Vinyl polymerization versus [1,3] O to C rearrangement in the ruthenium-catalyzed reactions of vinyl ethers with hydrosilanes

Article abstract of DOI:10.1016/j.tet.2012.02.025

Two reactions, vinyl polymerization and [1,3] O to C rearrangement of vinyl ethers, are investigated in the ruthenium-catalyzed reaction with hydrosilanes. The reaction pathways are dependent on the substituents of the vinyl ether, in particular, those of the alkoxy group. Primary-, secondary-, and tertiary-alkyl vinyl ethers, ROCHCH₂, are polymerized with ease to give the corresponding polymer in good yields. When R is electron-donating benzyl groups, the reaction does not give the polyvinyl ether but results in [1,3] O to C rearrangement to give the corresponding aldehyde, RCH₂CHO in moderate to good yields. The rearrangement selectively proceeds when vinyl ethers having α-substituents are used as the starting materials to give the corresponding ketones in high yields. With catalytic amounts of hydrosilanes, the rearrangement gives ketones or aldehydes selectively. In sharp contrast, use of excess amounts of hydrosilanes leads to the rearrangement followed by reduction of the formed carbonyl group to give the corresponding silyl ethers in good yields. Nature of catalytically active species is discussed. Crown Copyright

Full text of DOI:10.1016/j.tet.2012.02.025

Tetrahedron 68 (2012) 3243e3252
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Vinyl polymerization versus [1,3] O to C rearrangement in the
ruthenium-catalyzed reactions of vinyl ethers with hydrosilanes
,b,
Nari-aki Harada a, Takashi Nishikata b, Hideo Nagashima a
*
a Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
b Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 January 2012
Received in revised form 8 February 2012
Accepted 8 February 2012
Available online 23 February 2012
Two reactions, vinyl polymerization and [1,3] O to C rearrangement of vinyl ethers, are investigated in the
ruthenium-catalyzed reaction with hydrosilanes. The reaction pathways are dependent on the sub-
stituents of the vinyl ether, in particular, those of the alkoxy group. Primary-, secondary-, and tertiary-
alkyl vinyl ethers, ROCH]CH2, are polymerized with ease to give the corresponding polymer in good
yields. When R is electron-donating benzyl groups, the reaction does not give the polyvinyl ether but
results in [1,3] O to C rearrangement to give the corresponding aldehyde, RCH2CHO in moderate to good
Keywords:
Catalyst
Hydrosilane
Vinyl polymerization
Rearrangement
Cationic Mechanism
yields. The rearrangement selectively proceeds when vinyl ethers having a-substituents are used as the
starting materials to give the corresponding ketones in high yields. With catalytic amounts of hydro-
silanes, the rearrangement gives ketones or aldehydes selectively. In sharp contrast, use of excess
amounts of hydrosilanes leads to the rearrangement followed by reduction of the formed carbonyl group
to give the corresponding silyl ethers in good yields. Nature of catalytically active species is discussed.
Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.
1. Introduction
O
R
O
R
It is known that vinyl ethers are unstable under acidic condi-
tions, and their treatment with Brønsted acids or Lewis acids
generates carbocationic intermediates, which provide several in-
teresting reactions in both organic and polymer synthesis.1 In
polymer synthesis, cationic polymerization of vinyl ethers is one of
the well-investigated reactions from both synthetic and mecha-
nistic points of view.2 As shown in Scheme 1, the reaction of vinyl
ethers with a cationic initiator gives a carbocation stabilized by
adjacent OR group, which undergoes nucleophilic attack of another
molecule of vinyl ether to accomplish the propagation. It is known
that the counter anion of the cationic polymer end is important:2a if
the counter anion is highly nucleophilic, it is tightly bonded to the
propagation chain end to disturb the chain growth. Thus, appro-
priate selection of the cationic initiator is important. For instance,
Lewis acids (LA) such as BF3$OEt2 and EtAlCl2 generating
LAꢀCH2CHOþR are frequently used for this purpose, whereas cat-
ions bearing weakly coordinating anions (Yꢀ)3 such as ClO4ꢀ, BF4ꢀ,
and SbClꢀ6 are alternatively used for the ionic initiators, e.g.,
C7Hþ7 Yꢀ.4
Lewis Acid
Lewis Acid
LA: EtAlCl2 etc.
LA
Y
:C7H9SbCl6 etc.
Y
R
O
R
R
O
R
O
LA
Y
O
LA
LA
R
LA
O
Y
R
O
R
O R
R
or
O
LA
Y
O
LA
LA
LA
O-R
or
O-R
Vinyl Polymerization
OR
[1,3]O to C Rearrangement
O
n
R
In organic synthesis, vinyl ethers have been investigated in re-
lation to Claisen rearrangement, i.e., thermal reaction of allyl vinyl
Scheme 1. Vinyl polymerization versus [1,3]-O to C rearrangement by Lewis acid
catalysis.
* Corresponding author. E-mail address: nagasima@cm.kyushu-u.ac.jp (H.
Nagashima).
0040-4020/$ e see front matter Crown Copyright Ó 2012 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.02.025

3244
N. Harada et al. / Tetrahedron 68 (2012) 3243e3252
ethers to give
g,d
-unsaturated carbonyl compounds.5 The rear-
O
O
O
CO
OC
Ru
OSiR3
R"
rangement generally falls under the classification of concerted
[3,3]-sigmatropic shift; however, discovery of catalysts, such as
Lewis acids and transition metals, to accelerate the reaction pro-
vides new synthetic as well as mechanistic aspects.6 Interestingly,
treatment of allyl vinyl ethers with Lewis acids gives a mixture of
the products derived from both [3,3] and [1,3] shift; the latter is
unable to be explained by the concerted process. Further studies
showed that [1,3] O to C rearrangement of vinyl ethers was ac-
complished by heterolytic cleavage of the OeR bond of CH2]CHOR
assisted by Lewis acids, which generates carbocationic species Rþ as
the intermediate. The reaction was completed by coupling of the
resulting Rþ species with the CH2]CHOꢀ counter part to give
RCH2CHO as shown in Scheme 1.7 The mechanism suggests that
vinyl ethers capable of generating relatively stable Rþ potentially
results in the [1,3] O to C shift, and recent studies revealed that
careful choice of Lewis acids as well as the appropriate design of
vinyl ethers resulted in the rearrangement of vinyl ethers having
benzyloxy, tertiary-alkoxy, and alkolymethoxy groups.7,8
HSiR3
HSiR3
CO
R'
R'
R'
R"
R'
Ru
CO
Ru
CO
OR"
NR"2
R'
OSiR3
OC
CO
A
HSiR3
catalyst
R1
NR"2
(eq. 1)
[Ru]-H
+
[Ru]
O
H-SiR3
+
SiR3
SiR3
OR"
OSiR3
O
[Ru]-H
R'
OR"
R'
OR"
R'
H
OSiR3
H
OSiR3
OSiR3
[Ru]-H
[Ru]-H
[Ru]-H
R'
R'
R'
OR"
H
R'
H
H
SiR3
R3SiOR"
(eq. 2)
OR"
H
OR"
OR"
[Ru]-H
R'
OSiR3
SiR3
R'
H
H
It is important that both of vinyl ether polymerization and [1,3]
O to C rearrangement of vinyl ethers proceeds through the same
initial step, activation of electron-rich vinyl ethers by electron de-
ficient Lewis acids. As shown in Scheme 1, there are two reaction
points in the vinyl ether; one is the oxygen atom and the other is
H
R3SiOSiR3
Scheme 2. Possible generation of R3Siþ species from R3SiH and the ruthenium catalyst
A leading to carbonyl reduction.
the b-carbon. Thus, the reaction with Lewis acids gives two tauto-
A
cat.
A
OR1
cat.
mers. The C-tautomer initiates the vinyl polymerization by contact
with another molecule of vinyl ether, whereas the O-tautomer
undergoes the subsequent CeO bond cleavage leading to the
rearrangement. Since there is equilibrium between the C and O
tautomers, initiators providing vinyl ether polymerization poten-
tially induce [1,3] O to C rearrangement of vinyl ethers, and vice
versa.
R1
R2
O
R3SiH
cat.R3SiH
O R1
R3Si
H
n
R3
R2
R3
R2
R3 = H
Scheme 3. Vinyl polymerization versus [1,3] O to C rearrangement by combination of
R3SiH and a catalytic amount of A.
