Al-MCM-41 as a mild and ecofriendly catalyst for Michael addition of indole to α,β-unsaturated ketones

Article abstract of DOI:10.1016/j.molcata.2012.05.024

Mesoporous Al-MCM-41 catalyzes the chemoselective Michael addition reaction between indoles and α,β-unsaturated ketones to afford β-indolylketones at room temperature with excellent yields. The higher catalytic activity is attributed to Lewis acidic Al and the large surface area. The catalyst is readily recovered and reused more than six times without loss in its catalytic activity. The substitution at the indole nucleus occurs exclusively at the 3-position and N-alkylation products are not observed.

Full text of DOI:10.1016/j.molcata.2012.05.024

Journal of Molecular Catalysis A: Chemical 363–364 (2012) 115–121
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Al-MCM-41 as a mild and ecofriendly catalyst for Michael addition of indole to
␣,␤-unsaturated ketones
Thirumeni Subramaniana, Mayilvasagam Kumarrajab, Kasi Pitchumania,∗
a School of Chemistry, Madurai Kamaraj University, Madurai 625021, India
b Centre for Research & Post-Graduate Studies in Chemistry, Ayya Nadar Janaki Ammal College, Sivakasi 626124, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Mesoporous Al-MCM-41 catalyzes the chemoselective Michael addition reaction between indoles and
␣,␤-unsaturated ketones to afford ␤-indolylketones at room temperature with excellent yields. The
higher catalytic activity is attributed to Lewis acidic Al and the large surface area. The catalyst is readily
recovered and reused more than six times without loss in its catalytic activity. The substitution at the
indole nucleus occurs exclusively at the 3-position and N-alkylation products are not observed.
© 2012 Elsevier B.V. All rights reserved.
Received 24 March 2012
Received in revised form 29 May 2012
Accepted 31 May 2012
Available online 8 June 2012
Keywords:
Indoles
␣,␤-Unsaturated ketones
Michael addition/Friedel–Crafts alkylation
Mesoporous Al-MCM-41
1. Introduction
reported nano TiO2 as a catalyst for Michael addition between
indole and enone [35]. Use of lanthanide triflates [18,20,36] rep-
Michael addition and Friedel–Crafts alkylation of heteroaromat-
ics with electron deficient ␣,␤-unsaturated carbonyl compounds
constitute powerful methods for direct C C bond forming reac-
tions extensively used for functionalization of biologically active
derivatives with pharmaceutical applications [1–5]. They are also
atom efficient and thus are inherently green transformations
[6–8]. The development of effective routes to indole architectures
has attracted considerable attention as 3-substituted indoles are
important building blocks for the synthesis of biologically active
compounds and natural products [9–16]. It is well established
that regioselectivity in the addition of indoles to electron deficient
alkenes is strongly controlled by the reaction medium. Indoles are
N-alkylated by conjugate addition under alkaline conditions. On
the other hand, the formation of C-3 substituted indoles is usually
achieved in acid catalyzed addition [17–25]. They are usually car-
ried out in the presence of catalytic and stoichiometric amounts of
Lewis acids. During the past few years, various catalysts [26–28]
were used for the synthesis of 3-substituted indoles from ␣,␤-
unsaturated carbonyl compounds including Lewis and Bronsted
acid catalysts such as CuBr2 [29], InBr3 [3], [Al(DS)3]·3H2O [30],
Au(III) [31], CeCl3·7H2O–NaI [2], SmI3 [32,33] and K10–FeO [34].
Most of these reactions have been studied using highly nucle-
ophilic indoles and yields are unsatisfactory. Recently Kantam et al.
resents an attractive alternate to catalysts such as AlCl3, TiCl4 and
SnCl4. Unfortunately lanthanide triflates are expensive and their
use in large scale methodology is limited. Consequently Lewis acid
catalysts which are more cost efficient than lanthanide triflates are
desirable. Many of the homogeneous systems for conjugate addi-
tion of indoles require careful control of acidity to prevent side
reactions including dimerization or polymerization. Furthermore,
many of the reported procedures with homogeneous catalysts
involve drawbacks such as strong acidic conditions, expensive
reagents, lower yield of products and longer reaction time [37].
