Unprecedented alkylation of silicon enolates with alcohols via carbenium ion formations catalyzed by tin hydroxide-embedded montmorillonite

Article abstract of DOI:10.1016/j.tetlet.2017.03.073

The solid acid, tin hydroxide-embedded montmorillonite, catalyzes the unprecedented alkylation of various silicon enolates with primary, secondary and tertiary benzylic alcohols as well as secondary allylic alcohols. The acid catalysis of Sn-Mont was not only higher than that of the other ion-exchanged montmorillonites (M-Mont; M?=?H, Ti, Fe and Al), but also higher than that of the typical homogeneous acid catalysts such as BF₃·OEt₂, TMSOTf and TfOH.

Full text of DOI:10.1016/j.tetlet.2017.03.073

Accepted Manuscript
Unprecedented alkylation of silicon enolates with alcohols via carbenium ion
formations catalyzed by tin hydroxide-embedded montmorillonite
Michael Andreas Tandiary, Masashi Asano, Taiki Hattori, Satoshi Takehira,
Yoichi Masui, Makoto Onaka
PII:
S0040-4039(17)30392-1
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.03.073
TETL 48774
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
28 January 2017
18 March 2017
23 March 2017
Please cite this article as: Tandiary, M.A., Asano, M., Hattori, T., Takehira, S., Masui, Y., Onaka, M., Unprecedented
alkylation of silicon enolates with alcohols via carbenium ion formations catalyzed by tin hydroxide-embedded
montmorillonite, Tetrahedron Letters (2017), doi: http://dx.doi.org/10.1016/j.tetlet.2017.03.073
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Graphical Abstract
To create your abstract, type over the instructions in the template box below.
Fonts or abstract dimensions should not be changed or altered.
Unprecedented alkylation of silicon enolates
with alcohols via carbenium ion formations
catalyzed by tin hydroxide-embedded
montmorillonite
Leave this area blank for abstract info.
Michael Andreas Tandiary, Masashi Asano, Taiki Hattori, Satoshi Takehira, Yoichi Masui, and Makoto Onaka*
O
R3
OH
R4
R5
OSi
Sn-Mont
R2
R1
R3
R5
PhCl, 120 oC,
10-15 min
R1
R4
R2
t
Si = SiMe3 or SiMe2 Bu
up to 98% yield

1
Tetrahedron Letters
journal homepage: www.els evier.com
Unprecedented alkylation of silicon enolates with alcohols via carbenium ion
formations catalyzed by tin hydroxide-embedded montmorillonite
Michael Andreas Tandiarya, Masashi Asanob, Taiki Hattoria, Satoshi Takehiraa, Yoichi Masuib, Makoto
Onakab,∗
aGraduate School of Science, The University of Tokyo, Bunkyo-Ku Hongo 7-3-1, Tokyo 113-0033, Japan
bGraduate School of Arts and Sciences, The University of Tokyo, Mefuro-Ku Komaba 3-8-1, Tokyo 153-8902, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
The solid acid, tin hydroxide-embedded montmorillonite, catalyzes the unprecedented alkylation
of various silicon enolates with primary, secondary and tertiary benzylic alcohols as well as
secondary allylic alcohols. The acid catalysis of Sn-Mont was not only higher than that of the
other ion-exchanged montmorillonites (M-Mont; M=H, Ti, Fe and Al), but also higher than that
of the typical homogeneous acid catalysts such as BF3•OEt2, TMSOTf and TfOH.
Received in revised form
Accepted
Available online
2017 Elsevier Ltd. All rights reserved.
Keywords:
Alkylation of silicon enolates
Alcohols
Tin hydroxide-embedded montmorillonite
Sn-Mont
Carbenium ions
Alcohols are generally not efficient alkylation reagents due to
the poor leaving ability of the hydroxyl group. Therefore, the
alcohols are normally transformed into the corresponding more
reactive halides, carboxylates, carbonates, sulfonates, etc., and
applied to the substitutions with nucleophiles using equimolar
amounts of bases, co-producing stoichiometric amounts of waste
salts. The direct alkylation with alcohols is an intriguing process,
but the concurrent formation of water often confines the
alkylation to some specific types of reactions and catalysts.1
Silicon enolates (silyl enol ethers) are some of the useful
nucleophiles which can be easily prepared from the
corresponding carbonyl compounds by various methods and have
relatively high chemical and thermodynamic stabilities when
handling.2 In the presence of a stoichiometric or catalytic amount
of Lewis acids, tertiary and secondary benzylic halides react as
alkylating reagents with silicon enolates to produce α−substituted
carbonyl compounds:3 The Lewis acid promotes the formation of
carbenium ions from the halides, which are subsequently trapped
by the silicon enolates to form adduct intermediates. Rapid
desilylation of the intermediates then resulted in the formation of
the final products (Scheme 1).3c Surprisingly, although Brønsted
and Lewis acids, such as TfOH and BF3•OEt2, can generate the
corresponding carbenium ions directly from alcohols, there have
been no reports on the acid catalyzed-one step alkylations of
Scheme 1 Acid-catalyzed alkylation of silicon enolates with alkyl
halides.
