysis of 6-methoxy-
flavone (7) did not give two hydrodimers of rac-6,6²-dimeth-
oxy-2,2²-biflavanone (8a) and meso-6,6²-dimethoxy-2,2²-
biflavanone (8b) in the reaction conditions of 1/10 molar ra-
tio of substrate to triethylamine in acetonitrile or benzene
with irradiation of more than thirty hours by using a 254 nm
lamp. Therefore, photolysis of 6-methoxyflavone (7) can af-
ford two hydrodimers of 6,6²-dimethoxy-2,2²-biflavanones
(8a and 8b) and 6-methoxyflavanone (9) with irradiation of
the wavelengths of 306 nm or 352 nm lamps.
a,b-Unsaturated carbonyl compounds with amines can
follow a photoreaction via a dominant pathway of single elec-
tron transfer (SET).7 Photolysis of 6-methoxyflavone (7) was
proposed as shown in Scheme III. Excitation of 6-methoxy-
Scheme III
Ph
Ph
Ph
h v
O
O
O
O
O
O
-
+
or
.
.
Et3N
Et3N
Et3N
MeO
MeO
MeO
10
11
7
Ph
.
hydrogen transfer
or proton transfer
.
O
+
CH3CHNEt2
MeO
OH
13
12
.
7
+H
O
Ph
Ph
Ph
O
O
.
MeO
OMe
MeO
OH
O
OH
16
14a,b
.
+H
tautom.
Ph Ph
O
Ph
O
O
MeO
MeO
OMe
O
OH
O
15a,b
9
tautom.
Ph
O
Ph
O
O
OMe
MeO
O
8a.b

1392 J. Chin. Chem. Soc., Vol. 51, No. 6, 2004
Chen et al.
flavone (7) via irradiation followed a SET photochemical
process with amines serving as electron donors to give an
exciplex (10) or a contact radical ion pair (CIRP) (11) and
then to follow a hydrogen transfer or a proton transfer to form
a radical pair (12-13) in a cage. After escape out of a cage, the
radical (12) could go two ways. One way was to attack a mol-
ecule of 6-methoxyflavone (7), accept a hydrogen atom and
then follow tautomerism to afford rac-6,6²-dimethoxy 2,2²-
biflavanone (8a) and meso-6,6²-dimethoxy 2,2²-biflavanone
(8b). The other way was to accept a hydrogen atom to give
enol (16) and then to undergo tautomerism to afford 8-meth-
oxyflavanone (9).
mol) and anhydrous aluminum chloride (47.70 g, 0.320 mol)
was heated for 3 hours at 180 °C in an oil bath. The reaction
mixture was cooled to room temperature and then was added
28 mL of concentrated hydrochloric acid and 250 mL of
icewater to produce a precipitate. The precipitate was col-
lected and washed with icewater. The product was recrys-
tallized from ethanol to give a brown crystal of 8.56 g of
2,5-dihydroxyacetophenone (3) with a yield of 54.4%, m.p.
203-204 °C (Lit.13: 202-203 °C). 1HNMR (CDCl3, 500 MHz):
d 2.60 (s, 3H), 6.79 (d, 1H, J = 14.5 Hz), 7.08 (d, 1H, J =
14.5), 7.28 (s, 1H), 8.20 (s, 1H), 11.71 (s, 1H); 13CNMR
(CDCl3, 125 MHz): 26.99, 116.43, 119.41, 120.36, 125.76,
150.21, 156.55, 206.27; MS (EI, m/z, %): 109 (16.7), 137
(100.0), 152 (M, 68.3), 153 (M+1, 16.1); HRMS: 152.0473
(M+), calcd. 152.0473; Anal.: Calcd. for C8H8O3: C: 63.15%,
H: 5.30%; Found: C: 63.11%, H: 5.25%.