In our continuous efforts for the development of catalytic re-
duction of carbonyl compounds with hydrosilanes, we have re-
ported a ruthenium cluster A to be a good catalyst for reduction of
carboxylic acid derivatives.9 Transition metal catalyzed reactions of
hydrosilanes are usually explained by schemes involving oxidative
addition of a SieH bond to the metal center (M), insertion of an
unsaturated molecule between either MeH or MeSi bond, and
reductive elimination of the product from the resulting in-
termediate.10 However, detailed studies on the ruthenium-
catalyzed reductions suggest that ionic mechanism involving het-
erolytic cleavage of a HeSi bond by A to form R3Siþ and hydride
ruthenium species is rather suitable for reasonable explanation of
the experimental results though both hydrosilanes and the ruthe-
nium catalyst are neutral (Scheme 2, Eq. 1).9 A proposed mecha-
nism for the reduction of esters is shown in Eq. 2 as the
representative. Activation of hydrosilanes by A has provided an-
other two interesting reactions: one is aromatic alkylation of 1,3,5-
trimethoxybenzene as ester as the alkylating reagent,11 and another
is vinyl ether polymerization, in which several commercially
available vinyl ethers [R2CH]C(R3)OR1, where R1¼iPr, nBu, iBu, and
tBu, R2¼R3¼H] are polymerized by the action of a system consisting
of R3SiH and a catalytic amount of A.12,13 It is important that both of
the reactions can be reasonably explained, if Lewis acidic R3Siþ
species is in situ generated from neutral hydrosilanes and A.14 As
described above, the mechanism of vinyl ether polymerization is
similar to that of [1,3] O to C rearrangement; this prompted us to
examine combination of hydrosilanes with A to be a new catalyst
system for [1,3] O to C rearrangement. In this paper, we wish to
report a study on the possible two reactions, vinyl polymerization
and [1,3] O to C rearrangement by systematic change of the sub-
stituents of vinyl ethers. As we expected, the results clearly dem-
onstrate that the reaction course is dependent on stability of Rþ
group generated in situ from the OR1 group of the vinyl ether as
shown in Scheme 3.
2. Results and discussion
2.1. Preparation of vinyl ethers
Vinyl ethers shown in Fig. 1 were used for this study. Three of
the compounds, 1, 10, and 16 were commercially available. Most of
the other compounds except 25, and 26 were prepared by Ishii’s
iridium-catalyzed reactions of vinyl acetates with alcohols.15 Three
primary-alkyl vinyl ethers, 1e3, four secondary-alkyl vinyl ethers,
10, 12, 14, 15, and two tertiary-alkyl vinyl ethers, 16, 17, are re-
portedly polymerized by initiation of Lewis acids.2,16 Derivatives of
benzyl vinyl ethers have potentials realizing two reaction pathways
dependent on the R1 group. Vinyl polymerization of benzyl vinyl
ether 4 was investigated in detail,17a,18 but that of p-MeOC6H4
-
CH2OCH]CH2 (8) was only described in the patent.17b There is no
record on CAS for polymers of other benzyl vinyl ethers (5e7). It is
important that furylmethyl vinyl ether 9 is one of the least
substituted vinyl ethers, which is clearly demonstrated to undergo
the [1,3] O to C rearrangement; the reaction is reportedly catalyzed
by LiClO4 in Et2O at room temperature to give 3-(2-furyl)propanal
in moderate yields.6a There are no reports on the vinyl polymeri-
zation of 9. Aryl vinyl ethers are generally less reactive than alkyl
vinyl ethers because of their lower
checking the possibility of polymerization, we prepared a relatively
electron-rich vinyl ether, MeOC6H4OCH]CH2 (20).
p
-donor property.16,18 For
From our literature survey, there are two expected factors for
possible [1,3] O to C rearrangement. One is the introduction of R
group giving relatively stable Rþ species to the vinyl ethers.7 Vinyl
ethers where R1 is alkoxymethyl (Ferrier-Patasis type rear-
rangement),7b,c tertiary-alkyl, allyl, and p-methoxybenzyl groups
are generally used in literature; the rearrangement of benzyl vinyl
ethers is more difficult than FerrierePatasis type rearrangement,
whereas the reaction of tertiary-alkyl vinyl ethers and allyl vinyl

N. Harada et al. / Tetrahedron 68 (2012) 3243e3252
3245
R1OCH=CH2
α or β-substituted vinyl ethers
n
R1 = primary alkyl
1
2
3
Bu ( ), Me(OCH2CH2)3 ( ), C6F13CH2CH2 ( )
R2 = alkyl or benzyl;
3 = H
R2 = H; R3 = alkyl or phenyl
O
R
PhCH2 (4), p-MeC6H4CH2 (5), p-ClC6H4CH2 (6)
1 = benzyl
Ph
Ph
R
9
( )
R3
7
8
O
p-CF3C6H4CH2 ( ), p-MeOC6H4CH2 ( )
CH2
O
O
Me
23
OMe
(
)
R3 = Me (21), Ph (22)
OMe
(25)
R
1 = secondary alkyl
(10)
(11)
O
O
(CH2)7CH3
O
O
Ph
Ph
Ph
(26)
CH
CH
Me
Me
12
)
13
(
(
)
14
15
(+)- ( ) (-) (
)
24
(
)
OMe
27)
(
CH2Ph
Ph
C
R
1 = tertery alkyl
O
t
O
OMe
16
Bu (
(17)
)
Me
C
18
)
19
(
Me
(
)
Me
Me
Me
Me
R1 = aryl
O
OMe
(20)
28
29
(
)
(
)
Fig. 1. Vinyl ethers used for this study. No square¼substrates giving polymers.
¼substrates giving the rearrangement product.
¼no reaction takes place.
ethers are often sluggish due to the side reactions such as elimi-
nation reaction to form alkenes and [3,3] rearrangement to give
a mixture of isomers.7def Since the result of the rearrangement can
be roughly expected from the electrophilicity parameter of R1þ
generated from vinyl ethers,8 we focused in this study on the re-
actions of benzyl vinyl ethers, in particular, those bearing p-
methoxybenzyl (8, 21, 22, 25), furylmethyl (9, 24), diphenylmethyl
(13, 23), and 1-phenyl-1-methylethyl (19) groups on the oxygen
atom. For making the rearrangement selective, possible vinyl ether
polymerization should be suppressed. It is known that one methyl
reactivity with either a 13C resonance due to the -carbon19aec or
a
comparison with the relative reactivity of the reaction with
diphenylketene.19d The rates of the polymerization shown in Table
1 were similar to those expected from the 13C signals of the cor-
responding vinyl monomers.
Tacticity of the formed polymer is another entry to understand
the mechanism. The stereoregulation in the cationic polymeriza-
tion of vinyl ethers is generally determined by the steric circum-
stances around the growing cations at the propagation step. The R1
group, catalyst, and counter anions are discussed as the factors to
determine the tacticity.20 It was reported that careful choice of
Lewis acidic metal catalysts and reaction conditions sometimes
gives relatively high isotacticity [(2,6-iPr2C6H4O)2TiCl2 catalyst; m/
r¼90:10 (iBuOCH]CH2), 88:12 (iPrOCH]CH2)];20a however, our
group at the
b
-position (R2¼Me) does not disturb the polymer-
ization,13b whereas
a-substituents inhibited the propagation of vi-
nyl polymerization.2 In this context, substituted vinyl ethers, where
R3sH, were used for many of [1,3] O to C rearrangement studies,7
and they should also be useful for our study on selective [1,3] O to C
rearrangement. A series of vinyl ethers, 21e24, and 27e29 were
prepared.
i
previous study on the tacticity of the polymers of 1, 16, BuOCH]
CH2, and iPrOCH]CH2 formed by the R3SiH/Ru system indicated no
stereoregulation (m/r¼48:52 to 61:39).12 To obtain further insights
Vinyl ethers, which fulfill the requirement of R1þ¼stable and
having a suitable electrophilicity parameter and R3¼H, are the
borderline of the above two categories, and have possibility that
both polymerization and [1,3] O to C rearrangement take place. A
study on the rearrangement of these types of vinyl ethers is missing
except the reaction of furylmethyl and thienylmethyl vinyl ethers
reported by Palani and Balasubramanian.7a We synthesized benzyl
vinyl ethers, 4e8, 12, and 13 a furylmethyl benzyl ether 9, tertiary-
alkyl vinyl ethers, 16e19 for this study. Two vinyl ethers, 25 and 26,
where R2¼Me, were also prepared and subjected to the study.