OSiMe3
R3
OSiMe3
R
O
RX
acid
desilylation
R
R3
R1
R1
R1
R3
-X
R2
R2
R2
alcohols.4 Because most acid catalysts are water-sensitive and
significantly deactivated by water, the alkylation of silicon
enolates with alcohols is impeded.5
Montmorillonite (Mont) is one of the abundant naturally-
occurring clays. It is composed of stacked, negatively charged,
aluminosilicate layers with intercalated exchangeable cationic
species, mostly sodium ions, between the layers. When the
sodium ions in the Mont are substituted by multivalent metal ions
or protons, the clays become strongly acidic. Such acidic clays
have been utilized in various acid-catalyzed organic reactions.
We
originally
developed
tin
hydroxide-embedded
montmorillonite (Sn-Mont),6 and applied it as a solid acid
catalyst to various organic transformations of carbonyl
compounds and alcohols. As the reactions of carbonyl
compounds, we reported the cyanosilylation,7 the one-pot
Strecker synthesis of α-amino nitriles8 and the Mukaiyama aldol
reactions.9 We also found that Sn-Mont promoted various
silicon enolates with
———
∗ Corresponding author.
e-mail: conaka@mail.ecc.u-tokyo.ac.jp

2
Tetrahedron
Table 2 Scope of benzylic and allylic alcohols.a, d
reactions of benzylic and allylic alcohols with
allyltrimethylsilane,10 1,3-dicarbonyl compounds,11 trialkylsilyl
cyanide,12 and trialkylsilanes.13 For such SN1-type reactions of
alcohols with typical nucleophiles, it is noteworthy that Sn-Mont
plays an essential role as an efficient acid catalyst for not only
generating the corresponding carbenium intermediates from
benzylic or allylic alcohols but also embracing and stabilizing the
unstable carbenium ions, tolerating deactivation by the water
molecules produced in the reaction. Therefore, we envisioned
that the direct alkylation of silicon enolates with alcohols would
be possible using the acidic montmorillonite catalysts.
O
R1
OTMS
OH
R2
R3
Sn-Mont
PhCl
120 °C
+
R1
R3
R2
1a
2
3
2.0 mmol
1.0 mmol
Entry
1
2
Reaction time
10 min
Yield of 3b
63%e (77%)f
2a
OH
First, the direct alkylation of trimethylsilyl (TMS) enolates 1a
with benzhydrol 2a to afford the alkylated product 3aa was
investigated as a model reaction using various heterogeneous and
homogeneous acid catalysts according to the protocol of Ref. 14,
and the results are summarized in Table 1.
2
1 h
0%
Cl
Cl
2b
OH
Various ion-exchanged montmorillonites, such as Al-Mont,
Fe-Mont, Ti-Mont, Sn-Mont as well as H-Mont, exhibited
different catalytic activities.15 Among the montmorillonite
catalysts, Sn-Mont showed the highest catalytic activity (entry 1).
On the other hand, Na-Mont, which was pristine, natural
montmorillonite, exhibited no catalytic activity (entry 6). The
strongly acidic proton-type mordenite zeolite (H-Mor) also had
no catalytic activity. Typical homogeneous acids, such as TfOH,
TMSOTf and BF3•Et2O, were also examined (entries 8-10).
TfOH and BF3•Et2O exhibited a much lower activity than Sn-
Mont, while TMSOTf had no activity.
R
3
4
5
2c (R = H)
10 min
10 min
10 min
0%
2c’ (R = OMe)
2c’’ (R = Me)
97%
97%
R1
OH
R3
R2
6
7
2d (R1 = R2 = R3 = H)
2d’ (R1 = R2 = R3 = OMe)
10 min
10 min
0%
In order to uncover the applicability of alcohols, various
benzylic and allylic alcohols were tested for the alkylation of 1a.
