Dodecatungestophosphoric acid (H3PW12O40) as a solid green Br?nsted acid catalyzes high yielding and efficient trimethylcyanosylilation reactions of aldehydes and ketones by trimethylsilyl cyanide

Article abstract of DOI:10.1016/j.jorganchem.2004.12.025

An efficient solvent-free method is described for the addition of TMSCN to carbonyl groups employing dodecatungestophosphoric acid (H₃PW ₁₂O₄₀) as a heterogeneous and environmentally benign catalyst. By this method, aromat

Full text of DOI:10.1016/j.jorganchem.2004.12.025

Journal of Organometallic Chemistry 690 (2005) 1556–1559
www.elsevier.com/locate/jorganchem
Dodecatungestophosphoric acid (H PW O ) as a solid green
3
12 40
Brønsted acid catalyzes high yielding and efficient
trimethylcyanosylilation reactions of aldehydes and ketones by
trimethylsilyl cyanide
*
Habib Firouzabadi , Nasser Iranpoor , Abbas Ali Jafari
*
Department of Chemistry, Shiraz University, Shiraz 71454, Iran
Received 11 September 2004; accepted 20 December 2004
Available online 19 January 2005
Abstract
An efficient solvent-free method is described for the addition of TMSCN to carbonyl groups employing dodecatungestophos-
phoric acid (H PW O ) as a heterogeneous and environmentally benign catalyst. By this method, aromatic, aliphatic, cyclic
3
12 40
and heterocyclic aldehydes and ketones are converted into their corresponding cyanotrimethylsilyl ethers in excellent yields (89–
8%) in short reaction times (<10 min).
9
Ó 2004 Published by Elsevier B.V.
Keywords: Dodecatungestophosphoric acid; Aldehyde; Ketone; Cyanotrimethylsilyl ethers
1
. Introduction
tion between the reactants and the adduct product. In
order to surmount this problem, the reaction of
TMSCN with carbonyl groups in the presence of Lewis
acid or Lewis base catalysts has been under attention in
the last decade [3]. Very recently new catalysts such as;
indium tribromide [4a], layered zirconium hydrogen
phosphate [4b], and several N-oxide compounds [4c–h]
have been reported for this purpose. However, general,
mild, and high-yielding processes for cyanation of hin-
dered carbonyl groups are still very limited in the
literature.
Development of methods using heteropolyacids
(HPAs) as catalysts for fine organic synthetic pro-
cesses related to fine chemicals, such as flavors, phar-
maceuticals and food industries [5] have been under
attention in the last decade. Heteropolyacids are more
active catalysts than conventional inorganic and or-
ganic acids for various reactions in solution [6]. They
are used as industrial catalysts for several liquid-phase
The development of practical protocol for the prepa-
ration of a-hydroxy-, a-substituted acids, ketones, alde-
hydes, and a-hydroxy amines from readily available
carbonyl compounds is an important achievement in or-
ganic synthesis. One of the most straightforward entries
to this important goal is through their cyanohydrin
preparations [1]. They are also components of commer-
cially important compounds such as the pyrethroid
insecticides, cypermetrin and fluvaliate [2]. Preparation
of cyanohydrins by the addition of highly toxic HCN
to carbonyl group is not a straightforward process and
the procedure should be undertaken with caution. The
other problem which affects the yields of the products
stems from the existence of inevitable equilibrium condi-
*
Corresponding author. Tel.: +987112284822; fax: +987112280926.
E-mail address: firouzabadi@chem.susc.ac.ir (H. Firouzabadi).
0
022-328X/$ - see front matter Ó 2004 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2004.12.025

