A. Lahyani, M. Trabelsi / Ultrasonics Sonochemistry 31 (2016) 626–630
627
We purpose in this work an improved synthesis of flavones
2.3.1. 2-Phenyl-4H-chromen-4-one
, cm 1] 3088 (C@C–H, Ar–H), 1645 (C@O), 1568 (C@C, Ar),
ꢁ
using an equimolar amount of iodine monochloride with DMSO
under ultrasound irradiation. This method allows for high yields
in a short time and at low reaction temperatures.
IR [m
1
1128 (COC). H NMR [d, ppm] 8.17 (dd, 1H, JH–H = 1.2 Hz; JH–H = 8 -
Hz), 7.85–7.83 (m, 2H), 7.63 (t, 1H, JH–H = 8 Hz), 7.50–7.44 (m, 4H),
1
3
7.35 (t, 1H, JH–H = 8 Hz), 6.76 (s, 1H); C NMR [d, ppm] 178.5,
164.4, 156.3, 134.3, 132.1, 131.3, 129.1 (2C), 126.5 (2C), 125.7,
125.6, 123.1, 118.1, 106.8.
2
. Experimental
2
.1. Chemicals and apparatus
2
.3.2. 2-(4-chlorophenyl)-4H-chromen-4-one
ꢁ1
IR [
Ar), 1132 (COC). H NMR [d, ppm] 8.23 (dd, 1H, JH–H = 1.6 Hz;
H–H = 8 Hz), 7.88 (d, 2H, JH–H = 8.4 Hz), 7.75–7.71 (m, 1H), 7.58 (d,
m, cm ] 3086 (C@C–H, Ar–H), 1647 (C@O), 1601, 1568 (C@C,
All solvents and reagents were purchased from Fluka and
1
0
Sigma–Aldrich and used without further purification. 2 -hydroxy
substituted chalcones were prepared by base-catalyzed condensa-
tion between 2 -hydroxyacetophenone and the appropriate ben-
J
1
6
1
H, JH–H = 8 Hz), 7.50 (d, 2H, JH–H = 8.4 Hz), 7.44 (t,1H, JH–H = 8 Hz),
0
13
.87 (s, 1H); C NMR [d, ppm] 178.1, 162.1, 156.1, 137.8, 133.8,
zaldehyde using
a literature procedure [36]. Wijs’ Reagent
30.2, 129.3 (2C), 127.5 (2C), 125.7, 125.3, 123.8, 118.0, 107.6.
(
0.1 mol/l, 0.2 N) was purchased from Panreac. The ultrasonication
was performed in a Bioblock 750 W ultrasound cleaner with a low
frequency of 20 kHz (amplitude of 30%). The melting points of the
isolated products were measured on a Reichert-Heizbank appara-
2.3.3. 2-(4-methoxyphenyl)-4H-chromen-4-one
ꢁ
1
IR [m, cm ] 3051 (C@C–H, Ar–H), 1640 (C@O), 1602, 1572 (C@C,
1
Ar), 1132 (COC). H NMR [d, ppm] 8.22 (dd, 1H, JH–H = 1.2 Hz;
1
13
3
tus. H and C NMR spectra were acquired in CDCl on a Bruker
JH–H = 8 Hz), 7.88 (d, 2H, JH–H = 8.8 Hz), 7.72–7.67 (m, 1H), 7.55 (d,
1
13
Avance III HD (400 MHz for H and 100 MHz for C) spectrometer
using TMS as internal standard.
1H, JH–H = 8 Hz), 7.41 (m, 1H), 7.01 (d,2H, J
1H), 3.88 (s, 3H); C NMR [d, ppm] 178.2, 165.4, 163.2, 156.2,
H–H
= 8.8 Hz), 6.82 (s,
1
3
1
1
34.5, 128.7 (2C), 125.8, 125.6, 123.1, 122.3, 118.0, 114.7, 114.6,
04.7, 55.6.
