Cage Like Al-KIT-5 Mesoporous Materials for C-C Bond Formation Reactions under Solvent Free Conditions

Article abstract of DOI:10.1007/s10562-015-1611-7

The C-C bond forming reactions are of fundamental importance in chemistry. As a result there is ever growing interest for chemists to develop new methods for C-C bond formation. We report here three dimensional nano-cage mesoporous aluminosilicate materia

Full text of DOI:10.1007/s10562-015-1611-7

Catal Lett
DOI 10.1007/s10562-015-1611-7
Cage Like Al-KIT-5 Mesoporous Materials for C–C Bond
Formation Reactions Under Solvent Free Conditions
Pranjal K. Baruah1 Prantu Dutta1 Pranjal Kalita2
•
•
Received: 7 April 2015 / Accepted: 18 August 2015
Ó Springer Science+Business Media New York 2015
Abstract The C–C bond forming reactions are of fun-
damental importance in chemistry. As a result there is ever
growing interest for chemists to develop new methods for
C–C bond formation. We report here three dimensional
nano-cage mesoporous aluminosilicate materials Al-KIT-5
which exhibited very good catalytic activity for
Mukaiyama-aldol and Mukaiyama–Michael reactions
under solvent free condition. Mukaiyama-aldol and
Mukaiyama–Michael reactions of silyl ketene acetal with
aldehyde and a, b-unsaturated carbonyl compounds pro-
duced b-hydroxy esters and 1, 5-dicarbonyl compounds,
respectively in good yields. The product selectivity was
found to be 100 % in a short reaction period. The high
acidity, 3D pores, and a huge space in the nano-cages
materials make them attractive candidate for carrying out
important organic reactions. The catalyst provide a simple,
easy to handle method, and could be used to solve the
problems of corrosion, toxicity, waste production, and high
cost that are being currently encountered by the conven-
tional homogeneous catalysts.
Graphical Abstract
Keywords Acid catalyst Á Al–KIT-5 mesoporous
materials Á Mukaiyama-aldol and Michael reaction Á
Silyl ketene acetal Á Silyl enol ether Á Aldehyde and a Á
b-unsaturated carbonyl compounds
1 Introduction
Because of unique well-ordered 3D structure with high
porosity, high specific surface area and pore volume of
mesoporous materials, they have found wide range of
applications in areas of adsorption, separation, sensing, fuel
cells and catalysis [1–6]. 3D cage like KIT-5 mesoporous
material with cubic Fm3m close packed symmetry has more
advantages than hexagonal pore structures (MCM-41 and
SBA-15) [1–7]. These materials allow faster diffusion of
reactants, avoid pore blockage, provide more adsorption
sites, and can be used for processing large-sized molecules
[1–7]. Recently, Vinu et al. reported the KIT-5 mesoporous
material by controlling the amount of HCl during synthesis
of the material [4, 7, 8]. They also studied the amount of Al
content, pore diameter and the morphology of the KIT-5
materials and observed superior catalytic activity than zeo-
lites and Al-MCM-41 catalysts for acetylation reaction [4,
7]. Several other organic reactions including three compo-
nent one-pot reaction of synthesis of a-aminophosphonates,
Electronic supplementary material The online version of this
article (doi:10.1007/s10562-015-1611-7) contains supplementary
material, which is available to authorized users.
& Pranjal K. Baruah
pranjal@gauhati.ac.in
& Pranjal Kalita
Pranjal.Kalita@teri.res.in
1
Department of Applied Sciences, Gauhati University,
GUIST, Guwahati 781014, Assam, India
2
Energy Environment Technology Division, The Energy and
Resources Institute, Darbari Seth Block, India Habitat Centre,
Lodhi Road, New Delhi 110 003, India
123

P. K. Baruah et al.
ring opening of epoxides with indoles and primary amines
over nano-cage mesoporous Al-KIT-5 catalysts [9–11] were
also studied by this research group. Very recently, we
observed excellent results for aza-Michael reaction catal-
ysed over the same Al-KIT-5 mesoporous materials under
solvent free condition [12]. Moreover, Kalita et al. reported
the functionalization of mesoporous KIT-5 materials using
super acid like triflic acid and found very good catalytic
activities for the synthesis of coumarin via Pechmann reac-
tion of resorcinol and ethyl acetoacetate under solvent free
system [13].
environmental pollution, etc. Here, we report a synthetic
methodology for preparation of b-hydroxy esters and 1,
5-dicarbonyl compounds through Mukaiyama-aldol and
Michael reaction by utilization of the highly acidic Al-
incorporated KIT-5 catalysts addressing many of these
issues. The catalyst was found to be highly active with
100 % of product selectivity and affording excellent yield
in short reaction time.