EXPERIMENTAL SECTION
General
The melting points were measured without correction
2-Hydroxy-5-methoxyacetophenone (4)
on a Yanagimoto Micro-melting Point Apparatus. 1H and 13
C
To a solution of 2,5-dihydroxyacetophenone (3) (5.00
g, 32.86 mmol) dissolved in 50 mL of 90% aqueous acetone
was added dimethyl sulfate (4.15 g, 32.85 mmol) and potas-
sium carbonate (1.364 g, 9.87 mmol) and then it was refluxed
for 3 hours in a water bath. The reaction solution was poured
into 40 mL of 1 M hydrochloric acid and then extracted with
ethyl ether. The organic layer was evaporated to remove the
solvent under reduced pressure. The residue was chromato-
graphed on silica gel and eluted with n-hexane-ethyl acetate
(v/v = 4/1) to give a slightly yellow crystal of 3.40 g of 2-
hydroxy-5-methoxyacetophenone (4) (20.46 mmol) with a
yield of 62.3%, m.p. 51-52 °C. 1HNMR (CDCl3, 500 MHz): d
2.61 (s, 3H), 3.80 (s, 3H), 6.92 (d, 1H, J = 15.0 Hz), 7.11 (d,
1H, J = 15.0 Hz), 7.16 (s, 1H), 11.85 (s, 1H); 13CNMR
(CDCl3, 125 MHz): 26.74, 55.98, 113.49, 119.18, 119.23,
124.11, 151.67, 156.74, 204.00; MS (EI, m/z, %): 107 (18.6),
123 (12.4), 137 (19.2), 151 (100.0), 165 (75.1), 166 (M,
77.6), 167 (M+1, 7.4); Anal.: Calcd. for C9H10O3: C: 65.05%,
H: 6.07%; Found: C: 65.08%, H: 6.13%.
nuclear magnetic resonance spectra were measured on a
Varian INOVA-500 spectrometer. Mass spectra were deter-
mined on a VG Quattro GC/MS/MS DS spectrometer. High
resolution mass spectra were performed on a VG 70-250S
GC/MS spectrometer. Elemental analyses were measured on
a Heraeus CHN-O-Rapid Analyzer. Photolysis was carried
out on a PanChum Photochemical Reaction Apparatus,
equipped with Sankyo 306 nm UV-B Lamp or 352 nm Black-
light Blue Lamp.
Synthesis of 6-methoxyflavone (7)
1,4-Diacetoxybenzene (2)
To a solution of p-dihydroxybenzene (1) (40.00 g,
0.363 mol) and acetic anhydride (74.20 g, 0.727 mol) was
added 1-2 drops of concentrated sulfuric acid. The reaction
solution was stirred for 30 minutes at room temperature and
then poured into icewater (200 mL) to produce a white pre-
cipitate. The precipitate was collected to give a white crystal
of 67.54 g of 1,4-diacetoxybenzene (2) with a yield of 95.9%,
m.p. 123-124 °C.8 1HNMR (CDCl3, 500 MHz): d 2.29 (S,
6H), 7.09 (S, 4H); 13CNMR (CDCl3, 125 MHz): 21.05, 122.40,
148.01, 169.37; MS (EI, m/z, %): 110 (100.0), 152 (27.3), 194
(M, 4.3), 195 (M+1, 0.6); MS (FAB, m/z, %): 136 (86.9), 154
(100.0), 194 (M, 18.6), 195 (M+1, 49.0); Anal.: Calcd. for
C10H10O4: C: 61.85, H: 5.19; Found: C: 61.78, H: 5.23.
2-Benzoyloxy-5-methoxyacetophenone (5)
A solution of 2-hydroxy-5-methoxyacetophenone (4)
(3.30 g, 17.84 mmol) and pyridine (4 mL) in a flask was
stirred in a water bath at 50 °C and benzoyl chloride (3.59 g,
25.61 mmol) was added. The reaction solution was stirred for
30 minutes at 50 °C and then poured into a solution of 1 M
HCl (40 mL). The solution was extracted with ethyl ether.
The organic layer was evaporated to remove the solvent un-
der reduced pressure. The residue was chromatographed on
2,5-Dihydroxyacetophenone (3)
A mixture of 1,4-diacetoxybenzene (2) (20.00 g, 0.103

Photohydrodimerization of Flavones
J. Chin. Chem. Soc., Vol. 51, No. 6, 2004 1393
silica gel and eluted with n-hexane-ethyl acetate (v/v = 8/1) to
give a white crystal of 3.40 g (12.58 mmol) of 2-benzoyloxy-
5-methoxyacetophenone (5) with a yield of 70.5%, m.p.
