Solid supported reaction of substituted 2-oxazoline with amines under microwave irradiation

Article abstract of DOI:10.1002/jccs.200300152

1,2-Diaryl-4-phenylmethylene-2-imidazolin-5-ones were obtained by the interaction of primary amines with 2-phenyl-4-phenylmethylene-2-oxazolin-5-one using acidic alumina or montmorillonite K10 clay under microwave irradiation (MWI). The same reaction over

Full text of DOI:10.1002/jccs.200300152

Journal of the Chinese Chemical Society, 2003, 50, 1075-1078
1075
Solid Supported Reaction of Substituted 2-Oxazoline with Amines under
Microwave Irradiation
Mazaahir Kidwai* and Richa Mohan
Department of Chemistry, University of Delhi, Delhi-110007, India
1,2-Diaryl-4-phenylmethylene-2-imidazolin-5-ones were obtained by the interaction of primary amines
with 2-phenyl-4-phenylmethylene-2-oxazolin-5-one using acidic alumina or montmorillonite K10 clay under
microwave irradiation (MWI). The same reaction over basic alumina gave arylamides of a-arylamido-b-
arylacrylic acids in good yield. Usage of acidic alumina for cyclization gave better results in comparison with
clay. This procedure highlights the versatility of various solid supports.
Keywords: Oxazoline; Amines; Microwave irradiation; Solid support; Imidazoline.
INTRODUCTION
RESULTS AND DISCUSSION
The reaction of amines with 2-aryl-4-arylmethylene-
2-oxazolin-5-ones using a variety of reagents have been de-
scribed in the literature.1,2 It has been reported that interac-
tion of amines with 2-aryl-4-arylmethylene-2-oxazolin-5-
ones generally leads to ring opening at C5 to give the aryl-
amides of a-arylcarboxamido-b-aryl acrylic acids3 which
could be recyclized in some cases to corresponding 1,2-di-
aryl-4-arylmethylene-2-imidazolin-5-ones, either by heating
at 200 °C under vaccum or under the influence of acetic acid
and sodium acetate.4,5
2-Phenyl-4-phenylmethylene-2-oxazolin-5-one (1)
was prepared according to the literature method.12 The reac-
tion of 1 with amines 2a-f was carried out using basic alumina
under MWI (Scheme I). Arylcarboxamides of a-arylcarbox-
amides-b-arylacrylic acid 3a-f were obtained in good yield
(Table 1). The products were characterized by their spectral
(Table 3) and analytical data. In IR spectra the appearance of
a band at 3300-3200 cm-1 due to N–H and the disappearance
of a band at 1780 cm-1 due to C=O of lactone, confirmed the
formation of 3a-f. However, when the reaction was carried
out over acidic alumina under MWI, 1,2-diaryl-4-phenyl-
methylene-2-imidazolin-5-ones 4a-f (Scheme I) were ob-
tained (Table 2), indicating the requirement of acidic condi-
tions for the formation of cyclized product. The structures of
the products were established on the basis of their spectral
(Table 3) and analytical data. In IR spectra, the bands at 1720
and 1640 cm-1 due to –CONR and C=N, respectively, con-
firmed the formation of product.
The increasing environmental consciousness through-
out the world has enforced the application of solventless con-
ditions6 into practice. In this endeavour, the use of inorganic
solid supports (alumina, zeolite, bentonite, montmorillonite
K10 clay) have become a landmark as the reactions can be
performed in “dry media”7 or solvent-free conditions.8,9 The
coupling of microwave irradiation (MWI)10 with the use of
inorganic solid support11 offers benefits of shorter reaction
time, milder reaction conditions, yield enhancement, and
high catalytic activity with optimum utilization of energy. In
addition, this methodology also provides an opportunity to
work with open vessels and an enhanced possibility of up-
scaling the reaction on a preparative scale.
The above reactions were also carried out over mont-
morillonite K10 clay giving 4a-f in good yield. This can be
attributed to the ditopic13 nature of montmorillonite K10 clay.
However, the reaction took more time for completion in com-
parison with acidic alumina. In addition, compounds 4a-f
were also obtained on subjecting compounds 3a-f to micro-
wave irradiation using acidic alumina/montmorillonite K10
clay as solid supports.
In view of the eco-friendly role of dry media using mi-
crowaves and our ongoing endeavour towards green synthe-
sis, the reaction of 2-phenyl-4-phenylmethylene-2-oxazolin-
5-one with primary amines was carried out under microwave
irradiation using various solid supports viz. acidic alumina,
basic alumina and montmorillonite K10 clay.
Thus, we have developed a simple, economical and en-
vironmentally benign synthesis keeping modernization and
simplification of classical procedures, and avoiding volatile
* Corresponding author. Tel: (91 11) 27666235; e-mail: mkidwai@mantraonline.com