2 Experimental
Mukaiyama-aldol and Mukaiyama–Michael reactions are
powerful methods for preparation of C–C bond in organic
synthesis [14–16]. Mukaiyama-aldol reaction produces b-
hydroxy/a, b-unsaturated carbonyl compounds which are
used for the preparation of several drug molecules [17]. The
Michael product of 1, 5-dicarbonyl compounds can also
serve as starting materials for total synthesis of the antitumor
diterpenoid bruceantin and the cytotoxic natural product
sesbanimide A [18, 19], preparation of bridged- or fused-ring
bicyclic ketone [20], preparation of heterocyclic [21, 22] and
polyfunctional compounds [23, 24].
2.1 Synthesis of Al-KIT-5 Catalyst
and Characterization
Al-incorporated highly ordered mesoporousKIT-5 catalyst
was synthesised using pluronic F127 (EO106PO70EO106
,
molecular weight 12,500), and tetraethyl orthosilicate and
aluminium isopropoxide as a structure directing agent, and
the sources of silica and aluminium, respectively. The
materials were obtained from Sigma-Aldrich chemicals,
Bangalore, India and used without further purification. The
detailed synthesis procedure and characterization of the
textural properties of the materials is available in the recent
literature [4, 8, 12]. Al-KIT-5(10) where the number in the
parenthesis denotes the Si/Al ratio was used in our previous
study [4, 8–12]. In a typical synthesis, 5.0 g of F127 is
dissolved in the required amount of HCl (35 wt%) and
240 g of distilled water. To this mixture, 24.0 g of TEOS
and the required amount of the desired Al source were
added, and the resulting mixture was stirred for 24 h at
373 K. Subsequently, the reaction mixture was heated for
24 h at 373 K under static condition for hydrothermal
treatment. The solid product was filtered off and then dried
at 373 K without washing. The product was calcined at
813 K for 10 h. Moreover, we also synthesised Si/Al ratio
28 and 44 for comparison studies.
Several authors have reported the reaction between
silylenol ether or silyl ketene acetal with aldehydes and a,
b-unsaturated carbonyl compounds using several homo-
geneous Lewis acid such as TiCl4, SnCl4, Ti(O-iPr)4,
Ti(OEt)4, using stoichiometric amounts and at lower tem-
peratures [14, 17]. Among the heterogeneous catalyst, solid
acid catalysts such as amorphous SiO2–Al2O3 and zeolites
are also known for promoting C–C bond formation
[25–29]. However, only a few heterogeneous catalysts and
inorganic salts, like CsF, Al-clay montmorillonite, metal-
incorporated mesoporous materials & montmorillonite K10
have shown Mukaiyama-aldol reaction under different
reaction conditions [30–33].
Recently, Kalita et al. showed exciting catalytic activities
for Mukaiyama-aldol and Michael reaction using calcined
Ce–Al-MCM-41 catalyst under solvent free and solvent
system, respectively [34, 35]. Sn-incorporated into different
kinds of 2D (MCM-41) and 3D (MCM-48) mesoporous
materials have potential capacity for Mukaiyama-aldol
reaction under solvent free condition [36, 37]. Corma and co-
workers have reported the same reaction using heteroge-
neous solid oxophilic Lewis acid catalyst such as Ti-MCM-
41 [38]. Zeolytic microporous materials like titanium silicate
molecular sieve (TS-1) is also responsible for catalyzing the
C–C bond formation in Mukaiyama type aldol and Michael
reactions and reported by Kumar et al. [39–41]. Over this TS-
1 catalyst, they were able to report distereoselective syn/anti
product in the case of aldol reaction.
