Paper-

ISSN: 2231 – 3087(print) / 2230 – 9632 (Online)
http://heteroletters.org Vol. 1: (4), 2011, 359-364
MICROWAVE ASSISTED SYNTHESIS OF 6-BENZOYL-5-METHYL-2-[(Z)-1-ARYL
METHYLIDENE]-2,3-DIHYDROFURO [3’,2’ :4,5] BENZO[b] FURAN-3-ONES AND
THEIR ANTIBACTERIAL ACTIVITY
Ashok D*, Sudershan K1 and Khalilullah M2
*Department of chemistry, Osmania University, Hyderabad -500 007, India,
1Sven Genetech Ltd, I.D.A. Phase-II, Cherlapally, Hyderabad-500 051, India 2Department of Chemistry, JNTU, Kupkatpally, Hyderabd-500 072, India
Abstract:
A
6-Benzoyl-5-methyl-2-[(Z)-1-arylmethylidene]-2,3-dihydrofuro[3’,2’:4,5] benzo[b]furan-3-ones have been prepared by an efficient oxidation of (E)-1-(2-Benzoyl-
6-hydroxy-3-methyl benzo[b] furan-5-yl)-3-aryl-2-propen-1-ones with cupric bromide or
mercuric acetate under microwave irradiation. The structures of newly synthesized compounds
have been established on the basis of elemental analysis, IR, 1H-NMR, 13C-NMR and mass
spectral data. All the compounds were screened for their antibacterial activity.
Key Words: Furanoaurones, benzofuran, cupric bromide, mercuric acetate, microwave
irradiation, antibacterial activity.
Introduction
A number of benzofuran derivatives are known to possess anti-inflammatory1,2, anticancer3,4,
antibacterial5, antifungal6, antiallergic7, antihistaminic8, estrogenic and anti-implantation9,10
properties. Aurones have been reported to exhibit various pharmacological activities11 such as
antifungal, antibacterial, antiviral, antileishmenial activities12-14. In order to know the combined
effect of both benzofuran and aurone moieties on biological activities, herein we report the
synthesis
6-Benzoyl-5-methyl-2-[(Z)-1-arylmethylidene]-2,3- dihydrofuro[3’,2’:4,5]benzo[b]furan-3-ones (furanoaurones) (3a-f) by an efficient oxidation of
(E)-1-(2-Benzoyl-6-hydroxy-3-methyl benzo[b] furan-5-yl)-3-aryl-2-propen-1-ones with cupric
bromide or mercuric acetate. The use of microwave irradiation in organic synthesis has become
increasingly popular as an environmental benign technology. Microwave assisted synthesis15,16
leads to significantly reduced reaction times, enhanced yields and environment friendly.
Therefore in the present study we have synthesized the title compounds under microwave
irradiation.

Results and Discussion
The required starting materials, (E)-1-(2-Benzoyl-6-hydroxy-3-methyl benzo[b] furan-5-yl)-3-
aryl-2-propen-1-ones17 were synthesized by condensing 5-Acetyl-2-benzoyl-6-hydroxy-3-methyl
benzofuran18 with aromatic/hetero aromatic aldehydes in the presence of sodium methoxide
under solvent-free microwave irradiation. The title compounds 6-Benzoyl-5-methyl-2-[(Z)-1-
arylmethylidene]-2,3-dihydrofuro[3’,2’:4,5]benzo[b]furan-3-ones (3a-f) were synthesized in
good yields by oxidizing (E)-1-(2-Benzoyl-6-hydroxy-3-methyl benzo[b] furan-5-yl)-3-aryl-2-
propen-1-ones with cupric bromide in dimethyl sulphoxide or mercuric acetate in pyridine, under
microwave irradiation. The synthesis of 3a-f was also carried out under conventional heating.
The physical data of compounds 3a-f are given in Table-1. The geometry of the exocyclic
double bond of aurone was confirmed by diagnostic 13C-NMR signal19 at δ 111.8.
Scheme:


Table-1: Physical data of 6-Benzoyl-5-methyl-2-[(Z)-1-arylmethylidene]-2,3-dihydrofuro
[3’,2’:4,5]benzo [b]furan-3-ones(3a-f)

Compound M.P
Conventional heating
Microwave irradiation
Hg(OAc)2
Hg(OAc)2

Antibacterial Activity
The activity was determined using cup-plate agar diffusion method20 by measuring the inhibition
zone in mm. All the compounds were screened for their antibacterial activity against a variety of
bacterial strains such as Bacillus subtilis (ATCC-6633), Staphylococcus aureus (ATCC-29737),
Escherichia coli (ATCC-10536), and Pseudomonas aeruginosa (ATCC-27853) using
Streptomycin, Tetracycline, Chloramphenicol, Carbenicillin as standard drugs. Nutrient agar was
used as a culture medium. A 1mg/ml solution in dimethylformamide was used. DMF showed no
inhibition zones. The agar medium was inoculated with bacterial cultures tested. After 24 hours
of incubation at 37oC, the diameter of inhibition zone (mm) was measured. The results of the
antibacterial activity are given in Table-2. Among the compounds screened, 3c, 3d, 3e exhibited
good antibacterial activity.
Table-2:
6-Benzoyl-5-methyl-2-[(Z)-1-arylmethylidene]-2,3- dihydrofuro [3’,2’:4,5]benzo[b]furan-3-ones (3a-f) and inhibition zones.

