JOURNAL OF CHEMICAL RESEARCH 2010 29
chalcone 4 under reflux in DMSO16 containing a crystal of I2.
In conclusion, our simple synthetic route has furnished the
natural isoflavone 1 along with the new flavanone 5 and the
new flavone 6. Our definitive synthesis of the structure 1 and
the discrepancies (in the melting point, IR and 1H NMR data)
observed are so significant that the natural product in ref. 1
needs further investigation.
7,8-Methylenedioxy-4p-methoxyisoflavone (1) and 7,8-methylene-
dioxy-4p-methoxyflavone (6): To a solution of thallium(III) acetate
(0.168 g, 0.4 mmol) and 70% perchloric acid (0.168 g, 1.17 mmol) in
acetonitrile (7 mL) was added 5 (0.1 g, 0.33 mmol) and the reaction
mixture was heated in a boiling water bath for 30 min. The reaction
mixture was then cooled to room temperature, CH2Cl2 (15 mL) was
added and kept at 0 °C for 15 min. The solid so obtained was filtered
to remove thallium (I) salt and washed with CH2Cl2. The combined
filtrate was washed successively with water, saturated NaHCO3 solu-
tion, water and dried over Na2SO4. Evaporation of the solvent gave
a crude residue (0.102 g) which was purified by silica gel column
chromatography using petroleum ether:ethyl acetate (9:1) to give 1
as a white solid (0.025 g, 25%). Recrystallisation from petroleum
ether-chloroform mixture gave crystals, m.p. 198 °C in agreement
with literature values.2–4 UV (nm): 294, 241, 217. IR (cm−1): 1657
(CO). 1H NMR (CDCl3) δ: 3.86 (s, 3H, OCH3), 6.23 (s, 2H, OCH2O),
6.99 (d, 1H, H-6, J = 8.7 Hz), 6.99 (d, 2H, H-3p & H-5p, J = 8.7 Hz),
7.49 (d, 2H, H-2p & H-6p, J = 8.7 Hz), 7.91 (d, 1H, H-5, J = 8.7 Hz),
Experimental
Melting points were determined in open capillary tubes and are uncor-
rected. UV spectra were recorded in methanol using matched quartz
cells on a Shimadzu (UV-2450) spectrophotometer. IR spectra were
recorded as KBr diluted pellets on a Shimadzu (IR Prestige-21) FTIR
spectrophotometer. 1H and 13C NMR spectra were recorded at 300 and
75 MHz respectively on a Bruker WT 300 FT-NMR instrument with
TMS as internal standard and chemical shifts are recorded in δ values.
The multiplicities of carbon signals were obtained from distortionless
enhancement by polarisation transfer (DEPT). HRESITOFMS was
recorded on QSTARXL MS/MS, Applied Biosystems, Switzerland.
All yields refer to isolated products unless stated otherwise.
Petroleum ether refers to hydrocarbon fraction boiling in the range
60–80 °C.
1
7.92 (s, 1H, H-2). H NMR (DMSO-d6) δ: 3.78 (s, 3H, OCH3), 6.12
(s, 2H, OCH2O), 6.75 (d, 1H, H-6, J = 8.4 Hz), 6.75 (d, 2H, H-3p &
H-5p, J = 8.4 Hz), 6.99 (d, 2H, H-2p & H-6p, J = 8.4 Hz), 7.44 (d, 1H,
H-5, J = 8.4 Hz), 7.48 (s, 1H, H-2).
