A facile synthesis of 2-benzoyl-3-methyl-6-substituted aryl-5H-furo [3,2-g] [1] benzopyran-5-ones

Article abstract of DOI:10.1081/SCC-100104340

The synthesis and characterisation of some new furoisoflavones prepared from 4, 6-diacetylresorcinol is reported.

Full text of DOI:10.1081/SCC-100104340

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A FACILE SYNTHESIS OF 2-BENZOYL-3-METHYL-6-
SUBSTITUTED ARYL-5H-FURO [3,2-g] [1]
BENZOPYRAN-5-ONES
K. Vishnu Vardhan Reddy a & D. Ashok b
a Department of Chemistry, P. G. College of Science, Saifabad Osmania University,
Hyderabad, A.P., 500 004, India
b Department of Chemistry, P. G. College of Science, Saifabad Osmania University,
Hyderabad, A.P., 500 004, India
Published online: 16 Aug 2006.
To cite this article: K. Vishnu Vardhan Reddy & D. Ashok (2001) A FACILE SYNTHESIS OF 2-BENZOYL-3-METHYL-6-
SUBSTITUTED ARYL-5H-FURO [3,2-g] [1] BENZOPYRAN-5-ONES, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 31:12, 1893-1899, DOI: 10.1081/SCC-100104340
To link to this article: http://dx.doi.org/10.1081/SCC-100104340
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SYNTHETIC COMMUNICATIONS, 31(12), 1893–1899 (2001)
A FACILE SYNTHESIS OF 2-BENZOYL-3-
METHYL-6-SUBSTITUTED ARYL-5H-FURO
[3,2-g] [1] BENZOPYRAN-5-ONES
K. Vishnu Vardhan Reddy and D. Ashok*
Department of Chemistry, P. G. College of Science, Saifabad
Osmania University, Hyderabad - 500 004, A.P., India
ABSTRACT
The synthesis and characterisation of some new furo-
isoflavones prepared from 4, 6-diacetylresorcinol is reported.
In continuation of our interest in exploring synthetic heterocyclic com-
pounds as potential antifeedants, we have synthesised a number of furocou-
marins,1 distyryl benzodifurans,2 angular benzodifurans,3 styryl
benzodifurans,4 1,5-benzothiazepines,5 pyrazolines,6 1,5-benzodiazepines,7
benzothiazoles8 and tested for their antifeedant activity.
Recently from our laboratory, we have synthesised several furofla-
vones (A) i.e., 2-benzoyl-3-methyl-7-substituted aryl-5H-furo[3,2-g][1]
* Corresponding author.
1893
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

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VISHNU VARDHAN REDDY AND ASHOK
benzopyran-5-ones9 and tested for their antifeedant activity. Among them
2-benzoyl-3-methyl-7-phenyl-5H-furo[3,2-g][1]benzopyran-5-one exhibited
highest antifeedant activity against Spodoptera litura F. which destroys
commercial crops like castor, cabbage, grapes etc. All the furoflavones
tested earlier for their antifeedant activity contained aryl group at C-7 posi-
tion. To understand the effect of aryl group at C-6 position on antifeedant
activity, it was thought worthwhile to take up the synthesis of some new
furoisoflavones i.e., 2-benzoyl-3-methyl-6-substituted aryl-5H-furo[3,2-g][1]
benzopyran-5-ones (6a–h) possessing aryl group at C-6 position. Thus the
synthesis of some new furoisoflavones was undertaken in the present inves-
tigation, with a view to test their antifeedant activity. Till now nobody has
reported the synthesis of title compounds.
The required precursors, 2-benzoyl-5-substituted cinnamoyl-
6-hydroxy-3-methyl benzofurans (3a–h) were prepared by the condensation
of 4,6-diacetylresorcinol10 (1) with o-bromoacetophenone11 (1:1) in acetone
in the presence of anhydrous K2CO3 to yield 5-acetyl-2-benzoyl-6-hydroxy-
3-methyl benzofuran12 (2), followed by condensation of 2 with aromatic
aldehydes in the presence of 60% aq. KOH. Compounds 3(a–h) were
characterised by comparison with authentic samples.1
To a solution of a, b-unsaturated ketones (cinnamoyl benzofurans
(3a–h, 1 mmol) in analytical grade methanol (200 ml), thallium(III) nitrate
(2 mmol) was added in small portions and stirred at room temperature for
5h. They were monitored by TLC. At the end of the reaction in each case
the methanol solution containing the acetal15 (4a–h) was treated with 10%
aq. hydrochloric acid and the mixture was refluxed on a steam bath for 5h.
Work-up of the reaction yielded crude product which was crystallised from
methanol as yellow crystals (6a–h). As a representative case the spectral
identification of 2-benzoyl-3-methyl-6-(3,4-dimethoxy phenyl)-5H-furo
[3,2-g] [1] benzopyran-5-one (6g) is discussed.
The IR spectrum of compound 6g exhibited broad absorption band
at 1649 cmꢀ1 suggesting the presence of a carbonyl group characteristic
of simple isoflavones.13 The spectrum also exhibits another broad absorption
band due to benzoyl carbonyl group at 1702 cmꢀ1. The UV spectrum of the
compound 6g in methanol exhibited absorption maxima at 297 nm (log e
4.75) and 368 nm (log e 4.92) which are characteristic of simple isoflavones.13
The 1H-NMR spectrum of 6g strongly suggests 2-benzoyl-3-methyl-6-
(3,4-dimethoxyphenyl)-5H-furo[3,2-g][1]benzopyran-5-one structure. The
spectrum showed
a
singlet integrating for one proton in the
downfield at d 8.47. This signal was assigned to the proton at C-7 position
and it was the characteristic proton of furoisoflavone skeleton formed after
1,2-aryl shift and simultaneous condensation15 of the 2-benzoyl-5-(3,4-
dimethoxycinnamoyl)-3-methyl-6-hydroxy benzofuran (3g) in thallium(III)