The results are summarized in Table 2.
98%
In an attempt to perform the alkylation of 1a using 2b, a
benzhydrol derivative bearing an electron-withdrawing chlorine
atom did not yield any desired product (entry 2). The efficiency
of the alkylation of 1a with phenethyl alcohols was closely
related to the stability of the carbenium ions derived from the
benzylic alcohols: Although an attempt to alkylate 1a with the
pristine phenethyl alcohol 2c failed (entry 3), the alkylation of 1a
with phenethyl alcohol derivatives bearing an electron-donating
substituent, 2c’ or 2c’’, yielded the corresponding products in
almost quantitative yields (entries 4 and 5). These results suggest
that the reaction should proceed through an SN1-type mechanism
OH
8
10 min
97%
2e
OH
R
9
2f (R = Me)
2f’ (R = Ph)
10 min
10 min
93%c
97%
10
a1a: 2.0 mmol, 2: 1.0 mmol, Sn-Mont: 20 mg, PhCl: 2.0 mL,
Temp.: 120 oC. b1H-NMR yield using mesitylene as the internal
standard. cThe total yields of the regioisomeric products. dData in
parentheses of Entry 1 were obtained using the mechanical
injection. eSymmetric ether 4a and trimethylsilyl ether 5a were
produced as the byproducts in 3% and 23% yields, respectively.
fThe figure in the parenthesis shows the yield according to the
mechanical slow-injection procedure.
Table 1 Comparison of various acid catalysts for the alkylation of
silicon enolate 1a with an alcohol 2a as the alkylating reagent.
OTMS
OH
Catalyst
PhCl
120 °C
O
+
1a
2.0 mmol
2a
1.0 mmol
3aa
Reaction Time Yield of 3aaa
in a fashion similar to that of the acid-catalyzed alkylations of
silicon enolates with halides (Scheme 1).
Entry
Catalyst
1
2
3
Sn-Montb
H-Montb
Ti-Montb
Al-Montb
Fe-Montb
Na-Montb
H-Morb
10 min
10 min
20 min
20 min
20 min
3 h
63 %
46 %
45 %
18 %
20 %
0 %
The protocol is also applicable for primary benzylic alcohols.
Although a simple benzyl alcohol 2d was not reactive as an
alkylating agent (entry 6), the alkylation with a benzylic alcohol
bearing three methoxy groups 2d’ successfully proceeded in
almost quantitative yield (entry 7), indicating that the relatively
stabilized primary carbenium ions are effective alkylating agents
in the reaction.
4
5
6
7
8
3 h
0 %
5 %
TfOHc
10 min
10 min
3 h
BF3・Et2Od
TMSOTfc
-
8 %
0 %
The alkylation of 1a with tertiary benzylic alcohol 2e almost
quantitatively proceeded (entry 8) even via the formation of a
bulky trityl cation.
9
10
11
3 h
0 %
The alkylation with allylic alcohols was also explored. With
the symmetrical allylic alcohol 2f’, the alkylation was successful
in almost quantitative yield (entry 10). Using the unsymmetrical
allylic alcohol 2f gave a regioisomeric mixture of products, the
a1H-NMR yield based on mesitylene as the internal standard. b20
mg of catalyst was employed. c5 mol% of the catalyst was
employed. d10 mol% of BF3・Et2O was employed.

3
non-rearranged product (3-methyl-1,5-diphenylpent-4-en-1-one)
and the rearranged one (1,3-diphenylhex-4-en-1-one), were
produced in 58% and 35% yields, respectively (entry 9).
The alkylation of 1a with benzhydrol 2a produced not only
3aa in 63% yield, but a symmetric ether 4a in 3% and silyl ether
5a in 23% as well as acetophenone, a hydrolyzed product of 1a
as side products (entry 1 of Table 2). Acetophenone was another
by-product of 1a with water. Considering the formation of such
main and side products, we proposed that the alkylations would
proceed as depicted in Scheme 2. The alcohol 2a is adsorbed and
protonated in Sn-Mont, followed by dehydration resulting in an
intermediate carbenium ion 6a on the surface of Sn-Mont (Path
A). 6a then reacts with the silicon enolate 1 to yield an alkylated
product 3aa (Path B), while the reaction of 6a with 2a produces a
symmetrical ether 4a (Path C). Concurrently, alcohol 2a also can
react with 1 to afford a silylated alcohol 5 (Path D), leading to a
further reaction with 1 to finally produce 3aa (Path E). The
possibility of Path E will be discussed later in Table 4.
