Ruthenium-Catalyzed Silylation of 1,3-Butadienes with Vinylsilanes

Article abstract of DOI:10.1021/acs.orglett.5b00865

A novel method for the synthesis of 1-silyl-substituted 1,3-butadienes, based on [RuHCl(CO)(PCy₃)₂]-catalyzed silylative coupling of terminal (E)-1,3-dienes with vinylsilanes, is reported. The reaction provides a facile and straightf

Full text of DOI:10.1021/acs.orglett.5b00865

Letter
pubs.acs.org/OrgLett
Ruthenium-Catalyzed Silylation of 1,3-Butadienes with Vinylsilanes
Justyna Szudkowska-Frątczak,† Bogdan Marciniec,†,‡ Grzegorz Hreczycho,† Maciej Kubicki,†
and Piotr Pawluc*,†
́
†Faculty of Chemistry, Adam Mickiewicz University in Poznan, Umultowska 89b, 61-614 Poznan, Poland
‡Center for Advanced Technologies, Adam Mickiewicz University in Poznan, Umultowska 89c, 61-614 Poznan, Poland
S
* Supporting Information
ABSTRACT: A novel method for the synthesis of 1-silyl-substituted 1,3-
butadienes, based on [RuHCl(CO)(PCy3)2]-catalyzed silylative coupling of
terminal (E)-1,3-dienes with vinylsilanes, is reported. The reaction provides a
facile and straightforward access to (E,E)-dienylsilanes in a highly stereo-
selective fashion (especially for aryl-substituted dienes) and opens a valuable
and general synthetic route for the direct catalytic silylation of conjugated
dienes with elimination of ethylene as a single byproduct. Preliminary results
on synthetic application of the synthesized silylated 1,3-butadienes in desilylation reactions are described.
ilyl-substituted 1,3-dienes are versatile building blocks that
have significant potential in stereoselective organic syn-
bis(silyl)-1,3-butadienes by hydrolysis of the corresponding
metallacyclopentadienes (M = Zr, Ti), being derivatives of silyl-
substituted diynes or alkynes.12 The most popular approaches
to 2-silicon substituted 1,3-butadienes involve ruthenium-
catalyzed ene-yne cross-metathesis of silylacetylenes with
olefins13 and reaction of chlorosilanes with Grignard reagents
derived from chloroprene.14
One of the most powerful methods for the synthesis of
stereodefined alkenylsilanes yet proposed is the transition-
metal-catalyzed silylative coupling of functionalized olefins with
vinylsilanes.15 The reaction of silylative coupling involves the
cleavage of the C−H bond at the α and β carbon atoms from
the vinyl group and activation of the C−Si bond in vinylsilane,
accompanied by release of the ethylene molecule. This process
is catalyzed by transition metal (M = Ru, Rh, Co, Ir) complexes
either containing M−H and M−Si bonds or capable of their in
situ generation. The mechanism of silylative coupling involves
insertion of vinylsilane into the M−H bond and β-Si transfer to
the metal, accompanied by release of ethylene so that the M−Si
complex could be generated. This step is followed by insertion
of alkene and β-H transfer to the metal with a simultaneous
elimination of substituted vinylsilane.16,17
On the basis of our previous results on the highly
stereoselective synthesis of substituted vinylsilanes from
terminal alkenes,15 we have envisaged that the transition-
metal-catalyzed silylative coupling of olefins with vinyl-
substituted organosilicon compounds can be successfully
extended for systems based on conjugated dienes (Scheme
1). The silylative coupling of terminal 1,3-dienes with
vinylsilanes opens a valuable and general synthetic route for
the direct silylation of conjugated dienes at the terminal
position with ethylene as a single byproduct.
S
thesis.1 They can be used as substrates in enantioselective
ruthenium catalyzed alcohol C−H crotylation via diene
hydrohydroxyalkylation.2 Silylated 1,3-butadienes have been
demonstrated as useful building blocks to construct cyclic
compounds through the Diels−Alder reaction and can be used
for allylation and desilylation reactions.1 Under different
reaction conditions they can be converted to a variety of
functional molecules, including a cyclohexene moiety or
functionalized (halogen-, aryl-, acyl-substituted) diene frag-
ment. The highly functionalized products of this type are
difficult to obtain by other methods, which proves the
importance of selective transformations of silyl-substituted
1,3-butadienes.