Table 1
Vinyl polymerization of the monomers listed in Fig. 1a
Run Monomer Temp Time
(ꢁC)
Conv.b Yield Mn
Mw/Mn
Tg
(ꢁC)
c
c
(min) (%)
(%)
1d
2
3
4
5
6
7
8
9
1
2
4
5
6
7
10
11
12
14
15
rt
rt
rt
rt
50
80
rt
rt
rt
rt
rt
rt
rt
rt
60
30
>99
>99
87
80
95
86
92
90
88
91
97
>99
>99
94
84
85
74
46
89
53
86
86
42
87
86
65
86
86
17,300 1.6
12,400 2.0
9600 1.9
3900 1.5
5500 1.9
7200 1.5
11,300 2.3
10,900 2.4
3300 1.4
10,300 2.2
7800 2.6
15,100 1.4
6100 2.5
11,100 2.1
ꢀ54.8
ꢀ78.6
7.7
240
180
120
120
30
1.1
20.4
18.0
60.1
51.2
26.3
86.3
87.4
77.6
de
2.2. Vinyl polymerizations by Ru/R3SiH systems
60
240
180
120
5
5
60
The catalyst A (1.65 mmol) dissolved in dioxane (30 mL) was
10
11
treated with PhMe2SiH (0.165 mmol) at room temperature for
30 min. Addition of monomer (1.65 mmol) initiates the polymeri-
zation. In Table 1 are shown results of polymerization, Mn, Mw/Mn,
and Tg data of 14 of 24 vinyl monomers, which includes previously
reported nBu and tBu vinyl ethers for comparison.12 It is known that
reactivity of vinyl ethers R1OCH]CH2 in the cationic polymeriza-
tion in the absence of chemical species, which is able to bound to
the cationic polymer end, is increased in the order, R1¼primary-
alkyl<secondary-alkyl<tertiary-alkyl.16,19 The rate of polymeriza-
tion of 4, 10, and 16 was in accord with this general trend. The re-
12d 16
13
14
17
18
39.5
a
All reactions were carried out with HSiMe2Ph (0.165 mmol) and a vinyl ether
mol) dissolved in 1,4-dioxane
L) at room temperature under an argon atmosphere.
Determined by 1H NMR.
(1.65 mmol) in the presence of the catalyst A (1.65
m
(30
m
b
c
Number-average molecular weight and weight-average molecular weight are
expressed as Mn and Mw, respectively, which were determined by GPC calibrated by
polystyrene standard. Molecular weight distribution is estimated by Mw/Mn.
d
See Ref. 12.
e
Neither exothermic nor endothermic peak were observed from ꢀ100 ꢁC to
activity order was discussed in terms of
p-donor property of the
vinyl ethers, which were investigated by correlation of the
240 ꢁC (heating rate¼10 ꢁC/min).

3246
N. Harada et al. / Tetrahedron 68 (2012) 3243e3252
Table 2
for stereoregularity at the propagation step, we carried out poly-
merization of chiral monomers, poly- -menthyl vinyl ether (14)
Optimization of the [1,3] O to C rearrangement of the vinyl ether 21 to 21aa
D
25
Run Cat.
(mol %)
0.1
R3SiHb,c (mol %)
Solvent (
m
L)
Temp Time Yield
and poly-
L
-menthyl vinyl ether (15). The [
a
]
values of the poly-
D
(ꢁC)
(h)
(%)
mers were measured in benzene (c¼0.5) to be þ181ꢁ and ꢀ186ꢁ for
1
2
3
4
5
6
7
8
PhMe2SiH (10)
PhMe2SiH (10)
PhMe2SiH (5)
PhMe2SiH (10)
PhMe2SiH (10)
PhMe2SiH (10)
PhMe2SiH (10)
Et2MeSiH (10)
Et3SiH (10)
Dioxane (40)
Dioxane (40)
Dioxane (40)
Dioxane (200) 50
Dioxane (180) 50
Toluene (40)
CHCl3 (40)
Dioxane (40)
Dioxane (40)
rt
50
50
20
1
12
17
3
1
1
17
14
2
5
99
7
poly-14 and poly-15, respectively. The latter is similar to those of
0.1
0.1
0.1
1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
the polymers obtained by BF3$OEt2-initiated cationic polymeriza-
25
tion of 15 at 30 ꢁC ([
a
]
ꢀ191ꢁ).21 Chiellini and co-workers re-
D
3
ported determination of stereoregularity of polyvinyl ethers
produced by polymerization of 15 by several cationic initiators.22a
They measured 13C NMR of poly-15 and determined the iso-
tacticity to be 75e78% (dyads) from the relative intensity of two
peaks appearing at dc 48.4 and 49.1 ppm, which were assigned as
racemi and meso dyads. 13C NMR spectra of poly-14 and poly-15
synthesized by the Ru/SieH system showed very similar signals, of
which relative intensity was m/r¼74:26. In contrast to our previous
data of several vinyl ethers showing no stereoregulation, poly-14
and poly-15 have higher isotactic dyads. This is not unusual, be-
cause Ledwith and co-workers suggest that bulky and optically
active 15 tends to give highly isotactic polymers by stereoregulation
induced by the chirality during the chain growth process.22b The
results concerning stereoregularity provided by the present poly-
merization by Ru/HSiR3 system are similar to those obtained by the
free-ion propagation often seen in Lewis acid-initiated polymeri-
zation of vinyl ethers. In other words, there is no strong interaction
of the cationic species at the polymer end and the counter anion;
this is in accordance with the rate tendency descried above.4
Two monomers listed in Fig. 1, 3 and 20, were unable to be po-
lymerized by the Ru/R3SiH system due to the low electron density of
the vinyl ether moiety of these monomers. Although cationic poly-
89
99
99
3
50
50
50
50
50
50
50
9
1
10
11
12
Me3SiOSiMe2H (10) Dioxane (40)
99
99
50
TMDS (10)d
TMDS (5)d
Dioxane (40)
Dioxane (40)
1
14
a
All of the reactions were carried out with the silane (0.025e0.10 mmol) and
mol) dis-
L) at room temperature under an argon
a vinyl ether 21 (1.0 mmol) in the presence of the catalyst A (1.0 or 10
solved in 1,4-dioxane (40e200
m
m
atmosphere.
b
Figures in parenthesis are the amount of the hydrosilane (mol % based on 21).
TMDS¼Me2HSiOSiHMe2.
c
d
The mol % was calculated based on one SieH group.
Treatment of 21 with HSiMe2Ph (0.1 equiv to 21) and 1 (0.1 mol % to
21) at 50 ꢁC resulted in selective formation of ketone 21a (run 2). A
small amount of a solvent such as dioxane, toluene, and chloroform
is necessary to dissolve the catalyst (runs 2, 6, 7);24 however, ad-
dition of larger amounts of the solvent retards the reaction (runs 4,
5). Trialkylsilanes other than PhMe2SiH gave 25 in poor yield (runs
8, 9), whereas hydrosiloxanes, Me3SiOSiHMe2 and 1,1,3,3-
tetramethyldisiloxane (TMDS) afforded 25 in high yields (runs
10e12) (Scheme 4).
merization of a fluorinated monomer 3 was reported by two groups
23a
by using HI/ZnI2
or TfOH/Me2S,23b no polymerization occurred
under the Ru/SiH system. It was reported that PhOCH]CH2 was not
polymerized by BF3$OEt2.18 We attempted to increase
density of the vinyl ether by p-OMe group; however, no polymer was
obtained in the reaction of 20 with the Ru/R3SiH system.
p-electron
O
A
cat.
OMe
cat.R3SiH
It is known that a b-substituent of vinyl ethers does not inhibit
21a
the vinyl polymerization and the [1,3] O to C rearrangement.2 In fact,
there are several reports on the successful polymerization of
MeCH]CHOR.2,13b In particular, Crivello and co-workers reported
polymerization of CH3CH]CHOR by Ph2SiH2/Co2(CO)8 system.13b
The same catalyst system also induces the alkene isomerization of
CH2]CHCH2OR, which is followed by polymerization of the result-
ing CH3CH]CHOR. Attempted polymerization of CH3CH]CHOC8H19
(26) by PhMe2SiH and a catalytic amount of 1 at either rt or 50 ꢁC
gave rise to quantitative recovery of 26. Slow alkene isomerization
took place in the reaction of CH2]CHCH2OC8H19 under similar
conditions; but no polymerization of the resulting 26 was observed.
MeO
OSiMe2Ph
O
21
Me
cat.A
excessR3SiH
21b
MeO
Scheme 4. [1,3] O to C rearrangement and the rearrangement followed by hydrosilane
reduction.
