Synthesis of Benzo[c]silole Derivatives Bearing a Tetrasubstituted Exocyclic C=C Double Bond by Palladium-Catalyzed Domino Reactions

Article abstract of DOI:10.1002/chem.201701736

The synthesis of diversely substituted 2,3-dihydro-benzo[c]siloles through an unprecedented palladium-catalyzed domino sequence is reported, involving a cyclocarbopalladation of an internal silylalkyne. This reaction proceeds with complete stereoselectivity to lead to a fully substituted exocyclic C=C double bond. Notably, the overall domino sequence appears to be crucial to obtain the desired cyclic vinylsilanes.

Full text of DOI:10.1002/chem.201701736

A Journal of
Accepted Article
Title: Synthesis of Benzo[c]silole derivatives Bearing a Tetrasubstituted
Exocyclic C=C Double Bond by Palladium-Catalyzed Domino
Reactions.
Authors: Patrick Wagner, mihaela gulea, jean suffert, and Morgan
Donnard
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To be cited as: Chem. Eur. J. 10.1002/chem.201701736
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Synthesis of Benzo[c]silole derivatives Bearing a
Tetrasubstituted Exocyclic C=C Double Bond by Palladium-
Catalyzed Domino Reactions.
Patrick Wagner,[a] Mihaela Gulea,[a] Jean Suffert,[a] and Morgan Donnard*[a]
In memory of Prof. Robert Corriu who was an inspirational researcher in the field of silicon chemistry.
aromatic ring. When applied to substrate
5 bearing an
Abstract: We are reporting the synthesis of diversely substituted
2,3-dihydro-benzo[c]siloles via an unprecedented palladium
catalyzed domino sequence involving a cyclocarbopalladation of an
alkynylsilane (equation B, Scheme 1), no traces of the silacyclic
compound was observed as only the product 6 rising from the
migration of the alkyne was obtained in a 74% yield. From these
preliminary results, it appeared that the 5-exo-dig cyclization
would be challenging. We concluded that the product and/or the
intermediate in this type of cyclizations was perhaps too
sensitive and systematically rearranged to the undesired acyclic
silane 6. Based on this assessment we considered that our
approach involving an additional step of cross coupling could
overcome this issue by potentially stabilizing the palladium
intermediate that would be involved in the Suzuki-Miyaura
coupling[14] and also the product of the cyclization by having a
more substituted exocyclic C=C double bond. We hoped that all
together these stabilizations could be the key to access
efficiently the targeted exocyclic vinylsilanes 8.
internal silylalkyne. This reaction proceeds with
a complete
stereoselectivity to lead to a fully substituted exocyclic C=C double
bond. Notably the overall domino sequence appears to be crucial to
obtain the desired cyclic vinylsilanes.
Silicon containing heterocycles are highly valuable scaffolds as
they have shown specific properties in very different fields such
as,
non-exhaustively,
materials,[1]
fragrances[2]
and
pharmaceuticals.[3,4] Notably, most of the time these specificities
are due to the silicon atom itself as it changes dramatically the
polarity as well as the conformational characteristics of an
organic compound compared to its carbon analog (these effects
are encompassed in what is generally called the C/Si switch).[5]
Despite an ever-increasing interest in silacyclic compounds, the
number of efficient synthetic methodologies to reach these
scaffolds remains low in comparison to other heterocycles[6] and
it undoubtedly represents the main barrier to the use of such
molecules in many fields. For these reasons, we have decided,
during the course of our studies to develop original scaffolds,[7]
to focus our attention on silacycles. Based on our experience on
Another point that had to be addressed was the usual
regioselectivity of carbopalladation reactions on silylalkynes
(Figure 1). As reported in the literature the carbo-
functionalization classically takes place at the β position of the
alkyne installing the palladium on the geminal position of the
silicon.[15] Due to the regiospecificity of cyclocarbopalladation
reactions when applied to alkynes (i.e. syn addition forcing the
C=C double bond to be exocyclic), the carbopalladation would
have to take place at the α position of the alkynylsilane. For
instance Keese neutralized this issue by using a 1,2-disilyl-
alkyne (5) as substrate (Scheme 1 equation B).
