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Chemistry Letters Vol.32, No.7 (2003)
Allylation of Aldehydes Catalyzed by Zeolites under Liquid Phase
M. Sasidharanꢀ and Takashi Tatsumiy
Laboratory for Membrane Science, Tohoku AIST, 4-2-1 Nigatake, Miyagino-ku, Sendai 983-8551
yDivision of Material Science and Chemical Engineering, Graduate School of Engineering,
Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501
(Received March 31, 2003; CL-030274)
Dealuminated zeolite-Y exchanged with rare earth metals
After the reaction, the mixture was quenched with aqueous
(RE-Y)is found to catalyze the allylation of different aldehydes
using allyltrimethylsilane to afford the corresponding allylic
compounds in moderate to good yields by refluxing in nitro-
methane.
NaHCO3 and extracted with diethyl ether (3 ꢂ 15 mL). The
combined extracts were dried over anhydrous sodium sulphate,
and the solvent was removed in rotary evaporator under reduced
pressure. The products were extracted with column chromato-
graphy and identified with GC, GC-MS splitting pattern, and
1H NMR.
Table 1 exhibits the activity of different modified catalyst
for the reaction between benzaldehyde and allyltrimethylsilane
(Scheme 1). The catalyst prepared by successive dealumination
followed by rare earth exchange, shows the best activity (Entry
1)than that prepared without dealumination step (Entry 2). The
poor activity observed over H-Y (Entry 3)indicates that
Brꢀnsted acid sites may less favor this reaction. Furthermore,
mild basic Na-Y did not show any activity under similar condi-
tion (Entry 4). Thus the increased activity of the RE-Y may pos-
sibly due to the creation of Lewis acidic trigonally coordinated
aluminum species by dealumination coupled with rare earth
metal exchange. However, other modified catalysts such as
RE-mordenite and RE-b, (Entries 5 and 6)exhibit slightly less
Allylation of aldehydes with allyltrialkylsilanes is one of
the most important carbon–carbon bond forming reactions in or-
ganic synthesis. This reaction is generally effected over tradi-
tional Lewis acids such as SnCl4, TiCl4, AlCl3, NbCl3, and in-
dium (III)chloride. 1{4 Several rare earth triflates like Sc(OTf)3,
Yb(OTf)3, Zr(OTf)4, and Hf(OTf)4 have also been investigated
under the homogeneous conditions.5{8 However, most of these
conventional Lewis acids are corrosive as well as moisture sen-
sitive, and also the metal triflates are very expensive. Further-
more, there is intense research around the world to replace these
conventional catalysts by greenish, environmentally safer het-
erogeneous catalysts. Although several catalysts are reported
for the allylation of aldehydes under homogeneous condition,
there is no report over the heterogeneous catalyst under the liq-
uid-phase.
Microporous aluminosilicates (zeolites)have been exten-
sively studied for the vapor-phase carbon–carbon bond forma-
tion reactions by replacing the conventional Fridel–Crafts alkyl-
ation catalysts for the production of a variety of fine chemicals
in industry. The regenerability as well as tunable acidity of zeo-
lites makes them as a potential catalyst for various chemical
transformations. Here we report, for the first time the utility
of rare earth metals exchanged zeolite-Y for the successful re-
action of allyltrimethylsilane with different aldehydes under op-
timum reaction conditions.
Lewis-acidity of zeolite-Y was increased by modifying the
Na-Y through exchange with rare earth solution according to
the following two different methods. In the first method, Na-
Y was first converted into NH4 form by exchange with 2 M am-
monium acetate solution at 80 ꢁC for 24 h. Then the NH4-Y was
stirred with rare earth solution at 90 ꢁC and this procedure was
repeated three times to maximize the exchange of rare earths
cations (method I). In the second method, the NH4-Y was sub-
jected to dealumination with (NH4)2SiF6 (1 N solution, 10 mL)
slowly under 90 ꢁC for 24 h. Then, the dealuminated zeolite was
exchanged with rare earth solution as mentioned above (method
II). Similarly, mordenite and b were also prepared by adopting
similar procedure of the method II.
Table 1. Activity of various modified aluminosilicates over al-
lylation of benzaldehydea
Entry Catalyst
Solvent
SiO2/Al2O3 Yield, %
ratio
1
2
3
4
5
6
7
8
9
10
RE-Yb
RE-Yc
H-Y
Nitromethane
Nitromethane
Nitromethane
Nitromethane
11.5
2.5–3.0
2.5–3.0
2.5–3.0
22.5
60.0
80
11.5
11.5
52.0
30.0
16.0
Nil
43.0
35.0
12.0
50.0
21.0
17.0
Na-Y
RE-mordenite Nitromethane
RE-b
RE-ZSM-5
RE-Yb
RE-Yb
RE-Yb
Nitromethane
Nitromethane
Acetonitrile
THF
Dichloromethane
11.5
aReaction conditions: 10 mmol of benzaldehyde, 10 mmol of
allyltrimethylsilane, 20 mL of dry solvent, 30 wt% of catalyst,
temperature 90 ꢁC, reaction time 18 h.
bCatalyst prepared by dealumination followed by rare earth ex-
change.
cCatalyst prepared by direct ion-exchange with rare earth solu-
tion.
In a typical allylation reaction, 10 mmol of aldehydes and
10 mmol of allyltrimethylsilane were mixed in dry nitromethane
in a round bottom flask, to which 30 wt% (with respect to alde-
hyde)of the catalyst was added. Then the reaction mixture was
refluxed under vigorous stirring using magnetic bar for 18 h.
O
OH
RE-Y(cat)
Reflux
SiMe3
+
H
R
Scheme 1.
Copyright Ó 2003 The Chemical Society of Japan
Sasidharan