Interestingly, silyl ether 21b was obtained selectively by using
excess amounts of hydrosilanes (>1 equiv to 21). In a typical ex-
ample, the reaction of 21 in the presence of A (1 mol %) and
PhMe2SiH (1.3 equiv to 21) at 50 ꢁC for 1 h gave the corresponding
silyl ether 21b in 91% yield. The reaction is stepwise; NMR obser-
vation showed the formation of 21a, which was followed by the
ruthenium-catalyzed hydrosilane reduction to form 21b. The
Lewis-acid promoted [1, 3] O to C rearrangement of vinyl ethers
generally gives ketones; however, alcohols are reportedly formed
when a stoichiometric amount of particular Lewis acid, iBu3Al, was
used as the promoter.7d The promoter (iBu3Al) acts as both Lewis
acid for rearrangement and reducing reagent for the resulting ke-
tones to alcohols. In other words, change of Lewis acids realizes the
formation of alcohols. This indicates one of the advantages of the
Ru/SiH promoter over the other catalysts, in which both ketones
and silyl ethers are selectively synthesized by simply changing the
amount of hydrosilanes.
2.3. The [1,3] O to C rearrangements by Ru/R3SiH systems
Lewis-acid promoted rearrangement of several benzyl and ter-
€
tiary-alkyl vinyl ethers were studied by Ganasuer and co-work-
ers,7e,f who examined the reactions of vinyl ethers having a R3
group to avoid possible vinyl polymerization with several Lewis
acids. Selection of Lewis acid is important for successful rear-
rangement; BF3/Et2O, Cu(OTf)2, B(C6F5)3, and Bu2BOTf were useful
for the reaction,7f but BPh3, ZnI2, Zn(OTf)2, Mg(OTf)2, La(OTf)3 did
not promote the reaction.7e The rearrangement took place with
TfOH, but was accompanied by hydrolysis of the vinyl ether.7e,f In
a typical example, rearrangement of p-MeOC6H4CH2OC(Me)]CH2
(21) was carried out by treatment with B(C6F5)3 (1 mol %) at room
temperature to give the ketone 21a in 78% yield.
Treatment of 21 with the ruthenium catalyst A (1 mol % to 21)
and catalytic amounts of hydrosilane (0.05e0.1 equiv to 21) was
found to give the desired rearrangement product 21a in good
yields. In Table 2 are summarized the optimization of the reaction.
The rearrangement of several vinyl ethers, where R3sH, was
examined, and the results are summarized in Table 3, runs 1e6. The
reactions of vinyl ethers bearing p-methoxybenzyl groups, 21, 22,

N. Harada et al. / Tetrahedron 68 (2012) 3243e3252
3247
Table 3
[1,3] O to C rearrangement of various benzyl vinyl ethersa
Run
Substrate
Cat. (%)
R3SiHb,c (mol %)
Product
Temp (ꢁC)
Time (h)
Conv.e (%)
Yield (%)
1
21
0.1
PhMe2SiH (10)
50
1
>99
88
2
3
21
22
1
PhMe2SiH (130)
PhMe2SiH (10)
50
60
1
1
>99
>99
91
94
0.1
4
5
23
24
1
PhMe2SiH (10)
PhMe2SiH (10)
50
50
3
3
90
12
86
0.1
12f
6
7
27
0.1
0.1
PhMe2SiH (10)
PhMe2SiH (10)
50
1
>99
83
rt
50
1
1
>99
80
24f
26
8
8
9
13
13
0.1
1
PhMe2SiH (30)
TMDS (200)d
50
50
3
1
77
60
61
>99
rt
50
1
2
>99
69
19f
6
10
11
19
0.1
PhMe2SiH (10)
25
25
0.1
1
TMDS (20)d
50
50
1
1
>99
>99
46
50
12
TMDS (200)d
a
All reactions were carried out with a silane (0.10e1.3 mmol) and a vinyl ether (1.0 mmol) in the presence of the catalyst A (1.0 or 10
L) at rt w50 ꢁC under an argon atmosphere.
mmol) dissolved in 1,4-dioxane
(40e180
m
b
Figures in parenthesis are the amount of the hydrosilane (mol % based on substrate).
TMDS¼Me2HSiOSiHMe2.
c
d
e
f
The mol % was calculated based on one SieH group.
Conversion was determined by 1H NMR.
Yield was determined by 1H NMR (Internal standard: benzyl methyl ether).
and 27, proceeded smoothly at 50 ꢁC to give the corresponding
ketones in high yields. Although the reaction of 27 could be resulted
in elimination to form p-methoxystyrene, 27a was synthesized in
high yields without forming any by-products. Diphenylmethyl vinyl
ether 23 is another successful example to afford the corresponding
ketone 23a in high yields. Since stability and electrophilicity of

3248
N. Harada et al. / Tetrahedron 68 (2012) 3243e3252
PhCHþ2 are lower compared with p-MeOC6H4CH2þ and Ph2CHþ, no
reaction took place with p-tolyl vinyl ether 28. It is worthwhile to
point out that there are cases that the reaction did not proceed
smoothly, though R1þ is enough stable and electrophilic. One is the
reaction of o-methoxybenzyl vinyl ether 29 leading to complete
starting material recovery, whereas another is unexpectedly slow
reaction of a furfurylmethyl vinyl ether 24. Possible reasons of these
results will be discussed later.
than that of 19a, which could be assignable to oligomers like 30. A
small amount of -methylstyrene (3%) was detected, which was
a
formed by proton elimination from PhMe2Cþ. The reaction of p-
methoxybenzyl-1-propenyl ether (25) is interesting in the point
that use of TMDS is essentially important for the reaction. Con-
version of 25 reached >99% after 1 h at 50 ꢁC. 1H NMR spectrum of
the crude compound indicates formation of 25a almost as a single
product, though a tiny aldehyde signal was visible in the crude
product. Purification gave 25a in a moderate isolated yield (46%).
Although furfuryl vinyl ether 9 reportedly undergoes the rear-
rangement by the Liþ promoted reaction, the reaction with the Ru/
hydrosilane system resulted in the starting material recovery. As
shown in Table 3, runs 9 and 12, selective preparation of alcohols
was achieved by using excess amounts of TMDS as the promoter of
the rearrangement and subsequent reduction of the aldehyde in-
termediate. In both of the reactions, no side product was seen, and
the corresponding alcohols were obtained in 61% (run 9) and 50%
(run 12) yields after hydrolysis with TBAF.
2.4. The borderline of vinyl ether polymerization and [1,3] O
to C rearrangement
As described above, vinyl ethers of R3¼H are generally useful for
vinyl polymerization, whereas those, where R3sH and R1þ¼stable
and electrophilic, easily undergo [1,3] O to C rearrangement.2 Of
interest is reactions of vinyl ethers where R3¼H and R1þ¼stable and
electrophilic, which potentially undergo both vinyl polymerization
and [1,3] O to C rearrangement. Reactions of these types of vinyl
ethers have not yet been undertaken in Lewis acid catalyzed re-
actions to our knowledge except the rearrangement of furfuryl and
thienyl vinyl ethers.7
2.5. Mechanistic considerations
As described above, the Ru/R3SiH system is useful for activation of
vinyl ethers, giving rise to either vinyl polymerization or [1,3] O to C
rearrangement. The reaction course is dependent on the sub-
stituents of the vinyl ether; electronic and steric properties of R1, and
steric property of R2 and R3. The vinyl polymerization is explained by
a simple cationic mechanism, which is initiated by R3Siþ species
generated from A and R3SieH as shown in Scheme 6. The attack of
the R3Siþ species occurs at the terminal carbon atom of the vinyl
ether. As described earlier, NMR studies showed that R3Si group
derived from the hydrosilane used was an end group of the polymer;
this supports the polymerization to be initiated by interaction of
vinyl ethers with R3Siþ species.12,13 Compared with other Lewis
acids, the R3Siþ species generated by the present method is a weaker
cationic initiator, which cannot promote polymerization of electron-
Examination of four vinyl ethers 8, 13, 19, and 25 revealed that
there are two features dependent on the R1 group. One is the case
that selective rearrangement took place. Similar to the reaction of
the propenyl analogue 23, diphenylmethyl vinyl ether 13 proceeds
smoothly in contact with 1 (1 mol %) and PhMe2SiH (30 mol %)
leading to formation of the aldehyde 13a as a single product (entry
8). Since the reaction was terminated at 77% conversion, the iso-
lated yield of 13a was as high as 60% with recovery of 13 in ca. 20%.
