HClO4-supported on silica gel: A mild and efficient catalyst for Hosomi-Sakurai reaction

Article abstract of DOI:10.1016/j.tetlet.2011.08.145

Perchloric acid supported on silica gel was found to be an efficient catalyst (2 mol %) for the Hosomi- Sakurai allylation of numerous aldehydes with allyltrimethylsilane in the presence of benzyl alcohol. This method was also effective for the allylation of secondary alcohols under mild experimental conditions.

Full text of DOI:10.1016/j.tetlet.2011.08.145

Tetrahedron Letters 52 (2011) 5827–5830
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Tetrahedron Letters
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HClO4-supported on silica gel: a mild and efficient catalyst for Hosomi–Sakurai
reaction
⇑
Kaliyappan Murugan, Chinpiao Chen
Department of Chemistry, National Dong Hwa University, Soufeng, Hualien 974, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
Perchloric acid supported on silica gel was found to be an efficient catalyst (2 mol %) for the Hosomi–
Sakurai allylation of numerous aldehydes with allyltrimethylsilane in the presence of benzyl alcohol. This
method was also effective for the allylation of secondary alcohols under mild experimental conditions.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 17 June 2011
Revised 19 August 2011
Accepted 24 August 2011
Available online 31 August 2011
Keywords:
Hosomi–Sakurai reaction
Brønsted acids
Allylation
Homoallylic ether
Perchloric acid
The allylation of carbonyl compounds and acetals using allyltri-
methylsilane in the presence of Lewis or Brønsted acids is called a
Hosomi–Sakurai reaction,1 which is an important carbon–carbon
bond forming reaction in organic synthesis.2 From a synthetic per-
spective, the allylation of acetals or ketals has been extensively
explored compared to the free carbonyl compounds using Lewis
acid catalysts.3 However, this synthetically important transforma-
tion using Brønsted acid catalysts4 has been less explored. The ally-
lation of acetals is a useful method to generate homoallylic ethers
and can be catalyzed by several Lewis acids. However, numerous
acetals are not commercially available and have to be prepared
from the corresponding aldehydes. In addition, most of these
Hosomi–Sakurai reactions give the homoallyl alkyl ethers that re-
quire harsh conditions to be cleaved. Additionally, a direct ap-
proach prepares the homoallylic ethers from the corresponding
carbonyl compounds with the silyl ether or the corresponding
alcohol and an allylsilane. Catalysts that have been employed for
such three-component Hosomi–Sakurai reactions using alkoxysil-
anes include Lewis acids such as Fe(OTs)35, Ph2BOTf,6 TMSOTf,7
TMSOFs,8 TMSOMs,9 FeCl3,3i TMSI,10 and Bi(OTf)3.11 Some of these
methods have potential drawbacks such as higher catalyst loading,
lower yields, and longer reaction time. Furthermore, many of these
catalysts are expensive, toxic, and moisture sensitive, and require
stringent anhydrous reaction conditions or low temperatures.
Brønsted-acid-catalyzed direct allylation of carbonyl com-
pounds the available method was reported by List,4i where
2,4-dinitrobenzenesulfonic acid was used as the catalyst. In the
List’s method, benzyl trimethyl silyl ether afforded the best results
in comparison to that of benzyl alcohol together with carbonyl
compounds. The continued interest in asymmetric allylation12 of
carbonyl compounds and the replacement of conventional
Brønsted acid catalysts with more selective, acidic, and greener
solid acid catalysts for various functional group transformations13
leads to explore the direct allylation of carbonyl compounds.
Perchloric acid supported on silica gel was found to be a promising
catalyst for numerous synthetically relevant organic transforma-
tions.14 The advantages of this catalyst method include high
efficiency, and low-cost. Herein, this study reports the Hosomi–
Sakurai allylation of aldehydes in the presence of perchloric acid
supported on silica gel.
Initially, this study investigated the Hosomi–Sakurai allylation
of benzaldehyde as a model substrate with allyltrimethylsilane
and benzyl alcohol in the presence of silica gel supported
perchloric acid (Scheme 1, Table 1). A high yield of homoallyl ben-
zyl ether 1a (90%) in a short reaction time was achieved in the
OBn
CHO
TMS
Benzyl alcohol
HClO4-Silica gel/ Solvent
1a
1
⇑
Corresponding author. Tel.: +886 3 863 3597; fax: +886 3 863 04750.
E-mail address: chinpiao@mail.ndhu.edu.tw (C. Chen).
Scheme 1. HClO4–SiO2-catalyed Hosomi–Sakurai reaction of benzaldehyde, benzyl
alcohol, and allyltrimethylsilane.
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.08.145

