New catalytic route to (E)-β-silyl-α,β-unsaturated ketones

Article abstract of DOI:10.1016/j.catcom.2012.03.004

(E)-β-(Silyl)-α,β-unsaturated ketones have been efficiently synthesized via one-pot sequential ruthenium-catalyzed silylative homo-coupling of dimethylphenylvinylsilane or trimethylvinylsilane (Marciniec coupling) and rhodium-catalyzed selective desilylative acylation (Narasaka coupling) of (E)-1,2-bis(silyl)ethenes with acid anhydrides. Synthetic strategy relies on the selective mono-substitution of the bis(silyl)ethene intermediate.

Full text of DOI:10.1016/j.catcom.2012.03.004

Catalysis Communications 23 (2012) 10–13
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
☆
New catalytic route to (E)-β-silyl-α,β-unsaturated ketones
⁎
Piotr Pawluć
Department of Organometallic Chemistry, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
(E)-β-(Silyl)-α,β-unsaturated ketones have been efficiently synthesized via one-pot sequential ruthenium-
catalyzed silylative homo-coupling of dimethylphenylvinylsilane or trimethylvinylsilane (Marciniec coupling)
and rhodium-catalyzed selective desilylative acylation (Narasaka coupling) of (E)-1,2-bis(silyl)ethenes with
acid anhydrides. Synthetic strategy relies on the selective mono-substitution of the bis(silyl)ethene intermediate.
© 2012 Elsevier B.V. All rights reserved.
Received 30 December 2011
Received in revised form 23 February 2012
Accepted 1 March 2012
Available online 9 March 2012
Keywords:
α,β-Unsaturated ketones
Silylative coupling
Acylation
β-Silyl carbonyl compounds
Homogeneous catalysis
1. Introduction
or generating in situ M\H and M\Si bonds) [11] appears to be a valu-
able step in a combination with subsequent desilylation reactions [12].
β-Silyl carbonyl compounds are versatile building blocks that
have significant potential in stereoselective synthesis [1]. Their use
as precursors for a number of reactions such as asymmetric conju-
gate addition [2], Robinson annulation [3], Diels–Alder reaction [4]
etc., greatly stimulates their synthetic advancements (Scheme 1).
Conventional approaches to (E)-β-silyl-α,β-unsaturated ketones
involve multi-step reactions starting from alkyne derivatives [1]. Acy-
clic (E)-β-silyl-α,β-unsaturated ketones have been obtained in three-
steps from silylacetylenes via sequential homologation–hydride
reduction–Swern oxidation [2b,5]. The hydrosilylation of propargyl
alcohols followed by oxidation provides an alternative route to β-
silyl carbonyl systems [6]. Several independent methods such as con-
secutive alkyne hydrosilylation–carbonylation [7], silylmetalation–
acylation [8], hydroacylation of silylalkynes [9] or silylation of acetals
of β-sulfonyl ketones [10] have also been investigated. However, the
application of these methods is often limited by complicated synthet-
ic procedures involving the use of harmful starting materials and
highly reactive organometallic compounds.
The mechanism of the process proposed for the Ru-complexes proceeds
via insertion of vinylsilane into Ru\H bond and β-Si transfer to the
metal with elimination of ethylene to generate Ru\Si species, followed
by insertion of alkene and β-H transfer to the metal with elimination of
the substituted vinylsilane [11].
On the other hand, acylation of stereodefined vinylsilanes by acid
halides in the presence of Lewis acids proceeds in a regioselective
manner to afford α,β-unsaturated ketones [13]. Recently, Narasaka
and co-workers have developed a rhodium complex-catalyzed acyla-
tion of vinylsilanes with acid anhydrides which avoids the use of large
quantities of strong Lewis acids and highly reactive and harmful acid
The silylative coupling of olefins with vinyl-substituted organosili-
con compounds (Marciniec coupling), which has been developed in
the last two decades as a new effective catalytic activation of the
C\H bond of olefins and C\Si bond of organosilicon compounds
(generally occurring in the presence of complexes containing initially
☆
Dedicated to Professor Bogdan Marciniec on the occasion of his 70th birthday in
recognition of his significant contribution to organometallic chemistry and homoge-
neous catalysis.
