A new selective approach to 1,1-bis(silyl)-2-arylethenes and 1,1-bis(silyl)-1,3-butadienes via sequential silylative coupling-heck coupling reactions

Article abstract of DOI:10.1021/jo0616254

A novel selective route to 1,1-bis(silyl)-1-alkenes has been developed. Sequential one-pot silylative coupling exo-cyclization of 1,2- bis(dimethylvinylsiloxy)ethane followed by the reaction with Grignard reagents leads to the desired 1,1-bis(silyl)ethene

Full text of DOI:10.1021/jo0616254

SCHEME 1. Synthetic Utility of 1,1-Bis(silyl)-1-alkenes
A New Selective Approach to
1,1-Bis(silyl)-2-arylethenes and
1,1-Bis(silyl)-1,3-butadienes via Sequential
Silylative Coupling-Heck Coupling Reactions
Piotr Pawluc, Grzegorz Hreczycho, and Bogdan Marciniec*
Department of Organometallic Chemistry,
Faculty of Chemistry, Adam Mickiewicz UniVersity,
Grunwaldzka 6, 60-780 Poznan, Poland
marcinb@amu.edu.pl
ReceiVed August 4, 2006
Since geminally silylated alkenes are versatile reagents in
organic and organosilicon synthesis, considerable effort has been
made to find new routes for the preparation of these compounds
and for their selective reactions with a range of electrophiles.
Conventional approaches to 1,1-bis(silyl)-1-alkenes involve
multistep reactions of carbonyl compounds with commercially
unavailable dihalodisilylmethanes.2e-f,4 Hodgson and co-workers
have developed a chromium(II)-mediated reaction of aldehydes
with dibromodisilylmethanes.2e Oshima et al. have reported a
synthesis of 1,1-bis(silyl)-1-alkenes from ketones or acyl chlor-
ides and 1,1-bis(silyl)-substituted allylic copper derivatives, ob-
tained via a cooper(I)-mediated vinylation of chlorodisilyllith-
ium.4a The reaction of dibromodisilylmethanes with lithium
trialkylmagnesate or R3SiCH2MgCl followed by dehydrobro-
mination of the resulting 1-bromo-1,1-disilylalkanes provides
an alternative route to 1,1-bis(silyl)-1-alkenes.4b-d However, the
application of these methods is limited by complicated synthetic
procedures involving the use of harmful starting materials and
highly reactive organolithium compounds.
The palladium-catalyzed reaction of aryl and alkenyl halides
with alkenes (the Heck reaction) is regarded as one of the most
versatile tools in modern synthetic chemistry and has great
potential for industrial applications.5 Although this particular
reaction can in principle be applied to any kinds of alkene, it is
already known that there are significant difficulties with the
Heck coupling of vinylsilane.6 Palladium-catalyzed reaction of
aryl and alkenyl halides with vinylsilanes under typical Heck
coupling conditions have been described leading mostly to
styrene derivatives as a result of carbon-silicon bond cleavage.7
Itami et al. have reported that the catalyst-directing 2-pirydyl
group on silicon enable the Heck coupling of vinylsilanes with
A novel selective route to 1,1-bis(silyl)-1-alkenes has been
developed. Sequential one-pot silylative coupling exo-
cyclization of 1,2-bis(dimethylvinylsiloxy)ethane followed
by the reaction with Grignard reagents leads to the desired
1,1-bis(silyl)ethenes, which are then efficiently coupled in
the presence of silver nitrate and palladium acetate with aryl
or alkenyl idodides to give the corresponding 1,1-bis(silyl)-
2-arylethenes or 1,1,4-trisubstituted 1,3-butadienes with high
yield.
1,1-Dimetalated-1-alkenes constitute an important class of
organometallic reagents which are currently widely used as
potential intermediates in the organic and organometallic
syntheses.1 Among the most notable and commonly employed
gem-diorganometallics, the 1,1-bis(silyl)-1-alkenes are of unique
importance. Their use as precursors for the preparation of ke-
tones2a-c as well as a variety of important organosilicon inter-
mediates such as acylsilanes,2d-e epoxysilanes,2e-f 1-halovin-
ylsilanes,2e silyl enol ethers,2g (E)-alkenylsilanes2h, silyl enol
acetates2i etc., stimulates interest in their synthetic availability
(Scheme 1). Silylated 1,3-dienes are also well established as
useful intermediates in regio- and stereoselective organic
synthesis due to their high reactivity and stereospecificity toward
various dienophiles and electrophiles.3
(3) (a) Denmark, S. E.; Tymonko, S. A. J. Am. Chem. Soc. 2005, 127,
8004. (b) Xi, Z.; Liu, X.; Lu, J.; Bao, F.; Fan, H.; Li, Z.; Takahashi, T. J.