cascade
reactions,
we
have
envisioned
that
the
cyclocarbopalladation of silylalkynes in a domino sequence
could represent a straightforward access to this family of
compounds with an interesting level of molecular
diversification.[8] Interestingly, the resulting vinylsilanes would
bear an exocyclic fully substituted carbon-carbon double bond.[9]
This singular family of cyclic vinylsilanes are of high interest and
represents one of the most challenging sub-classes to
synthesize.[10] Many of the methods to access exocyclic
vinylsilanes are based on intramolecular modifications of
Xi et al. (ref. 12)
[Pd(!-allyl]2 (2.5 mol%)
XPhos (10 mol%)
Si
Si
Br
LiOt-Bu (3 equiv.)
toluene, 120 °C, 12 h
2 (61%)
1
established
alkyne
hydrosilylation
and
silylformylation
methodologies. In addition, most of the substrates used are silyl
ethers when those leading to a cycle incorporating a silicon atom
linked to four carbons are more rare.[11] To the best of our
knowledge, only two groups have focused their attention on
such kind of cyclization on all-carbon quaternary silicon atoms.
Notably, none of them have integrated it in a domino sequence.
Xi et al. reported a 5-endo-dig cyclocarbopalladation (Heck-type
cyclization) on an acyclic vinylsilane (Scheme 1). This
transformation offered the corresponding benzosilole in 61%
yield.[12] On their side Keese et al.[13] attempted to synthesize
benzo[c]siloles using 5-exo Mizoroki-Heck reactions on vinyl and
alkynyl silanes, respectively 3 and 5 (Scheme 1). In the first
case (equation A, scheme 1), the reaction led to the targeted
compound 4 in a modest 23% yield and notably the major
compound 4’ (60% yield) resulted from the migration of the
alkene moiety from the silicon atom to the ortho position of the
Keese et al. (ref. 13)
A
PdCl2(PPh3)2 (5 mol%)
Et3N (4 equiv.)
Si
Si
Si
MeO
+
I
MeOH (2 equiv.)
MeCN/Ph-H 1:1
reflux, 4 h
3
4 (23%)
4’ (60%)
B
PdCl2(PPh3)2 (5 mol%)
Et3N (4 equiv.)
Si
Si
MeO
SiMe3
SiMe3
I
MeOH (2 equiv.)
MeCN/Ph-H 1:1
reflux, 4 h
5
6 (74%)
This work
1 R2
Si
R1
Si
R
R2
[Pd], R’-B(OH)2
R
R
Br
Base
R’
cyclocarbopalladation
cross coupling
15 examples
up to 78%
[a]
P. Wagner, Dr. M. Gulea, Dr. J. Suffert and Dr. M. Donnard
Université de Strasbourg, CNRS (LIT UMR 7200)
F-67000 Strasbourg
8
7
Scheme 1. Cyclocarbopalladation of vinyl and alkynyl silanes.
E-mail: donnard@unistra.fr
Supporting information for this article is given via a link at the end of
the document.
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Classical mode of
carbopalladation
This work mode of
carbopalladation
Table 1. Synthesis of benzosiloles starting from silylalkynes and reaction
optimisation.
[Si]
[Si]
R2
2 PdX
R
2 PdX
R
R
R1
R1
XPd
R1
Si
R
PdX
R
α
β
R2
B(OH)2
Conditions[a]
18h, 130°C
Si
Si
n-pent
n-pent
n-pent
R’, R’’, R’’’ = alkyl or aryl
Br
+
Figure 1. Regioselectivity of the carbopalladation of silylalkynes.
7a
8a
8a’
Yield
Entry
Catalyst/ligand
Base
Solvent
(ratio
8a/8a’)
We first prepared, using Keese’s synthesis, a range of nine
original alkynylsilanes 7a-i bearing a 2-bromo benzyl group on
silicon (Figure 2).[13] Then the reaction conditions were optimized
using (2-bromobenzyl)(hept-1-yn-1-yl)dimethylsilane 7a as
substrate and phenyl boronic acid as the coupling partner (Table
1). To start this study we decided to use our classical conditions
i.e. Pd(PPh3)4 as catalyst, K3PO4 as base in a mixture of 2-
MeTHF and H2O as solvent at 130 °C for 18 h (Table 1, entry
1).[16] To our delight, under these conditions, we succeeded in
performing the first cyclocarbopalladation on an alkynylsilane
that led to the formation of a silacycle. The domino process was
validated as the targeted benzosilole 8a was obtained in an
encouraging 52% yield. Notably, no traces of the direct coupling
between the aryl moiety of the starting material and the phenyl
boronic acid or of the migration of the alkyne to the ortho
position of the benzyl silane (compound 8a’) were detected. A
similar result was obtained when the reaction was performed
under microwave irradiation at 130 °C during 3 hours. After
having confirmed that the presence of water has a beneficial
effect on the yield of this domino transformation (Table 1, entry
2), we turned our attention to the influence of the catalytic
system. To do so, we have decided to use Pd(OAc)2 as
palladium source in addition to diverse phosphines.