⁎
Fax: +48 618291508.
E-mail address: piotrpaw@amu.edu.pl.
Scheme 1. Synthetic utility of β-silyl-α,β-unsaturated ketones.
1566-7367/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2012.03.004

P. Pawluć / Catalysis Communications 23 (2012) 10–13
11
(SiCH_CH), 200.4 (CO). MS m/z (rel. int.): 231 ([M]+ 10%), 190
(15), 189 (100), 145 (10), 135 (25). HRMS calcd for C14H19OSi:
231.12051; found 231.12124.
halides [14]. The mechanism of the catalytic acylation proceeds via
transmetalation between the Rh(I) complex and vinylsilane to afford
vinylrhodium intermediate, followed by sequential oxidative addition
of acid anhydride and reductive elimination of α,β-unsaturated ke-
tone with regeneration of Rh(I) catalyst [14]. The sequential Hiyama
cross-coupling/Narasaka acylation of (E)-1-(diethoxymethylsilyl)-2-
(dimethylphenylsilyl)-ethene has been also successfully applied to
the synthesis of α,β-unsaturated carbonyl motifs [15].
Recently, we have reported a new efficient protocol for the
highly stereoselective one-pot synthesis of (E)-styryl ketones from
styrenes based on sequential ruthenium-catalyzed silylative cou-
pling–rhodium-catalyzed desilylative acylation reaction [17]. We have
envisaged that the ruthenium-catalyzed (E)-selective silylative homo-
coupling of dimethyl-phenylvinylsilane (Marciniec coupling) followed
by rhodium-catalyzed desilylative acylation (Narasaka coupling) can
be a valuable synthetic method for one pot conversion of vinylsilanes
into (E)-β-silyl-α,β-unsaturated ketones, which are versatile interme-
diates in organic and organosilicon syntheses.
(E)-1-(Dimethylphenylsilyl)-4-methylpent-1-en-3-one (2d)
1H NMR (300 MHz, CDCl3): δ=0.43 (s, 6H, SiMe2), 1.12 (d, 6H,
J=6.8 Hz, CH(CH3)2), 2.92–2.96 (m, 1H, CH(CH3)2), 6.56 (d, 1H, J=
19.1 Hz, SiCH_CH), 7.20 (d, 1H, J=19.1 Hz, SiCH_CH), 7.35–7.40
(m, 3H, Ph), 7.49–7.52 (m, 2H, Ph). 13C NMR (75 MHz, CDCl3): δ=
−3.0 (SiMe2), 18.6 (CH3), 37.5 (CH), 128.0, 129.6, 133.9, 136.6
(Ph), 142.2 (SiCH_CH), 144.4 (SiCH_CH), 202.8 (CO).HRMS calcd
for C14H19OSi: 231.12051; found 231.12112.
(E)-3-(Dimethylphenylsilyl)-1-phenylprop-2-en-1-one (2e)
1H NMR (300 MHz, CDCl3): δ=0.43 (s, 6H, SiMe2), 7.20 (d, 1H,
J=18.7 Hz, \SiCH_CH\), 7.34–7.42 (m, 4H, Ph and \SiCH_
CH\), 7.48–7.52 (m, 5H, Ph), 7.85–7.89 (m, 2H, Ph). 13C NMR
(75 MHz, CDCl3): δ=−3.0 (\SiMe2\), 128.0, 128.6, 128.8, 129.6,
132.8, 133.8, 136.5, 137.4 (Ph), 139.4 (SiCH_CH), 147.4 (SiCH_CH),
190.4 (CO). MS m/z (rel. int.): 265 ([M]+ 100%), 251 (25), 189 (20),
135 (18), 105 (30), 77 (25). HRMS calcd for C17H17OSi: 265.10486;
found 265.10380.
