ISSN 2319-7625 (Online)
(An International Research Journal), www.chemistry-journal.org
Synthesis of β-enaminones Catalyzed by In/AlMCM-41
Under Microwave Irradiation and Solvent-free Condition
Santosh S. Katkara and Amol H. Kategaonkarb
aDepartment of Chemistry,
MSS’s Arts, Commerce and Science College, Ambad, Dist Jalna, Maharashtra, INDIA.
bDepartment of Chemistry,
MVP Samjaj’s S.V.K.T. Arts, Science and Commerce College, Deolali Camp, Nashik, Maharashtra, INDIA.
(Received on: November 4, 2015)
ABSTRACT
We have developed a fast and efficient method for the synthesis of β-enaminones by using indium modified mesoporous material AlMCM-41 viareaction ofaniline and dimedone under microwave irradiation and solvent-free condition. The present protocol contributes remarkable advantages, such as shorter reaction time, solvent-free condition, simple work-up procedure, environmentally benign methodology, recoverable and reusability of catalyst. All the synthesized compounds have been characterized on the basis of elemental analysis, IR, 1H NMR, and 13C NMR spectral studies.
Keywords: β-enaminones, Mesoporous zeolite In/AlMCM-41, Heterogeneous
catalyst.
INTRODUCTION
Ever since the mesoporous materials came into the spotlight during the last decade, rigorous and consistent efforts in this area have paved the way for alternative and new synthetic strategies in the realm of synthetic organic chemistry. Conventional organic syntheses are generally based on homogeneous catalysts. Homogeneous catalyst suffers disadvantages in separation, regeneration, etc. From the viewpoint of green chemistry, the use of heterogeneous catalysts is urgently essential. Thus, catalysis of inorganic solid materials has attracted intense interest as compiled in recent reviews.
non-conventional energy source for activation of reactions, in general and under solvent-free conditions in particular, has now gained popularity over the usual homogeneous and heterogeneous reactions1-4, because it provides enhanced reaction rates and improved product yields along with several eco-friendly advantages in the context of green chemistry which have been extended to modern drug discovery processes5,6.
β-enaminones have been extensively used as key intermediates in organic synthesis7 and serve as very important intermediate in the synthesis of natural products8 and heterocyclic compounds9,10. In particular, they have been employed as synthetic building blocks of a wide variety of heterocycles11 and pharmaceutical compounds those present anti-epileptics12, larvicidal activities13 and anticonvulsivant activity14.
The applications of zeolites in the field of catalysis are growing continuously. Zeolites possess unique properties such as Bronsted and Lewis acidity, possibility to modify their acid: base and redox properties by changing their chemical composition by using different metals, ability to accept and release electrons, high proton mobility, easy work-up procedures, easy filtration, and minimization of cost and waste generation due to reuse and recycling of these catalysts. Because of their stronger acidity, they generally exhibit higher catalytic activity than conventional catalysts such as mineral acids, ion exchange resins, and mixed oxides. In the context of green chemistry, the substitution of harmful liquid acids by solid reusable zeolites or mesoporous materials as catalysts in organic synthesis is the most promising application. Recently the benzimidazole derivatives synthesized by using homogeneous and heterogeneous catalysts such as LaCl3 15, PW/SiO216, CAN17, Sc(OTf)318, Cu-nanoparticles19, silica chloride20 and ZrOCl2.8H2O 21. However, these methods require prolonged reaction time, exotic reaction condition, hazardous solvent and low yield of the products. Thus, the development of a new method for the synthesis of β-enaminones would be highly desirable.
In continuation of our ongoing research on zeolite as a solid as a solid catalyst for organic transformations22-26, herein we report, the efficient method for the synthesis of various β-enaminones derivatives using heterogeneous catalyst indium modified mesoporous zeolite AlMCM-41.
RESULT AND DISCUSSION
Effect of catalyst concentration
Santosh S. Katkar, J. Chem. & Cheml. Sci. Vol.5(11), 591-596 (2015) 593
were found to be constant (Table 1, entries 4 and 5). So, the use of 0.1 gm of catalyst is sufficient to push the reaction forward.
O
O
In/AlMCM-41
N H O
Ar-NH2
1(a-h) 2 3(a-h)
Ar 450 W
Scheme 1 Synthesis of β-enaminones under microwave irradiation catalyzed by In/AlMCM-41.