Org. Chem. 2004, 69, 8547 (c) Carter, M. J.; Fleming, I.; Percival, A. J.
Chem. Soc., Perkin Trans. 1 1981, 2415.
(4) (a) Kondo, J.; Inoue, A.; Shinokubo, H.; Oshima, K. Tetrahedron
Lett. 2002, 43, 2399. (b) Inoue, A.; Kondo, J.; Shinokubo, H.; Oshima, K.
Chem. Lett. 2001, 956. (c) Inoue, A.; Kondo, J.; Shinokubo, H.; Oshima,
K. Chem. Eur. J. 2002, 8, 1730. (d) Ohmiya, H.; Yorimitsu, H.; Oshima,
K. Angew. Chem., Int. Ed. 2005, 44, 3488.
(5) (a) Beller, M.; Zapf, A. In Handbook of Organopalladium Chemistry
for Organic Synthesis; Negishi, E., Ed.; Wiley-Interscience: New York,
2002; Vol. 1, pp 1209-1222. (b) Beletskaya, I. P.; Cheprakov, A. V. Chem.
ReV. 2000, 100, 3009.
(6) Daves, G. D.; Hallberg, A. Chem. ReV. 1989, 89, 1433-1445.
(7) (a) Hallberg, A.; Westerlund, C. Chem. Lett. 1982, 1993. (b)
Karabelas, K.; Hallberg, A. J. Org. Chem. 1989, 54, 1773.
(1) Reviews on gem-diorganometallics: (a) Marek. I.; Normant, J.-F.
Chem. ReV. 1996, 96, 3241-3267. (b) Marek, I. Chem. ReV. 2000, 100,
2887-2900. (c) Normant, J.-F. Acc. Chem. Res. 2001, 34, 640-644.
(2) Gro¨bel, B. Th.; Seebach, D. Angew. Chem., Int. Ed. Engl. 1974, 13,
83. (b) Seebach, D.; Bu¨rstinghaus, R.; Gro¨bel, B. Th.; Kolb, M. Liebigs
Ann. Chem. 1977, 830. (c) Inoue, A.; Kondo, J.; Shinokubo, H.; Oshima,
K. Chem. Commun. 2002, 114. (d) Inoue, A.; Kondo, J.; Shinokubo, H.;
Oshima, K. J. Am. Chem. Soc. 2001, 123, 11109. (e) Hodgson, D. M.;
Comina, P. J.; Drew, M. G. B. J. Chem. Soc, Perkin Trans. 1 1997, 2279.
(f) Hodgson, D. M.; Comina, P. J. Chem. Commun. 1996, 755. (g) Cuadrado,
P.; Gonzales-Nogal, A. M.; Sarmentero, M. A. Chem. Eur. J. 2004, 10,
4491. (h) Hudrlik, P. F.; Agwaramgbo, E. L. O.; Hudrlik, A. M. J. Org.
