An improved method for the synthesis of flavanones

Article abstract of DOI:10.1023/A:1015081726977

An isomerization of 2′-hydroxychalcones into the corresponding flavanones in ethanol in the presence of triethylamine is described.

Full text of DOI:10.1023/A:1015081726977

Russian Journal of Bioorganic Chemistry, Vol. 28, No. 2, 2002, pp. 165–166. Translated from Bioorganicheskaya Khimiya, Vol. 28, No. 2, 2002, pp. 189–190.
Original Russian Text Copyright © 2002 by Aitmambetov, Kubzheterova.
An Improved Method for the Synthesis of Flavanones
1
A. Aitmambetov* and A. Kubzheterova**
*Nukus Branch, Tashkent Institute of Pediatric Medicine, ul. Kurbanova 223, Nukus, 742016 Uzbekistan
**Complex Institute of Natural Sciences, Kara-Kalpak Division, Academy of Sciences of Uzbekistan,
pr. Berdakha 41, Nukus, 742000 Uzbekistan
Received April 27, 2001; in final form, October 12, 2001
Abstract—An isomerization of 2'-hydroxychalcones into the corresponding flavanones in ethanol in the pres-
ence of triethylamine is described.
Key words: chalcone, flavanone, isomerization, synthesis
Flavanones, 2,3-dihydroflavones, attract the atten- chloride are also used sometimes [2–6]. However, the
tion of researchers as physiologically active substances
with a diverse spectrum of activities. Cholagogues,
hepatoprotectors, antiphlogistics, and compounds with
other valuable medicinal properties are among them.
conditions that displace the equilibrium to flavanones
are impossible to predict.
Here we report the isomerization of some 2'-hydrox-
ychalcones into the corresponding flavanones in etha-
nol in the presence of triethylamine.
Flavanones are usually obtained by the isomeriza-
tion of 2'-hydroxychalcones in acidic or alkaline media.
The methods of 2'-hydroxychalcone isomerization into
the corresponding flavanones by the use of hot ethanol;
diluted alkali; sulfuric, hydrochloric, or phosphoric
acid are known. Methanolic hydrogen chloride, sodium
acetate, and ion exchanger Amberlist [1] are also used
for this purpose. Pyridine, glacial acetic acid, n-butyl-
amine, and silica gel with adsorbed concentrated sulfu-
When refluxed in ethanol in the presence of triethy-
lamine, chalcones (I) are transformed into the corre-
sponding flavanones (II) for 2 h in good yields (60–
85%). The chalcones containing electronodonor or
electronoacceptor substituents in position 5', as well as
those with no substituents were obtained in the highest
yields. They were purified to homogeneous state by
ric acid, ethylenediamine, or hydroxylamine hydro- crystallization or fractional crystallization (table).
Characteristics of flavanones (IIa)–(IIm)
Compound
Yield, %
Mp, °C
Empirical formula
Crystallization solvent
(IIa)
(IIb)
(IIc)
(IId)
(IIe)
(IIf)
(IIg)
(IIh)
(IIi)
47.6
69.4
72.1
78.5
73.3
75.2
58.8
85.2
73.3
82.3
79.8
81.7
84.1
76–78
109–110
76–77
C15H12O2
C17H16O3
C15H11FO2
C15H11ClO2
C17H14O4
C16H14O3
C16H14O3
C16H12O4
C17H14O4
C18H16O5
C17H13FO4
C17H13ClO4
C17H13BrO4
EtOH
EtOH
EtOH
96–97
EtOH
76–78
EtOH
94–95
MeOH
97–98
EtOH
127–128
108–109
180–181
120–121
115–116
121–122
MeOH
MeOH
(IIj)
(IIk)
(IIl)
MeOH
MeOH
MeOH
(IIm)
AcOEt/petroleum ether
1
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166
AITMAMBETOV, KUBZHETEROVA
R4
R3
R3
OH
O
R4
R
O
2
R
R2
R1
R1
R
O
(I)
(II)
a: R = R1 = R2 = R3 = R4 = H,
h: R = R1 = R2 = H, R3 = R4 = –OCH2O–,
i: R = R1 = R2 = H, R3 = R4 = –OCH2CH2O–,
j: R = R2 = H, R1 = OCH3, R3 = R4 = –OCH2CH2O–,
k: R = R2 = H, R1 = F, R3 = R4 = –OCH2CH2O–,
l: R = R2 = H, R1 = Cl, R3 = R4 = –OCH2CH2O–,
m: R = R2 = H, R1 = Br, R3 = R4 = –OCH2CH2O–.
b: R = R2 = R3 = H, R1 = CH3, R4 = OCH3,
c: R = R2 = R3 = R4 = H, R1 = F,
d: R = R2 = R3 = R4 = H, R1 = Cl,
e: R = R2 = H, R1 = CH3, R3 = R4 = –OCH2CH2O–,
f: R = R2 = R3 = R4 = H, R1 = OCH3,
g: R = R1 = R2 = R3 = H, R4 = OCH3,
Scheme.
The structures and the compositions of the fla- triethylamine (0.28 ml, 2 mmol) in ethanol (25 ml) was
vanones were confirmed by elemental analysis, melting refluxed for 2–3 h and poured out into cold water con-
points of mixed samples, TLC, and chemical transfor- taining 1 ml of 10% hydrochloric acid. The precipitated
mations.
solid was filtered, washed with water, and crystallized
from an appropriate solvent (see table).
Thus, we suggested an improved and efficient
method for obtaining flavanones and studied the effect
of substituents in rings A and B on the isomerization
course and the yields of target products.
REFERENCES
1. Patonay, T., Litkei, G., Zsuga, M., and Kiss, A., Org.
Prep. and Procedures, 1984, vol. 16, pp. 315–319.
2. Dutta, C.P. and Roy, P.K., Ind. J. Chem., 1975, vol. 13,
EXPERIMENTAL
pp. 425–426.
The reactions were monitored and the purities of
resulting compounds were checked by TLC on pre-
coated Silufol UV-254 plates. As an eluent, a 9 : 1 ben-
zene–ethanol mixture was used. The data of elemental
analyses of all the compounds corresponded to the cal-
culated values.
3. Bagade, M.B., Thool, A.W., Lokhande, P.D., and
Ghiya, B.J., Ind. J. Chem., 1991, vol. 30, pp. 973–975.
4. Aitmambetov, A. and Khilya, V.P., Khim. Prir. Soedin.,
1994, no. 3, pp. 351–355.
5. Aitmambetov, A. and Khilya, V.P., Khim. Prir. Soedin.,
1994, no. 4, pp. 480–483.
General procedure of the chalcone (Ia)–(Im)
isomerization into flavanones (IIa)–(IIm). A solution
of the corresponding 2'-hydroxychalcone (2 mmol) and
6. Aitmambetov, A., Shinkaruk, S.N., Bondarenko, S.P.,
and Khilya, V.P., Khim. Prir. Soedin., 1994, no. 4,
pp. 494–497.
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 28 No. 2 2002