Monophosphine ligands such as PPh3 and SPHOS led to similar
results to Pd(PPh3)4 (Table 1, entries 3 & 4). The use of a more
hindered ligand like P(Cy)3 resulted in a dramatic decrease of the
conversion and the desired product 8a was obtained in only 12%
yield (Table 1, entry 5). The use of a more electron donating
phosphine ligand as P(2-furyl)3 led to product 8a in 34% yield
with the rest of the reaction mixture mainly remaining as starting
material (Table 1, entry 6). Remarkably, bisphosphine ligands
such as BINAP or Xantphos drove the reaction to a complete
inversion of selectivity as product 8a’ was exclusively obtained
in good yields (Table 1, entries 7 & 8).
1
Pd(PPh3)4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K2CO3
Na2CO3
Cs2CO3
K3PO4
K3PO4
K3PO4
Na2CO3
Na2CO3
Na2CO3
Na2CO3
2-MeTHF/H2O
2-MeTHF
52 (1:0)
40 (1:0)
57 (1:0)
50 (1:0)
12 (1:0)
34 (1:0)
78 (0:1)
80 (0:1)
55 (1:0)
26 (1:0)
45 (1:0)
63 (1:0)
06 (1:0)
32 (1:0)
52 (1:0)
68 (1:2)
73 (2:1)
78 (1:0)
2
Pd(PPh3)4
3
Pd(OAc)2/PPh3
Pd(OAc)2/SPhos
Pd(OAc)2/P(Cy)3
Pd(OAc)2/P(Furyl)3
Pd(OAc)2/Binap
Pd(OAc)2/Xantphos
Pd(OAc)2/PPh3
Pd(OAc)2/PPh3
Pd(OAc)2/PPh3
Pd(OAc)2/PPh3
Pd(OAc)2/PPh3
Pd(OAc)2/PPh3
Pd(OAc)2/PPh3
Pd(OAc)2/PPh3
Pd(OAc)2/PPh3
Pd(OAc)2/PPh3
2-MeTHF/H2O
2-MeTHF/H2O
2-MeTHF/H2O
2-MeTHF/H2O
2-MeTHF/H2O
2-MeTHF/H2O
2-MeTHF/H2O
2-MeTHF/H2O
2-MeTHF/H2O
Toluene/H2O
4
5
6
7
8
9
10
11
12
13
14
15
16[b]
17[b, c]
18[b, d]
MeCN/H2O
1,4-dioxane/H2O
1,4-dioxane/H2O
1,4-dioxane/H2O
1,4-dioxane/H2O
1,4-dioxane/H2O
[a] The reactions were performed under argon using Pd complex (10 mol%),
ligand when required (20 mol%), base (3 equiv.), phenyl boronic acid (1.5
equiv.), silane 7a (1 equiv.) at 0.1 M concentration in the indicated solvent. [b]
Addition of TBAI (25 mol%). [c] Reaction performed at 100 °C. [d] Reaction
performed at 70 °C.
Ph Ph
Si
We can then hypothesize that the use of BINAP or Xantphos
decreases dramatically the kinetics of the transmetallation with
the coupling partner and so favors the competition with the β-
elimination of the palladium species. This hypothesis is
supported by the result of a control experiment that consisted of
setting up the reaction without any coupling partner. In that case
the compound 8a’ was obtained in 76% yield as the sole
product. These observations support that the success of this
approach lies on the overall domino process (i.e. cyclocarbo-
palladation/Suzuki-Miyaura reaction). According to Keese’s
experimental observations and ours, the most probable
hypothesis for the formation of compound 8a’ is based on the
attack of an hydroxide ion on the silicon that results in the
opening of the silacycle coming from the carbopalladation step
and the β-elimination of the palladium (II) complex (Scheme 2).
Si
Si
R
n-pent
n-pent
Br
Br
Br
R
7a R = n-pentyl
7b R = (CH2)3Ph
7c R = Ph
7e R = F
7f R = OMe
7g
Ph
7d R = p-MeO-Ph
Si
Si
n-pent
n-pent
Br
7h
Br
7i
Figure 2. Substrates synthesized to study the domino reaction.