Another case is that both the rearrangement and side reactions
took place. Reaction of p-methoxybenzyl vinyl ether 8 under the
same conditions as the rearrangement of 21 resulted in rapid
consumption of 8 within 1 h at room temperature. The corre-
sponding polymer was not formed, whereas the rearrangement
product 8a was detected in 24% yield (determined by 1H NMR). At
50 ꢁC, the reaction was terminated after 80% conversion and the
yield of 8a was somewhat increased [33% (determined by 1H NMR),
26% (isolation)]. The remaining 40e50% was a mixture of products,
from which the product 30 was isolated in 14% yield. The new
product 30 is apparently formed by the reaction of two molecules
of 8 as the mechanism discussed later. There were several other
unidentified products, of which NMR spectra showed signals due to
aldehydes. Although the unequivocal assignment is difficult, we
assume the formation of oligomeric compounds of 8, namely, those
formed from several molecules of 8 (Scheme 5).
withdrawing vinyl ether 3 and b-substituted vinyl ether. Crivello and
co-workers reported vinyl polymerization of a b-substituted vinyl
ether 26 by a catalyst system composed of Co2(CO)8 and Ph2SiH2.13
The polymerization of 26 was not accomplished by A and PhMe2
-
SiH; this may be ascribed to steric bulkiness of a trisubstituted
PhMe2Siþ as the initiator, of which reaction with 26 is disturbed by
the b-methyl group. It is important that the present study on the
stereoregulation using menthyl vinyl ethers 14 and 15 suggests the
counter anion of R3Siþ, in which we assume anionic hydride ruthe-
nium carbonyl species, to be less nucleophilic. No or small in-
teraction with the polymer end provided the same trend of
isotacticity previously reported for the free ionic polymerization.20
Electrophilicity of the R1 group is important for determination of
the reaction course, vinyl polymerization or [1,3] O to C rear-
rangement. Although heterolytic cleavage of a CeO bond of 10, 11,
14, 15, and 16e18 possibly produces secondary- and tertiary-alkyl
OMe
Cat. A (0.1 mol%)
O
PhMe2SiH (10 mol%)
r.t. ~ 50oC
8
cations stabilized by hyperconjugation of adjacent CeH or CeC s-
OMe
O
bonds, no rearrangement was observed in the reactions under the
Ru/hydrosilane system. These electron-donating secondary- and
tertiary-alkyl groups contribute to accelerate the vinyl polymeri-
zation, but does not promote the rearrangement. The results pre-
sented in this paper indicate that the CeO bond cleavage occurred
CHO
+
MeO
CHO
others
+
8a
MeO
30
14 % (r. t.)
21% (r.t.)
14% (50oC)
33% (50oC)
only when the Rþ is strongly stabilized by conjugated
p-electrons.
As shown in Scheme 6, activation of the oxygen atom of vinyl ethers
Scheme 5. Rearrangement of 8.
by R3Siþ species results in formation of Rþ species and enol silyl
ether, of which coupling leads to a-alkylation of ketones or alde-
Reactions of 19 and 25 are other examples that the oligomeri-
zation is involved. The reaction was terminated after 69% conver-
sion of 19, and the major product was the desired aldehyde 19a
[36% (determined by NMR), 6% (isolation)]. 1H NMR spectrum of the
crude product showed several minor signals of aldehydes other
hydes. Since the rearrangement is accompanied by regeneration of
R3Siþ species, only catalytic amounts of hydrosilanes are necessary
for the reaction. The reactions of a series of benzyl vinyl ethers
showed clear features; (1) introduction of electron-donating OMe
group to the aromatic ring is important for the rearrangement of

N. Harada et al. / Tetrahedron 68 (2012) 3243e3252
3249
[Ru]
+ H-SiR3
[Ru]-H
+
SiR3
CO
OC
Ru
CO
Ru
CO
O R1
R3
Ru
CO
CO
R2
OC
A
cat.
R1
R2
R3Si
O R1
R3
O SiR3
[Ru]-H
[Ru]-H
R2
R3
R2, R3 = H
R1 = electrophilic
R1 = not electrophilic
R2, R3 = H
certain R
R1
R1
R2
O SiR3
R3
O R1
O SiR3
O R1
O-R1
O-R1
R3Si
H
OR1
OR1
R1
R2
O
R1
+ other oligomers
CHO
R3Si
H
n
R3
R2
Oligomerization
Vinyl Polymerization
[1,3]O to C Rearrangement
Scheme 6. Mechanisms of vinyl polymerization versus [1,3] O to C rearrangement.
primary benzyl vinyl ethers; the corresponding rearrangement
products were obtained from 8, 21, 22, 25, and 27, whereas no
rearrangement took place in the reaction of 4e7. (2) In the cases
where Rþ species is stabilized by two phenyl groups (vinyl ethers 13
and 23) or by two methyl and one phenyl moieties (a vinyl ether
19), the rearrangement took place, but stabilization by one methyl
and one phenyl group (a vinyl ether 12) is not strong enough to
promote the rearrangement. Pseudo-first-order rate constants of
carbocations with water were proposed to be a probe for the esti-
mation of the electrophilicity factor proposed by Mayer.8 By the
azide clock method at 20 ꢁC, the rate constant (kw/sꢀ1) was de-
creased in the order, PhMeCHþ (1ꢂ1011), PhMe2Cþ (1.7ꢂ1010),
þCH2(p-C6H4OMe) (2ꢂ108), þCHPh2 (3ꢂ108), MeCHþ(p-C6H4OMe)
(5ꢂ107). The results shown in Table 1 and 3 indicate the electro-
philicity between PhMeCHþ and PhMe2Cþ (1.7ꢂ1010) to be the
border of vinyl ether polymerization and [1,3] O to C rearrange-
ment. In other words, carbocations of which electrophilicity is
larger than PhMeCHþ is to be the R1þ leading to the [1,3] O to C
rearrangement.
from 8 reacts another moleculeof 8 prior tothe couplingwiththe silyl
enol ether. If two molecules of 8 react with each other in similar
fashion, it is expected that oligomers, R1(CH2CHOR1)nCH2CHO, would
be formed; this is supported by NMR evidence for appearance of dual
aldehyde signals. It is also reasonable to assume that sterically bulky
R1 group such as Ph2CH and PhMe2C would slow down the insertion
of vinyl ethers leading to oligomerization. The reason why vinyl
ethers 13 and 19 provided no or little formation of oligomers would
be ascribed to this steric reason of R1.
Another problem is termination of the reaction before the
conversion of the starting vinyl ether reaches to 100%. This is more
significant in the rearrangement of furfuryl vinyl ether 24; only 12%
conversion of 24 was achieved under the conditions shown in Table
2. As described above, neither the polymerization nor the rear-
rangement took place in the reactions of two vinyl ethers 9 and 29,
where oxygen functions are closely located to the vinyl ether
moiety. It is noteworthy that two oxygen atoms in 9, 24, and 29 are
located closely enough to make a chelate with the ruthenium cat-
alyst; this may deactivate the catalyst. Deactivation of the catalyst is
also seen in the rearrangement giving aldehydes as the product; the
reason is not clear at present.
The R2 and R3 groups sterically disturb the vinyl polymerization,
contributing to the efficient rearrangement of 21e23, 25, and 27,
which gave the desiredketones inhighyields. Inthe cases where both
R2 and R3 are H, there are two problems, which disturb to form the
rearrangement product in good yields. One is the oligomerization
noted above; a dimer 30 was isolated from the reaction of 8 with the
Ru/hydrosilane system. A probable mechanism for the formation of
30 is shown in Scheme 6, the p-MeOC6H4CHþ2 (R1þ) species generated
3. Conclusion
As described above, combination of hydrosilanes and the ru-
thenium catalyst A efficiently induces both vinyl ether polymeri-
zation and [1,3] O to C rearrangement. Although these reactions

3250
N. Harada et al. / Tetrahedron 68 (2012) 3243e3252
have been well investigated in literature,2,7 they are surprisingly
independent, and studies on the borderline of polymer chemistry
and organic chemistry have been obscure presumably due to the
difference of the research fields. Present paper has made scope of
the reactions more clear than previous reports; in particular, the
reaction course is dependent on the substituents of vinyl ethers.
Primary-, secondary-, and tertiary-alkyl vinyl ethers where R2 and
R3 are hydrogen atoms generally undergo vinyl polymerization,
whereas the vinyl ethers where R1þ is stabilized by adjacent
electron-rich aromatic groups induce [1,3] O to C rearrangement. In
our series of studies on the reactions mediated by tertiary hydro-
silanes and the ruthenium catalyst A, this is the first example of the
[1,3] O to C rearrangement. It is worthwhile to point out that the
present rearrangement has three synthetic merits; (1) both
hydrosilanes and the ruthenium complex A are neutral and their
handling is easy, (2) only catalytic amounts of hydrosilanes are
needed for preparation of ketones or aldehydes, and (3) selective
formation of alcohols is possible when excess amounts of hydro-
silanes are used.