2.2 General Procedure for Mukaiyama-aldol
Reaction
The catalytic reaction was performed in liquid-phase using
a two-necked continuously stirred round bottom flask,
equipped with a water condenser. The catalyst was pre-
activated at 393 K in a vacuum oven and the reactions were
carried out under N2 atmosphere. In a typical procedure,
the methyl trimethylsilyl dimethylketene acetal (10 mmol)
was added to a pre-activated catalyst (0.1 g), followed by
addition of p-NO2-benzaldehyde (10 mmol) to reaction
vessel. The reaction mixture was stirred at 373 K for a
period of 6 h. The progress of the reaction was monitored
by thin layer chromatography (TLC). After completion of
the reaction, the catalyst was filtered out and the filtrate
Many of the above methods suffered from drawbacks,
such as they need large excess of reagents, extreme pre-
caution for making the catalyst, long reaction time,
123

Cage Like Al-KIT-5 Mesoporous Materials for C–C Bond Formation Reactions Under Solvent Free…
Scheme 1 Solvent-free Mukaiyama-aldol reaction of methyl trimethylsilyl dimethylketene acetal with p-NO2-benzaldehyde
was diluted with DCM and then washed with 1 N HCl and
finally washed with water. The organic layer was separated
and dried with anhydrous Na2SO4. The solvent was
removed by rotary evaporator and the product was purified
through column chromatography using silica gel (100–200
mesh) as a stationary phase and petroleum ether ? ethyl
acetate (4:1) as eluent. The final products were identified
The nitrogen adsorption–desorption isotherms were
measured at -196 °C on a Quantachrome Autosorb 1
volumetric adsorption analyzer. The surface area of syn-
thesized catalyst was determined by BET technique and
surface areas of calcined Al-KIT-5 (10), Al-KIT-5 (28) and
Al-KIT-5 (44) catalysts were 989, 815 and 713 m2g-1
,
respectively [4, 8]. The details of characterization of Al-
KIT-5 catalysts and their physicochemical data were
reported by Vinu et al. [4, 8] and are not shown here. The
total acidity of the calcined Al-KIT-5 samples were
determined through temperature-programmed desorption
(NH3-TPD) techniques using Micromeritics Autochem
2910 instrument. The total acidities of calcined Al-KIT-5
(10), Al-KIT-5 (28) and Al-KIT-5 (44) catalysts were 0.50,
0.32 and 0.14 mmolg-1, respectively [4].
1
with the help of H and 13C NMR and compared with
literature data (Scheme 1) (see Supporting information).
3 Results and Discussion
Powder X-ray diffraction patters were collected on a
Rigaku diffractometer using Cu Ka (k = 0.15406 nm)
radiation, operated at 40 kV and 40 mA. The diffrac-
tograms were recorded in the 2h range of 0.7°–10° with a
2h step size of 0.01° and a step time of 6 s. The calcined
samples show well-ordered characteristic properties of
mesoporous materials with well-ordered cage type three
dimensional silica networks and it is shown in Fig. 1. From
XRD pattern it is seen that the peaks are slightly shifted
towards lower 2h values with increasing Al-content in the
Al-KIT-5 samples which increases the unit cell constant
parameters. This is due to the formation of Al–O bond in
the silica network which is longer than Si–O bonds.
3.1 Catalytic Activity
3.1.1 Screening of the Catalysts
The catalytic activity of different Al-content calcined Al-
KIT-5 catalyst was examined for Mukaiyama-aldol reac-
tion of methyl trimethylsilyl dimethylketene acetal with p-
NO2-benzaldehyde and the results are given in Table 1.
The reaction was carried out at 373 K under solvent free
condition for 6 h. The progress of the reaction was moni-
tored by thin layer chromatography (TLC). The percentage
of yield of the desired product is found to have increased
with increasing the mole ratio of Al/Al ? Si in KIT-5
catalyst. This is clearly observed by plotting of percentage
of yield against the mole ratio of Al/Al ? Si in Fig. 2. The
yields of products were 71, 80 and 88 % for Al-KIT-5 (44),
Al-KIT-5 (28), Al-KIT-5 (10) catalysts respectively
(Table 1, Entries 2–4). However, the turn over number
(TON) for individual catalyst is calculated to know the
better understanding of catalytic activity of each reaction
and shown in Table 1. High yields under solvent free
condition could be explained due to the more interaction
between substrate with active catalyst. We observed similar
result when we conducted the same reaction in the identical
reaction condition over calcined Ce–Al-MCM41 catalyst
[34]. However, in this case we reported 98 % of product
selectivity which was based on GC analysis. Although the
a
b
c
d
2
4
6
8
2θ Degree
Fig. 1 The powder XRD patterns of the calcined Al-KIT-5 samples
of a pure KIT-5, b Al-KIT-5 (44), c Al-KIT-5 (28) and d Al-KIT-5
(10)
123

P. K. Baruah et al.
Table 1 Screening of different
catalysts for Mukaiyama-aldol
reaction of methyl trimethylsilyl
dimethylketene acetal with
p-NO2-benzaldehyde
Entries
Catalyst
Solvent
Al/Al ? Si (mole/mole). 10-3
Yields (%)a
TONc
1.