Table 3 Scope of silicon enolates.a
Yield (%)b
Entry
1
1
Si of 1
3
4a
5
77 [74]c
8
5
7
OSi
TMS (1a)
TBS (1a')
2
68
20
3
4
TMS (1b)
TBS (1b')
72 (61)d
82
8 (3)d 15 (29)d
3
9
5
6
TMS (1c)
TBS (1c')
77
71
13
2
3
12
As the number of the formed carbenium ions 6a is very limited
due to the small amount of acidic protons contained in Sn-Mont,
it is required to maintain the concentration of 2a as low as
possible in order to prevent such as the Path D side reaction.
Therefore, we adopted a mechanical slow-injection16 through a
syringe pump of a mixture of 1a and 2a into a suspension of Sn-
Mont in PhCl instead of a manual slow-injection14 of the
substrates, and we successfully increased the yield of 3aa from
63% to 77% together with 4a and 5a in Table 2.
To determine the scope of the enolates, various silicon enolates
were used for the alkylation with alcohol 2a employing the
mechanical slow-injection method (Table 3).
The cyclic TMS enolates 1b and 1c afforded the desired
alkylation products in good yields (entries 3 and 5). The aliphatic
TMS enolates 1d and 1e derived from pinacolone and 3-
pentanone also gave the alkylated products in high yields (entries
7 and 9).
The mechanical slow-injection method for the reactions of 2a
with the TMS enolates 1b and 1d was also confirmed to be
superior to the manual slow-injection method in which the
formation of the by-product 5a was promoted (entries 3 and 7).
This assures that maintaining the concentration of the alcohol 2
as low as possible is essential for the effective alkylation of the
silicon enolates with 2.
In our previous research regarding the cyanation of benzylic
alcohols with R3SiCN, we encountered curious phenomena such
that the cyanation using the bulkier tert-butyldimethylsilyl (TBS)
cyanide proceeded more effectively than that with trimethylsilyl
(TMS) cyanide. Thus, we were interested in how the silyl groups
of the silicon enolates affected the present alkylations by
7
8
TMS (1d)
TBS (1d')
76 [74]c (20)d 11 (3)d 10 (66)d
78
11
7
9
10
TMS (1e)e
TBS (1e')f
86 [85]c
92
8
1
1
2
a1: 2.0 mmol, 2a: 1.0 mmol, Sn-Mont: 20 mg, PhCl: 2.0 mL,
Temp.: 120 oC, mechanical injection by syringe pump for 15 min,
reaction time: 15 min. b1H-NMR yield using mesitylene as the
internal standard. cFigures in brackets show isolated yields. dData
in parentheses were obtained using the manual injection method
(Entries 3 and 7). eE/Z = 1/6.6. fE/Z = 1/5.5.
employing more powerful nucleophiles, the TMS enolates, and
less reactive ones, the TBS enolates, as shown in Table 3. The
TBS enolates 1b', 1d' and 1e' afforded the desired product 3 in
higher yields than the corresponding TMS enolates (entries 3, 4,
and 7-10), while the enolates 1a’ and 1c’ gave lower yields than
the corresponding TMS enolates (entries 1, 2, 5 and 6).
The reaction rates of the paths B, D and E were compared
between the TMS enolates and TBS ones: For Path B, the
reaction with 1a would be faster than that with 1a’ because we
observed that the aldol reaction of acetophenone with 1a
proceeded more effectively than that with 1a’ in the presence of
Sn-Mont.17 Similarly, it can be suggested that Path D with the
TMS enolates should be faster than that with the TBS enolates.
We also observed that the alkylation of the TMS ether 5a with 1a
produced 3aa in the presence of Sn-Mont, while TBS ether 5a’
did not react with the TBS enolate 1a’ at all as shown in Table 4.
Combining the results in Tables 3 and 4, it is understood that
using the TBS enolates gave higher product yields if the reaction
with the TBS enolates via Paths A and B was much faster than
that via Path D, but using the TMS enolates was a better choice if
the reaction rate of Paths A and B was comparable to that of Path
D because 5a was able to be finally transformed into alkylated
products 3. If Path D was impeded by the use of the TBS
enolates, the formation of 3 was favorable, but if not, the yield of
3 was lower than that in the case of the TMS enolates because the
TBS ether of 5 was not transferable to 3.