5828
K. Murugan, C. Chen / Tetrahedron Letters 52 (2011) 5827–5830
Table 1
Table 2
Catalyst and solvent screening
The HClO4–SiO2-catalyzed allylation of aldehydes16
Entry
Product
Time (min)
15
Yielda (%)
97
OBn
OBn
TMS
Benzyl alcohol
CHO
1
2
HClO4-Silica gel (x mol%)
Solvent
1a
1
1a
45
30
30
90
92
88
OBn
1b: o-isomer
1c: p-isomer
1d: m-isomer
Entry
Cat (Â mol %)
Solvent
Time (min)
Yielda (%)
1
2
3
4
5
6
7
8
2
2
2
2
5
4
3
2
1
2
2
2
CH3CN
DCM
Toluene
THF
CH3CN/DCM (1:1)
CH3CN/DCM (1:1)
CH3CN/DCM (1:1)
CH3CN/DCM (1:1)
CH3CN/DCM (1:1)
CH3CN/DCM (6:4)
CH3CN/DCM (7:3)
CH3CN/DCM (8:2)
30
90
90
5
240
720
720
10
10
20
20
30
20
20
Me
OBn
NR
95
95
96
94
89
92
97
90
3
4
60
98
1e
t-Bu
30
30
30
95
98
98
9
OBn
OBn
OBn
OBn
1f: o-isomer
1g: p-isomer
1h: m-isomer
10
11
12
20
a
Cl
Br
F
Isolated yields.
30
10
90
99
1i: o-isomer
1j: p-isomer
5
6
presence of 2 equiv of benzyl alcohol in acetonitrile using a 2 mol %
of the catalyst. To further optimize the reaction solvent and pre-
vent undesired impurities, several solvents were examined. Among
the various solvents employed, dichloromethane provided a better
yield compared to that of acetonitrile, but required a longer
reaction time for complete conversion. Only traces of product were
observed in toluene, and in THF the reaction failed to occur. Sur-
prisingly, a mixture of acetonitrile and dichloromethane (1:1) in-
creased the product yield to 94% and lowered the reaction time
(Table 1, entry 8). Further tuning of the catalyst loading and the
CH3CN-DCM ratio identified (Table 1, entries 5–12) the optimal
condition as a 7:3 ratio of CH3CN and DCM solvent system and a
2 mol % of the catalyst at room temperature.
20
30
99
98
1k: p-isomer
1l: m-isomer
60
60
30
90
95
98
1m: o-isomer
1n: p-isomer
1o: m-isomer
7
NO2
OBn
30
60
95
90
1p: p-isomer
1q: m-isomer
Having determined the optimal experimental conditions, the
HClO4–SiO2-catalyzed allylation of a broad number of aldehydes
was then examined (Table 2). The reaction of isomeric tolualdehy-
des and 4-tert-butylbenzaldehyde provided the homoallyl ethers
(1b–1e) in a high yield (entries 2 and 3). Similar results were ob-
served from aldehydes containing electron withdrawing (halogens,
NO2, CN) and releasing (OMe) groups (entries 4–9). The position of
substituents on the aryl ring did not affect the yield of the reaction,
as observed in the aforementioned substrates. Interestingly, cyano-
substituted benzaldehydes provided the desired homoallyl ether
1p and 1q in good yields without the potential byproducts of
hydrolysis and a Ritter reaction (entry 8).15 Though methoxy
substituted (ortho and meta) benzaldehydes reacted in similar to
provide homoallyl ethers 1r and 1t in high yields, p-anisaldehyde
provided a 1:1 mixture of the desired homoallyl ether 1s and the
diallyl derivative 3 (entry 9). All attempts to avoid the byproducts
failed. Di- and trisubstituted benzaldehydes, irrespective of the
nature of the substituents, were also equally effective and provided
the corresponding allylated products (1u–1w) in good to excellent
yields (entries 10–12). Compound 3 was obtained perhaps because
the desired product 1s was converted to an intermediate (2) and
then reacted with allyltrimethylsilane to yield the product (3) that
was ultimately obtained (Scheme 2). The diallylation did not occur
in compound 1r that might be the intramolecular hydrogen bond-
ing between methoxy and benzoxy groups (4), and inhibited the
formation of compound 5. The 3,4-dimethoxy compounds 1u and
1v might form the intramolecular hydrogen bonding like
8
9
CN
OBn
30
15
90
1r: o-isomer
1s: p-isomer
1t: m-isomer
80b
15
10
15
91
96
86
OMe
OBn
10
11
1u
1v
MeO
MeO
OMe
NO2 OBn
OMe
OBn
12
30
70
1w
OMe
NO2