2.
3.
4.
5.
6.
No catalyst
Al-KIT-5 (44)
Al-KIT-5 (28)
Al-KIT-5 (10)
ZSM-5
No solvent
No solvent
No solvent
No solvent
No solvent
No solvent
–
8b
71b
80b
88b
45b
50b
–
0.37
0.57
1.51
ndd
ndd
191
139
58
ndd
ndd
Mordenite
Reaction conditions: methyl trimethylsilyl dimethylketene acetal (10 mmol), p-NO2-benzaldehyde
(10 mmol), 100 mg of catalyst, no solvent, 373 K
a
Isolated yield
b
6 h
c
TON (turn over number) is calculated in terms of moles of reactant converted with respect to per mole of
active Al-site
d
Not determined
90.0
80.0
70.0
60.0
dispersed active sites on the uniform pore surface, which
are easily accessible for the reactant molecules. The high
yield of aldol product could also be explained due to the
total acidity of Al-incorporated KIT-5 materials. The total
acidity of Al-KIT-5 materials is increased by decreasing
the Si/Al ratio and the results are adequately reported by
Vinu et al. in his previous studies. The same research group
concluded that Al is in tetrahedral position in Al-KIT-5
materials which are confirmed by temperature programmed
desorption (TPD) and solid state NMR spectroscopy. These
50.0
0.4
0.8
1.2
1.6
catalytic results also confirm that the Al-KIT-5 (10)
material indeed possesses higher amount of tetrahedral Al,
which provide the Bronsted acid sites [4, 8–12]. The same
trends of results were observed for three component one-pot
synthesis of a-aminophosphonates [9], ring opening of
epoxides with indoles and amines [10, 11] and acetylation
of veratrole [4, 8] and aza-Michael reaction [12], etc.
Moreover, the same Mukaiyama-aldol reaction of methyl
trimethylsilyl dimethylketene acetal with p-NO2-benzalde-
hyde was examined with other catalysts for comparison
purpose in the identical reaction condition (Table 1, Entries
5 & 6). It is observed that mordenite produced moderate
yield of aldol product of 50 % than ZSM-5 of 45 %. This is
may be due to the larger pore size of the mordenite mate-
rials. Hence, the catalyst Al-KIT-5 (10) was used for further
studies of Mukaiyama-aldol reactions. From the above
discussion, it is found that the high mole ratio of Al/Al ? Si
with catalyst AlKIT-5 (10) is carrying the less TON than
other AlKIT-5 (28) and AlKIT-5 (44) catalysts. The
decrease in TON may be due to the high agglomeration of
metal particles in the surface of the mesoporous KIT-5
material although it has high total acidity and it was
determined by TPD of ammonia [4]. The similar trend of
TON was observed in our previous studies for synthesis of
coumarin and Michael-addition reaction [43–45].