Scheme 2 Plausible reaction pathways for the alkylation.
Si = TMS or TBS
OSi
Ph
Sn-Mont, -H2O
(A)
1
O
Ph
Ph
OH
Ph Ph
2a
Ph Ph
(B)
Ph
6a
3aa
OH
Ph Ph
2a
Ph
Ph
O
2
The present protocol requires two equivalents or more of
silicon enolates to obtain alcohols in good yields because part of
the enolates reacts with the produced water to the corresponding
ketones. When we performed the alkylation using 1.1 equiv. of
1a to 2a with or without use of a drying agent of Molecular
Sieves 4A (MS4A), the yields of 3aa were 62% and 59%,
respectively.18 These results indicate that MS4A does not work to
preferentially trap the water in the present reaction.
(C) Etherification
4a
OSi
OSi
Ph
Ph
OSi
1
1
Ph Ph
(D) Silyl etherification
(E) Alkylation of 5
5

4
Tetrahedron
In summary, the direct alkylations of silicon enolates with
6.
(a) Onaka M.; Hosokawa Y.; Higuchi K.; Izumi Y.
Tetrahedron Lett. 1993 34, 1171. (b) Highuchi, K.; Onaka M.;
Izumi Y. Bull. Chem. Soc. Jpn. 1993 66, 2016. (c) Onaka M.;
,
primary, secondary and tertiary benzylic alcohols as well as
secondary allylic alcohols were realized by the acid catalysis of
tin hydroxide-embedded montmorillonite (Sn-Mont), while the
alkylation using typical homogeneous acid catalysts, such as
TfOH, TMSOTf and BF3•OEt2, failed. The constant slow
addition of the substrates to the catalyst is preferred to afford the
alkylated products in higher yields and to suppress the formation
,
Higuchi K.; Nanami H.; Izumi Y. Bull. Chem. Soc. Jpn. 1993
66, 2638. (d) Masui Y.; Wang J.; Teramura K.; Kogure T.;
Tanaka T.; Onaka M. Micropor. Mesopor. Mater., 2014, 198,
,
129.
7.
(a) Wang J.; Masui Y.; Watanabe K.; Onaka M. Adv. Synth.
Catal. 2009, 351, 553. (b) Wang J.; Masui Y.; Hattori T.; Onaka
M. Tetrahedron Lett. 2012 53, 1978.
,
Table 4 Comparison of the rate of alkylation by silyl ether.a
8. Wang J.; Masui Y.; Onaka M.; Eur. J. Org. Chem. 2010, 9,
1763.
O
Ph
OTMS
OSi
O
Sn-Mont
9. Takehira T.; Masui Y.; Onaka M.; Chem. Lett. 2014, 43, 498.
10. Wang J.; Masui Y.; Onaka M. Tetrahedron Lett. 2010, 51,
2
Ph Ph
PhCl
120 °C, 15 min
Ph
Ph
Ph
Ph Ph
3300.
11. Wang J.; Masui Y.; Onaka M.; Synlett
1a
5
3aa
4a
,
12. Wang J.; Masui Y.; Onaka M.; ACS Catal. 2011
2010, 16, 2493.x
, 446.
(2.0 mmol) (1.0 mmol)
t
Si = SiMe3 (TMS) or SiMe2 Bu (TBS)
,
1
13. Tandiary M. A.; Masui Y.; Onaka M.; Tetrahedron Lett. 2014
55, 4160.
,
Yield (%)
3aa 4a
Entry
1
5
14. Most of the experiments in Tables 1 and 2 were performed
according to the manual slow-injection procedure: Into a flask
Recovery of 5 (%)
OTMS
were placed Sn-Mont (20 mg) (or other solid/homogeneous acid)
and PhCl (0.5 mL), and then the mixture was heated to 120 oC.
Into the flask was added by hand a solution of 1.0 mmol of an
alcohol and 2.0 mmol of silicon enolate 1a in 1.5 mL of PhCl over
20 min. The mixture was then further heated at 120 oC for 10 min,
and then cooled to room temperature. Sn-Mont was filtered-off,
and the filtrate was concentrated and analyzed by NMR.
15. Detailed protocols for the preparation of the montmorillonite
catalysts are shown in the Supporting Information.