Therefore, the development of an efficient, cost-effective and envi-
ronmentally benign solid Lewis acid catalyst for Michael addition
is desirable for this process.
Ordered mesoporous materials like MCM-41 are attractive het-
erogeneous solid catalysts for fine chemicals synthesis because
their high surface area which ensure high dispersion of active
sites while the large pores may facilitate the diffusion of reac-
tant molecules from bulk solution onto the catalyst surface [38].
MCM-41 has a regular pore diameter of ca. 5 nm and a specific
surface area >700 m2 g−1 [39,40]. Its larger pore size allows the pas-
sage of larger organic molecules and metal complexes through the
pores to reach the surface of the channels [41–43]. For instance,
aluminium substituted mesoporous silica acts as a solid acid cata-
lyst for fine chemicals syntheses through Aldol [44], Friedel–Crafts
[45], Diels–Alder [46] and acetalization reaction [47,48]. In continu-
ation our interest in developing heterogeneous clays/zeolites based
solid acid catalysts for organic transformations [49–53], herein we
∗
Corresponding author. Fax: +91 0452 2459181/2459105.
E-mail address: pit12399@yahoo.com (K. Pitchumani).
1381-1169/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molcata.2012.05.024

116
T. Subramanian et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 115–121
Table 1
Screening of reaction parameters with various catalyst for the formation of 3-(3-indolyl)-1,3-diphenylpropan-2-one.a
.
Entry
Catalyst
Solvent
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
None
–
24
12
12
12
12
12
12
10
1
1
1
2
2
2
2
2
1
1
1
1
1
–
18
10
18
56
35
40
71
30
55
68
76
78
81
83
80
>5
10
44
69
95
56
10
34
MCM-41c
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
THF
CH2Cl2
Toluene
n-Hexane
DMF
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
SiO2
Al2O3
SiO2–Al2O3
Na–Yc
H–Yc
Al–Yc
Al-MCM-41 (100)
Al-MCM-41 (75)
Al-MCM-41 (50)
Al-MCM-41 (25)
Al-MCM-41 (25)
Al-MCM-41 (25)
Al-MCM-41 (25)
Al-MCM-41 (25)
Al-MCM-41 (25)d
Al-MCM-41 (25)e
Al-MCM-41 (25)f
Al-MCM-41 (25)g
Al-MCM-41 (25)h
Al-MCM-41 (25)h
Al-MCM-41 (25)i
Al-MCM-41 (25)j
0.5
10
10
a
Reaction conditions: indole (1 mmol), chalcone (1 mmol), catalyst (100 mg), solvent 2 mL, room temperature.
Isolated yield.
b
c
d
e
f
Calcination at 450 ◦C for 6 h.
20 mg (calcination at 500 ◦C for 5 h) of the catalyst is used.
40 mg (calcination at 500 ◦C for 5 h) of the catalyst is used.
60 mg (calcination at 500 ◦C for 5 h) of the catalyst is used.
80 mg (calcination at 500 ◦C for 5 h) of the catalyst is used.
100 mg (calcination at 500 ◦C for 5 h) of the catalyst is used.
Al-MCM-41 catalyst used without calcination.
g
h
i
j
Calcination at 300 ◦C for 3 h.
Bruker DRX spectrometer operating at 300 MHz for 1H and 75 MHz
for 13C NMR. All 1H NMR and 13C NMR spectra are measured in
CDCl3 with TMS as the internal standard. The aluminium content
in Al-MCM-41 for Si/Al ratio 25 is recorded by ICP-AES with Allied
Analytical ICAP-9000.
describe the synthesis and characterization of mesoporous alu-
minium MCM-41, which is subsequently used for the Michael
addition of indoles with, ␣,␤-unsaturated carbonyl compounds at
room temperature. This regioselective methodology is significant
from an environmental point of view. It is also interesting to note
that the catalyst is recovered and reused for several times without
loss of activity.