In this communication we report a facile one-pot preparation of
(E)-β-(silyl)-α,β-unsaturated ketones from vinylsilanes via the corre-
sponding (E)-1,2-bis(silyl)ethene intermediate.
(E)-1-(dimethylphenylsilyl)-4-methylpenta-1,4-dien-3-one (2f)
1H NMR (300 MHz, CDCl3): δ=0.44 (s, 6H, SiMe2), 1.94 (s, 3H, CH3),
5.82–5.92 (m, 2H, _CH2), 7.05 (d, 1H, J=18.6 Hz, SiCH_CH),
7.36–7.40 (m, 3H, Ph), 7.50–7.54 (m, 2H, Ph). 13C NMR (75 MHz,
CDCl3): δ=−3.0 (SiMe2), 17.9 (CH3), 125.3, 127.9, 133.8, 138.5
(Ph), 129.5 (>C_CH2), 142.2 (>C_CH2), 144.7 (SiCH_CH), 145.5
(SiCH_CH), 196.6 (CO). MS m/z (rel. int.): 229 ([M−1]+ 25%),
215 (100), 197 (10), 141 (30), 135 (50), 105 (10). HRMS calcd for
C14H17OSi: 229.10487; found 229.10530.
2. Experimental
2.1. General procedure for the synthesis of (E)-β-(dimethylphenylsilyl)-
α,β-unsaturated ketones and spectroscopic data of the selected products
A mixture consisting of 0.91 mL (5 mmol) of dimethylphenylvi-
nylsilane, and 72.6 mg (0.1 mmol) of RuHCl(CO)(PCy3)2, and 10 mL
of dry toluene was placed under Ar atmosphere in a Schlenk bomb
flask fitted with a plug valve and heated at 110 °C for 24 h. After the
action was completed (GC analysis), 0.25 mmol (97.2 mg) of
[RhCl(CO)2]2 and 15 mmol of anhydride were added. The mixture
was stirred for 24 h at 120 °C. After this time the solvent was evapo-
rated and the mixture was diluted with 15% aqueous solution of
NaOH (50 mL) and Et2O (50 mL) and stirred for 10 min. At this
time, the layers were separated and the aqueous layer was washed
with Et2O (3×50 mL). The combined organic layers were dried
over Na2SO4, filtered and concentrated in vacuo. The remaining yel-
low oil was purified by silica gel chromathography (25:1 hexane:
Et2O) to give the corresponding ketone.
2.2. General procedure for the synthesis of (E)-β-(trimethylsilyl)-α,β-
unsaturated ketones
A mixture consisting of 0.73 mL (5 mmol) of trimethylvinylsilane,
and 25.6 mg (0.05 mmol) of [RuCl2(CO)3]2, and 10 mL of dry toluene
was placed under Ar atmosphere in a Schlenk bomb flask fitted with
a plug valve and heated at 110 °C for 48 h. After the reaction was
completed (GC analysis), 0.25 mmol (97.2 mg) of [RhCl(CO)2]2 and
15 mmol of anhydride were added. The mixture was stirred for 24 h
at 120 °C. After this time the solvent was evaporated and the mixture
was diluted with 15% aqueous solution of NaOH (50 mL) and Et2O
(50 mL) and stirred for 10 min. At this time, the layers were separated
and the aqueous layer was washed with Et2O (3×50 mL). The com-
bined organic layers were dried over Na2SO4, filtered and concentrated
in vacuo. The remaining oil was purified by silica gel chromathography
(25:1 hexane:Et2O) to give the corresponding ketone. The structures of
synthesized compounds were confirmed by GC–MS and NMR spectros-
copy maching data reported in the literature: (E)-4-(trimethylsilyl)but-
3-en-2-one (70% yield) [2a] and (E)-1-(trimethylsilyl)pent-1-en-3-one
(75% yield) [20].