1076 J. Chin. Chem. Soc., Vol. 50, No. 5, 2003
Kidwai and Mohan
Scheme I
Table 1. Reaction Times and Yield for the Compounds 3a-f
Compd.
No.
R
mp
(°C)
Microwave Heating
Basic alumina
Time (min)
Yield (%)
3a
3b
3c
3d
3e
3f
phenyl
3-chloro-4-fluorophenyl
2-pyridyl
2-furfuryl
5-methyl-1,3,4-thiadiazolyl
5-phenyl-1,3,4-thiadiazolyl
232-234*
250-252
175-177
220-224
185-187
178-180
2.0
2.5
3.5
3.5
4.0
4.5
92
91
92
90
89
88
* Lit. m.p. 2304
and toxic organic solvents. In comparison with classical
methodology, the reaction time has been brought down from
hours to minutes with improved yield. The solid supports
used not only act as catalysts but also as an energy transfer
medium resulting in very rapid and homogeneous heating.
melting point apparatus and are uncorrected. IR spectra were
recorded on a Perkin-Elmer FTIR-1710 spectrophotometer.
1H NMR spectra were recorded on a Bruker Avance (300
MHz) spectrometer using tetramethylsilane as an internal
standard. Microwave irradiation was carried out in a Kenstar
Microwave Oven, Model No. OM9925E (2450 MHz, 800
watts). Elemental analysis were performed by means of a
Heraeus CHN-Rapid Analyzer and their results agreed satis-
factorily with the calculated values. The purity of the com-
pounds were checked on silica gel coated Al plates (Merck).
EXPERIMENTAL
Melting points were determined on a Thomas Hoover

Solid Supported Reaction of 2-Oxazoline
J. Chin. Chem. Soc., Vol. 50, No. 5, 2003 1077
Table 2. Reaction Time and Yield for Compounds 4a-f under MWI
Compd.
No.
R
mp
(ºC)
Acidic*
Alumina
Montmorillonite*
K10 Clay
Acidic**
Alumina
Montmorillonite**
K10 Clay
Time
(min)
Yield
(%)
Time
(min)
Yield
(%)
Time
(min)
Yield
(%)
Time
(min)
Yield
(%)
4a
4b
phenyla
3-chloro-4-
fluorophenyl
2-pyridyl
2-furfuryl
5-methyl-1,3,4- 160-162
thiadiazolyl
172-174
265-269
3.0
3.5
94
93
3.5
4.0
93
92
2.5
3.0
94
92
3.0
3.5
93
93
4c
4d
4e
175-178
184-186
4.5
5.0
6.0
93
91
89
5.5
6.0
6.5
93
90
89
3.5
4.0
5.0
92
90
88
4.0
5.0
5.5
92
89
87
4f
5-phenyl-1,3,4-
thiadiazolyl
149-151
6.5
87
7.0
88
5.5
88
6.0
87
* for conversion of 1 to 4a-f.
** for conversion of 3a-f to 4a-f.
a lit. m.p. 175.4
Table 3. Spectral Data of Compounds 3a-f and 4a-f
Compd.
IR (n cm-1) / 1H NMR d (ppm)
3b
1614 (CO), 3343 (N-H); (DMSO-d6): d 6.6 (s, 1H, CH=C), 7.2-7.8 (m, 13H, Ar-H),
9.3 (s, 1H, N-H), 9.4 (s, 1H, N-H)
3c
3d
3e
3f
1612 (CO), 3267 (N-H); (DMSO-d6): d 6.8 (s, 1H, CH=C), 7.2-8.3 (m, 14H, Ar-H),
9.4 (s, 1H, N-H), 9.5 (s, 1H, N-H)
1620 (CO), 3268 (N-H); (DMSO-d6): d 3.2 (s, 2H, CH2), 6.7 (s, 1H, CH=C), 6.3-7.4
(m, 13H, furan & Ar-H), 9.3 (s, 1H, N-H), 9.4 (s, 1H, N-H)
1624 (CO), 3243 (N-H); (DMSO-d6): d 2.6 (s, 3H, 5'CH3), 6.9 (s, 1H, CH=C), 7.2-
7.4 (m, 10H, Ar-H), 9.5 (s, 1H, N-H), 9.6 (s, 1H, N-H)
1628 (CO), 3248 (N-H); (DMSO-d6): d 6.8 (s, 1H, CH=C), 7.2-7.8 (m, 15H, Ar-H),
9.6 (s, 1H, N-H), 9.7 (s, 1H, N-H)
4b
4c
1642 (C=N), 1715 (CO); (CDCl3): d 6.9 (s, 1H, CH=C), 7.0-7.4 (m, 13H, Ar-H)
1640 (C=N), 1720 (CO); (DMSO-d6): d 7.0 (s, 1H, CH=C), 6.9-7.6 (m, 14H, Ar-H
& pyridyl)
4d
1652 (C=N), 1710 (CO); (DMSO-d6): d 3.2 (s, 2H, CH2), 6.9 (s, 1H, CH=C), 6.3-
7.4 (m, 13H, furyl & Ar-H)
4e
4f
1649 (C=N), 1720 (CO); (DMSO-d6): d 2.7 (s, 3H, 5'CH3), 7.2-7.5 (m, 10H, Ar-H)
1650 (C=N), 1725 (CO); (DMSO): d 7.2-7.8 (m, 15H, Ar-H)
Melting points, yields and spectroscopic data are given in Ta-
bles 1, 2 and 3.
subjected to MWI. On completion of reaction, as monitored
by TLC (at an interval of 30 s), the product was extracted into
ethanol (3 ´ 15 mL). Recovery of solvent under reduced pres-
sure gave the product 3a-f which was recrystallized from eth-
anol.
2-Phenyl-4-phenylmethylene-2-oxazolin-5-one (1)
Compound 1 was prepared according to the literature
method.12
1,2-Diaryl-4-phenylmethylene-2-imidazolin-5-ones (4a-f)
from (1)
Arylcarboxamides of a-arylcarboxamido-b-arylacrylic
acids (3a-f) from (1)
To the solution of 1 (0.05 mole) and primary amines
2a-f (0.05 mole) in ethanol, acidic alumina or montmorillo-
nite K10 clay14 was added. The reaction mixture was stirred
well, dried in air and subjected to MWI for a specified time
To the solution of 1 (0.05 mole) and primary amine 2a-f
(0.05 mole) in ethanol (10 mL), basic alumina14 (20 g) was
added. The reaction mixture was stirred well, air dried and