Chem. 1989, 54, 5613. (i) Hudrlik, P. F.; Hudrlik, A. M.; Rona, R. J.; Misra,
R. N.; Withers G. P. J. Am. Chem. Soc. 1977, 99, 1993.
10.1021/jo0616254 CCC: $33.50 © 2006 American Chemical Society
Published on Web 09/23/2006
8676
J. Org. Chem. 2006, 71, 8676-8679

SCHEME 2. One-Pot Synthesis of 1,1-Bis(silyl)ethenes
benzene. In early experiments, we investigated the influence
of phosphine, base, and the solvent on the selectivity of the
silver nitrate-mediated reaction with commonly used catalysts
such as Pd(OAc)2, Pd(dba)2, or Pd2(dba)3. The reactions were
performed at 60 or 80 °C in DMF, THF, toluene, or MeCN in
the presence of a ratio 1/2 of [Pd]/phosphine as a catalyst (3
mol %/6 mol %) and triethylamine as a base. In the presence
of the dibenzylideneacetone palladium/phosphine (PPh3, P(2-
furyl)3, P(o-Tol)3) catalytic system, the Heck-coupled product
was obtained with moderate yield, but the reaction was not
selective and the formation of a large amounts of desilylation
products (1-phenyl-1-(trimethylsilyl)ethene and stilbene) as well
as iodobenzene homocoupling product (biphenyl) was also
observed. Disappointingly low selectivities were also obtained
using potassium carbonate, sodium acetate, or potassium
fluoride. The highest selectivity in terms of the formation of
arylated 1,1-bis(trimethylsilyl)ethene was observed using an
excess of triethylamine and palladium(II) acetate/triphenylphos-
phine as catalyst. After several attempts, we found that the
reaction of compound 1 (1 equiv) with 1 equiv of aryl iodide,
1 equiv of AgNO3, and 2 equiv of Et3N, in the presence of 3
mol % of Pd(OAc)2 and 6 mol % of PPh3, conducted in dry
acetonitrile at 60 °C for 2 h exclusively afforded the corre-
sponding 1,1-bis(trimethylsilyl)-2-arylethene in excellent yield
(compounds 3a-7a, Table 1). Similarly to the compound 1,
the application of 1,1-bis(dimethylphenylsilyl)ethene 2 under
analogous conditions also gave the Heck coupled products with
slightly lower yields (compounds 3b-8, Table 1); however, this
particular reaction had to be carried out for a longer time (4-6
h). To our surprise, in all the cases examined, the only products
detected in the reaction mixture (using GC-MS method) were
the desired â-aryl-substituted 1,1-bis(silyl)ethenes 3-8, which
clearly signifies the high reactivity of 1,1-bis(silyl)ethenes 1
and 2 toward Heck reaction. Thus, the noteworthy features of
these processes are that the formation of styrene and stilbene
derivatives (via desilylation) was completely suppressed and
the formation of biaryls (by homocoupling of the aryl iodides)
was not observed. Moreover, the Heck coupling occurred under
mild conditions with a wide array of electronically (similar
reaction rates were obtained with electron-rich and electron-
poor aryl iodides) and structurally diverse aryl iodides.
aryl halides by the agency of a strong complex-induced prox-
imity effect.8 On the other hand, Hallberg has discovered that
otherwise difficult Heck reaction of vinylsilanes can be ef-
ficiently realized when equimolar amount of silver nitrate is
added.9 However, in this reaction, biaryls are the major products
formed, which unfortunately limits the yields of the desired
products considerably. A mechanistic study has shown that silver
ions not only act as an iodide abstractor but also facilitate the
oxidative addition of catalytically active Pd(0) species by
attachment to the iodo substituent and also by formation of an
electron donor-acceptor complex with the aromatic ring.6
Although there are several reports on the successful arylation
and olefination of simple vinylsilanes, the application of the
Heck reaction to 1,1-bis(silyl)ethenes lags far behind mainly
due to the complexity of their synthesis. During the course of
our recent studies on the silylative coupling cyclization of
divinyl-substituted organosilicon compounds10 we have devel-
oped new simple and efficient methods for the synthesis of
alkyl-, aryl-, alkenyl-, or alkoxy-substituted 1,1-bis(silyl)ethenes
using cyclic silyl ether or cyclic silylamine selectively obtained
via ruthenium-catalyzed silylative coupling exo-cyclization of
divinyl-substituted monomers, followed by their reaction with
Grignard reagents11a,c or alcohols.11b
Herein, we report a new facile and selective two-step protocol
for synthesis of 1,1-bis(silyl)-2-arylethenes and 1,1-bis(silyl)-
1,3-butadienes from easily available 1,2-bis(dimethylvinylsi-
loxy)ethane. Our synthetic methodology involves a one-pot
reaction sequence-ruthenium hydride complex-catalyzed sily-
lative coupling exo-cyclization followed by the reaction with
Grignard reagents to generate respective 1,1-bis(silyl)ethene and
their subsequent silver nitrate-mediated and palladium-catalyzed
Heck-type functionalization with aryl and alkenyl iodides.
The starting 1,1-bis(trimethylsilyl)ethene 1 and 1,1-bis-
(dimethylphenylsilyl)ethene 2 were easily prepared by the one
pot implementation of our recently reported procedure.11a This
facile synthetic methodology involved consecutive ruthenium-
catalyzed silylative coupling cyclization of 1,2-bis(dimethyl-
vinylsiloxy)ethane and the reaction of the resulting cyclic silyl
ether with methylmagnesium iodide or phenylmagnesium
bromide without isolation of the cyclic bis(silyl) intermediate
(Scheme 2).