2.3. Synthesis of Al-MCM-41
2. Experimental
The Al-MCM-41 (Si/Al ratio = 25) is synthesis according to
the previous report [53–55] with the gel composition of
SiO2:XAl2O3:0.2 CTAB:0.89 H2SO4:120H2O using sodium meta
silicate as the silicon source, H2SO4, cetyltrimethylammonium bro-
mide as the structure directing agent and aluminium sulphate
as the aluminium source. 21.21 g of sodium meta silicate is dis-
solved in 80 mL of water and allowed to stir for half an hour. Then
required quantity of aluminium sulphate, which is dissolved in
15 mL of water, is added and allowed to stir for 1 h. Then 40 mL
of 4 N sulphuric acid is added drop by drop until the gel formed.
The stirring is continued for 2 h. Exactly 7.28 g of cetyltrimethy-
lammonium bromide (CTAB), dissolved in 25 mL of water is added
and stirred for further 2 h. After that, the gel is transferred to an
autoclave and it is kept in a hot air oven at 145 ◦C for 36 h. The
obtained product is filtered, washed several times with double
distilled water and dried at 80 ◦C in an air oven for 2 h. Then it
2.1. Materials
Sodium metasilicate (Na2SiO3·5H2O, ≥98% Sigma), aluminium
sulphate (Al2(SO4)3·18H2O, ≥98% Sigma), cetyltrimethylammo-
nium bromide (C16H33(CH3)3N+Br− ≥99% Sigma), sulphuric acid
(H2SO4, >98% Merck) all the chemicals are purchased as A.R. grade
and other chemicals for Michael addition are purchased from
Sigma–Aldrich (≥98%) and used without purification.
2.2. Characterization of materials
The XRD pattern of the catalyst samples is measured with a
PW3050/60 (XPERT-PRO Diffractometer system) instrument using
a Cu K␣ radiation at room temperature. The electron diffraction pat-
tern is recorded for the selected area. NMR spectra are recorded on

T. Subramanian et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 115–121
117
Table 2
Al-MCM-41 catalyzed Michael addition reaction of various substituted indoles with ␣,␤-unsaturated ketones.a
.
Entry
1
2
Time (h)
Product
Yield (%)b
1
1
3a
95
2
1
3b
92
3
4
1
1
3c
91
94
3d
5
6
0.5
3e
3f
95
83
1
7
8
1
1
3g
3h
85
84
9
1
3i
88

118
T. Subramanian et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 115–121
Table 2 (Continued)
Entry
10
1
2
Time (h)
Product
Yield (%)b
1
3j
89
94
11
0.5
3k
12
0.5
3l
91
13
0.5
3m
93
a
Reaction conditions: indole (1 mmol), chalcone (1 mmol), Al-MCM-41 (100 mg), ACN (2 mL), room temperature.
Isolated yield.
b
is calcined in a muffle furnace at 550 ◦C for 6 h to remove the
(Al2O3) sources are tested independently to promote the reaction
and lesser amount of the product (10% and 18% respectively) are
observed (Table 1, entries 3 and 4). On the other hand, SiO2–Al2O3
affords an improved yield of 56% (Table 1, entry 5). These results
clearly indicate that both the ordered mesoporous structure and
the presence of aluminium are essential for promoting the Michael
addition. Microporous zeolite catalysts such as Na–Y and H–Y are
less effective (Table 1, entries 6 and 7). However the reaction is
facile with Al–Y (Table 1, entry 8), whereas mesoporous Al-MCM-
41 afford the desired Michael adduct in 95% yield. The catalytic
activity observed with Al-MCM-41 having different Si/Al ratio, such
as Al-MCM-41 (25) > Al-MCM-41 (50) > Al-MCM-41 (75) > Al-MCM-
41 (100) is also reported (Fig. 1).
Lower yield in the presence of Al-MCM-41 with high Si/Al ratios
(Table 1, entries 9–11 and 21) may be due to its high hydrophobic-
ity, with which it can retain most of the reactants inside the pores
thereby blocking their diffusion. We also screened different sol-
vents to optimize the reaction conditions. Organic solvents such as
THF, CH2Cl2, toluene, DMF and acetonitrile resulted in formation of
Michael adduct in moderate to good yields (Table 1, entries 12–16).
Among them, acetonitrile affords the Michael adduct in an excellent
yield of 95% within 1 h (Table 1, entry 21). Better catalytic perfor-
mance is observed with 100 mg of Al-MCM-41 catalyst (Fig. 1) and
the yield is also dependent on amount of catalyst (Table 1, entries
17–21).
template. After synthesized Al-MCM-41 is characterized by pow-
der XRD, nitrogen adsorption–desorption isotherm (BET), FT-IR,
ICP-AES and SEM techniques (Figs. S.1–S.3, supporting informa-
tion).