1078 J. Chin. Chem. Soc., Vol. 50, No. 5, 2003
Kidwai and Mohan
C., Ed.; John Wiley: New York, 1957; Vol. 5, p 336.
3. Islam, A. M.; Khalil, A. M.; Abd Ed-Gawad, I. I. Aust. J.
Chem. 1973, 26, 827.
4. Islam, A. M.; Khalil, A. M.; El-Houseni, M. S. Aust. J.
Chem. 1973, 26, 1701.
(Table 2). On completion of reaction, as monitored by TLC
examination (at an interval of 30 s), the product was extracted
into ethanol (3 ´ 15 mL). Recovery of solvent gave the re-
quired product 4a-f which was recrystallized from ethanol.
5. Badr, M. Z. A.; El-Sherief, H. A. H.; Tadros, M. E. Indian J.
Chem. 1979, 18B, 240.
6. Dittmer, D. C. Chem. and Ind. 1997, 779.
7. Kidwai, M. Pure Appl. Chem. 2001, 73(1), 147.
8. Kidwai, M.; Venkataramanan, R.; Dave, B. Green Chemistry
2001, 3, 278.
9. Kidwai, M.; Saxena, S.; Mohan, R.; Venkataramanan, R. J.
Chem. Soc., Perkin Trans. 1 2002, 16, 1845.
10. Varma, R. S. Green Chemistry 1999, 1, 43.
11. Clark, J. H. Catalysis of Organic Reactions by Supported In-
organic Reagents; VCH: Weinheim, 1994.
12. Erlenmeyer, E. Liebig’s Ann. 1893, 275, 1.
13. Bigi, F.; Chesini, L.; Maggi, R.; Sartori, G. J. Org. Chem.
1999, 64, 1033.
14. (a) Aluminium oxide, Basic Brockmann 1 (Aldrich Chem.
Co., Cat No. 19, 944-3, ~ 150 mesh, 58 Å, surface area 155
m2/g) was used. (b) Aluminium oxide, acidic, Aldrich 26,
774-0, Brockmann 1, ~ 150 mesh, 58 Å CAMAG 506-C-1,
surface area 155 m2/g was used. (c) Montmorillonite K10
clay, Aldrich 11, 6168, surface area 220-270 m2/g, Bulk den-
sity 300-370 g/l.
1,2-Diaryl-4-phenylmethylene-2-imidazolin-5-ones (4a-f)
from (3a-f)
To the solution of 3a-f (0.05 mole) in ethanol, acidic
alumina (20 g) or montmorillonite (20 g) was added. The re-
action mixture was stirred well, dried in air and subjected to
MWI for a specified time (Table 2). On completion of reac-
tion, as followed by TLC examination (at an interval of 30 s),
the product was extracted into ethanol (3 ´ 10 mL). Removal
of solvent under reduced pressure gave the required product
4a-f which was recrystallized from ethanol.
Received November 5, 2002.
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