1,3-Dipolar cycloaddition reactions assisted by microwave radiation and gamma radiation

Article abstract of DOI:10.1081/SCC-100104820

Microwave irradiation and gamma irradiation are shown to be new and most suitable techniques for 1,3-dipolar reactions using unsaturated oximes with conventional dipolarophile.

Full text of DOI:10.1081/SCC-100104820

Synthetic Communications
An International Journal for Rapid Communication of Synthetic Organic
Chemistry
ISSN: 0039-7911 (Print) 1532-2432 (Online) Journal homepage: http://www.tandfonline.com/loi/lsyc20
1,3-DIPOLAR CYCLOADDITION REACTIONS
ASSISTED BY MICROWAVE RADIATION AND GAMMA
RADIATION
Radhika S. Kusurkar & Uma D. Kannadkar
To cite this article: Radhika S. Kusurkar & Uma D. Kannadkar (2001) 1,3-DIPOLAR
CYCLOADDITION REACTIONS ASSISTED BY MICROWAVE RADIATION AND GAMMA RADIATION,
Synthetic Communications, 31:15, 2235-2239, DOI: 10.1081/SCC-100104820
To link to this article: http://dx.doi.org/10.1081/SCC-100104820
Published online: 09 Nov 2006.
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SYNTHETIC COMMUNICATIONS, 31(15), 2235–2239 (2001)
1,3-DIPOLAR CYCLOADDITION
REACTIONS ASSISTED BY MICROWAVE
RADIATION AND GAMMA RADIATION
Radhika S. Kusurkar* and Uma D. Kannadkar
Department of Chemistry, University of Pune,
Pune, 411 007, India
ABSTRACT
Microwave irradiation and gamma irradiation are shown to
be new and most suitable techniques for 1,3-dipolar reactions
using unsaturated oximes with conventional dipolarophile.
Earlier we have reported1 thermal reactions using unsaturated oximes
with conventional dipolarophiles which furnished 1,3-dipolar cycloadducts.
Use of other techniques may change the course of the reaction. Gamma
radiation is a source of energy which is 106 times higher than the thermal
energy. Reactions carried out using gamma radiation take place at room
temperature and thus the products are expected to be purer and in high
yields.2 Various types of reactions induced by gamma radiation have been
studied2 however this method is not used for synthetic purpose.
Recently microwave induced rate acceleration technology has become a
powerful tool for synthetic purpose because of the enhanced selectivity, easy
reaction condition, rapid reactions and increased yields.3 Various
* Corresponding author.
2235
Copyright & 2001 by Marcel Dekker, Inc.
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2236
KUSURKAR AND KANNADKAR
organic reactions like Diels Alder reactions, cyclization and radical reactions
are reported3 using this technique. There is a recent report4 of 1,3-dipolar
reactions carried out using microwave radiation. In the present paper we
are reporting the results obtained in the 1,3-dipolar reactions using gamma
and microwave radiation.
REACTIONS USING GAMMA RADIATION
Earlier reported thermal reactions of unsaturated oximes with conven-
tional dipolarophiles are shown in Scheme I. In the present work the
unsaturated oximes were mixed with acrylonitrile in benzene and irradiated
with gamma radiation. Reactions were monitored using tlc. Two products
were isolated from these reactions. The major one was shown to be a
mixture of isomers of 1,3-dipolar cycloadducts with Michael addition
(I & II, Scheme I) and the minor was Michael adduct (III, Scheme I).
The presence of Michael adduct indicated that it was the intermediate in
the formation of 1,3-dipolar cycloadduct. The probable mechanism might
be first Michael addition and then cycloaddition reaction. The role
of Michael adduct as an intermediate was confirmed by carrying out further
reaction of the isolated Michael adduct, with the dipolarophile which
furnished the same mixture of isomers of 1,3-dipolar cycloadducts.
The yields and time intervals required for the reactions using gamma
Scheme I.