2.4. General procedure for the Al-MCM-41 catalyzed Michael
addition of indoles with ˛,ˇ-unsaturated ketones
Indole 1 mmol and chalcone 1 mmol are successively added to
Al-MCM-41 100 mg (calcination at 500 ◦C in air for 5 h), 2 mL of
acetonitrile and stirred at room temperature for 30–60 min, after
completion of the reaction, the mixture is extracted with ethyl
acetate. After removing the catalyst by simple filtration, followed
by solvent evaporation the resulting crude product is obtained and
purified by column chromatography (silica gel). The recovered cat-
alyst is thoroughly washed with ethylacetate and used for the next
run. The purified products are characterized by their 1H and 13C
NMR as well as by mass spectral data (S.6. and Figs. S.4–S.31 in
supporting information).
3. Results and discussion
The efficiency of the Al-MCM-41 as catalyst in the Michael addi-
tion of indoles to unsaturated ketones has been explored. Indole (1)
and chalcone (2) are selected as model substrates and are screened
for a range of parameters such as effect of different catalysts, sol-
vents and reaction times. The observed results are summarized in
Table 1.
There is no reaction in the absence of any catalyst (Table 1,
entry 1). Only a moderate conversion is observed with aluminium-
free mesoporous silica (Table 1, entry 2). Silica (SiO2) and alumina
This facile and clean protocol for the synthesis of 3-substituted
indoles is extended to various substituted indoles and electron defi-
cient ␣,␤-unsaturated carbonyl compounds using Al-MCM-41 in
acetonitrile at room temperature. The observed results are pre-
sented in Table 2. ␣,␤-Unsaturated ketones with electron deficient
(chloro, bromo and nitro) and electron rich (hydroxyl, methyl and
methoxy) substituents react readily giving good to excellent yields

T. Subramanian et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 115–121
119
Fig. 1. Michael addition of indole to chalcone with various amounts of catalyst and Si/Al ratio of Al-MCM-41.
Table 3
with high selectivity (Table 2, entries 1–8). It is observed that the
substitution on the indole nucleus occurs exclusively at the 3-
position. 2-Methylindole gave higher amount of yields (Table 2,
entries 2, 3, 8 and 10).
Reusability of Al-MCM-41 catalyzed Michael addition reaction indole to chalcone.a
Reuse
1st
95
2nd
94
3rd
94
4th
92
5th
90
6th
89
7th
87
Yield (%)b
In case of
a
sterically hindered enone namely 3,4-
a
Reaction conditions: indole (1 mmol), chalcone (1 mmol), Al-MCM-41 (100 mg,
dichlorochalcone, the reaction proceeds smoothly with good
yield within 1 hr (Table 2, entries 9 and 10). Among the various
Michael acceptors, the reactions proceed smoothly with methyl
vinyl ketone, cyclohexenone and cyclopentenone to afford cor-
responding Michael adducts within 30 min with excellent yields
91–94% (Table 2, entries 11–13). In all these cases of cyclic enones,
the reactions proceed at room temperature with high selectivity.
It is also important to note that products arising from 1,2-addition
are not observed under conditions. The reactions are clean and
the products are obtained in high yields, without formation of any
side products such as N-alkylation product. This result provides an
interesting contrast to similar reactions with palladium catalyst
[56].
calcination at 300 ◦C for 5 h), ACN 2 mL, room temperature.
b
Isolated yield.
Table 4
Sheldon test.a
Catalyst Al-MCM-41
Time
Reused catalyst (1 h)
94
30 min
59
30 min + 2 h
60
Yield (%)b
a
Reaction conditions: indole (1 mmol), chalcone (1 mmol), Al-MCM-41 (100 mg,
calcination at 500 ◦C for 5 h), ACN 2 mL, room temperature.
b
Isolated yield.
Table 5
Comparison with reported catalytic systems for Michael addition of indole with ␣,␤-unsaturated ketones.