Experimental
Melting points were determined on Polmon MT 96 melting point apparatus and are uncorrected.
IR Spectra were measured as KBR pellets on shimadzu FTIR-8400S 1H-NMR Spectra and 13C-
NMR spectra were recorded in DMSO-d6 on Avance 300 spectrometer using tetramethyl silane
as an internal standard. Elemental analysis was determined on Thermo Finnigan CHNS analyzer.
Mass spectra were recorded on LCMS-2010A Shimadzu spectrophotometer. The purity of the
compounds was checked by TLC using precoated silica gel plates (F-254), Merck. Microwave
irradiations were carried out in Multisynth series microwave system.
General procedure for the synthesis of (E)-1-(2-Benzoyl-6-hydroxy-3-methyl benzo
[b]furan-5-yl)-3-aryl-2-propen-1-ones (2a-f)
Thoroughly mixed mixture of 1 (0.001 mol), appropriate aromatic/hetero aromatic aldehydes
(0.001mol) and sodium methoxide (0.004 mol) was taken in a quartz tube and inserted into teflon
vial with screw capped and then subjected to microwave irradiation at the constant temperature
70°C for 5-6 min. After the completion of reaction as an indicated by TLC, the reaction mixture
was poured on to crushed ice and acidified with dil. HCl. The solid separated was filtered and
recrystallized from methanol as yellow powder.
Synthesis of 6-Benzoyl-5-methyl-2-[(Z)-1-arylmethylidene]-2,3-dihydrofuro[3’,2’:4,5] benzo
[b]furan-3-ones (3a-f).
Conventional method
A mixture of (E)-1-(2-Benzoyl-6-hydroxy-3-methyl benzo[b] furan-5-yl)-3-aryl-2-propen-1-ones
(2a-f) (0.001 mol) and cupric bromide (0.001 mol) in DMSO (5ml) or mercuric acetate (0.0015
mol) in pyridine (5ml) was refluxed for appropriate time (Table-1). The progress of the reaction
was monitored with TLC. The reaction mixture was diluted with chilled water and acidified with
dil. HCl. The solid separated was filtered and recrystallized from methanol as pale yellow
powder.

Microwave irradiation method
A mixture of (E)-1-(2-Benzoyl-6-hydroxy-3-methyl benzo[b] furan-5-yl)-3-aryl-2-propen-1-ones
(2a-f) (0.001 mol) and cupric bromide (0.001 mol) in DMSO (5ml) or mercuric acetate (0.0015
mol) in pyridine (5 ml) was taken in a quartz tube and inserted into teflon vial with screw
capped and then subjected to microwave irradiation at the constant temperature 100°C for
appropriate time (Table-1). After the completion of reaction as indicated by TLC, the reaction
mixture was diluted with chilled water and acidified with dil. HCl. The solid separated was
filtered and recrystallized from methanol as pale yellow powder.

6-Benzoyl-5-methyl-2-[(Z)-1-phenylmethylidene]-2,3-dihydrofuro[3’,2’:4,5]benzo[b] furan-
3-one (3a).
IR (KBr, cm-1):1718(furanone C=O), 1648 (C=C), 1612(benzoyl C=O)17, 18. 1H-NMR (300
MHz, DMSO-d6) δ 2.66(s, 3H, CH3), 6.89 (s, 1H, benzylidene-H), 6.93 (s, 1H, C8-H), 7.45-
7.71(m, 5H, phenyl), 7.95-8.03 (m, 3H, C3, 4, 5-H of benzoyl), 8.09-8.15 (m, 2H, C2, 6-H of
benzoyl), 8.29(s, 1H, C4-H); MS: m/z = 381[M+H]+, Anal. Calcd. for C25H16O4 C, 78.9; H,
4.21%. Found: C, 78.7; H, 4.21%.