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substituted with an aryl group the yield decreased significantly.
For instance, substrates 7c and 7d, bearing a phenyl and a p-
methoxyphenyl respectively, were submitted to the domino
sequence and the corresponding products 8i and 8j were
reached in 52% and 42% yields, respectively. Next, we focused
on the effect of substitution on the benzyl moiety worn by the
silicon. Pleasingly, the presence of an electron-withdrawing
group such as fluorine at the position 5 of the aromatic ring
(substrate 7e) did not impact the efficiency of the reaction and
the targeted vinylsilanes 8k and 8l were obtained in comparable
yields to those obtained with an unsubstituted benzyl group
(respectively 74% and 55%). Interestingly, the electron-rich
subtrate 7f, bearing a methoxy group, led efficiently to the
desired vinylsilane 8m in a slightly lower yield (63%). Finally,
the influence of the substituents on the silicon atom has been
investigated. When performed on substrate 7g bearing two
phenyl groups, the reaction led only to traces of the
corresponding silacycle 8n. However, this issue was easily
overcome by using Pd(PPh3)4 as catalyst and 8n was obtained
in a good 66% yield. Unfortunately, substrate 7h bearing a
siletane did not convert to the targeted spirocyclic product 8o.
OH
HO
Si
Si
R
R
R
Si
Br
R
H2O
Base
[Pd]II
[Pd]0
Br -
7
8’
Scheme 2. Potential mechanism for the formation of 8’ from silane 7.
In followup studies, we decided to turn our attention to the
effects of the base under our optimal conditions to date (i.e.
Pd(OAc)2/PPh3,130°C, 2-MeTHF/H2O as solvent). Substituting
K3PO4 by K2CO3 appeared to have no effect on the yield and the
selectivity of the reaction (table 1, entry 9), whereas the use of
Na2CO3 or Cs2CO3 gave the desired compound in yields
reduced by 30% and 10%, respectively (Table 1, entry 10 & 11).
We then focused our attention on the effects of the solvent.
When the reaction was performed in toluene, the desired
compound was obtain selectively in a respectable 63% yield
(Table 1, entry 12). The use of acetonitrile yielded only traces of
compound 8a’ and starting material 7a was mainly degradated
(Table 1, entry 13). 1,4-dioxane was then tested and resulted in
only a modest 32% yield of 8a (Table1, entry 14). Remarkably,
in this solvent, when the base was shifted from potassium
phosphate to sodium carbonate, the yield of 8a increased by
20% (52%, Table 1, entry 15). The use of an additivie such as
TBAI increased the yield by 15% but with a clear erosion of the
selectivity in favor of the desilylated product 8a’ (8a/8a’ 1:2)
(Table 1, entry 16). Lowering the reaction temperature to 100°C
allowed for an equivalent yield but with a complete inversion of
selectivity in favor of the desired silacyclic product (8a/8a’ 2:1)
(Table 1, entry 17). Finally, our best result was obtained when
the reaction was performed with Pd(OAc)2/PPh3 as catalyst,
sodium carbonate as base in a mixture of water in 1,4-dioxane
at 70°C. In that case compound 8a was obtained selectively in a
synthetically useful 78% yield after 18 h (table 1, entry 18).
The reaction led only to
a degradation of the starting
Table 2. Scope of the domino carbopalladation/Suzuki-Miyaura coupling
sequence.[a]
Si
Si
Si
8b (75%)
8c (64%)
8d (63%)
O
O
O
F
CF3
Si
Si
Si
N
O
N
8e (67%)
8f (65%)
8g (66%)
With these optimized conditions in hand we then decided to
study the scope and limitations of the reaction (Table 2). For a
first time, the influence of the coupling partner was evaluated.
