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FriedelЦCrafts -Silylvinylations.

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[7] Cyclophane 3c was synthesized according to Diederich et al.: S B. Ferguson,
E. M. Sanford, E. M. Seward, F. Diedench, 1 Am. Chem. SOC.1991,113,54105419.
181 Aggregation constants were determined by ' H N M R spectroscopy in DLO at
298 K in the concentration range 1 0 ~ 2 - 1 0 ~ 5 ~ .
191 Several photochemically interesting rotaxanes have been investigated: a) D. B.
Amahilino, P. R. Ashton. V. Balzani, C. L. Brown, A Credi, J. M J. Frechet.
J. W. Leon. F. M. Raymo. N. Spencer, J F Stoddart, M. Venturi, J Am. Chem
Sot. 1996. / / a , 12012-12020; b) N. Solladie, J.-C. Chamhron, C. 0. DietrichBuchecker. J.-P. Sauvage, Angew. Chem. 1996.108.957-960; Angew Chen?.Inr
Ed. EngI. 1996.35.906-909; c) A. C. Benniston, A. Harriman, V. M. Lynch. J
Am Chrm Soc. 1995, 117. 5275-5291; d ) J.-C Chambron, A Harriman. V
Heitz. J:P. Sauvage, ihid. 1993,115. 6109-6114; e) P. L. Anelli, P. R. Ashton.
R. Ballardini. V. Balzani, M. Delgado. M. T. Gandolfi. T. T. Goodnow, A. E
Kaifer. D Philp. M. Pietraszkiewicz. L. Prodi, M. V. Reddington, A. M. 2
Slawin. N Spencer, J. F. Stoddart. C. Vicent, D. J. Williams. ibid. 1992, 114,
193--2 I X
0
1) GaCI,
+
HCECSiMe,
2) MeLi
3) HzO
R
R
$I
"I
+
[51
76%,49%[b], 41%[c]
54%[a]
59%
Me
Friedel- Crafts P-Silylvinylations**
L-1
Masahiko Yamaguchi,* Yoshiyuki Kido,
Akio Hayashi, and Masahiro Hirama
68%
59%
57%
Me
Me
The Friedel Crafts reaction is a fundamental method for
converting aromatic C - H bonds to C - C bonds. Although
Friedel-Crafts alkylations and acylations are often used in organic synthesis, the corresponding vinylations have not been
successful. Attempts at vinylation using either ethyne o r vinyl
halides have given polymeric substances and 1,1-diarylethanes,
even when the arenes are present in large excess."] This is due to
the instability of the vinylated products under the reaction conditions. Even 2-propenylations gave very low yields, and formed
various by-products.Iz1 Low efficiency in generating the electrophilic species may be another reason why the electrophilic
vinylations failed. We report here the Friedel- Crafts (E)-asilylvinylation of aromatic hydrocarbons promoted by GaC1,
This reaction is a direct C,-olefination of arenesr3]that proceeds
via novel organogallium intermediates.
An aromatic hydrocarbon (1 equiv) and trimethylsilylacetylene (3 equiv) were treated with GaCl, (3 equiv) in a mixture of methylene chloride and methylcyclohexane at - 78 "C.
After 30 min, methyllithium (9 equiv) in ether was added, and
the (E)-[(p-trimethylsilyl)vinyl]arene was obtained by aqueous
workup (Scheme 1). The C - C bond was formed at the a-carbon
atom of the silylacetylene, and the (E)-configuration of the
product was determined by 'H NMR spectroscopy. When only
one equivalent of silylacetylene and GaC1, were used the yield
was much lower. The regioselectivity of the aromatic substitution indicates an electrophilic mechanism,[41and is consistent
with the low reactivity of chlorobenzene, which can be used as
solvent. Steric factors are also important. F o r example, 2,6dimethylnaphthalene reacted a t C-4 rather than at the most
reactive position (C-I), and a considerable amount of 2-vinylated product was obtained from naphthalene. The electrophilic
species involved in this reaction appears to be considerably
~
[*I Prof. Dr M. Yumaguchi. Y Kido
Faculty of Pharmaceutical Sciences, Tohoku University
Aoba. Sendai 980-77 (Japan)
Fax: Int. code +(22)217-6811
Dr. A. Hayashi. Prof. Dr. M. Hirdma
Department of Chemistry. Graduate School of Science
Tohoku University. Sendai (Japan)
[**I This work was \upported by a Grant-in-Aid for Scientific Research from the
Ministry of Education. Science, Sports and Culture. Japan (no. 07554065 and
08404050). We also thank the Shin-Etsu Chemicals Co. Ltd for the generous
gifts of silicon reagents.
AnKen. C h m
Inr.