The reactions changing the substituents of vinyl ethers also
provide fresh mechanistic insights. It is likely that treatment of
hydrosilanes with A generates R3Siþ species, which acts as Lewis
acids to promote both vinyl polymerization and [1,3] O to C rear-
rangement. Stereoregulation of polymers of chiral vinyl ether
monomers indicates weak coordinating ability of the counter an-
ionic species of R3Siþ to the polymer end. This also contributes to
the success of the rearrangement; a less nucleophilic counter anion
does not disturb the coupling of intermediary Rþ species and the
enolate.
performed with a JASCO-GPC system consisting of DG-1580-53
degasser, PU-980 HPLC pump, UV-970 UV/Vis detector, RI-930 RI
detector, and CO-2065-plus column oven (at 40 ꢁC) using two
connected Shodex GPC-KF-804L columns in THF (sample concen-
tration¼1 wt %; flow rate¼1.0 mL/min). The molecular weight was
calibrated with a commercially available polystyrene (Shodex: SM-
105); seven standard solutions, of which Mn range is 1.31ꢂ103 to
7.36ꢂ105 (Mw/Mn¼1.07). DSC 6220 (Seiko Instruments Inc.) was
used for analyses of the thermal behavior of the polymers. The
polymer samples (5e15 mg), pretreated at 100 ꢁC under reduced
pressure (0.05 Torr) overnight, were heated from ꢀ100 ꢁC to 100 ꢁC
in aluminum pans under N2 flow (13e50 mL/min), heating rate was
10 ꢁC/min. HRMS analysis was performed at the Analytical Center
in Institute for Materials Chemistry and Engineering, Kyushu Uni-
versity. Analytical thin-layer chromatography (TLC) was performed
on glass plates and aluminum sheets precoated with silica gel
(Merck, Kieselgel 60 F254, layer thickness 0.25 and 0.2 mm, re-
spectively). Visualization was accomplished by UV light (254 nm),
anisaldehyde, and phosphomolybdic acid. Preparation of
(m3, , ,h
h2 h3 5-acenaphthylene)Ru3(CO)7 (A) was reported earlier.9c,25
4.2. Preparation of vinyl ethers
Preparation of most of vinyl ethers was performed by Ishi’s
iridium-catalyzed reaction of vinyl acetate with alcohols.15 The
following is
a representative example: [IrCl(COD)]2 (719 mg,
1.07 mmol) was dissolved in dry toluene (55 mL). To this solution,
diphenylmethanol (9.86 g, 53.5 mmol), isopropenyl acetate (16.1 g,
161 mmol), and Na2CO3 (3.40 g, 32.1 mmol) were added, and the
mixture was heated at 100 ꢁC for 6 h. Insoluble salts were removed
by filtration, and the filtrate was concentrated. After concentration,
chromatographic purification of the residue (Al2O3, hexane) gave
We started a project for the development of new synthetic re-
actions by the Ru/hydrosilane catalyst system from reductions of
carbonyl compounds.9 Now the chemistry is expanded to other
types of reactions including CeC bond forming reactions.11,12 The
present study is important that [1,3] O to C rearrangement of cer-
tain vinyl ethers facilely takes place by judicious choice of vinyl
ethers, and scope of the vinyl ethers, which makes either vinyl
polymerization or the rearrangement possible. We are currently
investigating further reactions by the Ru/hydrosilane catalyst sys-
tem based on the mechanistic considerations described in this
paper.
13 as colorless oil in 50% isolated yield. Rf (hexane) 0.77; IR (neat)
3029, 1656, 1264, 1056, 798, 741, 694 cmꢀ1 1H NMR (395 MHz,
CDCl3) 7.30e7.12 (m, 10H, Ph), 5.88 (s, 1H, eOeCHe(Ph)2), 3.85 (s,
1H, CH2]C(CH3)eOe), 3.76 (s, 1H, CH2]C(CH3)eOe), 1.85 (s, 3H,
CH2]C(CH3)eOe). 13C NMR (99 MHz, CDCl3)
158.1 (CH2]
n
;
d
d
C(CH3)eOe), 141.5 (ipso of Ph), 128.4, 127.4, 126.6 (Ph), 84.7 (CH2]
C(CH3)eOe), 80.5 (CHe(Ph)2), 21.3 (CH2]C(CH3)eOe). HRMS (EI)
calcd for C16H16O (Mþ) 224.1201, found 224.1198.
4. Experimental section
4.1. General
Two vinyl ethers, 25 and 26, were prepared by isomerization of
allyl p-methoxybenzyl ether and allyl n-octyl ether, respectively. In
a typical example, the ruthenium catalyst embedded in a silicone
gel, Ru3@SiEGcap, prepared according to the literature method,26
was suitable for preparation of ruthenium-free vinyl ether. A mix-
ture of the catalyst (9.09 g, 1 mol % of Ru3), allyl p-methoxylbenzyl
ether (3.56 g, 20 mmol), and dry hexane (60 mL) was heated at
60 ꢁC overnight. The catalyst was recovered by decantation, and the
resulting colorless solution was concentrated. Distillation of residue
gave 25 as colorless liquid (3.32 g, 93%, E/Z¼41:59). (E)-25 and (Z)-
All reactions were carried out under an argon atmosphere. An-
hydrous solvents (THF, hexane, 1,4-dioxane, chloroform, toluene)
and sodium carbonate, calcium hydride were purchased from
Kanto Chemical Co., Ltd., and used as received. tert-Butyl vinyl
ether was purchased from Aldrich Chemical Co. Dieth-
ylmethylsilane, triethylsilane, and dimethylethoxysilane, 1,1,1,3,3-
pentamethyldisiloxane, 1,1,3,3-tetramethyldisiloxane were pur-
chased from Gelest. Inc. Sodium hydride was purchased from
Kishida Chemical Co., Ltd. 1H,1H,2H,2H-Perfluorooctan-1-ol was
purchased from Daikin Finechemical Laboratory, Ltd. All reagents
except the above-mentioned were purchased from Tokyo Chemical
Industry Co., Ltd. 1H, 13C, and 19F spectra were measured on JEOL
GSX-270 (270 MHz), ECA 400 (396 MHz), and ECA 600 (600 MHz)
spectrometers. Chemical shifts for 1H NMR were described in parts
per million downfield from tetramethylsilane as an internal stan-
25: IR (neat)
NMR (395 MHz, CDCl3)
n
2934, 1513, 1246, 1171, 1034, 820 cmꢀ1; (E)-25: 1H
d
7.27 (d, J¼8.70 Hz, 2H, Ph), 6.89 (d,
J¼8.70 Hz, 2H, Ph), 6.30 (d, J¼12.57 Hz,1H, (CH3)CH]CHeOe), 4.88
(dq, J1¼12.57 Hz, J2¼6.77 Hz, 1H, (CH3)CH]CHeOe), 4.63 (s, 2H,
eOeCH2ePh), 3.81 (s, 3H, PheOCH3), 1.55 (d, J¼6.77 Hz, 3H, (CH3)
CH]CHeOe). 13C NMR (99 MHz, C6D6)
d 159.7 (ipso of Ph), 147.0
((CH3)CH]CHeOe), 130.0 (ipso of Ph), 129.3 (Ph), 114.0 (Ph), 98.9
((CH3)CH]CHeOe), 70.8 (eOeCH2ePh), 54.7 (PheOCH3), 12.7,
((CH3)CH]CHeOe). (Z)-25: 1H NMR (395 MHz, CDCl3)
d 7.27 (d,
dard (
d
¼0) in CDCl3, unless otherwise noted. Chemical shifts for 13
C
J¼8.70 Hz, 2H, Ph), 6.89 (d, J¼8.70 Hz, 2H, Ph), 6.03 (d, J¼6.77 Hz,
1H, (CH3)CH]CHeOe), 4.72 (s, 2H, eOeCH2ePh), 4.43 (quint,
J¼6.77 Hz, 1H, (CH3)CH]CHeOe), 3.81 (s, 3H, PheOCH3), 1.60 (d,
NMR were expressed in parts per million in CDCl3 as an internal
standard (
NMR were described in parts per million downfield from tri-
d
¼77.0), unless otherwise noted. Chemical shifts for 19F
J¼6.77 Hz, 3H, (CH3)CH]CHeOe). 13C NMR (99 MHz, C6D6)
d 159.8
fluoroacetic acid as an external standard (
measured on JASCO FT/IR-4200 spectrometer. GPC analysis was
d
¼ꢀ79.0). IR spectra were
(ipso of Ph), 145.7 ((CH3)CH]CHeOe), 130.2 (ipso of Ph), 129.2 (Ph),
114.1 (Ph), 101.3 ((CH3)CH]CHeOe), 73.3 (eOeCH2ePh), 54.7

N. Harada et al. / Tetrahedron 68 (2012) 3243e3252
3251
(PheOCH3), 9.6 ((CH3)CH]CHeOe). HRMS (EI) calcd for C11H14O2
and treated with Me2PhSiH (25
m
L, 0.165 mmol) at room tempera-
(Mþ) 178.0994, found 178.0998.