Toward this end, we performed the reaction by using the silane
7a as substrate in presence of various subtituted aryl boronic
acids. Pleasingly, substituting the aromatic ring of the boronic
acid with an eletron-donating group such as OCF3 group at the
para position gave the targeted benzosilole 8b in a similar 75%
yield. Notably, when (4-methoxyphenyl)boronic acid was used
as coupling partner, the efficiency of the reaction slightly
decreased and the desired product 8c was obtained in 64%
yield. When electron withdrawing groups such as a fluorine or a
nitro group were used in position 4 of the arylboronic acid the
respective benzosiloles 8d and 8e were obtained in comparable
yields (63% and 67%). The use of heteroarylboronic acids as
coupling partners did not affect the behavior of the domino
process. For instance, products 8f and 8g bearing a furyl and a
pyridyl group respectively were attained in about 65% yield. For
a second time we investigated the effects of the substitution on
the alkyne moiety. Logically, replacing the heptynyl chain by a 5-
phenylpent-1-yn-1-yl chain (substrate 7b) did not impact the
quality of the reaction as the corresponding product 8h was
obtained in a similar 68% yield. However, when the alkyne was
O
O
Si
Si
Si
N
N
N
8h (68%)
8i (52%)
8j (42%)
Si
Si
Si
F
F
O
N
N
8k (74%)
8l (55%)
8m (63%)
Si
Si
Si
N
N
8n (66%)[b]
8o (0%)
8p (64%)[c]
[a] The reactions were performed under argon at 70 °C for 18 h using
Pd(OAc)2 (10 mol%), PPh3 (20 mol%), Na2CO3 (3 equiv.), TBAI (0.25 equiv.),
boronic acid (1.5 equiv.), silane 7 (1 equiv.) at 0.1 M concentration in the
indicated solvent; [b] Pd(PPh3)4 as catalyst; [c] Reaction performed at 90°C.
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COMMUNICATION
Drugs 2004, 13, 1149 – 1157; b) A. K. Franz, S. O. Wilson, J. Med.
Chem. 2013, 56, 388 – 405.
material. Presumably, this can be explained by the specific
reactivity of strained silacycles when brought into contact with
palladium complexes.[17] Finally, when substrate 7i, bearing a
silicon centre linked to four different substitutents, was submitted
to our optimal reaction conditions, no traces of the desired
product 8p were detected but increasing the temperature to
90°C allowed us to reach this vinylsilane in a 64% yield.
[4]
For recent relevant applications of silacycles in medicinal chemistry and
chemical biology please see: a) B. Seetharamsingh, R. Ramesh, S. S.
Dange, P. V. Khairnar, S. Singhal, D. Upadhyay, S. Veeraraghavan, S.
Viswanadha, S. Vakkalanka, D. S. Reddy, ACS Med. Chem. Lett. 2015,
6, 1105–1110 ; d) X.-P. He, Y. Zang, T. D. James, J. Li, G.-R. Chen, J.
Xie, Chem. Commun. 2017, 53, 82-90.
[5]
[6]
G. A. Showell, J. S. Mills, Drug Discovery Today 2003, 8, 551 – 556.
Reviews on silacycle synthesis see: a) J. Hermanns, B. Schmidt, J.
Chem. Soc., Perkin Trans. 1 1998, 2209-2230; b) J. Liu, S. Zhang, W.
Zhang, Z. Xi, Progress in Chemistry 2009, 1475-1486 ; c) review on the
synthesis of benzosiloles: B. Wu, N. Yoshikai, Org. Biomol. Chem.
2016, 14, 5402–5416.
In conclusion, an unprecedented synthesis of cyclic vinylsilanes
bearing an exocyclic fully substituted carbon-carbon double
bond has been developed. This approach is based on the first
examples of palladium-catalyzed domino reaction involving a
cyclocarbopalladation of (o-bromobenzyl)alkynylsilanes. This
transformation is tolerant to a broad range of substitutions both
on the silylalkyne and the aryl coupling partner. The overall
domino process appeared to be essential to avoid a competitive
migration of the alkynyl moiety. At the present time our group is
extending this methodology to the synthesis of other families of
silacycles and the results of these investigations will be reported
in due course.
[7]
Selected recent methodologies for silacycle synthesis: a) Y. Liang, W.
Geng, J. Wei, Z. Xi, Angew. Chem. Int. Ed. 2012, 51, 1934–1937; b) K.
Kubota, H. Iwamoto, E. Yamamoto, H. Ito, Org. Lett. 2015, 17, 620–
623; c) L. Mistico, O. Querolle, L. Meerpoel, P. Angibaud, M. Durandetti,
J. Maddaluno, Chem. Eur. J. 2016, 22, 9687–9692; d) H. Arii, Y. Yano,
K. Nakabayashi, S. Yamaguchi, M. Yamamura, K. Mochida, T.
Kawashima, J. Org. Chem. 2016, 81, 6314–6319; e) M. Ahmad, A.-C.