Continued elution with petroleum ether:ethyl acetate (6:4) gave 6
(0.014 g, 14%) which on recrystallisation from hot ethanol gave fine
cotton like clusters, m.p. 220 °C. UV (nm): 312, 267, 222. IR (cm−1):
2p-Hydroxy-3p,4p-(methylenedioxy)acetophenone (3):10 To a stirred
suspension of 2p,3p,4p-trihydroxyacetophenone 2 (1.0 g, 5.95 mmol)
and Cs CO3 (1.94 g, 5.95 mmol) in dry DMF (15 mL) was added
CH2I2 (20.48 mL, 1.595 g, 5.95 mmol) and the resulting mixture was
boiled under reflux. After 8 h, the mixture was allowed to cool to
room temperature, filtered through a pad of celite and washed with
EtOAc. The filtrate and washings were concentrated almost to dry-
ness, residue diluted with water and extracted with Et2O. The com-
bined ether extracts were washed with water, brine and dried over
Na2SO4. Evaporation of the solvent gave a dark-tan solid, which was
purified by silica gel column chromatography using 5% Et2O in petro-
leum ether to afford pure 2p-hydroxy-3p,4p-(methylenedioxy)acetophe
none 3 as a pale yellow solid (0.54 g, 50.5%). Recrystallisation from
petroleum ether gave colourless flakes, m.p. 96–98 °C as reported.10
1
1655 (CO). H NMR (CDCl3) δ: 3.87 (s, 3H, OCH3), 6.19 (s, 2H,
OCH2O), 6.64 (s, 1H, H-3), 6.92 (d, 1H, H-6, J = 8.4 Hz), 6.99 (d, 2H,
H-3p & H-5p, J = 9 Hz), 7.78 (d, 1H, H-5, J = 8.4 Hz), 7.85 (d, 2H,
H-2p & H-6p, J = 8.7 Hz). 13C NMR (CDCl3) δ: 55.5 (OCH3), 103.1
(OCH2O), 105.5 (C-3), 106.9 (C-6), 114.5 (C-3p, C-5p), 119.9 (C-4a),
120.0 (C-5), 123.7 (C-1p), 127.9 (C-2p, C-6p), 134.7 (C-8), 141.1 (C-
8a), 152.3 (C-2), 162.4 (C-4p), 162.6 (C-7), 177.3 (C-4). HRESIMS:
m/z 319.0571 [M + Na]+; Calcd for C17H12O5Na+: 319.0577.
7,8-Methylenedioxy-4p-methoxyflavone (6): To 2p-hydroxy-3p,4p-
methylenedioxy-4-methoxychalcone 4 (0.11 g, 0.36 mmol) suspended
in DMSO (5 mL), a crystal of I2 was added. The mixture was heated
to reflux for 45 min, cooled to room temperature, diluted with water
and extracted with ethyl acetate. The organic extracts were washed
with aq. sodium thiosulfate, water and dried over Na2SO4. Evapora-
tion of the solvent afforded 6 as white solid (0.104 g, 95%) which
on recrystallisation from hot ethanol gave fine cotton like clusters
m.p. 220 °C.
2p-Hydroxy-3p,4p-methylenedioxy-4-methoxychalcone (4): To
a
mixture of 3 (0.24 g, 1.3 mmol), p-methoxybenzaldehyde (0.199 g,
1.46 mmol) in EtOH (1 mL) was added aq. NaOH (2.5 g in 5 mL
H2O) dropwise and the reaction mixture was stirred for 1 h at 45 °C.
Stirring was further continued overnight at room temperature. The
yellow orange mixture obtained was diluted with water and acidified
with conc. HCl. The yellow solid separated was filtered, washed with
water and dried to give 4 (0.34 g, 86%). Recrystallisation from hot
ethanol gave fine yellow needles, m.p. 176 °C (lit.3 143 °C from
benzene). UV (nm): 363, 244, 212. IR (cm−1): 1657 (CO), 1605 (C=C).
1H NMR (CDCl3) δ: 3.87 (s, 3H, OCH ), 6.09 (s, 2H, OCH2O), 6.52
(d, 1H, H-5p, J = 8.4 Hz), 6.95 (d, 2H, 3H-3 & H-5, J = 8.7 Hz), 7.44
(d, 1H, H-α, J = 15.3 Hz), 7.58 (d, 1H, H-6p, J = 8.4 Hz), 7.61 (d, 2H,
H-2 & H-6, J = 9 Hz), 7.86 (d, 1H, H-β, J = 15.3 Hz), 13.05 (s, 1H,
OH). 13C NMR (CDCl ) δ: 55.4 (OCH ), 100.6 (OCH2O), 102.6
(C-5p), 114.5 (C-3, C-5),3117.3 (C-1p), 117.38 (C-α), 125.5 (C-6p), 127.4
(C-1), 130.4 (C-2, C-6), 134.5 (C-3p), 144.8 (C-β), 148.1 (C-2p), 153.9
(C-4), 161.9 (C-4p), 192.7 (CO).
We thank L D’Souza, Scientist, NIO, Goa, for recording NMR
and HRESIMS data on our samples.
Received 27 October 2009;accepted 11 December 2009
Paper 090847 doi: 10.3184/030823409X12613944078394
Published online: 22 January 2010
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134.6 (C-8), 145.6 (C-8a), 154.2 (C-4p), 160.0 (C-7), 190.3 (C-4).
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321.0733.
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