ELI Engl. 1997, 36, N o . 12
C
67%
58%
Me
53%[a,d], 36%[c]
41%[a,d]
T
50%
51%
Scheme 1. GaCI,-promoted /J-silylvinylations of arenes. The reaction sites on the
starting materials are marked with arrows; the relative regioselectivity in each case
is given in square brackets. [a] Yield determined by gas chromatography.
[b] Reaction in chlorobenzene. [c] Molar ratio GaC1,:acetylene:arene =
1 0:l.O: 1.0. [d] Molar ratio GaC1,:acetylene:arene = 2.0:2.0-1.0
bulky. Unlike previously reported Friedel - Crafts vinylations
and alkenylations,['.
this reaction does not require excess
arene. Therefore, nonvolatile polycyclic arenes can be /-isilylvinylated without the necessity to carry out the tedious separation of a large amount of unconverted starting materials.
There was very little divinylation and isomer formation under
the present reaction conditions. Triethylsilyl- and tertbutyldimethylsilylacetylene reacted analogously with rn-xylene
to give the corresponding products in yields of 54 and 5 2 % ,
respectively. When I-methylnaphthalene was treated with
GaCl, and ethyne at - 78 "C, the arene was consumed within
30min to give a polymeric compound. Thus, the silyl group
prevents the olefin group on the products from undergoing side
reactions.
The (8-silylviny1)arenes are useful synthetic intermediates for
a variety of aromatic compounds (Scheme 2). For example, the
trimethylsilyl group can be removed by trifluoroacetic acid to
give the parent vinylarene, and epoxidation followed by treatment with an acid gives an aryla~etaldehyde,[~]
which can be
reduced to a n arylethanol.
The use of GaC1,[61in these /I-silylvinylations is critical; other
Lewis acids (AlCl,, GaBr,, InCI,, SnCl,, SbCl,, SbF,), protic
acids (CF3S03H, HCI), and heterogeneous acids (Na-Mont-
VCH Wrlugsgesell.whoft mbH. 0-69451 Weinheim. 1997
0570-0833/97/3612-1313 $ 1 7 SO+ .SO'O
1313
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Me
P a
H-CGC-SIR,
Me
CF3C02;
Me
Me
86%
p
I
,SiR3
H
Ga -
GaCI,
1)cF&o2H,
A
2) NaBH,
Me
85%
,SiR,
(+I
\ I
H-C=C \ @SiMe3
p
‘c=c
B
c13
Me
Me
b
62%
Scheme 2. Examples of reactions of (~-silylvinyl)arenes.
Me
Me
morillonite, Sn-Montmorillonite, Montmorillonite K 10) were
not effective. Methylene chloride and chlorobenzene are the
preferred solvents, since they dissolve arenes at low temperatures. The methyllithium added prior to the aqueous quench can
be replaced by methylmagnesium bromide or diethylzinc. However, the yields vary substantially with subtle changes in the
workup procedures if the treatment with the organometallic
compound is omitted. When D,O was added after methyllithium, the (P-silylviny1)arenewas deuterated at the olefinic p-carbon atom (Scheme 3). Such deuteration did not take place when
/o
Me
1) GaCI,
+
HCECSiEt,
2) MeLi
m
Me H
S i E
t
Me
C
MeLi
1
R
6 = 149.17
Me
E
Me
3
D
=
SiMe2Bu
v
d/-siR’
Me
Me
b
Me D
Me
+
DCECSiEt,
Me
+
2) MeLi Me
3) H20
CD3
>95%D
1) GaCI,
‘QD+
D
HCECSiEt,
D
CD,
Scheme 4. Proposed mechanism of the GaC1,-promoted ~-silylvinylationof mxylene.
1) GaCI,
CD, u
w
S
i
E
t
3
2) MeLi
3)H20
D
CD3
Scheme 3. GaC1,-promoted P-silylvinylations of arenes with deuterated starting
materials or reagents.
the olefinic product was treated with methyllithium followed by
D,O either in the presence or in the absence of GaC1,. These
observations can be explained by formation of a (a-gallio-8sily1vinyl)arene. Methyllithium probably converts the GaCl,
group to a GaMe, group, which facilitates the protonation of
the organogallium intermediate. When a deuterated silylacetylene was used, the cc-carbon atom was deuterated. The
olefin group was not deuterated with [D,,lp-xylene as substrate.
The high reactivity of the electrophilic vinylating reagent is
clearly evident from the rapid reaction at a low temperature
without the use of excess arenes. We assume that a GaC1,-complexed silylacetylene is formed. The formation of a vinyl cation
by protonation of the silylacetylene with HGaCl, does not explain the results of the deuteration experiments. Furthermore,
the addition of 2,6-di(tert-butyl)-4-methylpyridine (0.3 equiv)
did not interfere with the reaction. Therefore, the mechanism
may be summarized as followed (Scheme 4): The activated silylacetylene, presumably either the open vinyl cation A or the
bridged cation B, is attacked by m-xylene at the P-carbon atom.