Al/Al+Si (mole/mole) x 10-3
Fig. 2 Plot of yield (%) versus Al/Al ? Si (mole/mole) 9 10-3
total acidity of Ce incorporated Al-MCM41 catalyst is less
(0.419 mmolg-1) than Al-KIT-5 (0.50 mmolg-1) catalyst
which is similar to the results in this present work. This is
due to the synergistic effect by simultaneous incorporation
of Ce and Al in MCM-41 silica network which created
more acidic sites in catalyst [34, 42]. The less yield
observed in the present result is may be due to the loss of
compound on handling process by separation of pure
compound by column chromatography. However, we also
carried out the blank experiment of the same Mukaiyama-
aldol reaction without using any catalyst under solvent free
system in the identical reaction condition for a period of
6 h. We observed significantly low yield of 8 % of desired
product (Table 1, Entry 1). Of the Al-KIT-5 catalysts
studied, Al-KIT-5 with Si/Al (10) found to be the best
catalyst for this particular Mukaiyama-aldol reaction and
we observed the same trend in our previous studies with the
same Si/Al ratio 10 [4, 8–12]. The higher activity of Al-
KIT-5 catalysts could be mainly attributed to their excel-
lent structural order with 3D pore symmetry and highly
123

Cage Like Al-KIT-5 Mesoporous Materials for C–C Bond Formation Reactions Under Solvent Free…
Scheme 2 represents the plausible reaction mechanism
of the Mukaiyama-aldol reaction of methyl trimethylsilyl
dimethylketene acetal with p-NO2-benzaldehyde for the
formation of b-hydroxy ester compounds. In the initial
step, the oxygen atom of carbonyl carbon (C = O) is
activated in the presence of acid sites in the reaction media
making the carbonyl carbon more electropositive (electron
deficient). Furthermore, the lone pair electron of oxygen
atom of silyl ether group is delocalized (due to the presence
of electropositive silicon atom) thus making the C-2 carbon
more electron rich. In the second step, the nucleophilic
attack takes place from C-2 position of silyl ketene acetal
to highly electropositive carbonyl carbon of p-NO2-ben-
zaldehyde to produce the intermediate compounds of
silyloxy form of Mukaiyama-aldol product. Finally,
hydrolysis of the silyloxy intermediate with 1 N HCl yields
the required Mukaiyama-aldol product of b-hydroxy ester
and chlorotrimethylsilane (SiMe3Cl) as by-product.
Table 2 Effect of catalyst amount for Mukaiyama-aldol reaction of
methyl trimethylsilyl dimethylketene acetal with p-NO2-benzalde-
hyde over Al-KIT-5 (10) catalyst
Entries
Catalyst amount (mg)
Yields (%)a
TONc
1.
2.
3.
4.
25
50
56b
71b
83b
88b
147
93
75
73
100
58
Reaction conditions: methyl trimethylsilyl dimethylketene acetal
(10 mmol), p-NO2-benzaldehyde (10 mmol), no solvent, 373 K
a
Isolated yield
b
6 h
c
TON (turn over number) is calculated in terms of moles of reactant
converted with respect to per mole of active Al-site
catalyst amount for this particular reaction, we have cal-
culated the TON and given in the Table 2. While
increasing the amount of catalyst from 25 mg to 100 mg,
the satisfactory yield of desired product obtained as men-
tioned in Table 2. The high yield could be explained on the
basis more interaction of the reactant molecules with the
active sites of the Al-KIT-5 (10) catalyst in the reaction
mixture. As we increased the catalyst amount from 75 mg
to 100 mg, the availability of the active site of the catalyst
getting saturated in the reaction mixture as indicated by
the increase in yield from 56 to 88 %, respectively. The
similar kinds of results were observed in our previous
studies [4, 8–13, 34, 43–45].
3.2 Effect of Catalyst Amount
The Mukaiyama-aldol reaction of methyl trimethylsilyl
dimethylketene acetal with p-NO2-benzaldehydewas
investigated over different amount of Al-KIT-5 (10) cata-
lyst and the results are given in Table 2. Individual reaction
was carried out under solvent free condition in the identical
reaction condition. The reaction was initially investigated
with lower amount such as 25 mg of catalyst and product
yield was found to be 56 %. To understand the effect of
Scheme 2 Plausible mechanism for Mukaiyama-aldol reaction of methyl trimethylsilyl dimethylketene acetal (silyl ketene acetal) and p-NO2-
benzaldehyde (aldehyde)
123

P. K. Baruah et al.
3.3 Effect of Reaction Temperature
Table 4 Recycle studies for Mukaiyama-aldol reaction of methyl
trimethylsilyl dimethylketene acetal with p-NO2-benzaldehyde over
Al-KIT-5 (10) catalyst
The role of temperatures for Mukaiyama-aldol reaction of
methyl trimethylsilyl dimethylketene acetal with p-NO2-
benzaldehyde was examined over 100 mg of calcined
Al-KIT-5 (10) catalyst under solvent free condition. The
yields of the products obtained at each reaction temperature
with TON are given in Table 3. The reaction was stirred
for a period of 6 h and progress of the reaction monitored
by thin layer chromatography (TLC). As expected, the
product of Mukaiyama-aldol reaction increased from 51 to
88 % with increasing the temperature from 313 to 373 K
(Table 3). This indicates that the catalyst is quite stable and
the reaction was free from the diffusion limitation at higher
temperatures. Furthermore, these results clearly showed
that the active sites are getting activated with increasing
temperatures from 313 to 373 K, which leads to a higher
rate of attack of nucleophile (silyl ketene acetal) to car-
bocation of carbonyl aldehyde (p-NO2-benzaldehyde).