Gaumont, M. Durandetti, J. Maddaluno, Angew. Chem. Int. Ed. 2017,
56, 2464-2468.
[8]
For reviews on cyclocarbopalladation in domino sequences see: a) S.
Blouin, G. Blond, M. Donnard, M. Gulea, J. Suffert, Synthesis 2017, 49,
1767-1789; b) A. Düfert, D. B. Werz, Chem. Eur. J. 2016, 22, 16718–
16732; c) H. Ohno, Asian J. Org. Chem. 2013, 2, 18–28 ; d) T. Vlaar, E.
Ruijter, R. V. A. Orru, Adv. Synth. Catal. 2011, 353, 809–841 ; e) A. de
Meijere, P. von Zezschwitz, S. Bräse, Acc. Chem. Res. 2005, 38, 413–
422.
Acknowledgements
The authors are grateful to the Centre National de la Recherche
Scientifique (CNRS) and the Université de Strasbourg for
financial support. Philippe Golema is acknowledged for
preliminary investigations. M.D. sincerely thanks the leading
committee of the Laboratoire d’Innovation Thérapeutique (UMR
7200) for its support and confidence.
[9]
The synthesis of stereodefined tetrasubstituted C=C double bonds
represents a real challenge especially when exocyclic. For a review on
this topic see: A. B. Flynn, W. W. Ogilvie, Chem. Rev. 2007, 107,
4698–4745.
[10] For a review on the synthesis of vinylsilanes see: D. Lim, E. Anderson,
Synthesis 2012, 44, 983–1010.
Keywords: silacycle • carbopalladation • domino • vinylsilane •
[11] For a relevant example using a silyl-ether substrate see: M. Leibeling,
D. B. Werz, Beilstein J. Org. Chem. 2013, 9, 2194-2201.
palladium
[12] K. Ouyang, Y. Liang, Z. Xi, Org. Lett. 2012, 14, 4572–4575.
[13] Z. Teng, R. Keese, Helv. Chim. Acta 1999, 82, 515–521.
[14] For recent investigations on Suzuki-Miyaura reaction mechanism see:
a) C. Amatore, A. Jutand, G. Le Duc, Chem. Eur. J. 2011, 17, 2492-
2503; b) B. P. Carrow, J. F. Hartwig, J. Am. Chem. Soc. 2011, 133,
2116-2119; c) C. Amatore, A. Jutand, G. Le Duc, Chem. Eur. J. 2012,
18, 6616-6625; d) A. A. Thomas, S. E. Denmark, Science 2016, 352,
329-332.
[1]
For relevant examples see: a) B. Z. Tang, X. Zhan, G. Yu, P. P. S. Lee,
Y. Liu and D. Zhu, J. Mater. Chem. 2001, 11, 2974–2978; b) X. Zhan,
C. Risko, F. Amy, C. Chan, W. Zhao, S. Barlow, A. Kahn, J.-L. Brédas,
S. R. Marder, J. Am. Chem. Soc. 2005, 127, 9021–9029; c) H.-Y. Chen,
J. Hou, A. E. Hayden, H. Yang, K. N. Houk, Y. Yang, Adv. Mater. 2010,
22, 371–375; d) M. Driess, M. Oestreich, Chem. Eur. J. 2014, 20,
9144–9145.
[15] For representative examples see: a) G. Blond, C. Bour, B. Salem, J.
Suffert, Org. Lett. 2008, 10, 1075-1078; b) M.-C. A. Cordonnier, S. B. J.
Kan, B. Gockel, S. S. Goh, E. A. Anderson, Org. Chem. Front. 2014, 1,
661-673.
[2]
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10.1002/chem.201701736
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Patrick Wagner, Mihaela Gulea, Jean
Suffert, and Morgan Donnard*
Page No. – Page No.
Synthesis of Benzo[c]silole
Derivatives Bearing a
Tetrasubstituted Exocyclic C=C
Double Bond by Palladium-Catalyzed
Domino Reactions.
Silicon prefers to play dominos. The synthesis of diversely substituted
benzo[c]silole derivatives via an unprecedented domino sequence involving the
cyclocarbopalladation of an internal silylalkyne is reported. This reaction proceeds
with a complete stereoselectivity to lead to a fully substituted exocyclic C=C double
bond. Notably the domino sequence appears to be crucial to the success of this
approach.
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