H. Firouzabadi et al. / Journal of Organometallic Chemistry 690 (2005) 1556–1559
1557
reactions [7–10], such as alcohol dehydration [11],
alkylation [12], or esterification [13] reactions. Among
heteropolyacids, polytungstic acids are the most
widely used catalysts owing to their high acid
strengths, thermal stabilities, and low reducibilities.
The catalysts based on heteropolyacids have many
advantages over liquid acid catalysts. They are non-
corrosive and environmentally benign, presenting
fewer disposal problems. Solid heteropolyacids have
attracted much attention in organic synthesis owing
to easy workup procedures, easy filtration, and mini-
mization of cost and waste generation due to reuse
and recycling of the catalysts [14].
We then applied our reaction conditions for addi-
tion of trimethylsilyl cyanide to structurally different
carbonyl compounds. The results are shown in
Table 2.
Table 2 clearly shows that aliphatic and aromatic
aldehydes with electron-donating or electron-withdraw-
ing groups give their corresponding cyanotrimethylsilyl
ethers in excellent yields. Cyclic and acyclic carbonyl
compounds (Table 2, entries 8, 15–20) are also con-
verted into their corresponding cyanotrimethylsilyl
ethers with excellent yields in less than 5 min. Further-
more, the reaction of acid sensitive substrates such as
furfuraldehyde, methylfuril ketone, cinnamaldehyde in
the presence of 0.1 mol% of the catalyst proceeds
smoothly in high yields and the lack of polymerization
is observed.
This catalyst is exceptionally effective for the cyano-
trimethylsilylation of conformationally constrained
camphor to produce the desired product in 95% yield
at room temperature within 10 min in the absence of sol-
vent (Scheme 2).
On the other hand, due to the current challenges for
developing solvent-free and environmentally benign syn-
thetic systems [15] and in continuation of our interests in
the applications of H PW O for various organic
3
12 40
transformations [16,17], we here report another catalytic
activity of H PW O for the high yielding cyanation of
3
12 40
carbonyl compounds with TMSCN in the absence of
solvent. When an aldehyde or a ketone was allowed to
react with TMSCN in the presence of catalytic amounts
In order to show the effectiveness of this catalyst, the
results obtained by some other catalysts used for the
similar reaction are as follows:
(
0.1–0.15 mol%) of H PW O , the cyanation of the
3 12 40
carbonyl compounds proceeds well to give the corre-
sponding trimethylcyanation adduct in excellent yields
within few minutes (Scheme 1, Table 1).
Acetophenone was chosen to optimize the reaction
conditions, such as temperature, time, and molar ratio
PðMeNMCH CH Þ N ð15 mol%; 5 h; 33% yieldÞ; [3p]
2
2
3
ZnI
2
ð5 mol%; 24 h; 98% yieldÞ; [4h]
of H PW O
0
to the substrate. We found that
.1 mol% of H PW O was sufficient to obtain the de-
3
12 40
LiOCH
2
CH
2
ðOCH
2
CH
2
Þ OCH
3
3
12 40
2
sired cyanohydrin trimethylsilyl ether in 96% yield with-
in 5 min at room temperature. In Table 1, we have
compared the catalytic activity of H PW O for the
ð50 mol%; 1 h; 96% yieldÞ: [4h]
The catalyst is also used effectively for the cyanation
of other hindered ketones such as 9-fluorenone, and
benzophenone (Table 2, entries 21, 22) to give their
3
12 40
reaction of acetophenone with trimethylsilyl cyanide
with those reported for other catalysts.
0
.15 mol % H PW12O40
3
O
0
.1-0.15 mol % H PW12O
NC
OSiMe3
3
40
+
Me SiCN
OSiMe3
3
+
Me SiCN
3
neat condition
10 min.
95% Yield
neat condition
O
CN
5
-10 min.
Scheme 1.
Scheme 2.
Table 1
Reaction of acetophenone with trimethylsilyl cyanide in the presence of different catalysts
ref.
Entry
Catalyst
PW12
Cu(OTf)
Yb(OTf)
(mol%)
Time (h)
Yield
1
2
3
4
5
6
7
8
9
H
3
O
40
0.1
5
5 min
3
20
96
84
0
2
[3e]
3
[3m]
20
Solid LiClO
LiOCH CH
Zr(KPO [4b]
N-methylmorpholine N-oxide [4f]
4
[3n,3o]
100
1
3
86
96
98
98
82
95
2
2
(OCH CH
2
2
)
2
OCH
3
[4g]
12 min
24
4
)
2
0.2 g
30
8
i
N-oxide–Ti(O Pr)
4
[2/1] [4d]
10
62
N-oxide-quaternary ammonium bromide [1/1] [4h]
2.5
15