Entry
Catalyst
Solvent
Temp (◦C)
Time (h)
Yield (%)
Reusability
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
CeCl3·7H2O–NaI (30 mol%) [2]
InBr3 (10 mol%) [3]
ZrCl4 (0.02 mmol) [4]
Zn-HAP (1 mmol) [9]
CH3CN
CH2Cl2
CH2Cl2
CH3CN
CH3CN
CH2Cl2
CH2Cl2
EtOH
RT
RT
RT
Reflux
80
RT
RT
Reflux
RT
Reflux
RT
RT
RT
RT
MW
RT
36
RT
RT
2–48
16–24
<1
4–36
4
24
6
3–6
18
6–9
12
>80
65–90
<90
5
NRa
NR
98–18
90–98
97–55
75–93
>90
80–90
80–90
99–64
52–68
>80
73–90
>80
>80
>90
80–90
>90
2 (75)b
3 (90)b
NR
Ionic liquid (0.02 mmol) [11]
TMSCl (20 mol%) [16]
Nano TiO2 (10 mol%) [35]
[Bmim]HSO4 (10 mol%) [14]
H3PW12O40 (0.4 mol%) [26]
SbCl3 (20 mol%) [27]
Fe–Mg (10 mol%) [28]
CuBr2 (0.45 mol) [29]
NaAuCl4·2H2O (5 mol%) [31]
K10–FeO (0.5 g) [34]
5 (71)b
3 (51)b
NR
H2O
CH3CN
CH3OH
CH3CN
EtOH
CH3CN
CH3CN
CH3CN
Ethyl ether
CH2Cl2
CH3CN
NR
NR
NR
NR
NR
NR
NR
NR
<1
2–6
1–5
15 min
1–5
2–8
1–3
>1
SmI3 (10 mol%) [33]
Bi(OTf)3−(5 mol%) [37]
NO+BF4 (20 mol%) [55]
GaI3 (10 mol%) [54]
NR
Al-MCM-41 (100 mg)c
7 (87)b
a
Not reported.
Percentage of yield after reused of the catalyst.
Our system.
b
c

120
T. Subramanian et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 115–121
Scheme 1. Plausible mechanism of role of Al-MCM-41 as a Bronsted acid (a) and Lewis acid (b) catalyst in Michael addition of indole to chalcone.
To account for the obtained results and by analogy with previ-
As recyclability is important for industrial applications of a good
catalyst, reuse performance of Al-MCM-41 is investigated. After
completion of reaction, catalyst is recovered by simple filtration,
washed, dried and calcined at 500 ◦C and reused for next cycle. Even
after the sixth recycle, it exhibits good catalytic activity with 87%
yield as shown in Table 3.
In order to verify the true heterogeneity of the process, Sheldon
test is performed on the reaction with the aim of evaluating possible
metal leaching. The reaction mixture is filtered after 30 min and the
filtrate is further stirred for an additional 2 h. The observed results
indicate that no appreciable leaching of metal ions in the filtrate is
noticed in the present reaction conditions (Table 4).
ous reports [5], two plausible reaction mechanisms are proposed
involving Brønsted and Lewis acidic sites of Al-MCM-41 for Michael
addition of indole to chalcone (Scheme 1). In the Bronsted acid cat-
alyzed mechanism (Scheme 1a), the enone is activated by the acidic
protons of Al-MCM-41. Indole then attacks the electron deficient
conjugated carbon–carbon double bond via its ␤-position to afford
(2), followed by H-transfer to give (3). Finally, (3) is rearranged to
target compound (4) and the catalyst is recycled.
A
Lewis acid catalyzed mechanism is also visualized
(Scheme 1b). In this, Al-MCM-41 readily coordinates to O atom
of ␣,␤-unsaturated ketone, which reacts with indole through its
␤-position to form an intermediate (5), which upon subsequent
electron reorganization followed by H-transfer yields (4), releasing
the catalyst for the next cycle.
Data on reaction conditions, activity and efficiency of the differ-
ent catalysts reported in literature for Michael addition of indole
with ␣,␤-unsaturated ketones are given in Table 5. Comparison of

T. Subramanian et al. / Journal of Molecular Catalysis A: Chemical 363–364 (2012) 115–121
121
the results indicates that our catalytic system (entry 19) exhibits
better activity compared to conventional catalysts which require
higher reaction time (entries 1, 2, 4–11, 13, 14 and 17), higher tem-
perature (entries 5, 8, and 10) and poor reusability of the catalyst
(entries 2–5 and 8–18).