Therefore, the results in this table clearly show that Al-
KIT-5 (10) catalyst could be used even at 373 K without
compromising the yield of the desired product.
Recycles no.
Yields (%)a
TONc
Fresh
Ist
88b
84b
81b
80b
58.0
57.9
57.8
57.6
2nd
3rd
Reaction conditions: methyl trimethylsilyl dimethylketene acetal
(10 mmol), p-NO2-benzaldehyde (10 mmol), no solvent, 373 K
a
Isolated yield
b
6 h
c
TON (turn over number) is calculated in terms of moles of reactant
converted with respect to per mole of active Al-site
catalyst even after three consecutive cycles at 373 K. The
decrease in yield of product could be due to the partial
leaching of Al from the framework and blockage of pores
in the channels of the catalyst by adsorption of reactants/
products. In our recent publications, similar trends were
observed for recycle studies over the same Al-KIT-5 cat-
alyst for the different types of reactions like one pot three
component reaction, Friedel-Craft alkylation of indole, ring
opening of epoxide with amines and aza-Michael reaction
[9–12] etc. In addition, we have also carried out to scale up
the Mukaiyama-aldol product with 10 gm of methyl
trimethylsilyl dimethylketene acetal and other reactant p-
NO2-benzaldehyde and catalyst Al-KIT-5 catalysts were
taken accordingly. We obtained ca. 85 % of product which
is almost similar to the reported yield in Table 1 (Entry 4),
revealing that the catalyst could easily be commercialized.
3.4 Recycle Studies
To find out the structure stability and regeneration of active
sites of the calcined Al-KIT-5(10) catalyst, the recycling
experiments were conducted for three consecutive cycles
under the identical reaction condition. The yield of the each
recycle and TON are given in Table 4. However, TON
remained almost unchanged for each recycle. After the
reaction, the catalyst was easily separated by centrifugation
and reused without any further activation. It can be seen
from the Table 4 that the yield of Mukaiyama-aldol pro-
duct decreased as the number of cycles increased. This
result is the indication of stability of the Al-KIT-5(10)
3.5 Effect of Different Substrates
Initially, the Mukaiyama-aldol reactions were investigated
with p-NO2-benzaldehyde with different silyl compounds
such as methyl trimethylsilyl dimethylketene acetal and
1-phenyl-1-trimethylsilyloxyethene under the solvent free
system in the identical reaction condition (Table 5). Indi-
vidual experiments were conducted for each reaction for a
period of 6 h. The main reason for choosing p-NO2-ben-
zaldehyde in this study is that it has more electropositive
character on carbon atom of the carbonyl group (C = O)
due to presence of very strong electron-withdrawing NO2
group in the p- position on the benzene ring which facilitate
faster nucleophilic addition of the silyl ketene acetal to the
carbonyl group.
Table 3 Effect of temperatures for Mukaiyama-aldol reaction of
methyl trimethylsilyl dimethylketene acetal with p-NO2-benzalde-
hyde over Al-KIT-5 (10) catalyst
Entries
Temperature (K)
Yields (%)a
TONc
1.
2.
3.
4.
313
333
353
373
51b
74b
84b
88b
33
48
55
58
Reaction conditions: methyl trimethylsilyl dimethylketene acetal
(10 mmol), p-NO2-benzaldehyde (10 mmol), 100 mg of catalyst, no
solvent, 373 K
Higher yield was obtained when reaction was performed
with methyl trimethylsilyl dimethylketene acetal (Table 5,
Entry 1) and p-NO2-benzaldehyde than 1-phenyl-1-
trimethylsilyloxyethene (Table 5, Entry 2). This result is in
agreement with our previously published report [34]. It
a
Isolated yield
b
6 h
c
TON (turn over number) is calculated in terms of moles of reactant
converted with respect to per mole of active Al-site
123

Cage Like Al-KIT-5 Mesoporous Materials for C–C Bond Formation Reactions Under Solvent Free…
Table 5 Mukaiyama-aldol and
Mukaiyama-aldol reactions
Michael reactions over Al-KIT-
5 (10) catalyst
Entry Silyl ketene acetal /
Silyl enol ether
Aldehydes /
Products
Yields
(%)a
α, β-Unsaturated
carbonyl compound
OMe
O
H
1.