1558
H. Firouzabadi et al. / Journal of Organometallic Chemistry 690 (2005) 1556–1559
Table 2
PW12
groups under neat conditions at room temperature
corresponding cynanotrimethylsilyl ethers in excellent
yields in very short reaction times (10 min).
H
3
O40 (0.1–0.15 mol%) mediated TMSCN addition to carbonyl
a
Entry
Substrate
Product
Yield
92
O
NC
OSiMe
3
1
2
.
.
H
H
2. Conclusion
O
NC
NC
OSiMe
3
H
H
90
95
91
93
90
94
93
96
H PW O can be considered as a mild and suitable
3
12 40
H
MeO
Cl
MeO
Cl
Brønsted acid catalyst for promoting high yielding
cyanosilylation of carbonyl compounds even hindered
ketones under mild and solvent-less condition. The
availability, low cost, environmentally benign and the
effectiveness of the catalyst are worthy to be mentioned.
O
OSiMe
3
3
4
5
6
7
8
9
.
.
.
.
.
.
.
H
Cl
O
Cl NC
Cl NC
NC
OSiMe
3
H
H
Cl
O
OSiMe
3
H
H
Cl
Cl
O
3. Experimental
O
O
OSiMe
3
H
H
O
NC OSiO3
H
Chemicals were purchased from Merck and Fluka
Chemical Companies. IR spectra were run on a Shima-
dzu model 8300 FT-IR spectrophotometer. NMR spec-
tra were recorded on a Bruker Avance DPX-250. The
purity of the products and the progress of the reactions
were accomplished by TLC on silica-gel polygram
SILG/UV254 plates or GC. All products are known
compounds.
H
O
H
CN
OSiMe
3
H
O
NC
OSiMe
3
O
NC
OSiMe
3
1
1
0.
1.
95
96
MeO
MeO
O
NC
NC
OSiMe
3
3.1. General procedure
Cl
Cl
O
A mixture of a carbonyl compound (5 mmol),
TMSCN (6 mmol, 0.6 g) and solid H PW O (0.005–
OSiMe
3
3
12 40
b
1
1
1
1
1
1
1
2.
3.
4.
5.
6.
7.
8.
98
O
2
N
O2
N
0.0075 mmol, 0.015–0.022 g) was magnetically stirred
at room temperature in 5–10 min. EtOAc or any other
appropriate organic solvent (10 mL) was added to the
reaction mixture and the solid H PW O was filtered
O
NC
O
O
OSiMe
3
93
97
89
91
94
92
O
NC OSiO
3
3
12 40
and washed the solid residue with organic solvent
(5 mL). The filtrate was evaporated on a rotary evapora-
tor and the crude product was purified by a short col-
umn chromatography on silica gel (eluted with
petroleum ether (40–60 °C)/EtOAc (95:5)) to afford the
pure product(s) in 89–98% yields (Table 1). All isolated
O
O
O
NC
OSiMe
3
NC OSiMe3
NC OSiMe
3
1
products gave satisfactory spectral data (IR, H NMR,
3
1
and C NMR, GC) and compared with those reported
in the literature [3n,3o,4d,f,g].
O
NC OSiMe3
Selected analytical data for 2-methyl-2-trimethylsilyl-
oxy-4-phenylbut-3-enenitrile (Table 2, Entry 14): IR
(
O
NC
OSiMe
3
ꢀ
neat): 2355 cm (CN). H NMR (CDCl , 250 MHz):
3
1
1
1
2
2
2
9.
0.
1.
2.
95
96
97
98
Ph
Ph
d = 0.24 (s, 9 H), 1.65 (s, 3 H), 6.12 (d, 1 H, J = 15.9
13
O
CN
OSiMe
Hz), 6.88 (d, 1 H, J = 15.9 Hz), 7.24–7.41 (m, 5H).
C
3
O
NC
NMR (CDCl3, 63 MHz): d = 1.30, 30.77, 69.85, 120.50,
126.72, 128.43, 128.62, 129.47, 130.80, 135.00 [4h].
OSiMe
3
NC
O
OSiMe3
Acknowledgement
2
3.
95
We are thankful to Iran TWAS Chapter based at
ISMO and Shiraz University Research Council for the
support of this work.
OSiMe
3
O
CN
a
Yields refer to the isolated products.

H. Firouzabadi et al. / Journal of Organometallic Chemistry 690 (2005) 1556–1559
1559
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