Microwave assisted knoevenagel condensation: A facile method for the synthesis of chalcones

Article abstract of DOI:10.1081/SCC-100105339

Microwave irradiation of aromatic aldehydes with acetophenones or malonic acid in presence of anhydrous zinc chloride was resulted exclusively chalcones and cinnamic acids respectively in high yields.

Full text of DOI:10.1081/SCC-100105339

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MICROWAVE ASSISTED KNOEVENAGEL
CONDENSATION: A FACILE METHOD FOR THE
*
SYNTHESIS OF CHALCONES
a
a
a
a
b
G. Venkat Reddy , D. Maitraie , B. Narsaiah , Y. Rambabu & P. Shanthan Rao
a
Organic Division-II, Indian Institute of Chemical Technology, Hyderabad, 500 007, India
Organic Division-II, Indian Institute of Chemical Technology, Hyderabad, 500 007, India
b
Version of record first published: 15 Aug 2006.
To cite this article: G. Venkat Reddy, D. Maitraie, B. Narsaiah, Y. Rambabu & P. Shanthan Rao (2001): MICROWAVE
*
ASSISTED KNOEVENAGEL CONDENSATION: A FACILE METHOD FOR THE SYNTHESIS OF CHALCONES , Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 31:18, 2881-2884
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SYNTHETIC COMMUNICATIONS, 31(18), 2881–2884 (2001)
MICROWAVE ASSISTED KNOEVENAGEL
CONDENSATION: A FACILE METHOD
FOR THE SYNTHESIS OF CHALCONES*
G. Venkat Reddy, D. Maitraie, B. Narsaiah,
y
Y. Rambabu, and P. Shanthan Rao
Organic Division-II, Indian Institute of Chemical
Technology, Hyderabad 500 007, India
ABSTRACT
Microwave irradiation of aromatic aldehydes with aceto-
phenonesormalonicacidinpresenceofanhydrouszincchloride
was resulted exclusively chalcones and cinnamic acids res-
pectively in high yields.
1
The basic skeleton of chalcones is widely figured in natural products
and are known to have multi pronged activity. Some of them are useful
2
–4
as drugs and agrochemicals.
on the synthesis of chalcones mainly from acetophenones and aromatic
Recently much attention has been paid
5
aldehydes. Several catalysts such as basic alumina, Al O –AlPO , P O –
6
2 3
9,10
4
2
5
7
8
piperidine, ultrasonic rays using C-200 and Lewis acid
for Knoevenagel condensation reaction. In addition, media such as
have been used
1
1
12
strong alkali or quarternary ammonium salts have also been employed.
*
IICT Communication No: 4643.
Correpsonding author. E-mail: shanthan@123india.com
y
2
881
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

ORDER
REPRINTS
2
882
VENKAT REDDY ET AL.
Further studies on the efficient synthesis of chalcones is of current interest
because of their wide range of applications. Thus we wish to report here for
the first time a simple and facile approach to chalcones and cinnamic acids.
The methodology involves the reaction of aromatic aldehydes with
various acetophenones or malonic acid independently in presence of cata-
lytic amount of zinc chloride under thermal as well as microwave conditions.
The reaction under thermal condition is found to be sluggish and took
longer time with yields in the range 45–50%. However in the microwave
conditions the rate of reaction is fast as a result the reaction times are
shorter and yields are high with easy isolation of products. In case of malo-
nic acid reaction, it is assumed to be initially the formation of benzylidene
product followed by decarboxylation. The details of schematic diagram cited
below in Scheme.
Scheme.
All the compounds have been characterised based on spectral data
and were comparable to the literature reports. The number of compounds
synthesised have been tabulated in Table.
EXPERIMENTAL
Melting points were determined in open glass capillaries on a Mettler
FP51 melting point apparatus and are uncorrected. IR spectra were recor-
ded on FT-IR Schimadzu Perkin-Elmer 1310 infrared spectrophotometer.

ORDER
REPRINTS
KNOEVENAGEL CONDENSATION
Table. Synthesis of Chalcones Under Microwave Conditions
2883
Reac. Time
(min)
Yield
(%)
M.p.
ꢀ
Lit. m.p.
ꢀ
Product
R
( C)
( C)
1
1
1
1
1
3
4
5
5
6
3
3
3
3
3
5
5
5
a
b
c
d
e
a
b
c
5
3
3
4
5
4
3
3
H
Cl
OCH3
CH
NO
H
Cl
CH
85
82
90
87
85
77
75
79
54
115
75
55
112
76
96
165
3
94
2
163
133
247
195
1
7
132.5
1
241
8
1
9
3
198
1
H NMR spectra were recorded on Varian Gemini (200 MHz) spectrometer
and TMS was used as internal standard. Mass spectra were recorded on a
VG-micromass 7070H instrument at 70 eV.
Synthesis of Chalcones: General Procedure
1. Thermal conditions: A mixture of aromatic aldehyde (0.01 mole)
active methylene compound (0.01 mole) and anhydrous zinc chloride
ꢀ
(
0.001 mole) was heated at 100 C for 6 h. The reaction mixture was cooled
and treated with aqueous alcohol (20 mL). The separated solid was filtered,
washed with n-hexane and dried. The product was recrystallised by
benzene–hexane to give chalcones.
2. Microwave conditions: A mixture of aromatic aldehyde (0.01 mole),
active methylene compound (0.01 mole) and zinc chloride (0.001 mole) was
taken in ACE tube, flushed with argon and tightly capped. The mixture is
subjected to microwave heating for 5 min in a domestic oven (600 W, BPL
BMO 700 T) and then it is allowed to reach to room temperature. The
reaction mixture was treated with aqueous ethanol (20 mL) and the sepa-
rated solid was filtered, washed with n-hexane and dried. The solid was
recrystallised by benzene–hexane.
CONCLUSION
The new synthetic methodology developed has universal applications
in the synthesis of a number of chalcones.

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884
VENKAT REDDY ET AL.
ACKNOWLEDGMENT
Authors are thankful to Dr. K. V. Raghavan, Director, IICT,
Hyderabad for constant encouragement. Mr. G. Venkat Reddy and
D. Maitraie are thankful to CSIR and IICT for Financial support in the
form of Junior Research Fellowship.
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Received in the UK September 13, 2000

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