ture. After 30 min, 8 (271 mg, 1.65 mmol) was added, which was
consumed within 1 h. After concentration, chromatographic purifi-
cation of the residue gave three fractions including 8a (70 mg, 26%),
30 (38 mg, 14%), and other unidentified products. Compound 8a: Rf
4.3. A general procedure for the vinyl polymerization
Polymerization was carried out by treatment of vinyl ethers
with A (0.1 mol %) preactivated by PhMe2SiH (10 mol %) at room
temperature. In a typical example, a vinyl ether 15 was prepared
(hexane/AcOEt¼4:1) 0.33. IR
n
(neat) 2835, 1720, 1511, 1244, 1033,
9.26 (s, 1H, eCHO), 6.83 (d,
812 cmꢀ1 1H NMR (395 MHz, C6D6)
;
d
J¼8.70 Hz, 2H, Ph), 6.73 (d, J¼8.70 Hz, 2H, Ph), 3.30 (s, 3H, PheOCH3),
from (ꢀ)-menthyl alcohol. The catalyst A (1.07 mg, 1.65
m
mol) was
2.55 (t, J¼7.73 Hz, 2H, PheCH2eCH2eCHO), 2.05 (t, J¼7.73 Hz, 2H,
dissolved in dioxane (30 L) and treated with Me2PhSiH (25
m
mL,
PheCH2eCH2eCHO). 13C NMR (99 MHz, C6D6)
d 200.2 (eCHO), 158.6
0.165 mmol) at room temperature. After 30 min, 15 (301 mg,
1.65 mmol) was added, and the mixture was stirred at room tem-
perature for 1 h. Precipitation from CH2Cl2/methanol gave the
polymer (259 mg, 86% yield). GPC (THF) Mn¼7.8ꢂ103, Mw/Mn¼2.6;
(ipso of Ph), 132.7 (ipso of Ph), 129.4 (Ph), 114.2 (Ph), 54.7 (PheOCH3),
45.4 (PheCH2eCH2eCOH), 27.4 (PheCH2eCH2eCHO). HRMS (EI)
calcd for C10H12O2 (Mþ) 164.0837, found 164.0840. Compound 30: Rf
(hexane/AcOEt¼2:1) 0.47. IR
n
(neat) 1721 cmꢀ1 (C]O); 1H NMR
[
a]
25 ꢀ185.8 (c 0.5, benzene); 1H NMR (395 MHz, C6D6)
d
4.33e3.24
(600 MHz, CDCl3)
d
9.76 (t, J¼2.06 Hz, 1H, eCHO), 7.22 (d, J¼8.94 Hz,
D
(m, 2H, eOeCH and e[CH2eCH(OR)]ne), 2.89e0.82 (m, 20H,
2H, Ph), 7.06 (d, J¼8.94 Hz, 2H, Ph), 6.86(d, J¼8.94 Hz, 2H, Ph), 6.81 (d,
J¼8.94 Hz, 2H, Ph), 4.45 (s, 2H, eOeCH2ePh), 3.92 (tt, J1¼6.87 Hz,
J2¼5.50 Hz, eCH2eCH(OR)eCH2eCHO), 3.78 (s, 3H, PheOCH3), 3.77
(s, 3H, PheOCH3), 2.71e2.53 (m, 4H, PheCH2eCH2e and
eCH2eCHO), 1.98e1.79 (m, 2H, PheCH2eCH2e). 13C NMR (151 MHz,
e[CH2eCH(OR)]ne and (ꢀ)-menthyl group). 13C NMR (99 MHz,
CDCl3)
d 75.0e71.5 (br, eOeCH), 69.4e66.6 (br, e[CH2eCH(OR)]ne),
49.5e47.9
(m,
(ꢀ)-menthyl
group),
41.9e38.7
(br,
e[CH2eCH(OR)]ne), 35.2e34.3, 31.8e31.2, 25.6e24.3, 23.9e22.2,
21.7e20.8, 17.1e15.9 (br, (ꢀ)-menthyl group).
CDCl3)
d 201.4 (eCHO), 159.2, 157.8, 133.5, 130.1 (ipso of Ph), 129.4,
129.1, 113.8 (Ph), 73.1 (eCHeOeCH2ePh), 70.9 (eCHeOeCH2ePh),
55.2, 55.2 (PheOCH3), 48.2 (PheCH2eCH2e), 36.2 (PheCH2eCH2e),
30.4 (CH2eCHO). HRMS (EI) calcd for C20H24O4 (Mþ) 328.1675, found
328.1679.
4.4. A general procedure for [1,3] O to C rearrangement
The reaction was carried out under similar conditions for vinyl
polymerization. In a typical example, A (0.65 mg, 1.0
mmol) dissolved
in dioxane (40 L) was pretreated with PhMe2SiH (15.5
m
m
L, 0.10 mmol)
Acknowledgements
at room temperature for 30 min. Then, 23 (224 mg, 1.0 mmol) was
added, and mixture was stirred for 3 h. After concentration, the resi-
due was purified by chromatography (silica gel, hexane/AcOEt) to give
This work is supported by Grant-in-Aid for Scientific Research
from the Ministry of Education, Culture, Sports, Science, and
Technology, Japan, and Japan Society for the Promotion of Science.
We thank to JST, CREST to complete the study.
23a (193 mg, 86%). Rf (hexane/AcOEt¼8:1) 0.23; IR
n
(neat) 3027,1715,
7.30e7.14 (m,
1494, 1158, 749, 696 cmꢀ1; 1H NMR (395 MHz, CDCl3)
d
10H, Ph), 4.59 (t, J¼7.73 Hz, 1H, Ph2CHeCH2eCOeCH3), 3.18 (d,
J¼7.73 Hz, 2H, Ph2CHeCH2eCOeCH3), 2.08 (s, 3H, eCOeCH3). 13C
Supplementary data
NMR (99 MHz, CDCl3)
d 206.8 (eCOeCH3), 143.8 (ipso of Ph),
128.5, 127.7, 126.4 (Ph), 49.6 (Ph2CHeCH2eCOeCH3), 46.0
(Ph2CHeCH2eCOeCH3), 30.6 (eCOeCH3). HRMS (EI) calcd for
C16H16O (Mþ) 224.1201, found 224.1201.
These data include experimental details, copies of 1H and 13C
NMR spectra. Supplementary data associated with this article can
be found, in the online version, at doi:10.1016/j.tet.2012.02.025.
4.5. A general procedure for one-pot process consisting of
[1,3] O to C rearrangement and subsequent hydrosilane
reduction
References and notes
1. (a) Effenberger, F. Angew. Chem., Int. Ed. Engl. 1969, 8, 295e312; (b) Winter-
nheimer, D. J.; Shade, R. E.; Merlic, C. A. Synthesis 2010, 2497e2511.
2. For representative reviews: (a) Goethals, E. J.; Prez, F. D. Prog. Polym. Sci. 2007,
32, 220e246; (b) Cationic Polymerizations: Mechanisms, Synthesis, and Applica-
tions; Matyjaszewski, K., Ed.; Marcel Dekker: New York, NY, 1996.
The reaction was carried out under similar conditions for vinyl
polymerization. In a typical example, A (6.51 mg, 10.0
mmol) dis-
solved in dioxane (40
m
L) was pretreated with PhMe2SiH (201 L,
m
3. Strauss, S. H. Chem. Rev. 1993, 93, 927e942.
1.30 mmol) at 50 ꢁC for 30 min. Then, 21 (178 mg, 1.0 mmol) was
added, and mixture was stirred for 1 h. After concentration, the
residue was purified by chromatography (silica gel, hexane/AcOEt)
4. Recent studies on living cationic polymerization showed that fine tuning of the
nucleophilicity of the counter anion could lead to equilibrium between active
species and a dormant species giving living nature to the polymerization. See,
Kanazawa, A.; Kanaoka, S.; Aoshima, S. Chem. Lett. 2010, 39, 1232e1237.