The resulting organogallium intermediate, the p-gallio-(/?si1ylvinyl)areniumcation C or the (p-gallio-a-silylviny1)arene D,
1314
VCH l/erlugsgesellschaft mhH. 0-69451 Weinheim. 1997
is then methylated, and the (P-silylviny1)arene is obtained by
protonation. The intermediate E was detected by NMR spectroscopy ([DJTHF): the olefin proton appeared as a singlet at
b =7.71, which disappeared on the addition of water. Its ( Z ) configuration was deduced by NOE studies.
GaC1, promotes alkenylation as well as 8-silylvinylation. For
instance, when tert-butylacetylene was treated with m-xylene
and GaC1, followed by methyllithium and D,O, a P-deuterated
rx-(tert-buty1)styrenederivative was obtained (Scheme 5). Since
Scheme 5. GaC1,-promoted alkenylation of m-xylene with tert-butylacetylene.
the reaction with [D,,lp-xylene did not lead to deuteration of the
olefin moiety, the mechanism of the alkenylation must be similar to that of the a-silylvinylation. The regioselectivity can be
ascribed to the ability of the substituents to stabilize the cations
in the electrophilic intermediates rather than to steric reasons.
Stabilization of the $cation by the silyl groupL7]is substantial in
the intermediate A and B, while the terr-butyl group stabilizes
the cc-cation. Notably, trans-addition occurred with tert-butylacetylene, and cis-addition with silylacetylene, although the
origin of the stereoselectivity is unclear at present. Vinyl cations
stabilized by a p-silicon group have attracted a great deal of
interest over the last few years.[*]However, their reactivity, particularly C-C bond-forming reactions, has received little atten-
0570-0833/97j3612-1314$17.50+ SOj0
Angew Chem In:. Ed. Engl. 1997,36, No. 12
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tion because of the very rapid desilylation to give acetylenic
compounds. The electrophilic activation of silylacetylenes genIt is therefore notable that the
erally results in sub~titution.[’~
formation of a C-C bond at the P-silicon-stabilized vinyl cation
can take place giving addition products. Thus, the chemistry of
this extremely reactive electrophilic vinylating reagent promises
to be very interesting.
In summary GaCl, promotes the C,-olefination of aromatic
hydrocarbons with silylacetylenevia novel organogallium intermediates. Organogallium compounds have received much less
attention in organic synthesis than organoaluminum compounds.[’] although both contain an element from group 13.
Thus, the strong activation of n compounds by GaCl, is a new
very promising approach to organogallium chemistry.
Experimental Section
Under an argon atmosphere, a 1 . 0 stock
~
solution of GaCI, in merhylcyclohexane
(3.0mL) was added to a solution of m-xylene (107 mg, 1.0mmol) in CH,CI,
(10 mL) at - 78 C. Trimethylsilylacetylene (295 mg, 3.0 mmol) in methylcyclohexane ( 1 .O mL) was then added, and the mixture was stirred for 30 min. Methyllithium
in diethyl ether, 6.5 mL) was added, and the mixture was stirred for
( 1 . 4 solution
~
another 30 min at - 78 “C. Aqueous workup gave (E)-l-(2-trimethylsilylethenyl)2.4-dimethylbenzene (155 mg, 76%).
Received: November 11. 1996
Revised version: February 17, 1997 [Z9752IE]
German version: Angew. Chem. 1997, 109, 1370-1372
Keywords: Friedel -Crafts reactions
- gallium - silicon
[ I ] R. Anschutz, Ann Chem. 1886, 235, 150, 299; 0. W. Cook, V. J. Chambers,
L Am. Chem. SOC.1921, 43, 334; J. S . Reichert, J. A. Nieuwland, ibid. 1923, 45,
3090; J. A. Reilly, J. A. Nieuwland, ibid. 1928,50,2564; I. P. Tsukervanik, K. Y
Yuldashev, J. G m . Cheni. USSR 1961, 3f, 790.
[2] 1. P. Tsukervanik, K Y. Yuldashev, J. Gun. Chem. USSR 1%3,33, 3429; A. G.
Martinez. R. M Alvarez. A. G. Fraile, M. Hanack, L. R. Subramanian, Chem.
Ber. 1987, 120. 1255.
[3] We recently reported the direct vinylation reaction of phenols: M. Yamaguchi,
A. Hayashi, M . Hirama, J. Am. Chem. SOC.1995, 117, 1151.
[4] See for example. C. C. Price, Org. Reacr. 1946, 3, 1; E. Berliner, &id. 1949, 5 ,
229; J B Kim. C. Chen. I. K. Krieger, K. R. Judd, C. C. Simpson, E. Berliner,
J. Am. Chrm. Soc. 1970, 92, 910.
[5] G. Stork. E. Colvin. J. Am. Chem. SOC.1971, 93. 2080.