(E)-4-(dimethylphenylsilyl)but-3-en-2-one (2a)
1H NMR (300 MHz, CDCl3): δ=0.44 (s, 6H, SiMe2), 2.28 (s, 3H, CH3),
6.48 (d, 1H, J=19.2 Hz, SiCH_CH), 7.13 (d, 1H, J=19.1 Hz,
SiCH_CH), 7.37–7.41 (m, 3H, Ph), 7.50–7.53 (m, 2H, Ph). 13C NMR
(75 MHz, CDCl3): δ=−3.3 (SiMe2), 26.3 (CH3), 128.0, 129.5, 133.8,
136.3 (Ph), 144.1 (SiCH_CH), 145.5 (SiCH_CH), 198.6 (CO). MS
m/z (rel. int.): 203 ([M−1]+ 52%), 190 (25), 189 (100), 127 (20).
HRMS calcd for C12H15OSi: 203.08922; found 203.08882.
(E)-1-(Dimethylphenylsilyl)pent-1-en-3-one (2b)
1H NMR (300 MHz, CDCl3): δ=0.43 (s, 6H, SiMe2), 1.08–1.12 (t, 3H,
J=7.3 Hz, CH3), 2.60–2.65 (q, 2H, J=7.3 Hz, CH2), 6.52 (d, 1H, J=
19.2 Hz, SiCH_CH), 7.14 (d, 1H, J=19.1 Hz, SiCH_CH), 7.37–7.39
(m, 3H, Ph), 7.49–7.52 (m, 2H, Ph). 13C NMR (75 MHz, CDCl3): δ=
−3.2 (SiMe2), 7.9 (CH3), 32.7 (CH2), 128.0, 129.5, 133.8, 136.5
(Ph), 143.2 (SiCH_CH), 144.0 (SiCH_CH), 200.8 (CO). MS m/z
(rel. int.): 217 ([M−1]+ 12%), 190 (20), 189 (100), 145 (10), 135
(24). HRMS calcd for C13H17OSi: 217.10487; found 217.10387.
(E)-1-(Dimethylphenylsilyl)hex-1-en-3-one (2c)
3. Results and discussion
During the course of our studies on the reactivity of bis(silyl)
alkenes towards carbon electrophiles, we have unexpectedly found
that (E)-1,2-bis(dimethylphenylsilyl)ethene 1, in the reaction with
3 equivalents of propionic anhydride in the presence of rhodium car-
bonyl catalyst [RhCl(CO)2]2 forms exclusively (instead of the expected
diketone–(E)-oct-4-ene-3,6-dione) mono-substitution product–(E)-1-
(dimethylphenylsilyl)pent-1-en-3-one, with perfect stereoselectivity
and good yield (Scheme 2).
1H NMR (300 MHz, CDCl3): δ=0.42 (s, 6H, SiMe2), 0.91–0.96 (t, 3H,
J=7.4 Hz, CH3), 1.58–1.67 (m, 2H, CH2), 2.55–2.60 (t, 2H, J=7.3 Hz,
CH2), 6.50 (d, 1H, J=19.0 Hz, SiCH_CH), 7.13 (d, 1H, J=19.1 Hz,
SiCH_CH), 7.38–7.40 (m, 3H, Ph), 7.49–7.53 (m, 2H, Ph). 13C NMR
(75 MHz, CDCl3): δ=−3.2 (SiMe2), 13.8 (CH3), 17.5 (CH2), 41.4
(CH2), 128.0, 129.5, 133.8, 136.2 (Ph), 143.5 (SiCH_CH), 144.2
Although mono-substitution of (E)-1,2-bis(silyl)ethenes contain-
ing differently-substituted silyl groups in AlCl3-mediated desilylative

12
P. Pawluć / Catalysis Communications 23 (2012) 10–13
Table 1
One-pot synthesis of (E)-β-(dimethylphenylsilyl)-α,β-unsaturated ketones from
dimethylphenylvinylsilane.