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1895
nitrate-methanol mediated reaction. The spectrum also revealed the pres-
ence of one sharp singlet at d 7.09 integrating for one proton which was
attributed to H-9. The spectrum contained two double doublets in the aro-
matic region. The first one which appeared at d 7.38 (J ¼ 9.8, 2 Hz) integrat-
ing for one proton was assigned to H-600. Another double doublet which
appeared at d 8.34 (J ¼ 9.8, 2 Hz) integrating for two protons was attributed
to H-20,60. One sharp doublet observed at d 6.97 (J ¼ 9.8 Hz) integrating for
one proton was assigned to H-500. The spectrum also exhibits two multiplets,
the first one appeared between d 7.52–7.70 for three protons was assigned to
H-30,40,50. The second multiplet appeared at d 8.08 integrating for two pro-
tons was attributed to H-4, 200. The aliphatic region of the spectrum con-
tained three singlets at d 2.78, 3.98 and 4.12 integrating for three protons,
each was attributed to C-3 (CH3), C-300 (OCH3), C-400 (OCH3) respectively.
Scheme.

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VISHNU VARDHAN REDDY AND ASHOK
The mass spectrum of the compound 6g exhibited the molecular ion
peak at m/z 440 (88%), consistent with its molecular formula C27H20O6. In
the mass spectrum of furoisoflavone, the observed isoflavone ring fragmen-
tation is in agreement with those reported for simple isoflavones.14 The
prominent ion fragments observed at m/z 439 (M-H, 19%), 425(6%), 278
(8%), 162 (7%), 129 (10%), 105(26%) and 77 (27%) are highly diagnostic
and supports furoisoflavone structure. The 13C-NMR spectrum of 6g exhi-
bited 24 signals corresponding to 27 carbons. The characteristic signals at d
184.30 (carbonyl carbon of C-2 benzoyl group), 180.15(C-5carbonyl
carbon), 56.76 (C-300, OCH3), (C-400, OCH3) and 9.87 (C-3, CH3) confirmed
its structure. On the basis of above analytical and spectral data the com-
pound 6g has been characterised as 2-benzoyl-3-methyl-6-(3,4-dimethoxy-
phenyl)-5H-furo[3,2-g][1]benzopyran-5-one.
Following the above method several furoisoflavones (6a–h) were
synthesised and their analytical and spectral data are given in table. This
method is one step reaction, the conditions are mild, there was no significant
substituent effect on the reaction, the yields are good to excellent and
by-products were not detected.
EXPERIMENTAL
Melting points were taken in open capillary tubes in sulfuric acid-bath
and are uncorrected. FT-IR spectra were obtained on Perkin-Elmer 1605
spectrophotometer. UV spectra were obtained on a Hitachi U-3410 spectro-
1
meter. H-NMR (200 MHz) and 13C-NMR (50.3 MHz) spectra were taken
Table. Analytical and Spectral Data of Title Compounds (6a–h)
IR KBr cmꢀ1
m.p
(ꢁC)
Yield
(%)
Benzoyl
C¼O str
UV(MeOH)
nm (log e)
Compd.
M+
C¼O str
6a
6b
6c
6d
6e
6f
380
394
410
414
398
414
440
424
192
168
186
173
169
176
198
162
61
68
651646
63
69
76
78
72
1640
1642
1676
1670
282 (4.68)
298 (4.53)
341 (4.86)
347 (4.78)
1690
290 (4.702) (4.9345)
1690
1685
29)6 (43.6650 (4.80)
1702
1686
1648
1642
16451688
1649
1648
294 (4.60)
290 (4.58)
356 (4.80)
358 (4.79)
6g
6h
297 (4.75)
294 (4.80)
368 (4.92)
364 (4.96)