HO
OMe
OSiMe3
O
88
NO2
H
NO2
Ph
O
O
O
HO
Ph
2.
OSiMe3
O
79
82
78
NO2
H
NO2
OMe
3.
HO
HO
OMe
OMe
OSiMe3
O
O
OMe
H
4.
OSiMe3
OMe
H
OMe
OMe
O
5.
HO
OMe
OSiMe3
O
84
92
Cl
Cl
For Mukaiyama-Michael reactions
OMe
O
O
6.
OSiMe3
Ph
Ph
Ph
Ph
Ph
O
OMe
Ph
O
O
7.
OSiMe3
Ph
Ph
Ph
89
87
84
Ph
O
CN
OMe
CN
8.
OSiMe3
e
M
O
O
OMe
O
O
9.
OSiMe3
OEt
OEt
O
O
OMe
OMe
O
10.
OSiMe3
61
O
OMe
Reaction conditions: silyl ketene acetal/silyl enol ether (10 mmol), aldehyde/a, b-unsaturated carbonyl
compound (10 mmol), 100 mg of catalyst, no solvent, 373 K, 6 h
a
Isolated yield
123

P. K. Baruah et al.
may be due to the presence of more negative character on
the b-carbon in case of methyl trimethylsilyl dimethylk-
etene acetal than 1-phenyl-1-trimethylsilyloxyethene. In
the former case, the b-carbon is attached with the electron-
donating (?I effect) methyl group, making the nucleophilic
addition more preferable (Table 5, entry 1). On the other
hand, low yield was observed when an electron-with-
drawing phenyl group was attached to the b -carbon of silyl
enol ether (Table 5, Entry 2). Hence, silyl compounds such
as methyl trimethylsilyl dimethylketene acetal was con-
sidered for Mukaiyama-aldol reaction with different
aldehydes.
carbonyl compounds) under solvent free condition using
the identical reaction condition to produce 1, 5-dicarbonyl
compounds (Scheme 3). The purpose of choosing chalcone
is that attack of nucleophile (silyl ketene acetal) to elec-
trophile (chalcone) via 1, 4-addition will be more faster
(Table 5, Entry 6). Since, chalcone consist of two electron-
withdrawing (phenyl) groups at both ends. As a result,
electropositive character at C-1 carbon increases which
facilitate more nucleophilic addition reaction to produce
high yield of Mukaiyama–Michael product. Moreover, the
same Mukaiyama–Michael reaction (Table 5, Entry 7) was
performed between 1-phenyl-1-trimethylsilyloxyethene
and chalcone (a, b-unsaturated carbonyl compounds). As
expected, the low yield of Michael product observed.
Similar trend was observed in the case of Mukaiyama-aldol
reaction Ce–Al-MCM41 catalysts in our previous study
[35]. Due to synergistic effect by simultaneous incorpora-
tion of Ce and Al into the MCM-41 network, the calcined
Ce–Al-MCM41 catalysts showed very promising results
for the same Mukaiyama-aldol and Michael reaction and
reported in our previous study [34, 35, 42]. As proposed
mechanism for Mukaiyama-aldol reaction in the Scheme 2,
we believe that Mukaiyama–Michael reaction also follows
the similar type of mechanism.
To extend the Mukaiyama-aldol reaction, we have
conducted the reaction between different aldehydes with
methyl trimethylsilyl dimethylketene acetal over calcined
Al-KIT-5 (10) catalyst under the same reaction condition.