Compound
R1
Yield (%)a
E/Z
Scheme 2. Rhodium-catalyzed acylation of (E)-1,2-bis(dimethylphenylsilyl)ethene by
propionic anhydride.
2a
2b
2c
2d
2e
2f
Me
Et
n-Pr
i-Pr
68
82
54
60
48
70
0
99/1
99/1
97/3
98/2
98/2
98/2
–
acylation with acyl chlorides has been previously reported [16], the
selective acylation of symmetrical (E)-1,2-bis(dimethylphenylsilyl)
ethene under Narasaka coupling conditions is unprecedented.
As was previously reported, the silylative coupling of dimethyl-
phenylvinylsilane in the presence of ruthenium hydride catalyst
RuHCl(CO)(PCy3)2 occurred stereoselectively to give (E)-1,2-bis
(dimethylphenylsilyl)ethene in high yield [18]. The silylative cou-
pling reaction of commercially available dimethylphenylvinylsilane
was conducted in toluene, under argon atmosphere in Schlenk
bomb flask fitted with a plug valve at 110 °C, to give (E)-1,2-bis
(dimethylphenylsilyl)ethene 1 as a predominant product (E/Z=98/2)
after 24 h (GC yield>99%). Pure compound 1 was isolated by evapo-
ration of toluene and simple bulb-to-bulb distillation from the reac-
tion mixture in 88% yield. Treatment of the isolated compound 1
with 3 equivalents of propionic anhydride in the presence of rhodium
catalyst [RhCl(CO)2]2 (5 mol%) in dry 1,4-dioxane at 90 °C for 24 h
under Ar atmosphere according to the method described by Narasaka
and co-workers [14] allowed isolation of stereochemically pure (E)-1-
(dimethylphenylsilyl)pent-1-en-3-one in 68% yield. Similar results
were achieved using higher excess of the anhydride and an increase
in the amount of propionic anhydride (from 1.5 to 3 equiv. per silyl
group) did not affect the selectivity of this process. Thus, by sequencing
the highly E-selective silylative coupling of dimethylphenylvinylsilane
with a stereospecific acylation, the configuration of the product is
preserved.
Since a single example of the efficient acylation of (E)-dimethylphenyl
(4-phenylbut-1-en-1-yl)silane by acetic anhydride in toluene has been
reported by Narasaka and co-workers [14], we tested this solvent for
the desilylative acylation of bis(silyl)ethene 1. After several attempts
we have found that acylation of 1 by acetic anhydride in the presence
of rhodium catalyst in dry toluene occurs more efficiently (90% GC
yield) at higher temperature (120 °C) in closed reaction vessel without
affecting the selectivity of the process. Since both reactions i.e. silylative
coupling and desilylative acylation can be performed in toluene, this
result prompted us to attempt the acylation step in one pot with silyla-
tive coupling without further purification of the (E)-1,2-bis(silyl)ethene
intermediate. In a typical procedure, dimethylphenylvinylsilane and
RuHCl(CO)(PCy3)2 catalyst (2 mol%) were dissolved in toluene (0.5 M
concentration) and heated in Schlenk bomb flask fitted with a plug
valve at 110 °C for 24 h under Ar atmosphere. Next, after cooling
the reaction to room temperature, 3 equiv. of acetyl anhydride and
5 mol% of solid [RhCl(CO)2]2 were added and the reaction mixture
was heated to 120 °C. Treatment of the silylative coupling product
with anhydride caused mono-acylation in a stereospecific manner
giving β-(dimethylphenylsilyl)-α,β-unsaturated ketones in high
geometrical purity (E/Z=97/3–99/1) within 24 h. Column chroma-
tography of the resulting products (silica gel, eluent: hexane/diethyl
ether 25:1) afforded pure ketones 2a–f in 48–82% overall yield
(Table 1). Unfortunately, when crotonic anhydride was applied as
acylating agent, no reaction took place.