Having established an efficient protocol for the Heck coupling
of 1,1-bis(silyl)ethenes 1 and 2 with aryl iodides, we subse-
quently investigated the synthesis of synthetically useful silylated
1,3-diene frameworks by means of coupling between 1 with
selected alkenyl iodides. Two stereodefined alkenyl iodides, (E)-
â-iodostyrene and (Z)-ethyl 2-iodopropenoate, have been se-
lected for testing the activity of compound 1 in the alkenylation
process. Unfortunately, under the identical reaction conditions
to those applied for the arylation process (Pd(OAc)2, PPh3,
acetonitrile, 60 °C), silver nitrate-mediated Heck coupling did
not take place when alkenyl iodides were used instead of aryl
iodides. After several attempts, we found that the palladium-
catalyzed (3 mol % of Pd(OAc)2 and 6 mol % of PPh3)
alkenylation of 1,1-bis(silyl)ethene 1 successfully proceeded in
DMSO to give coupling products 9 and 10 in moderate yield
(Table 1, entries 11-12); however, the reaction required a
considerably higher temperature (100 °C) and longer reaction
time (24 h). It is worth noting that under these optimized
conditions stereospecific products (E,E)-1,1-bis(trimethylsilyl)-
4-phenylbuta-1,3-diene 9 and (Z)-Ethyl 5,5-bis-(trimethylsilyl)-
penta-2,4-dienoate 10 were exclusively formed. GC-MS analy-
At the outset, we began by establishing the conditions for
the Heck arylation of 1,1-bis(trimethylsilyl)ethene 1 with iodo-
(8) (a) Itami, K.; Mitsudo, K.; Kamei, T.; Koine, T.; Nokami, T.; Yoshida,
J. J. Am. Chem. Soc. 2000, 122, 12013. (b) Itami, K.; Nokami, T.; Ishimura,
Y.; Mitsudo, K.; Kamei, T.; Yoshida, J. J. Am. Chem. Soc. 2001, 123, 11577.
(9) (a) Karabelas, K.; Hallberg, A. J. Org. Chem. 1986, 51, 5286. (b)
Karabelas, K.; Hallberg, A. Tetrahedron Lett. 1985, 26, 3131. (c) Karabelas,
K.; Hallberg, A. J. Org. Chem. 1988, 53, 4909.
(10) For a review, see: (a) Marciniec, B. Coord. Chem. ReV. 2005, 249,
2374-2390. (b) Marciniec, B.; Pietraszuk, C. Curr. Org. Chem. 2003, 7,
691-735. (c) Marciniec, B.; Pietraszuk, C. In Handbook of Metathesis;
Grubbs, R. H., Ed.; Wiley-VCH: Weinheim, 2003; Vol. 2; Chapter 13, pp
463-490.
(11) (a) Pawluc, P.; Marciniec, B.; Hreczycho, G.; Gaczewska, B.; Itami,
Y. J. Org. Chem. 2005, 70, 370. (b) Pawluc, P.; Hreczycho, G.; Marciniec,
B. Synlett 2005, 7, 1105. (c) Hreczycho, G.; Pawluc, P.; Marciniec, B.
Synthesis 2006, 8, 1370.
J. Org. Chem, Vol. 71, No. 22, 2006 8677

TABLE 1. Palladium-Catalyzed Heck Coupling of 1,1-Bis(silyl)ethenes with Aryl and Alkenyl Iodides
a Reaction conditions: 60 °C, [Pd(OAc)2]:[PPh3]:[AgNO3]:[Et3N]:[RI]:[(R3Si)2CdCH2] ) 3 × 10-2:6 × 10-2:1:2:1, aisolated yields of chromatographically
b
pure products, reaction performed at 100 °C.
sis of the byproducts of the reaction discussed revealed the
presence of a significant amount of alkenyl iodide coupling
products (1,4-diphenyl-1,3-butadiene (18%) and diethyl hexa-
2,4-dienedioate isomers (38%) respectively). Although they can
be easily separated by column chromatography, their formation
limited the yields of 9 and 10 considerably. All preparative
results are summarized in Table 1.
this particular method compares favorably with other accessible
methods for the preparation of these kinds of organosilicon
derivatives.