So far a large number of methods have been proposed to
synthesize silylated 1,3-dienes, usually employing different
organometallic reagents. Nevertheless, it is still a challenge to
perform a highly selective and effective synthesis of stereo-
defined conjugated dienes. Conventional methods for preparing
stereodefined dienylsilanes include a modified Peterson
olefination3 or Horner−Wadsworth−Emmons-type reactions.4
An alternative approach to dienylsilanes relies on the palladium-
catalyzed Heck coupling of vinylsilanes with vinyl halides or
triflates5 and silyl-substituted tosylates with olefins.6 The cross-
coupling of organometallic reagents, such as silyl-substituted
stannanes7 and organozinc8 or organoaluminum derivatives
with vinyl halides,9 has been also applied in the synthesis of 1-
silyl-1,3-butadienes. More recent approaches to silyl-substituted
1,3-butadienes involve reactions starting from alkyne deriva-
tives.1 Dixneuf and co-workers have reported ruthenium
catalyzed double-addition of silyl-substituted diazo compounds
to alkynes to give 1,4-bis(silyl)-substituted 1,3-dienes.10
Hydrozirconation of silyl-substituted enynes followed by
halogenation has been applied for the synthesis of halogen-
containing silyl-substituted 1,3-dienes.11 It has been established
that it is possible to obtain 1-silyl-1,3-butadienes and 1,4-
Received: March 24, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.5b00865
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
the presence of catalyst I and II. The reaction proceeded with
moderate yield (∼40%) and selectivity (E/Z = 8/2) when a
ruthenium-silyl complex (IV) was used; however, the reaction
required a longer time and even after 48 h the substrates did
not reach full conversion. Rhodium-siloxide (V) and rhodium-
hydride (VI) complexes showed significantly lower catalytic
activity in the silylation reaction of (E)-1-phenylbuta-1,3-diene
with vinyltrimethylsilane (10−20% yield of silylated diene after
48 h), whereas [RuCl2(CO)3]2 (III) and [RhCl(cod)]2 (VII)
proved to be inactive in this process.
Scheme 1. Extension of Catalytic Silylative Coupling of
Olefins with Vinylsilanes for 1,3-Dienes
Given our optimized conditions, we investigated the scope of
this reaction, using selected commercially available or
synthesized 1-substituted (E)-1,3-butadienes.19 The silylation
of terminal (E)-1,3-butadienes by various vinylsilanes and
vinylsiloxanes of general formula CH2CHSiR3 (where SiR3 =
SiMe3, SiMe2Ph, Si(OEt)3, Si(OEt)2Me, SiMe2OEt, Si-
(OSiMe3)2Me, Si(OSiMe3)Me2) proceeded efficiently in the
presence of 2 mol % catalyst (I) to give 1,3-butadienes silylated
at the terminal position (Scheme 3). In a typical procedure, the
In the letter we report a novel method to access
functionalized 1-silyl-substituted 1,3-butadienes based on
silylative coupling of terminal (E)-1,3-butadienes with vinyl-
silanes and vinylsiloxanes. To the best of our knowledge, the
selective silylation of terminal dienes by silylative agents is
extremely rare and there is only one report in the literature on
effective silylation of terminal 1,3-dienes with benzene-fused
silacyclobutane.18 The catalytic silylation of conjugated
butadienes by commercially available vinylsilanes opens a
new, direct, and highly stereoselective route for the synthesis of
1-silylated 1,3-dienes from simple substrates.
Scheme 3. Silylation of (E)-1,3-Butadienes with Vinylsilanes
We began the investigation with optimizing the reaction
conditions. Catalytic screenings have been applied in the model
catalytic process of (E)-1-phenylbuta-1,3-diene with vinyl-
trimethylsilane (Scheme 2). Selected ruthenium(II) and
substrates and catalyst were dissolved in toluene (0.1 M
concentration) and heated in a Schlenk bomb flask fitted with a
plug valve at 100 °C (for aryl-substituted 1,3-butadienes) or
120 °C (for methyl- and methoxy-substituted 1,3-butadienes)
for 24−48 h. The results are presented in Table 1.