[6] GaCI, has been used In some Friedel-Crafts alkylations: F. P. Dehaan, H. C.
Brown. L Am. Chem. SOC.1969,Yf. 4844, F. P. Dehaan, H. C. Brown, J. C. Hill,
ihid. 1969, 91. 4850.
[7] See for example- “Activating and directive effects of silicon”: A. R. Bassindale,
P. G. Taylor in The Chemistry of Organic Silicon Compounds (Eds.: S . Patai, 2.
Rappoport), 1989, Wiley, chapter 14, p. 893.
[8] H.-U. Siehl. E-P. Kaufmann, Y Apeloig, V. Braude, D. Danovich, A. Berndt,
N. Stamatis, AnFew. Chem. 1991,103,1546; Angew. Chem. Int. Ed. Engl. 1991,
30, 1479; G. K. S . Prakash, V. P. Reddy, G. Rasul, J. Casanova, G . A. Olah,
J. Am. Chem. Soc. 1992, f14,3076; C. Dallaire, M. A. Brook, Organomefallics
1993.12,2332: V Gabelica. A. J. Kresge,J Am. Chem. Sac. 1996,118,3838,and
references therein.
191 J. J. Eisch, J. Am. Chrm. Sor. 1962, 84, 3830.
Angeu. Chem. In,. Ed. EngI. 1997, 36, No. 12
0 VCH
Liquid-Crystal Templates for Nanostructured
Metals**
George S. Attard,* Christine G. Goltner,*
Judith M. Corker, Susanne Henke, and Richard
H. Templer
A rapidly developing new trend in materials science i s the
transfer of structure from surfactant aggregates to inorganic
solids.“ - 3 1 In water, surfactants aggregate into micelles or, at
higher concentrations, into lyotropic liquid-crystalline phases.
Despite their beauty, lyotropic mesophases have so far not been
utilized for their structure, but only for their properties (for
example in shampoos), because these ordered aggregates readily
undergo phase changes as a result of dynamic exchange processes.
Surfactant aggregates are, however, useful templates for the
synthesis of inorganic nanostructures. For example, the synthesis of ordered mesoporous ceramic oxides involves the use of
ionic surfactants as structure-directing additives in precipitation
processes.[41A more recent approach to mesoporous ceramic
oxides makes use of lyotropic liquid crystals as structure-directing bulk media.f51Here the sol-gel synthesis of inorganic ceramic oxides (for example silicates) is conducted in the aqueous
domains of the microphase-separated medium; hence a cast of
the liquid-crystalline phase is produced. In this way, different
nanostructures have been obtained from the H,, Ia3d, and L,
mesophase.[61 The generation of nanostructures from bulk
lyotropic mesophases is not restricted to sol - gel processes such
as the production of silicates; precipitation processes can also be
carried out without loss of long-range order.[’] Pileni et al. have
reported the generation of metal nanoparticles in surfactant
solutions or lamellar lyotropic liquid crystals. Here metal particles are produced with a high degree of control over shape and
size,@]but the particle morphology cannot be correlated with
the ordered structure of the liquid-crystalline phase.
Our aim was to apply the bulk liquid-crystal template method
to the generation of ordered, porous metal nanostructures and
to show that lyotropic liquid crystalline phases are versatile
media for nanostructure design. A mesoporous metal can be
expected to have advantages over classical metal colloids with
respect to stability and handling. In particular we show that the
reduction of platinum salts dissolved within the aqueous domains
of a hexagonal (H,) mesophase leads to platinum whose nanostructure is a cast of the liquid-crystalline phase architecture.
We employed hexachloroplatinic acid (HCPA) and ammonium tetrachloroplatinate (ATCP) as the platinum source. The
lyotropic liquid-crystalline phases were prepared from
C,,(EO), (octaethyleneglycol monohexadecyl ether), because
y ] Dr. G S . Attard, Dr. J. M. Corker
Department of Chemistry
University of Southampton
Southampton S0171BJ (UK)
Fax. Int. code +(1703)593781
e-mail- gza&soton.ac.uk
Dr. C. G. Goltner. DiplLChem. S . Henke
Max-Planck-Institut fur Kolloide und Grenzflachen
Kantstrasse 55, D-14513 Teltow (Germany)
Fax: Int. code +(3328)46204
e-mail: goeltner@mpikg-teltow.mpg.de
Dr. R. H. Templer
Department of Chemistry. Imperial College
London SW72AZ (UK)
[**I We are indebted to the Director of the Daresbury Laboratory for access to
facilities. We also thank Dr. E. Schaaf for carrying out the TGA measurements.
This work was supported by the UK Engineering and Physical Sciences Research Council
VerlagsgeselischaftmbH, D-6Y451 Weinheim, 1997
0570-0833lY7/3612-13lS$17.50+ SO10
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