Experimental Section
One-Pot Procedure for the Synthesis of 1,1-Bis(dimethylsilyl)-
ethenes. The glass reactor (50 mL, two-necked, round-bottomed
flask equipped with a magnetic stirring bar, reflux condenser and
argon bubbling tube) was evacuated and flushed with argon. 1,2-
Bis(dimethylvinylsiloxy)ethane (5.00 g, 0.217 mol) and [RuHCl-
(CO)(PPh3)3] (0.21 g, 0.022 mmol) were added to the reactor. The
reaction mixture was heated under the flow of argon for 2 h at 120
°C with stirring. After the mixture was cooled to room temperature,
a 1 M solution of the corresponding Grignard reagent in THF was
added dropwise (molar ratio 1,2-bis(dimethylvinylsiloxy)ethane/
Grignard reagent was 1:3). The reaction mixture was stirred under
argon at 65 °C for 18 h. After the reaction was complete, the excess
amount of the Grignard reagent was quenched by adding MeOH
and pentane, the suspended salt was filtered off, and the volatiles
In conclusion, we have described a novel and efficient
protocol for the synthesis of 1,1-bis(silyl)-2-arylethenes as well
as 1,1-bis(silyl)-1,3-butadienes from easily available starting
materials using the following sequential procedure: silylative
coupling-Grignard reagent treatment-Heck coupling. Other-
wise difficult to synthesize compounds were exclusively (ary-
lation) or predominantly (alkenylation) obtained via silver
nitrate-mediated and palladium-catalyzed Heck-type coupling
of 1,1-bis(silyl)ethenes with aryl and alkenyl iodides. Due to
the mildness and simplicity of the experimental procedure and
the tolerability of a wide range of substituents in the aryl group,
8678 J. Org. Chem., Vol. 71, No. 22, 2006

were evaporated in vacuo. After evaporation, the crude product was
chromatographed on silica gel and distilled under reduced pressure
to afford the analytically pure product (yield: compound 1 (72%),
compound 2 (80%)).
4 mmol of 1,1-bis(silyl)ethene 1 or 2 , 1.12 mL (8 mmol) of
triethylamine, and 10 mL of freshly distilled DMSO was placed in
a 50 mL, two-necked, round-bottomed flask equipped with a
magnetic stirring bar and reflux condenser. The suspension was
heated in an oil bath at 100 °C for 24 h. The reaction mixture was
then poured into 100 mL of water and extracted with pentane (2 ×
50 mL). The combined organic layers were dried (MgSO4) and
the crude product obtained was then purified by column chroma-
tography (silica gel/ pentane) to give the corresponding 1,1-bis-
(silyl)-1,3-butadiene.
Representative Procedure for the Synthesis of 1,1-Bis(silyl)-
2-arylethenes (3-8). A mixture consisting of 33.50 mg (0.15
mmol) of palladium(II) acetate, 78.60 mg (0.30 mmol) of triphen-
ylphosphine, 0.85 g of silver nitrate (5 mmol), 5 mmol of aryl
iodide, 5 mmol of 1,1-bis(silyl)ethene 1 or 2 , 1.40 mL (10 mmol)
of triethylamine, and 10 mL of acetonitrile was placed in 50 mL,
two-necked, round-bottomed flask equipped with a magnetic stirring
bar and reflux condenser. The suspension was heated in an oil bath
at 60 °C for the appropriate time (see Table 1). After being cooled
to room temperature, the reaction mixture was added to water (50
mL) and extracted twice with 30 mL of pentane. The combined
organic layers were dried (MgSO4), and the crude product obtained
was then purified by column chromatography (silica gel/ pentane)
to give the corresponding 1,1-bis(silyl)-2-arylethene.
Acknowledgment. Financial support from the Ministry of
Education and Science (Poland) (Grant No. 3 T09A 009 29 and
Project No. PBZ-KBN-118/T09/2004/17) is gratefully acknowl-
edged.
Supporting Information Available: Detailed experimental
procedures and characterization data of the compounds prepared
in this study. This material is available free of charge via the Internet
at http://pubs.acs.org.
Representative Procedure for the Synthesis of 1,1-Bis(silyl)-
1,3-dienes (9-10). A mixture consisting of 26.80 mg (0.12 mmol)
of palladium(II) acetate, 62.80 mg (0.24 mmol) of triphenylphos-
phine, 0.68 g of silver nitrate (4 mmol), 4 mmol of alkenyl iodide,
JO0616254
J. Org. Chem, Vol. 71, No. 22, 2006 8679