2.2. General procedure for the synthesis of flavones
2
.3.4. 2-(3,4-dimethoxyphenyl)-4H-chromen-4-one
0
For a typical synthesis, 2 -hydroxychalcones (0.5 mmol) was
ꢁ1
IR [
m, cm ] 3065 (C@C–H, Ar–H), 1696 (C@O), 1606 (C@C, Ar),
dissolved in Wijs’ reagent (5 mL). The acetic acid was removed in
vacuo. Then, the resulting solid and DMSO (5 mL) were charged
in a 10 mL glass reactor. The reaction mixture was heated in an
oil bath at 50 ± 2 °C. The ultrasound probe was immersed directly
in the reactor. The ultrasonic generator (Bioblock Scientific
50 W) emits the sound vibration into the reaction mixture. Soni-
fication was achieved at low frequencies of 20 kHz (amplitude of
0%). The reaction time was fixed at 30 min. When the reaction
time was over, the mixture was allowed to cool, poured into
0 mL water and extracted with chloroform (3 ꢀ 20 mL). The
organic layer was washed with sodium thiosulphate (3 ꢀ 10 mL)
until neutrality and dried with MgSO anhydrous. After filtration,
the solvent was removed under reduced pressure to furnish the
crude product. The yields of the reactions were calculated from
the mass of the isolated pure product.
It is noteworthy that flavones were obtained in excellent yields
without the use of any column chromatography. The reactions
were clean and isolated compounds provided an NMR pure
1
1
143 (COC). H NMR [d, ppm] 8.23 (dd, 1H, JH–H = 1.6 Hz; JH–H = 8 -
Hz), 7.72 (m, 1H), 7.59 (d, 2H, JH–H = 8.8 Hz), 7.44 (m, 1H), 7.40 (d,
1
3
1
1
H, JH–H = 2 Hz), 6.99 (d,1H, JH–H = 8.8 Hz), 6.90 (s, 1H), 3.99 (s, 3H),
1
3
.97 (s, 3H); C NMR [d, ppm] 178.3, 163.3, 156.1, 152.0, 149.2,
33.5, 125.6, 125.0, 124.2, 123.8, 119.9, 117.9, 111.1, 108.7,
06.4, 56.0 (2C).
7
3
2
.3.5. 2-(3,4,5-trimethoxyphenyl)-4H-chromen-4-one
ꢁ1
1
IR [m
, cm ] 3063 (C@C–H, Ar–H), 1694 (C@O), 1574 (C@C, Ar),
1
1
8
152 (COC). H NMR [d, ppm] 8.23 (dd, 1H, JH–H = 1.2 Hz; JH–H
=
Hz), 7.73 (m, 1H), 7.61 (d, 1H, JH–H = 8.4 Hz), 7.44 (t, 1H,
4
JH–H = 7.6 Hz), 7.15 (s, 2H), 6.88 (s,1H), 6.90 (s, 1H), 3.97 (s, 6H),
13
3
1
6
.94 (s, 3H); C NMR [d, ppm] 178.4, 163.5, 156.2, 153.5, 141.2,
33.9, 126.8, 125.7, 125.4, 123.6, 118.1 (2C), 107.2, 103.7 (2C),
1.1, 56.3 (2C).
Table 1
Optimization of the DMSO amount.
(
>97% purity) product.
Yielda,b (%)
Entry
Amount of DMSO (mL)
1
2
3
4
5
6
0
1
2
3
5
N.R
16
29
49
96
97
2
.3. Spectroscopic analysis
In general, no further purification method was required. All the
products were previously reported and characterized by the
melting point, IR, H NMR, C NMR.
The spectral data of the isolated compounds, taken as represen-
tative examples, are listed below.
10
1
13
a
0
Reaction condition: 2 -hydroxychalcone (0.5 mmol), ICl (0.5 mmol), acetic acid
5 mL), refluxed in open air for 60 min at 130 °C.
Isolated yield of flavone.
(
b
0
Scheme 1. Oxidative cyclization of 2 -hydroxychalcone to flavone.