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1897
in CDCl3 on Varian Gemini 200 MHz spectrometer with TMS as internal
standard (chemical shifts in d, ppm). EI mass spectra were obtained on V.G.
Micromass 70–70H instrument. Column chromatography was carried out
using silica gel (200 mesh).
Synthesis of 2-Benzoyl-5-substituted Cinnamoyl-6-hydroxy-3-methyl
Benzofurans (3a–h): General Procedure
An equimolar mixture of 1 (1.94 g) and o-bromoacetophenone (1.99 g)
was refluxed in acetone (50 ml) in the presence of anhydrous K2CO3 (5g)
for 6 hr. After distillation of the acetone in vaccum, the contents were
poured over crushed ice. The solid separated was filtered, washed with
water and extracted with hot 5% NaOH (3 ꢂ 40 ml) solution. The crude
product was obtained on neutralisation with 5% dil. HCl. It was crystallised
from methanol to afford the compound 2. A mixture of 2 (0.01 mole) and
the appropriate aldehyde (0.01 mole) in ethanol (40 ml) and aq. KOH (60%,
20 ml) was stirred at room temperature for 24 h. The product in each case
obtained on dilution and neutralisation with dil. HCl was subjected to
column chromatography over silica gel (18 cm ꢂ 3 cm, 200 mesh). Benzene-
chloroform (6:4, 3 ꢂ 40 ml) eluates on concentration afforded yellow
coloured crystalline compounds (3a–h).
Synthesis of 2-Benzoyl-3-methyl-6-substituted Aryl-5H-furo[3,2-
g][1]benzopyran-5-ones (6a–h): General Procedure
A mixture of 2-benzoyl-5-substituted cinnamoyl-6-hydroxy-3-methyl
benzofurans (3a–h, 1 mmol) in analytical grade methanol (200 ml) and
thallium(III) nitrate (4.44 g, 2 mmol) was stirred at room temperature for
5h. The reaction in each case was monitored by TLC. At the end of the
reaction period, the methanol solution containing the acetal15 was treated
with 10% aq. HCl (15ml) and the mixture was refluxed on steam bath for
5h. Removal of the solvent under reduced pressure yielded yellow coloured
solids which were crystallised from methanol as yellow crystals (6a–h).
5a: 1H-NMR (200 MHz, CDCl3): d 2.6 (3H, s, CH3-3), 7.0 (1H, s, H-9),
7.3–7.8 (8H, m, aromatic protons), 8.1 (1H, s, H-4), 8.3 (2H, dd, J ¼ 9.2,
2 Hz, H-20, 60), 8.5(1 H, s, H-7); Anal. calcd. for C 25H16O4: C, 78.94; H,
4.21; found: C, 78.90; H, 4.22%.
5b: 1H-NMR (200 MHz, CDCl3): d 2.5(3H, s, CH 3-3), 2.8 (3H, s, CH3-
Ar), 7.1 (1H, s, H-9), 7.3–7.4 (2H, m, H-300, 500), 7.6–7.7 (3 H, m,
H-30,40,50), 8.0 (2H, m, H-200, 600), 8.2 (1H, s, H-4), 8.3 (2H, dd, J ¼ 8.8,