5. (a) Castro, A. M. M. Chem. Rev. 2004, 104, 2939e3002; (b) Ziegler, F. E. Chem. Rev.
1988, 88, 1423e1452; (c) Rhoads, S. J.; Raulins, N. R. Org. React. 1975, 22, 1e252.
6. (a) Lutz, R. P. Chem. Rev. 1984, 84, 205e247; (b) Nasveschuk, C. G.; Rovis, T. Org.
Biomol. Chem. 2008, 6, 240e254; (c) Ferrier, R. J.; Middleton, S. Chem. Rev. 1993,
93, 2779e2831.
to give 21b (286 mg, 91%). Rf (hexane/AcOEt¼4:1) 0.64; IR
3068, 1510, 1245, 1035, 823, 782, 699 cmꢀ1 1H NMR (395 MHz,
CDCl3) 7.63e7.57 (m, 2H, Ph), 7.42e7.33 (m, 3H, Ph), 7.03 (d,
n (neat)
;
d
J¼8.70 Hz, 2H, Ph), 6.80 (d, J¼8.70 Hz, 2H, Ph), 3.90e3.75 (m, 1H,
eCHeOSi), 3.78 (s, 3H, eOCH3), 2.71e2.40 (m, 2H), 1.83e1.59 (m,
2H), 1.15 (d, J¼5.80 Hz, 3H, eCHeCH3), 0.40 (s, 6H, eOSi(CH3)2Ph).
7. (a) Palani, N.; Balasubramanian, K. K. Tetrahedron Lett. 1995, 52, 9527e9530; (b)
Petasis, N. A.; Lu, S.-P. J. Am. Chem. Soc. 1995, 117, 6394e6395; (c) Smith, A. B., III;
Verhoest, P. R.; Minbiole, K. P.; Lim, J. J. Org. Lett. 1999, 1, 909e912; (d) du Roizel,
13C NMR (99 MHz, CDCl3)
d 157.6 (ipso of Ph), 138.4 (ipso of Ph),
€
B.; Sollogoub, M.; Pearce, A. J.; Sinay, P. Chem. Commun. 2000, 1507e1508; (e)
€
Gansauer, A.; Fielenback, D.; Stock, C. Adv. Synth. Catal. 2002, 344, 845e848; (f)
133.5 (Ph), 132.9 (ipso of Ph), 129.4, 129.1, 127.7, 113.7 (Ph), 68.5
(eCHeOeSi), 55.2 (eOCH3), 41.3 (PhCH2CH2eCHe), 31.1
(PhCH2CH2eCHe), 23.6 (eCHeCH3), ꢀ1.0 (eOSi(CH3)2Ph). HRMS
(EI) calcd for C19H26O2Si 314.1702, found 314.1699.
€
Gansauer, A.; Fielenback, D.; Stock, C.; Geich-Gimbel, D. Adv. Synth. Catal. 2003,
345, 1017e1030.
8. Discussion on the nucleophilicity and electrophilicity: (a) Mayer, H.; Kempf, B.;
Ofial, A. R. Acc. Chem. Res. 2003, 36, 66e77; (b) Mayr, H.; Patz, M. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 938e957.
9. (a) Nagashima, H.; Suzuki, A.; Iura, T.; Ryu, K.; Matsubara, K. Organometallics
2000, 19, 3579e3590; (b) Matsubara, K.; Iura, T.; Maki, T.; Nagashima, H. J. Org.
Chem. 2002, 67, 4985e4988; (c) Motoyama, Y.; Itonaga, C.; Ishida, T.; Takasaki,
M.; Nagashima, H. Org. Synth. 2005, 82, 188e195; (d) Sasakuma, H.; Motoyama,
Y.; Nagashima, H. Chem. Commun. 2007, 4916e4918; (e) See also, a recent re-
view for hydrosilane reduction, Addis, D.; Das, S.; Junge, K.; Beller, M. Angew.
Chem., Int. Ed. 2011, 50, 280-284.6004.
4.6. [1,3] O to C rearrangement involving formation of
oligomers
Formation of oligomeric products was observed in the reaction of
8. The catalyst A (1.07 mg,1.65 mmol) wasdissolved in dioxane(30 mL)

3252
N. Harada et al. / Tetrahedron 68 (2012) 3243e3252
10. For general reviews on the catalytic hydrosilylation: (a) Ojima, I. In The
Chemistry of Organosilicon Compounds; Patai, S., Rappoport, Z., Eds.; John Wiley,
and Sons: New York, NY, 1989; (b) Comprehensive Handbook on Hydrosilylation;
Marciniec, B., Ed.; Pergamon: Oxford, 1992; (c) Hydrosilylation; Marciniec, B.,
Ed.; Springer: Oxford, 2009.
31e37; (c) Masuda, T. J. Polym. Sci. 1973, 11, 2713e2717; (d) Yuki, H.; Hatada, K.;
Nagata, K.; Eura, T. Polym. J. 1970, 1, 269e270.
20. (a) Ouchi, M.; Kamigaito, M.; Sawamoto, M. J. Polym. Sci., Part A 2001, 39,
1060e1066; (b) Ohgi, H.; Sato, T. Macromolecules 1999, 32, 2403e2409; (c)
Kunitake, T.; Aso, C. J. Polym. Sci., Part A-1 1970, 8, 665e678.
11. Nagashima, H.; Kubo, Y.; Kawamura, M.; Nishikata, T.; Motoyama, Y. Tetrahedron
21. Kuroiwa, M.; Minoura, Y. Makromol. Chem. 1980, 181, 707e713.
22. (a) Delfini, M.; Conti, F.; Paci, M.; Segre, A. L.; Solaro, R.; Chiellini, E. Macro-
molecules 1983, 16, 1212e1215; (b) Ledwith, A.; Chienelli, E.; Solaro, R. Macro-
molecules 1979, 12, 240e243.
2011, 67, 7667e7672.
12. Nagashima, H.; Itonaga, C.; Yasuhara, J.; Motoyama, Y.; Matsubara, K. Organo-
metallics 2004, 23, 5779e5786.
13. For a Co2(CO)8/hydrosilane system for cationic type polymerizations. (a) Chalk,
A. J. J. Chem. Soc., Chem. Commun. 1970, 847e848; (b) Crivello, J. V.; Rajaraman,
S. J. Tetrahedron 1997, 53, 15167e15186 and references cited therein.
14. Other ruthenium-catalyzed cationic type polymerizations. Harada, N.; Yasu-
hara, J.; Motoyama, Y.; Fujimura, O.; Tsuji, T.; Takahashi, T.; Nagashima, H. Bull.
Chem. Soc. Jpn. 2011, 84, 26e39 and references cited therein.
15. Okimoto, Y.; Sakaguchi, S.; Ishii, Y. J. Am. Chem. Soc. 2002, 124, 1590e1591.
16. Fishben, L.; Crowe, B. F. Macromol. Chem. 1961, 48, 221e228.
17. (a) Folder, C.; Armes, S. P.; Billingham, N. C. Polym. Bull. 1995, 35, 291e297; (b)
Higashimura, T.; Aoshima, S. JP 61254607 A, 1986.
23. (a) Hopkens, J.; Moller, M.; Lee, M.; Percec, V. Makromol. Chem. 1992, 193,
275e284; (b) Vandooren, C.; Jerome, R.; Teyssie, P. Polym. Bull.1994, 32, 387e393.
24. Although the catalyst A is stable to air and moisture, active species is generated
in contact with hydrosilanes. As shown in Table 2, runs 2 and 3, use of excess
amounts of hydrosilanes is recommended to obtain the polymer in high yields.
Activation of A by smaller amounts of hydrosilanes leads to inefficient gener-
ation of the active species, which lowers the yield of the product. Since A is not
very soluble to either hydrosilanes or most of vinyl ethers, addition of small
amounts of solvents helps the reaction medium homogeneous.
25. Nagashima, H.; Fukahori, T.; Aoki, K.; Itoh, K. J. Am. Chem. Soc. 1993, 115,
10430e10431.
18. Sakaguchi, T.; Koide, T.; Hashimoto, T. J. Appl. Polym. Sci. 2009, 114, 2339e2343.
19. (a) Hatada, K.; Nagata, K.; Hasegawa, T.; Yuki, H. Makromol. Chem. 1977, 178,
2413e2419; (b) Ledwith, A.; Lockett, E.; Sherington, E. C. Polymer 1975, 16,
26. Motoyama, Y.; Abe, M.; Kamo, K.; Kosako, Y.; Nagashima, H. Chem. Commun.
2008, 5321.