K. Murugan, C. Chen / Tetrahedron Letters 52 (2011) 5827–5830
5829
Table 2 (continued)
H+
BnO
Entry
Product
Time (min)
15
Yielda (%)
BnO
H+
TMS
13
99
1x
+OMe
2
OMe
1s
OMe
3
OBn
14
15
15
30
99
99
Bn
O
Bn
O
+H
1y
H+
BnO
MeO+
MeO
MeO
1z
4
5
1r
OBn
OBn
OBn
Me
O
H+
MeO
MeO
16
17
18
15
30
60
95
82
60
1aa
+H
S
O
1u
Me
6
1ab
S
OBn
NO2
OBn
OBn
OBn
Me
O
H+
MeO
MeO
+H
O
NO2
1ac
Me
1v
7
OBn
OBn
Scheme 2. The proposed mechanism of formation of 3.
19
20
30
15
85
90
1ad
1ae
Ph
Ph
OH
1. Allyl TMS (1.5 eq)
2. HClO4-SiO2 (2 mol%)
3. MeCN:DCM (7:3)
15 min, 92%
8
8a
a
Isolated yield.
Monoallyl and diallyl product (1:1).
b
OH
1. Allyl TMS (1.5 eq)
2.HClO4-SiO2 (2 mol%)
intermediates 6 and 7, and the diallylation could not occur.
Polycyclic aromatic aldehydes, including naphthaldehydes and
anthracenecarboxaldehyde, provided the corresponding allylated
products (1x–1z) in almost quantitative yields (entries 13–15).
Ph
3. MeCN:DCM (7:3)
15 min, 90%
Ph
9a
9
Scheme 3. Allylic substitution of alcohols.17
Heteroaromatic aldehydes and
a,b-unsaturated aldehydes also
underwent allylation to provide the products (1aa–1ae, entries
16–20). The aliphatic aldehydes could not produce the desired
products perhaps because the key intermediate in allylations of
aldehydes was presumably oxocarbenium ion, which could not
be stabilized via acid catalysis system.4i
To further explore the synthetic usefulness of HClO4–SiO2 cata-
lysts, this study also examined the reaction between secondary alco-
hols and allyltrimethylsilane (Scheme 3). Diarylmethanol 8 and
propargylic alcohol 9 provided allylated products 8a and 9a in excel-
lent yields, and allyltrimethyl silane was only used in a 1.5 equiv.
In summary, this study developed an efficient methodology for
the allylation of aldehydes and alcohols in the presence of HClO4–
SiO2. The significant features of this method are the low catalyst
loading (2 mol %) and reaction was performed at room tempera-
ture, benzyl alcohol was used instead of benzyloxytrimethyl ether,
and the catalyst is easy to handle and affordable.
Supplementary data
Supplementary data associated with this Letter can be found, in
the online version, at doi:10.1016/j.tetlet.2011.08.145.
References and notes
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Acknowledgment
We are grateful for the generous financial support of the Na-
tional Science Council of the Republic of China (NSC 97-2113-M-
259-002-MY3).

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16. Typical experimental procedure for HClO4–SiO2 catalysed Hosomi–Sakurai
reaction of aldehydes: To a solution of benzaldehyde 1 (100 mg, 0.942 mmol).
in acetonitrile:dichloromethane (7:3) 2 mL was added 10 wt % HClO4–SiO2
(0.018 mg, 0.018 mmol) followed by the addition of benzyl alcohol (0.195 mL,
1.88 mmol) and allyltrimethylsilane (0.449 mL, 2.82 mmol) dropwise at
ambient temperature. The reaction was stirred for a further 5 min. After the
completion of reaction (TLC), brine (10 mL) was added and the reaction
mixture was extracted with ether (2 Â 10 mL). The combined ether layer was
dried over MgSO4, filtered and concentrated under reduced pressure.
Purification of the crude product by column chromatography afforded pure
homoallylic benzyl ether 1a as colorless oil (217 mg, 97%).
18
5. Spafford, M. J.; Anderson, E. D.; Lacey, J. R.; Palma, A. C.; Mohan, R. S.
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17. Typical experimental procedure for HClO4–SiO2 catalysed Hosomi–Sakurai
reaction of alcohols: To
a solution of diphenyl methanol 8 (100 mg,
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0.542 mmol), in acetonitrile:dichloromethane (7:3) 2 mL was added 10 wt %
HClO4–SiO2 (10 mg, 0.011 mmol) followed by the addition of
allyltrimethylsilane (0.129 mL, 0.813 mmol) dropwise at ambient
temperature. The reaction was stirred for
a further 10 min. After the
completion of reaction (TLC), brine (10 mL) was added and the reaction
mixture was extracted with ether (2 Â 10 mL). The combined ether layer was
dried over MgSO4, filtered and concentrated under reduced pressure.
Purification of the crude product by column chromatography afforded pure
allylated diphenylmethane as colorless oil (102 mg, 92%).
18. Preparation of HClO4–SiO2: Followed the reported procedure19 HClO4 (2.5 g,
25 mmol, as a 70% aqueous solution) was added to the suspension of silica gel
(23.75 g, 60–230 mesh) in Et2O. The mixture was concentrated and the residue
heated at 100 °C for 24 h under vacuum to afford HClO4–SiO2 (1.0 mmol gÀ1) as
a free flowing powder.
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Panico, A. F.; Smith, R. C.; Mohan, R. S. J. Org. Chem. 2005, 70, 2091–2096.
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