Ph
\C(_CH2)Me
(E)-MeCH_CH\
2g
Silylative coupling conditions: [CH2_CHSiMe2Ph]:[RuHCl(CO)(PCy3)2]=1:0.02; toluene
(0.5 M), 110 °C, 24 h.
Narasaka coupling conditions:[CH2_CHSiMe2Ph]:[(R1CO)2O]:[[RhCl(CO)2]2]=1:3:0.05,
toluene, 120 °C, 24 h.
a.
Isolated yields of products.
catalyst RuHCl(CO)(PCy3)2 yielded a mixture of isomeric bis(silyl)
ethenes, i.e. (E)-1,2-bis(trimethylsilyl)ethene and 1,1-bis(trimethylsilyl)
ethene (E/gem=9:1), the homo-coupling of trimethylvinylsilane was
performed in the presence of [RuCl2(CO)3]2 complex which has been
previously reported as an efficient catalyst for the selective formation
of (E)-1,2-bis(trimethylsilyl)ethene [19]. Thus, silylative coupling of
trimethylvinylsilane was conducted in toluene (0.5 M concentration),
in the presence of [RuCl2(CO)3]2 (1 mol%) under argon atmosphere in
a Schlenk bomb flask fitted with a plug valve at 110 °C, to give (E)-
1,2-bis(trimethylsilyl)ethene after 48 h (GC yield 96%). Then, after cool-
ing the reaction mixture to room temperature, 3 equiv. of acetyl anhy-
dride and 5 mol% of solid [RhCl(CO)2]2 were added and the reaction
mixture was heated to 120 °C. Treatment of (E)-1,2-bis(trimethylsilyl)
ethene with acetic and propionic anhydrides caused mono-acylation in
a stereospecific manner giving β-(trimethylsilyl)-α,β-unsaturated ke-
tones in high geometrical purity (E/Z=99/1) and good yield (80–85%
measured by GC–MS) within 24 h (Scheme 3).
Efforts were made to further improve the procedure by exam-
ining tandem catalysis using one catalyst for both silylative cou-
pling and acylation steps. Unfortunately, the silylative coupling of
dimethylphenylvinylsilane in the presence of [RhCl(CO)2]2 was unsuc-
cessful. Other rhodium precursors which are known to be active in the
silylative coupling reaction, e.g., [RhCl(cod)]2, [Rh(OSiMe3)(cod)]2, and
RhH(CO)(PPh3)3, also failed as potential Narasaka acylation catalysts.
4. Conclusion
In conclusion, we have developed a new one-pot protocol for
stereoselective preparation of (E)-β-silyl-α,β-unsaturated ketones
via a highly selective catalytic silylative coupling/desilylative acylation
sequence. Starting from easily available dimethylphenylvinylsilane or
trimethylvinylsilane and carboxylic acid anhydrides the correspond-
ing unsaturated β-silylketones are obtained in generally good yields
and selectivities.
It has been found that one-pot sequential silylative coupling–
desilylative acylation protocol can be also applied to the synthesis
of (E)-β-(trimethylsilyl)-α,β-unsaturated ketones. Since silylative cou-
pling of trimethylvinylsilane in the presence of ruthenium hydride
Scheme 3. One-pot synthesis of (E)-β-(trimethylsilyl)-α,β-unsaturated ketones from
trimethylvinylsilane.

P. Pawluć / Catalysis Communications 23 (2012) 10–13
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13
Acknowledgment
[12] P. Pawluc, W. Prukała, B. Marciniec, European Journal of Organic Chemistry
(2010) 219–229.
Financial support from the Ministry of Science and Higher Education
(Poland); Grant Iuventus Plus IP2010 031170 is gratefully acknowledged.
The author wishes to express his sincere thanks to Justyna Szudkowska-
Frątczak for the assistance.
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