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MICROWAVE AND GAMMA RADIATION
2237
radiation are given in Table I. The substituted isoxazolidines obtained were
characterized using PMR and IR spectral data. The products were shown to
be mixtures of 4 and 5- cyno substituted isoxazolidines. The differentiation
between 4 and 5- cyno substituted cycloadducts was made on the basis of the
most down field signal (around 5d) of C5H of 5- cyano isomer in the alicyclic
region. In a few cases exclusively one isomer was obtained (Table II). It was
observed in general that though the time required was much more, the yields
of these reactions were almost comparable with that for the thermal reac-
tions (Table I). Dehydration of oximes was not observed during Gamma
irradiation except cinnamaldoxime (minor).
Table I.
Gamma
Irradiation
Microwave
Irradiation
Thermal
Time Yield
(hr.)
Time
(hr.)
Yield
(%)
Time
(min.)
Yield
(%)
Entry
Oxime
(%)
1.
2.
3.
4.
5.
6.
Benzaldoxime
Pipernaloxime
p.Nitrobenzaldoxime
Veratraldoxime
Furfuraldoxime
Cinnamaldoxime
48
120
36
48
12
90
71
98
72
76
72
96
160
72
168
96
81
69
71
70
66
09
22
08
30
05
07
92
85
85
83
93
73
18
–*
*Dehydration product and Michael adduct was obtained.
Table II.
Gamma
Microwave
Irradiation
Oxime
Thermal
Irradiation
4-Cyano
5-cyano
4-Cyano 5-cyano
4-Cyano 5-cyano
1. Benzaldoxime
–
cis
–
–
cis
trans
–
2. Pipernal oxime
3. p.Nitrobenzaldoxime
4. Veratraldoxime
5. Furfuraldoxime
6. Cinnamaldoxime
mixture
cis:trans 3:2
mixture
cis major
mixture
mixture
cis:trans1:2
mixture
–
–
cis
–
trans
mixture
2 : 1þ
exclusively
minor
2 : 1þ
nil*
–
þRatio is of 4-isomer and cis 5-cyano isomer.
*Dehydration product and Michael adduct was obtained.

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KUSURKAR AND KANNADKAR
REACTIONS USING MICROWAVE RADIATION
Unsaturated oximes were mixed with acrylonitrile in an Erlenmeyer
flask and exposed to microwave radiation in a domestic microwave oven.
In all the reactions substituted isoxazolidines were obtained along with
minor amounts of dehydrated products. These results were described in
Table I. In the reaction of cinnamaldehyde oxime after five minutes irradia-
tion, Michael adduct was formed. It was converted to 1,3-dipolar adduct
by exposing it to microwave radiation for further two minutes. This indicated
that Michael adduct was the intermediate in this reaction. A similar observa-
tion was obtained during gamma radiation reactions as mentioned above. A
remarkable decrease in the time required for the reaction was observed for all
oximes (Table I). Yields were also much more as compared to that in the
thermal reactions and reactions using gamma radiation. In most of the cases
the reactions were regioselective (Table II). It was also observed that when
nitro group was present on the benzene ring the reactions were fast as com-
pared to the reactions of oximes having electron donating methoxyl group on
the benzene ring (entry 3,2 & 4 respectively in Table I).
CONCLUSION
Gamma radiation are used for the first time for synthetic purpose
for 1,3-dipolar reactions. These reactions were clean and yields obtained
were similar to that of thermal reactions. No dehydration was observed in
general during these reactions. Microwave radiation reactions were very
clean and rapid. Moreover the yields were high. Thus this method is
shown to be most suitable for 1,3-dipolar reactions. These results introduced
two new techniques for 1,3-dipolar reactions.
EXPERIMENTAL
General Remarks
IR spectra were recorded on Perkin-Elmer FTIR 1600 spectro-
1
photometer. H NMR were recorded on Jeol FX90Q (90 MHz). The reac-
tions were carried out using 60Co Gamma rays source with Dose rate
2000 Gy(gray)/min. Microwave reactions were carried out in a domestic
microwave Oven (Daewoo, KOR-616T 1200 W). Oximes were prepared
by the reported procedures.

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MICROWAVE AND GAMMA RADIATION
General Procedure for Gamma Irradiation
2239
Oxime (0.002 mole) was mixed with acrylonitrile (2.5 ml) in dry ben-
zene (10 ml) in a conical flask and was exposed to Gamma radiation. The
reaction was monitored using tlc. Solvent was removed and the reaction
mixture was chromatographed using silica gel with hexane-ethyl acetate
(2.5%) as an eluent to furnish the products.
General Procedure for Microwave Irradiation
Oxime (0.002 mol) was dissolved in excess of acrylonitrile (5 ml)
and exposed to Microwave radiation. The reactions were monitored by tlc
after every two minutes. Acrylonitrile was evaporated and the reaction
mixture was chromatographed using silica gel with hexane-ethyl acetate
(2.5%) as an eluent to furnish the products.
ACKNOWLEDGMENTS
We are thankful to Mr. A. P. Gadgil for microanalysis,
Mrs. J. P. Chaudhari for PMR spectra and Nuclear Chemistry Division,
Chemistry department, University of Pune for gamma source.
REFERENCES
1. a) Kusurkar, R.S.; Gadre, L.A. and Kulkarni, M.M. Synthetic Commun.
1994, 24, 635. b) Kusurkar, R.S.; Bhosale, D.K.; Gadre, L.A.; Jain, J.J.
and Wadde, N.M. Indian J. Chem. 1998, 37B, 1239.
2. Arnikar, H.J. ‘‘Essentials of Nuclear Chemistry’’, John Wiley and Sons,
New Delhi, 1995, 18, 420.
3. Caddick, S. Tetrahedron 1995, 51(38), 10403.
4. Kalita, A.H.; Boruah, A.; Prajapati, D. and Sandhu, J.S. Indian J.
Chem. 1988, 37, 101.
Received in Japan July 4, 2000

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