Scheme 2. Silylation of (E)-1-Phenylbuta-1,3-diene with
Vinyltrimethylsilane
All of the silylated 1,3-butadienes were isolated and
characterized spectroscopically. The stereoselectivity of the
overall transformation was good. In all cases, the (E,E)-double
1
bond geometry was favored (68−100%) as measured by H
NMR; however, the isomer ratio depended on the substituents
in the butadiene molecule and vinylsilane used. DEPT analysis
of the 1-phenyl-4-(trimethylsilyl)-1,3-butadiene 1 obtained
(Table 1, entry 1) excluded the presence of the geminally
substituted dienylsilane. The stereochemical assignments for
products 1−21 confirmed that most of the reactions yielded a
mixture of (E,E) and (E,Z) isomers; however, in some cases
during the reaction, partial E → Z isomerization of double
bonds (2−13%) took place which resulted in the formation of
the (Z,Z) isomer (Table 1, entries 5, 10, and 14−20).
rhodium(I) complexes, i.e. [RuHCl(CO)(PCy3)2] (I),
[RuHCl(CO)(PPh3)3] (II), [RuCl2(CO)3]2 (III), [Ru-
(SiMe2Ph)Cl(CO)(PPh3)2] (IV), [Rh(μ-OSiMe3)(cod)]2
(V), [RhH(CO)(PPh3)3] (VI), and [RhCl(cod)]2 (VII),
known to be active in the silylative coupling of olefins with
vinylsilanes have been tested in this process. Since the synthetic
procedure requires the full conversion of 1,3-butadiene and
small amounts of byproducts of the vinylsilane homocoupling,
all the screening tests were performed with the 1:1.2 diene/
vinylsilane ratio. In a typical procedure, the substrates and
catalyst (2 mol %) were dissolved in toluene (0.1 M
concentration to avoid competitive diene polymerization) and
heated in a Schlenk bomb flask fitted with a plug valve at 100
°C for 24−48 h.
From among the tested catalysts, ruthenium-hydride
monocarbonyl complexes [RuHCl(CO)(PCy3)2] (I) and
[RuHCl(CO)(PPh3)3] (II) clearly showed higher catalytic
activity (99% yield of silylated diene after 24 h) than other
ruthenium(II) as well as rhodium(I) derivatives. The
ruthenium-hydride complex I showed the highest selectivity
(E/Z = 93/7) under the conditions applied and was selected
for further synthetic procedures. Despite the use of a slight
excess of vinylsilane, only trace amounts of the competitive
homocoupling product, 1,2-bis(silyl)ethene, were detected in
The (E,E)-configuration of the double bond of the
compounds 12 and 13 was further confirmed by single-crystal
X-ray diffraction analysis.20
Under the conditions applied, 1-substituted (E)-1,3-
butadienes bearing aryl groups reacted successfully to give the
corresponding 1-aryl-4-silyl-1,3-butadienes in high isolated
yields (80−96%), irrespective of the substituent’s electronic
character (Table 1, entries 1−13). Both alkyl- and alkoxy-
substituted vinylsilanes as well as vinylsiloxanes can be
employed for the silylation of aryl-substituted 1,3-butadienes
to give corresponding 1-aryl-4-silyl-1,3-butadienes. However,
the silylation of aryl-substituted (E)-1,3-butadienes by trialkyl-
substituted vinylsilanes seems to be more selective than that
using alkoxy-substituted vinylsilanes or vinylsiloxanes. Despite
the use of a slight excess of vinylsilane, only trace amounts of
the competitive homocoupling products, 1,2-bis(silyl)ethenes,
were detected. Detailed monitoring of the reaction of (E)-1-
B
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Organic Letters
Letter
a
Table 1. Silylation of (E)-1,3-Butadienes with Vinylsilanes
b
entry (product no.)
R
SiR3′
SiMe3
time [h]
isolated yield
selectivity (E,E)/(E,Z)/(Z,Z)
1.
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
24
24
24
24
24
24
24
24
24
24
24
24
24
48
48
48
48
48
48
48
24
89
80
86
87
89
90
87
96
85
90
94
89
90
78
79
75
76
80
82
69
89
93:7:0
2.
SiMe2Ph
SiMe2OEt
Si(OEt)2Me
Si(OEt)3
SiEt3
93:7:0
3.
94:6:0
4.
98:2:0
5.
83:15:2
99:1:0
6.
7.
Si(OSiMe3)2Me
Si(OSiMe3)Me2
SiMe3
90:10:0
96:4:0
8.
9.
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
4-ClC6H4
4-BrC6H4
MeO
94:6:0
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
Si(OEt)2Me
Si(OSiMe3)2Me
SiMe3
80:10:10
88:12:0
93:7:0
SiMe3
100:0:0
75:23:2
68:20:12
70:20:10
70:21:9
71:27:3
71:16:13
75:14:11
90:10:0
SiMe2Ph
MeO
Si(OEt)3
MeO
Si(OEt)2Me
Si(OSiMe3)2Me
SiMe2Ph
MeO
Me
Me
Si(OEt)3
Me
Si(OEt)2Me
SiMe3
N-phthalimide
a
Reaction conditions [diene]/[vinylsilane]/[RuHCl(CO)(PCy3)2] = 1:1.2:0.02; toluene, 100 °C (entries 1−13, 21) or 120 °C (entries 14−20).
b
1
EE/EZ/ZZ ratio determined by H NMR and GC-MS.
phenylbuta-1,3-diene with vinyltrimethylsilane (Table 1, entry
1) by GC-MS analysis allowed the detection of small amounts
of byproducts (less than 5%) which were assigned as a Diels−
Alder cycloaddition product and desilylated cycloaddition
product (3-phenylcyclohexene).