It is seen from Table 5 that p-Me-benzaldehyde (Entry 3)
produced more aldol product than p-OMe-benzaldehyde
(Entry 4) [34]. This could be explained on the basis of
electron donating power OMe group attached to the ben-
zene ring is more than the Me group. The presence of lone
pairs in the OMe group makes the carbonyl carbon
(C = O) less electrophilic due to delocalisation of lone pair
electrons on oxygen atom to this centre. As a result, the
nucleophilic addition silyl ketene acetal is more easier in p-
Me-benzaldehyde. Moreover, we obtained high yield of
aldol product when reaction was performed between p-Cl-
substituted benzaldehyde (Table 5, entry 5) with methyl
trimethylsilyl dimethylketene acetal than p-Me or p-OMe-
benzaldehyde. This is mainly due to the high electroneg-
ativity group (–Cl) is attached to the benzene ring [34].
To investigate the generality of the calcined Al-KIT-5
(10) catalyst, the Mukaiyama–Michael reaction of different
a, b-unsaturated carbonyl compounds with methyl
trimethylsilyl dimethylketene acetal was investigated under
solvent free system in the identical reaction condition and
the results are given in Table 5.It is evident that acryloni-
trile (Table 5, Entry 8) produced more Michael product
than ethyl acrylate (Table 5, Entry 9). It is due to the
presence of strong electron withdrawing (–CN) group
attached to the carbonyl (C = O) making the b–carbon
more electron deficient. As a result, attack of nucleophile to
electrophile is more facile. Moreover, we also investigated
with cyclic a, b-unsaturated carbonyl compound such as
cyclohexenone (Table 5, Entry 10) and obtained satisfac-
tory yield of desired product.
3.6 Mukaiyama–Michael Reaction
Mukaiyama-aldol and Mukaiyama–Michael reaction are
known to be catalysed by acidic catalyst. Because of
having high acidic properties of calcined Al-KIT-5 cata-
lyst, we found promising results for Mukaiyama-aldol
reaction. The results obtained prompted us to believe that
this catalyst should also be a promising candidate for
Mukaiyama–Michael reaction. Thus, we have carried out
Mukaiyama–Michael reaction of methyl trimethylsilyl
dimethylketene acetal with chalcone (a, b-unsaturated
From these results, we can strongly prove that three
dimensional aluminosilicate mesoporous materials Al-KIT-
5 (10) catalyst is also one of the useful heterogeneous
catalysts for the formation of carbon–carbon bond through
O
O
Ph
Ph
OMe
Catalyst
+ Me3SiCl
OSiMe3
+
No Solvent
O
OMe
Methyl trimethylsilyl
dimethylketene acetal
Chalcone
1, 5-Dicarbonyl compound
Scheme 3 Solvent-free Mukaiyama–Michael reaction of methyl trimethylsilyl dimethylketene acetal with chalcone
123

Cage Like Al-KIT-5 Mesoporous Materials for C–C Bond Formation Reactions Under Solvent Free…
6. Huo Q, Margolese DI, Ciesla U, Demuth DG, Feng P, Gier T,
Mukaiyama-aldol and Michael reaction. As seen from
Table 5, this Al-KIT-5 (10) catalyst can be utilized for a
wide range of substrates giving desired aldol and Michael
products. It also suggests that this reaction methodology
avoids the necessity of solvents, highly expensive and toxic
reagents. Moreover, the work is in progress to elaborate
this process using different kinds of silyl ketene acetal or
silyl enol ether and o- and m-substituted aldehydes or a, b-
unsaturated carbonyl compound to produce aldol and
Michael products, and detail work will be communicated
soon.
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4 Conclusion
Nano-cage three dimensional Al-incorporated mesoporous
material synthesized which have potential character of
large pores, high surface area, large pore volume, and a
high acidity. These materials have been investigated for the
preparation of b-hydroxy ester and 1, 5-dicarbonyl com-
pounds through the Mukaiyama-aldol and Michael reac-
tion, respectively. Among the various catalysts screened,
the sample Al-KIT-5 (10) catalyst showed higher catalytic
activity. This is due to the higher acidity of the catalyst.
The product yield was raised by simply increasing the
reaction temperature under the solvent free condition.
Further, higher conversions were observed when electron-
withdrawing (-I effect) groups are attached to the benzene
ring of aldehyde and b-position of a, b-unsaturated car-
bonyl compound for aldol and Michael reactions,
respectively.
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Acknowledgments The authors are grateful to Prof. M. Deka, Head
of Department, Applied Sciences, Gauhati University, Assam, India,
for his constant support and encouragement. PKB is thankful to DST,
Govt. of India for research funding (Grant No. SB/FT/CS-100/2012)
under Fast Track Scheme.
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