38-40 °C. 1HNMR (CDCl3, 500 MHz): d 2.53 (s, 3H), 3.87 (s,
3H), 7.11-7.14 (m, 2H), 7.36 (d, 1H, J = 4.5 Hz), 7.50-7.53
(m, 3H), 8.20-8.22 (dd, 2H, J = 7.0 Hz, J = 4.5 Hz); 13CNMR
(CDCl3, 125 MHz): 55.84, 100.42, 107.57, 114.41, 117.86,
126.16, 127.08, 129.00, 131.40, 131.89, 158.01, 163.02,
164.19, 177.87; MS (EI, m/z, %): 105 (100), 270 (M, 3.7%),
271 (M+1); MS (FAB, m/z, %): 105 (100), 270 (M, 9.9), 271
(13.6); Anal.: Calcd. for C16H14O4: C: 71.10%, H: 5.22%;
Found: C: 70.69%, H: 5.33%.
(CDCl3, 125 MHz): 55.95, 104.79, 106.85, 119.53, 123.85,
124.55, 126.24, 129.03, 131.51, 131.88, 151.10, 157.01,
163.19, 178.36; MS (EI, m/z, %): 107 (48.4), 135 (23.6), 150
(74.5), 222 (29.1), 251 (85.0), 252 (M, 100.0), 253 (M+1,
15.5); MS (FAB, m/z, %): 136 (91.9), 154 (100), 252 (M,
3.1), 253 (M+1, 19.8); Anal.: Calcd. for C16H12O3: C:
76.18%, H: 4.79%; Found: C: 75.97%, H: 4.84%.
Typical Photolysis of 6-Methoxylavone (7)
Photolysis of 6-methoxyflavone (7) was carried out by
using a quartz flask equipped with a Sankyo 306 nm UV-B
Lamp. A solution of 6-methoxyflavone (7) (101.0 mg, 0.40
mmol) and triethyl amine (404.8 mg, 0.40 mmol) in aceto-
nitrile (40 mL) was irradiated for twenty-four hours under a
dry nitrogen atmosphere. Then the reaction solution was
evaporated to remove the solvent under reduced pressure.
The residue was chromatographed on silica gel and was
eluted with n-hexane-ethyl acetate (v/v = 5/1) to give three
white crystals: rac-6,6²-dimethoxy-2,2²-biflavanone (8a)
(38.7 mg, 38.7%, m.p. 225-226 °C), meso-6,6²-dimethoxy-
2,2²-biflavanone (8b) (4.5 mg, 4.5%, m.p. > 300 °C) and 6-
methoxyflavanone (9) (12.9 mg, 12.9%, m.p. 141-142 °C);
rac-6,6²-dimethoxy-2,2²-biflavanone (8a): 1HNMR (CDCl3,
500 MHz): d 3.33 (d, 2H, J = 16.5 Hz), 3.76 (s, 6H), 3.94 (d,
2H, J = 16.5 Hz), 7.08-7.09 (m, 10H), 7.17-7.18 (m, 4H), 7.26
(s, 2H); 13CNMR (CDCl3, 125 MHz): 40.86, 55.63, 87.92,
107.10, 119.53, 121.22, 125.15, 127.67, 128.50, 128.87,
135.15, 153.81, 153.98, 191.38; MS (EI, m/z, %): 103 (41.2),
151 (100.0), 253 (M/2, 73.1), 254 (M/2+1, 12.5); Anal.:
Calcd. for C32H26O6: C: 75.88%, H: 5.17%; Found: C:
75.79%, H: 5.23%. meso-6,6²-dimethoxy-2,2²-biflavanone
(8b): 1HNMR (CDCl3, 500 MHz): d 3.07 (d, 2H, J = 16.0 Hz),
3.61 (d, 2H, J = 16.0 Hz), 3.67 (s, 6H), 7.01-7.07 (m, 4H),
7.23-7.26 (m, 10H), 7.37 (s, 2H,); 13CNMR (CDCl3, 125
MHz): 42.30, 55.64, 87.12, 107.12, 119.22, 121.12, 125.21,
128.03, 128.39, 129.18, 136.06, 153.30, 153.99, 190.66; MS
(EI, m/z, %): 103 (70.3), 151 (100.0), 253 (1/2M+); Anal.:
Calcd. for C32H26O6: C: 75.88%, H: 5.17%; Found: C:
75.75%, H: 5.22%. 6-methoxyflavanone (9): 1HNMR (CDCl3,
500 MHz): d 2.88 (dd, J = 3.0 Hz, J = 17.0 Hz, 1H), 3.07 (dd,
J = 13.5 Hz, J = 17.0 Hz, 1H), 3.62 (s, 3H), 5.45 (dd, J = 3.0
Hz, J = 13.5 Hz, 1H), 7.00 (d, J = 9.0 Hz, 1H), 7.13 (dd, J =