(Scheme 4). The reaction of 1 with 3 equiv of propionic
anhydride in the presence of rhodium catalyst [RhCl(CO)2]2
Scheme 4. Synthetic Application of 1-Phenyl-4-
(trimethylsilyl)-1,3-butadiene in Desilylation Reactions
The ruthenium-catalyzed silylative coupling proceeded
efficiently also for other dienes such as (E)-1,3-pentadiene
(Table 1, entries 18−20) as well as conjugated dienes
containing heteroatoms, (E)-1-methoxy-1,3-butadiene and
(E)-2-(buta-1,3-dien-1-yl)isoindoline-1,3-dione (Table 1, en-
tries 14−17, 21). The silylation of (E)-1-methoxy-1,3-butadiene
and (E)-1,3-pentadiene proceeded with lower selectivity,
irrespective of the vinylsilane used, to give a mixture of (E,E),
(E,Z), and (Z,Z) isomers, with (E,E)-dienylsilane as the
predominant product (68−75%). The lower selectivity of the
reaction with methoxy-substituted diene is consistent with
previous data on the silylative coupling of vinylsilanes with alkyl
vinyl ethers.21 The reaction of (E)-2-(buta-1,3-dien-1-yl)-
isoindoline-1,3-dione with CH2CHSiMe3 proceeded with
high yield and selectivity.
(5 mol %) in dry toluene at 120 °C for 48 h under an Ar
atmosphere according to the method described by Narasaka
and co-workers24 allowed isolation of 6-phenylhexa-3,5-dien-2-
one 24 in 70% yield (Scheme 4).
The reactivity of 2-substituted dienes in the reaction with
vinylsilanes has been also tested. Unfortunately, the reaction of
isoprene or myrcene with vinyltriethoxysilane or vinyldimethyl-
phenylsilane in the presence of catalyst I occurs to a low degree,
to give monosilylated products corresponding to up to 25%
conversion of diene, after 48 h under the conditions given.
To demonstrate the potential applications of silylated 1,3-
butadienes, we pursued transformation of the obtained 1-
phenyl-4-(trimethylsilyl)-1,3-butadiene 1 into halogeno and
ketone derivatives of 1,3-butadiene via halodesilylation or
desilylative acylation reactions. Treatment of the silylative
coupling product 1 with NIS (1.2 equiv) or NBS (2 equiv)
caused iodo-22 or bromodesilylation23 in a highly stereospecific
manner, giving (E,E)-(4-iodobuta-1,3-dien-1-yl)benzene 22 or
(E,E)-(4-bromobuta-1,3-dien-1-yl)benzene 23 as predominant
products in good geometrical purity (E/Z = 8/2) within 2 h
In summary, a novel type of ruthenium-catalyzed silylation of
1,3-dienes with vinylsilanes has been developed. This
unconventional way of introducing a silyl substituent at a
diene terminus extends the synthetic application of classical
silylative coupling of olefins with vinylsilicon compounds and
complements the conventional methodologies for the synthesis
of functionalized 1-silyl-1,3-butadienes.
ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental procedures, NMR spectra, and compound
characterization data as well as X-ray analysis details. The
Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.orglett.5b00865.
C
DOI: 10.1021/acs.orglett.5b00865
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Katayama, H.; Ozawa, F. J. Org. Chem. 2005, 70, 10511. (b) Smith, A.
B., III; Razler, T. M.; Ciavarri, J. P.; Hirose, T.; Ishikawa, T.; Meis, R.
M. J. Org. Chem. 2008, 73, 1192. (c) Fuwa, H.; Yamagata, N.; Saito, A.;
Sasaki, M. Org. Lett. 2013, 15, 1630.
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: piotrpaw@amu.edu.pl.
(24) Yamane, M.; Uera, K.; Narasaka, K. Bull. Chem. Soc. Jpn. 2005,
78, 477.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support from the National Science Centre (Poland),
Grant No. Opus 2011/03/B/ST5/01034 and Maestro 2011/
02/ST5/00472 are gratefully acknowledged.
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