Table 1. Effect of catalyst loading on the reaction of 4-chloroaniline with dimedone.a
Entry Catalyst amount Time (min) Yieldb (%)
1 0.01 4 61
2 0.05 3.5 79
3 0.10 2 91
4 0.15 2 91
5 0.20 2 91
aAll reactions were carried out under microwave irradiation using 4-chloroaniline (10 mmol),
dimedone (10 mmol), bIsolated yield.
Furthermore, we studied the effect of microwave irradiation power with same model reaction. Here, we have kept the concentration of catalyst constant varied the power inputs from 150-600W. The observation reveals that the reaction carried out at 150W and 300W exhibited low product yields (Table 2, entries 1 and 2). Interestingly, among these different power inputs 450W shows excellent product yield with a short reaction time (Table 2, entry 3). In addition, we have also increased the power input (600W) but results were not found any changes in reaction time as well as in product yield (Table 2, entry 4).
Table 2. Effect of power inputs for the reaction of 4-chloroaniline with dimedone.a
Entry Power (W) Time (min) Yieldb (%)
1 150 3 69
2 300 2.5 73
3 450 2 91
4 600 2 91
aAll reactions were carried in presence of 0.1 gm of catalyst using 4-chloroaniline (10 mmol)
and dimedone (10 mmol), bIsolated yield.
Table 3. Synthesis of β-enaminones derivatives catalyzed by In/AlMCM-41a .
Entry Ar-NH2 Time (min) Yieldb (%) M. P. (C)
3a
NH2
2 91 183-184
3b
NH2
Cl
2 91 190-192
3c
NH2
Me
3 89 195-196
3d NH2 2.5 87 124-126
3e
NH2
OMe
4 89 194-196
3f
NH2
O2N
5 85 193-195
3g
NH2
8 81 (viscous oil)
3h 7 80 (viscous oil)
aAll reactions were carried in presence of microwave irradiation at 450W by using Aniline (10
mmol), dimedone (10 mmol) and In/AlMCM-41 (0.1 gm), bIsolated yield.
Our attention was then directed towards the possibility of recovery and reuse of catalyst that is highly preferable for greener process. The separated catalyst can be reused after washing with n-hexane and drying at 120ºC. The catalyst shows the same activity as fresh catalyst without any significant loss of its activity.
Table 4. Reusability of In/AlMCM-41 catalyst for the reaction of 4-chloroaniline with dimedone.a
Entry Run Yieldb(%)
1 1st 91
2 2nd 91
3 3rd 90
4 4th 89
aAll reactions were carried under microwave irradiation at 450W using 4-chloroaniline (10
mmol), dimedone (10 mmol), bIsolated yield. N
Santosh S. Katkar, J. Chem. & Cheml. Sci. Vol.5(11), 591-596 (2015) 595
EXPERIMENTAL
All chemicals are purchased from Aldrich and Rankem chemical suppliers and used as received. The uncorrected melting points of compounds were taken in an open capillary in a paraffin bath. 1H NMR spectra were recorded on an 300 MHz FT-NMR spectrometer in CDCl3 as a solvent and chemical shifts values are recorded in δ (ppm) relative to tetramethylsilane (Me4Si) as an internal standard.
General procedure for the synthesis of β-enaminones catalyzed by In/AlMCM-41
Aniline (10 mmol) and dimedone (10 mmol) were taken in a beaker (50 mL) and to this In/AlMCM-41 (0.1 gm) was added. The reaction mixture was mixed properly with the help of glass rod and placed in a microwave oven at the power of 450W and irradiated for a period of 10 sec. at a time. After each irradiation the reaction mixture was removed from the microwave oven for shaking. After completion of reaction monitored by TLC (petroleum ether: ethyl acetate = 7:3 as eluent) ethyl acetate was added to separate the catalyst by simple filtration. The solvent was evaporated and crude product was obtained. The crude product was further purified by crystallization from ethanol and to give the corresponding β-enaminones (3a-h)in high to excellent yields.
Spectral data of representative compound (3b)
1H NMR (400 MHz, CDCl
3): δ 7.5 (s, 1H), 7.2 (d, 2H), 7.1 (d, 2H), 5.5 (s, 1H), 2.3 (s, 2H), 2.2 (s, 2H), 1.1 (s, 6H). IR (KBr): 3199, 3074, 2919, 1702, 1606, 1493, 1379, 1280, 1606, 605 cm-1.
CONCLUSIONS
In conclusion, we have introduced an efficient In/AlMCM-41 catalyst for the synthesis of β-enaminones under microwave irradiation. The promising points for the presented methodology are high to excellent yields, short reaction times, ease of handling as well as recover and reusability of catalyst, which makes it a useful and attractive process.
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