48
0
0
Ph Ph
5a
OTBS
Ph Ph
2
0
0
84
5a'
a1a: 2.0 mmol, 5: 1.0 mmol, Sn-Mont: 20 mg, PhCl: 2.0 mL,
Temp.: 120 C, slow addition by syringe pump for 15 min,
reaction time: 15 min. b1H-NMR yield using mesitylene as the
internal standard.
o
16. The experiments in Table 3 were performed according to the
mechanical slow-injection procedure: Into a flask were placed Sn-
Mont (20 mg) and PhCl (1.0 mL), and the mixture was heated to
120 oC. Into the flask was added by a syringe pump a solution of
1.0 mmol of an alcohol and 2.0 mmol of silicon enolate 1a in 1.0
mL of PhCl over 15 min. The mixture was then further heated at
120 oC for 15 min, and cooled to room temperature. Sn-Mont was
filtered-off, and the filtrate was concentrated and analyzed by
NMR.
of side-products. The efficiency of the alkylation is dependent on
the electronic and steric characteristics of both the alcohols and
the silicon enolates. Although part of silicon enolates reacts with
the water produced in the alkylation, the acid catalysis of Sn-
Mont is tolerant to the water.
17. For the Mukaiyama aldol reaction of TMS enolate 1a with
acetophenone in CH2Cl2 at room temperature in the presence of
a catalytic amount of Sn-Mont, the aldol product, 1,3-diphenyl-
3-trimethylsiloxybutan-1-one, was produced in 91%, while the
This paper is dedicated to Professor Teruaki Mukaiyama in
celebration of his 90th birthday (Sotsuju).
TBS enolate 1a’ yielded the corresponding one, 3-(tert
-
butyldimethylsiloxy)-1,3-diphenylbutan-1-one, in 63% yield
under the same reaction conditions. These results show the
poorer reactivity of the TBS enolate than that of the TMS
enolate.
A. Supplementary data
18. The alkylation of 1a (1.1 mmol) with 2a (1.0 mmol) was
conducted in PhCl (2.0 mL) at 120oC for 15 min using Sn-
Mont (20 mg) with or without MS4A (0.1 g) according to the
mechanical slow-injection procedure.
Supplementary data associated with this article can be found, in
the online version, at
References and notes
1. For example, InCl3-catalyzed of allylation of alcohols: Baba A.,
Yasuda M., Nishimoto Y., Saito T., Onishi Y., Pure Appl. Chem.
2008, 80, 845; Alkylation of 1,3-diketones with alcohol catalyzed
by Cu(OTf)3: Babu S. A., Yasuda M., Tsukahara Y., Yamauchi T.,
Wada Y., Baba A. Synthesis, 2008, 1717; The same alkylation
catalyzed by TfOH: Sanz R., Miguel D., Martinez A., Alvarez-
Gutierre J. M., Rodrıguez F. Org. Lett. 2007, 9, 2027.
2.
For the reviews of the synthesis and reactions of silicon
enolates: (a) Rasmussen J. Synthesis 1977, 91. (b)
Brownbridge P. Synthesis 1983, 1. (c) Brownbridge P.
Synthesis 1983, 85.
,
,
,
3.
For the alkylations of silicon enolates with alkyl halides: (a)
Chan T. H.; Paterson I.; Pinsonnault J. Tetrahedron. Lett. 1977
18, 4183. (b) Reetz M. T.; Huettenhein S.; Walz P.; Loewe U.
,
Tetrahedron Lett. 1979
Chem. Int. Ed. Engl. 1982
Yasuda M., Baba A. Tetrahedron
For various -alkylations of silicon enolates with other reactive
,
20, 4971. (c) Reetz M. T. Angew.
21, 96. (d) Nishimoto Y., Saito T.,
2009 65, 5462.
,
,
,
4.
5.
α
alkylating reagents: Larock R. C., In Comprehensive Organic
Transformations, Second Ed. Wiley-VCH, 1999, pp. 1494-
1505.
For example, TiCl4 as a catalyst would be easily hydrolyzed by
water to form titanium oxides/oxychlorides and lose its
intrinsic Lewis acid catalysis.

5
Research highlights
・Tin hydroxide-embedded montmorillonite
(Sn-Mont) is applied to C-C bond formations.
・The direct alkylations of silicon enolates
with alcohols are catalyzed by Sn-Mont.
・Benzylic and allylic alcohols alkylate the
enolates via carbenium ions on Sn-Mont.