3.5 Hz, J = 9.0 Hz, 1H), 7.26-7.49 (m, 6H); 13CNMR (CDCl3,
125 MHz): 44.56, 55.81, 79.70, 107.34, 119.43, 120.74,
125.40, 126.13, 128.79, 128.82, 138.82, 154.23, 156.28,
192.09; MS (EI, m/z, %): 103 (83.7), 104 (100.0), 150 (57.5),
254 (M+, 15.0), 255 (M+1, 2.5); Anal.: Calcd. for C16H14O3:
2-Hydroxy-5-methoxydibenzoylmethane (6)
2-Benzoyloxy-5-methoxy-acetophenone (5) (3.00 g,
11.10 mmol) was dissolved in 10 mL of dry pyridine. The so-
lution was heated to 50 °C in a water bath and 0.94 g of dry
potassium hydroxide (16.79 mmol) was added. The reaction
solution was stirred for 15 minutes at 50 °C. The solution was
acidified by adding 10% acetic acid (20 mL) and then ex-
tracted with ethyl ether. The organic layer was evaporated to
remove the solvent under reduced pressure. The residue was
chromatographed on silica gel and eluted with n-hexane-
ethyl acetate (v/v = 8/1) to give an orange-yellow crystal of
2.58 g of 2-hydroxy-5-methoxydibenzoylmethane (6) with a
yield of 86.0%, m.p. 42-44 °C. 1HNMR (CDCl3, 500 MHz): d
3.81 (s, 3H), 6.74 (s, 1H), 6.91-6.94 (m, 2H), 7.19 (d, 1H, J =
4.5 Hz), 7.46-7.49 (m, 3H), 7.92 (d, 2H, J = 13.5 Hz), 11.65
(s, 1H), 15.62 (s, 1H); 13CNMR (CDCl3, 125 MHz): 26.58,
31.72, 55.80, 92.15, 111.76, 119.34, 122.98, 123.98, 128.63,
132.32, 151.81, 156.58, 177.58, 194.98; MS (EI, m/z, %):
105 (100.0), 150 (14.2), 270 (M, 14.2), 271 (M+1, 2.4);
HRMS: 270.0892 (M), calcd. 270.0892; Anal.: Calcd. for
C16H14O4: C: 71.10%, H: 5.02%; Found: C: 71.06%, H:
5.08%.
6-Methoxyflavone (7)
A solution of 2-hydroxy-5-methoxy-dibenzoylmethane
(6) (2.00 g, 7.40 mmol) dissolved in 10 mL of glacial acetic
acid was heated in a boiling water bath and 1 mL of concen-
trated sulfuric acid was added. The reaction solution was
stirred for 1 hour in a boiling water bath and then poured into
50 mL of water. The precipitate was filtered and then recrys-
tallized from methanol to produce a red crystal of 1.16 g of
6-methoxyflavone (7) with a yield of 62.1%, m.p. 165-166
°C. 1HNMR (CDCl3, 500 MHz): d 3.92 (s, 3H), 6.83 (s, 1H),
7.26 (s, 1H), 7.50-7.55 (m, 5H), 7.91-7.95 (m, 2H); 13CNMR

1394 J. Chin. Chem. Soc., Vol. 51, No. 6, 2004
Chen et al.
R.; Paya, M.; Alcaraz, M. J. Biochem. Pharmacol. 1997, 53,
733. (d) Cimanga, K.; Bruyne, T. D.; Aper, S.; Pireters, L.;
Totte, J.; Kambu, K.; Tona, L.; Bakana, P.; Ufford, L. Q.;
Beukelman, C.; Labadie, R.; Vlietinok, A. J. Planta Med.
1999, 65, 213.
C: 75.57%, H: 5.55%; Found: C: 75.48%, H: 5.43%.
ACKNOWLEDGEMENT
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7, 748.
4. Zhu, J.; Wang, Q.; Li, Y. J. Chem. Soc. Chem. Commun.
1988, 1549.
This study was financially supported by the National
Science Council of the Republic of China.
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Received April 27, 2004.
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