[12] J.E. Taylor, M.D. Jones, J.M.J. Williams, S.D. Bull, Org. Lett. 12 (2010) 5740.
[13] H. Hagiwara, M. Sekifuji, T. Hoshi, T. Suzuki, B. Quanxi, K. Qiao, C. Yokoyama,
Synlett 4 (2008) 608.
[14] D.-G. Gu, S.-J. Ji, H.-X. Wang, Q.-Y. Xu, Synth. Commun. 38 (2008) 1212.
[15] K. Tabatabaeian, M. Mamaghani, N.O. Mahmoodi, A. Khorshidi, J. Mol. Catal. A:
Chem. 270 (2007) 112.
[16] L.-W. Xu, W. Zhou, L. Yang, C.-G. Xia, Synth. Commun. 37 (2007) 3095.
[17] S.-Y. Wang, S.-J. Ji, T.-P. Loh, Synlett 15 (2003) 2377.
[18] P.E. Harrington, M.A. Kerr, Synlett 11 (1996) 1047.
[19] G. Babu, P.T. Perumal, Aldrichim. Acta 33 (2000) 16.
[20] M. Kawatsura, S. Aburatani, J. Uenishi, Synlett (2005) 2492.
[21] P.E. Harrington, M.A. Kerr, Can. J. Chem. 76 (1998) 1256.
[22] K. Manobe, N. Aoyama, S. Kobayashi, Adv. Synth. Catal. 343 (2001) 174.
[23] G. Dujardin, J.M. Poirier, Bull. Soc. Chim. Fr. 131 (1994) 900.
[24] I. Komoto, S. Kobayashi, Org. Lett. 4 (2002) 1115.
[25] S.J. Ji, S.Y. Wang, Synlett 16 (2003) 2074.
4. Conclusions
In this study, we have demonstrated a, very simple, mild
reaction protocol with greater selectivity, short reaction time
and efficiency for Michael addition of indoles to ␣,␤-unsaturated
ketones catalyzed by Al-MCM-41. The unique properties of present
system are outlined as below: (a) the procedure is operationally
simple and can furnish a wide variety of 3-substituted indole
derivatives in good yields, (b) the catalyst can be recycled with com-
parable activity and (c) there is no need for any other additive to
promote the reaction. This method is a practical alternative due its
simplicity, environmental acceptability and inexpensiveness. This
report clearly exhibits the promising abilities of mesoporous alu-
minosilicates as catalysts in organic synthesis, especially for fine
chemical synthesis.
[26] N. Azizi, F. Arynasab, M.R. Saidi, Org. Biomol. Chem. 4 (2006) 4275.
[27] G. Maiti, P. Kundu, Synth. Commun. 37 (2007) 2309.
[28] W. Zhou, L. Li, L.-W. Xu, H.-Y. Qiu, G.-Q. Lai, C.-G. Xia, A.-S. Castanet, Synth.
Commun. 38 (2008) 1638.
[29] S.K. Nayak, Synth. Commun. 36 (2006) 1307.
[30] H. Firouzabadi, N. Iranpoor, F. Nowrouzi, Chem. Commun. 6 (2005) 789.
[31] A. Arcadi, G. Bianchi, M. Chiarini, G.D. Anniballe, F. Marinelli, Synlett 6 (2004)
944.
[32] Z.-P. Zhan, K. Lang, Synlett 10 (2005) 1551.
[33] Z.-P. Zhan, R.-F. Yang, K. Lang, Tetrahedron Lett. 46 (2005) 3859.
[34] D.U. Singh, P.R. Singh, S.D. Samant, Synth. Commun. 36 (2006) 1265.
[35] M.L. Kantam, S. Laha, J. Yadav, B.M. Choudary, B. Sreedhar, Adv. Synth. Catal.
348 (2006) 867.
Acknowledgements
[36] Y. Mori, K. Kakumoto, K. Manabe, S. Kobayashi, Tetrahedron Lett. 41 (2000)
3107.