6-Benzoyl-5-methyl-2-[(Z)-1-o-chlorophenyl methylidene]-2,3-dihydrofuro [3’,2’:4,5] benzo
[b]furan-3-one (3b).
IR (KBr, cm-1):1713(furanone C=O), 1649(C=C), 1618(benzoyl C=O).1H-NMR (300 MHz,
DMSO-d6) δ 2.56 (s, 3H, CH3), 7.05(s, 1H, benzylidene-H), 7.06 (s, 1H, C8-H), 7.44-7.73 (m,
4H, Ar-H), 7.86-7.96 (m, 3H, C3, 4, 5-H of benzoyl), 8.07-8.13 (d, 2H, C2, 6-H of benzoyl), 8.42
(s,1H, C
4-H); MS: m/z = 415[M+H]+, Anal. Calcd. for C25H15O4Cl ; C, 72.4; H, 3.62%. Found: C, 72.4; H, 3.72%.
6-Benzoyl-5-methyl-2-[(Z)-1-p-chlorophenylmethylidene]-2,3-dihydrofuro[3’,2’:4,5] benzo
[b]furan-3-one (3c).
IR (KBr, cm-1):1710(furanone C=O), 1647(C=C), 1622(benzoyl C=O). 1H-NMR (300 MHz,
DMSO-d6) δ 2.56 (s, 3H, CH3), 6.89(s, 1H, benzylidene-H), 6.93 (s, 1H, C8-H), 7.48-7.72 (m,
4H, Ar-H), 7.93-8.01 (m, 3H, C3, 4, 5-H of benzoyl), 8.05-8.08 (m, 2H, C2, 6-H of benzoyl), 8.27(s,
1H, C4-H); MS: m/z = 415[M+H]+, Anal. Calcd. for C25H15O4Cl; C, 72.4; H, 3.62%. Found: C,
72.52; H, 3.66%.
6-Benzoyl-5-methyl-2-[(Z)-1-m-nitro phenyl methylidene]-2,3-dihydrofuro [3’,2’:4,5] benzo
[b]furan-3-one (3d).
IR (KBr, cm-1):1715(furanone C=O), 1644(C=C), 1619(benzoyl C=O). 1H- NMR (300 MHz,
DMSO-d6) δ 2.55 (s, 3H, CH3), 7.08(s, 1H, benzylidene-H), 7.13 (s, 1H, C8-H), 7.54-7.84 (m,
2H, C-5, 6-H, Ar-H), 7.90-8.14 (m, 3H, C 3, 4, 5-H of benzoyl), 8.31(s, 1H, C4-H), 8.38-8.43 (m,
2H, C2, 6-H of benzoyl) 8.64-8.82 (m, 2H, C 2’, 4’ -H Ar-H); MS: m/z = 426[M+H]+, Anal. Calcd.
for C25H15O6N: C, 70.5; H, 3.52; N, 3.29%, Found: C, 70.52; H, 3.66; N, 3.33%.
6-Benzoyl-5-methyl-2-[(Z)-1-p-methoxyphenyl methylidene]-2,3-dihydrofuro
[3’,2’: 4,5] benzo [b]furan-3-one (3e).
IR (KBr, cm-1):1701(furanone C=O), 1646(C=C), 1618(benzoyl C=O). 1H-NMR (300 MHz,
DMSO-d6) δ 2.57 (s, 3H, CH3), 3.84(s, 3H, OCH3), 6.90(s, 1H, benzylidene-H), 7.03-7.08 (d,
2H, C 2’, 6’ -H Ar-H), 7.56-7.76 (m, 4H C3, 4, 5-H of benzoyl and C8-H), 8.08-8.15(d, 4H, C 2, 6-H
of benzoyl, and C3’, 5’ -H Ar-H), 8.29(s, 1H, C4-H); 13C-NMR (75MHz, DMSO-d6): δ 9.9, 55.38,
111.8, 114.5, 118.2, 124.4, 128.0, 128.5, 129.5, 133.0, 133.6, 137.0, 145.6, 148.2, 160.7, 184.1;
MS: m/z = 411[M+H]+, Anal. Calcd. for C26H18O5: C, 76.09; H%, 4.39. Found: C, 76.04; H,
4.48%.

6-Benzoyl-5-methyl-2-[(Z)-1-2-furyl phenyl methylidene]-2,3-dihydrofuro [3’,2’:4,5] benzo
[b]furan-3-one (3f).
IR (KBr, cm-1):1701(furanone C=O), 1642(C=C), 1617(benzoyl C=O). 1H-NMR (300 MHz,
DMSO-d6) δ 2.55 (S, 3H, CH3), 6.83(s,1H, benzylidene-H), 6.89 (s, 1H, H-8), 7.54-7.75 (m, 3H,
furyl), 7.94-8.03 (m, 3H, C3, 4, 5-H of benzoyl), 8.08-8.15(d, 2H, C2,6-H of benzoyl), 8.27(s, 1H,
C4-H); MS: m/z = 370[M]+, Anal. Calcd. for C23H14O5; C, 74.59; H, 3.78%. Found: C, 74.64; H,
3.87%.
Conclusion
In Conclusion, we have successfully synthesized new furanoaurones under microwave
irradiation. This methodology provides an efficient, time saving and environmentally benign
synthesis. The reaction time is dramatically reduced to 1.5-3.0 min. Also, solvent-free synthesis
of chalcones (2a-f) is non polluting green approach.
Acknowledgements
Authors are thankful to the Head, Department of Chemistry, Osmania University and Managing
Director, Sven Genetech Limited for providing laboratory facilities to carry out the research
work. The authors also thank General Manager IR Technologies Bombay for providing
Multisynth microwave system.

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