Microwave assisted synthesis of α,α′-bis(benzylidene)ketones in dry media

Article abstract of DOI:10.1081/SCC-120002700

Aromatic aldehydes undergo cross-aldol condensation with ketones in the presence of KF-Al₂O₃ under microwave irradiation in solvent-free conditions to afford the corresponding α,α′-bis(benzylidene) alkanones in high yields.

Full text of DOI:10.1081/SCC-120002700

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MICROWAVE ASSISTED SYNTHESIS OF α,α′-
BIS(BENZYLIDENE)KETONES IN DRY MEDIA*
a
a
a
a
J. S. Yadav , B. V. Subba Reddy , A. Nagaraju & J. A. R. P. Sarma
a
Organic-I Division , Indian Institute of Chemical Technology , Hyderabad, 500 007, India
Published online: 16 Aug 2006.
To cite this article: J. S. Yadav , B. V. Subba Reddy , A. Nagaraju & J. A. R. P. Sarma (2002) MICROWAVE ASSISTED SYNTHESIS
OF α,α′-BIS(BENZYLIDENE)KETONES IN DRY MEDIA*, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 32:6, 893-896, DOI: 10.1081/SCC-120002700
To link to this article: http://dx.doi.org/10.1081/SCC-120002700
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SYNTHETIC COMMUNICATIONS, 32(6), 893–896 (2002)
MICROWAVE ASSISTED SYNTHESIS
OF a,a -BIS(BENZYLIDENE)KETONES
IN DRY MEDIA*
0
y
J. S. Yadav, B. V. Subba Reddy,
A. Nagaraju, and J. A. R. P. Sarma
y
Organic-I Division, Indian Institute of Chemical
Technology, Hyderabad-500 007, India
ABSTRACT
Aromatic aldehydes undergo cross-aldol condensation with
ketones in the presence of KF-Al O under microwave irra-
2
3
diation in solvent-free conditions to afford the corresponding
0
a,a -bis(benzylidene) alkanones in high yields.
We report a rapid and convenient method for the synthesis of
1
bis(benzylidene)ketones using KF-Al O under microwave irradiation.
2
3
Scheme.
*
IICT Communication No. 4420.
Corresponding authors.
y
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93
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

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YADAV ET AL.
Table. Microwave Assisted Preparation of a,a -bis(Benzylidene)Ketones
0

0
a,a -BIS(BENZYLIDENE)KETONES
895
RESULTS AND DISCUSSION
Several aromatic aldehydes were rapidly reacted with ketones when
subjected to microwave irradiation in the presence of KF-Al O in dry
media. The condensation proceeded smoothly by 37% KF supported
2
3
0
on alumina to form a,a -bis(benzylidene)alkanones in good yields (75–90%)
in a short irradiation times (2–5 min). The reactions were clean and free
from aromatic by-products, which were normally observed under classical
2
reaction conditions. The conversions were partial (40–55%) when the reac-
tions were carried out under thermal conditions in refluxing acetonitrile for
a long reaction time (8–14 h) whereas similar reactions in the absence of
solvent under microwave irradiation afforded high yields of products
(
75–90%) within 2–4 min of irradiation time. This clearly indicates the
3
role of microwave in enhancing reaction rates and yields. Invariably the
products obtained in solvent free conditions were purified with more ease.
4
–6
Conventional approaches for the preparation of these compounds often
involves longer reaction times, harsh reaction conditions and environmen-
tally unfavorable solvents. The results as summarized in the table clearly
reveal the scope and generality of the reaction with respect to various
substituted aldehydes and ketones.
In conclusion we have described a rapid and convenient procedure for
0
the synthesis a,a -bis(benzylidene)alkanones using surface bound reagent
KF-Al O under microwave irradiation in solvent-free conditions. The
use of solid base KF-Al O and microwave activation makes this process
2
3
2
3
practical and simple for the preparation of these compounds.
EXPERIMENTAL
In a typical procedure, a mixture of benzaldehyde (1.06 g, 10 mmol)
cyclohexanone, (0.49 g, 5 mmol) and 37% w/w KF-Al O (4 wt eq. of alde-
2
3
hyde) was placed in Pyrex test tube and exposed to microwave irradiation at
50 watts (BPL, BMO – 700 T) for 4 min. After complete conversion, as
indicated by TLC, the reaction mass was cooled to room temperature,
4
washed with ethyl acetate (2 ꢀ 10 ml) and recrystallized from ethyl acetate
0
or ethanol to afford a,a -bis(benzylidene)cyclohexanone as a solid (1.22 g,
9
ꢁ ꢁ
0% yield) m.p. (115–117 C lit. 117 C).
ACKNOWLEDGMENTS
A.N. and B.V.S. thank UGC & CSIR New Delhi for award of
fellowships.

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YADAV ET AL.
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Received in the Netherlands April 12, 2001