[37] M.M. Alam, R. Varala, S.R. Adapa, Tetrahedron Lett. 44 (2003) 5115.
[38] K. Iwanami, H. Seo, J.-C. Choi, T. Sakakura, H. Yasuda, Tetrahedron 66 (2010)
1898.
[39] J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonowicz, C.T. Kresge, K.D. Schmitt, C.T.-
W. Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B. Higgins, J.L. Schlenker, J.
Am. Chem. Soc. 114 (1992) 10834.
We are grateful to the University of Grants Commission (UGC),
New Delhi for UGC-BSR grant and UGC-BSR-JRF.
Appendix A. Supplementary data
[40] M. Cai, J. Peng, W. Hao, G. Ding, Green Chem. 13 (2011) 190.
[41] S. Haldar, S. Koner, J. Org. Chem. 75 (2010) 6005.
[42] K. Iwanami, J.-C. Choi, B. Lu, T. Sakakura, H. Yasuda, Chem. Commun. 8 (2008)
1002.
[43] H. Li, J. Chen, Y. Wan, W. Chai, F. Zhanga, Y. Lu, Green Chem. 9 (2007) 273.
[44] M.J. Climent, A. Corma, H. Garcia, R. Guil-Lopez, S. Iborra, V. Forne, J. Catal. 197
(2001) 385.
Supplementary data associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.molcata.2012.05.024
References
[45] E. Armengol, M.L. Cano, A. Corma, H. Garcia, M.T. Navarro, J. Chem. Soc. Chem.
Commun. 5 (1995) 519.
[1] C.S. Schwalm, M.A. Ceschi, D. Russowsky, J. Braz. Chem. Soc. 22 (2011) 623.
[2] G. Bartoli, M. Bartolacci, M. Bosco, G. Foglia, A. Giuliani, E. Marcantoni, L. Sambri,
E. Torregiani, J. Org. Chem. 68 (2003) 4594.
[3] M. Bandini, P.G. Cozzi, M. Giacomini, P. Melchiorre, S. Selva, A.U. Ronchi, J. Org.
Chem. 67 (2002) 3700.
[4] V. Kumar, S. Kaur, S. Kumar, Tetrahedron Lett. 47 (2006) 7001.
[5] L.-T. An, J.-P. Zou, L.-L. Zhang, Y. Zhang, Tetrahedron Lett. 48 (2007) 4297.
[6] B.M. Trost, Acc. Chem. Res. 35 (2002) 695.
[7] B.M. Trost, Science 254 (1991) 1471.
[8] P. Anastas, J.C. Warner, Green Chemistry: Theory and Practice, Oxford, Oxford,
UK, 1998.
[9] R. Tahir, K. Banert, A. Solhy, S. Sebti, J. Mol. Catal. A: Chem. 246 (2006) 39.
[10] J. Ezquerra, C. Pedregal, C. Lamas, J. Org. Chem. 61 (1996) 5804.
[11] C.-J. Yu, C.-J. Liu, Molecules 14 (2009) 3222.
[46] M. Onaka, R. Yamasaki, Chem. Lett. 27 (1998) 259.
[47] B.R. Jermy, A. Pandurangan, J. Mol. Catal. A: Chem. 256 (2006) 184.
[48] C.T. Krege, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 (1992)
710.
[49] V. Rama, K. Kanagaraj, K. Pitchumani, J. Org. Chem. 76 (2011) 9090.
[50] K. Namitharan, K. Pitchumani, Org. Lett. 13 (2011) 5728.
[51] K. Namitharan, K. Pitchumani, Eur. J. Org. Chem. 3 (2010) 411.
[52] A. Dhakshinamoorthy, A. Sharmila, K. Pitchumani, Chem. Eur. J. 16 (2010)
1128.
[53] K. Namitharan, M. Kumarraja, K. Pitchumani, Chem. Eur. J. 15 (2009) 2755.
[54] Z.-H. Huang, J.-P. Zou, W.-Q. Jiang, Tetrahedron Lett. 47 (2006) 7965.
[55] G. Li Wu, L. Min Wu, Chin. Chem. Lett. 19 (2008) 55.
[56] B.M. Trost, G.A. Molander, J. Am. Chem. Soc. 103 (1981) 5969.