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VISHNU VARDHAN REDDY AND ASHOK
2 Hz, H-20,60), 8.4 (1H, s, H-7); Anal. calcd. for C26H18O4: C, 79.18; H, 4.56;
found: C, 79.15; H, 4.55%.
1
5c: H-NMR (200 MHz, CDCl3): d 2.5(3H, s, CH -3), 3.8 (3H, s,
3
Ar-OCH3), 7.1 (1H, s, H-9), 7.4–7.4 (2H, m, H-300,500), 7.6–7.7 (3H, m, H-
30, 40,50), 8.0 (2H, m, H-200,600), 8.1 (1H, s, H-4), 8.3 (2H, dd, J ¼ 9.2, 2 Hz, H-
20,60), 8.5(1H, s, H-7); Anal. calcd. for C 26H18O5: C, 76.09; H, 4.39; found:
C, 76.05; H, 4.37%.
1
5d: H-NMR (200 MHz, CDCl3): d 2.5(3H, s, CH -3), 7.1 (1H, s,
3
H-9), 7.3–7.4 (2H, m, H-300,500), 7.6–7.7 (3 H, m, H-30,40,50), 8.0 (2H, m,
H-200,600), 8.2 (1H, s, H-4), 8.3 (2H, dd, J ¼ 8.6, 2 Hz, H-20,60), 8.4 (1H,
s, H-7); Anal. calcd. for C25H15O4Cl: C, 72.46; H, 3.62; found: C, 72.48;
H, 3.60%.
1
5e: H-NMR (200 MHz, CDCl3): d 2.6 (3H, s, CH3-3), 7.1 (1H, s,
H-9), 7.3–7.4 (2 H, m, H-300,500), 7.6–7.7 (3H, m, H-30,40,50), 8.0 (2H, m,
H-200,600), 8.2 (1H, s, H-4), 8.3 (2H, dd, J ¼ 8.8, 2 Hz, H-20, 60), 8.4 (1H, s,
H-7); Anal. calcd. for C25H15O4F: C, 75.37; H, 3.76; found: C, 75.35; H,
3.77%.
5f: 1H-NMR (200 MHz, CDCl3): d 2.6 (3H, s, CH3-3), 7.1 (1H, s, H-9),
7.4–7.8 (7H, m, aromatic protons), 8.0 (1H, s, H-4), 8.3 (2H, dd, J ¼ 8.8,
2 Hz, H-20,60), 8.5(1H, s, H-7); Anal. calcd. for C 25H15O4Cl: C, 72.46; H,
3.62; found: C, 72.42; H, 3.60%.
1
5g: H-NMR (200 MHz, CDCl3): d 2.7 (3H, s, CH3-3), 3.9 (3H, s,
OCH3-300), 4.1 (3H, s, OCH3-400), 6.9 (1H, d, J ¼ 9.8 Hz, H-500), 7.0 (1H,
s, H-9), 7.3 (1H, dd, J ¼ 9.8, 2 Hz, H-600), 7.5–7.7 (3H, m, H-30,40,50), 8.0
(2H, m, H-4,200), 8.3 (2H, dd, J ¼ 9, 2 Hz, H-20,60), 8.4 (1H, s, H-7); 13C-
NMR (50.3 MHz, CDCl3): d 9.87 C-3 (CH3), 56.76 (C-300 OCH3 and C-400-
OCH3), 99.52 (C-9), 107.46 (C-6), 111.02, 112.98, 119.80 (C-4a), 122.08
127.28 (C-3a), 127.86 (C-4), 128.80, 129.54, 129.90, 131.96, 136.40, 141.40
(C-2), 143.66, 149.92, 150.86, 155.68 (C-8a), 162.46 (C-9a), 165.68 (C-7),
180.15(C-)5 and 184.30 (carbonyl carbon C-2 benzoyl group); Anal.
calcd. for C27H20O6: C, 73.63; H, 4.56; found: C, 73.60; H, 4.52%.
5h: 1H-NMR (200 MHz, CDCl3): d 2.7 (3H, s, CH3-3), 6.1 (2H,
s, O-CH2-O), 6.9 (1H, d, J ¼ 9.5Hz, H-5 00), 7.1 (1H, s, H-9), 7.3–7.7 (4H,
m, aromatic protons), 8.0 (2H, m, H-4,200), 8.3 (2H, dd, J ¼ 9.2, 2 Hz, H-
20,60), 8.5(1H, s, H-7); Anal. calcd. for C 26H16O6: C, 73.58; H, 3.77; found:
C, 73.55; H, 3.75%.
ACKNOWLEDGMENTS
Authors wish to express sincere thanks to Dr. P. Jaya Prasad Rao,
Associate Professor, Department of Chemistry, Osmania University for his

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1899
keen interest and encouragement in the work. Authors also thankful to
Prof. P.N. Sarma, Department of Chemistry, Osmania University for help-
ful discussions. One of the authors (KVVR) is grateful to CSIR, New Delhi
for the award of SRF.
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Received in the USA August 23, 2000

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