A Novel Regio- and Stereoselective Formal Cross-Coupling Reaction of Unsaturated Silanes with Arenediazonium Tetrafluoroborates

Full text of DOI:10.1021/jo9912451

1554
J . Org. Chem. 2000, 65, 1554-1557
Alkenylsilanes are absent among the array of organo-
metallic compounds used in palladium-catalyzed cross-
coupling reactions with arenediazonium salts. Actually,
Kikukawa and co-workers reported a palladium-cata-
lyzed aryldesilylation of alkenylsilanes by arenediazo-
nium salts,10 but the lack of regio-and stereospecificity
in this reaction is more compatible with an addition-
elimination mechanism rather than with a cross-coupling
process.
A Novel Regio- a n d Ster eoselective F or m a l
Cr oss-Cou p lin g Rea ction of Un sa tu r a ted
Sila n es w ith Ar en ed ia zon iu m
Tetr a flu or obor a tes
Francesco Babudri, Gianluca M. Farinola,
Francesco Naso,* and Daniela Panessa
Centro CNR di Studio sulle Metodologie Innovative di
Sintesi Organiche, Dipartimento di Chimica,
On the other hand, it is known that unsaturated
silanes cannot be easily subjected to palladium-catalyzed
cross-coupling reaction because of the low reactivity of
the silicon-carbon bond toward transmetalation. The
difficulty of performing these reactions with simple
trimethylsilyl compounds has been stressed,11 and the
use of alkenyl-fluoro or -alkoxysilanes in the presence of
fluoride ion12 is required in the reaction with unsaturated
organic halides. More recently, (E)- and (Z)-1-alkenyl-1-
methylsilacyclobutanes have been employed in stereospe-
cific cross-coupling reactions with aryl iodides in mild
conditions.13
In our previous work,14 we overcame the drawback of
the poor reactivity of trimethylsilyl derivatives disclosing
a novel and efficient protocol for the formal cross-coupling
reaction of alkenyl and polyenyl silanes with aryl or vinyl
halides consisting of an ipso-borodesilylation with boron
trichloride and subsequent in situ palladium-catalyzed
coupling reaction of the resulting boron derivative with
organic halides. The overall procedure, described in
Scheme 1, represents a formal Suzuki-Miyaura cross-
coupling reaction starting with unsaturated silanes.
In this paper we report our work dealing with the use
of alkenylsilanes as starting materials for an efficient,
formal Geneˆt cross-coupling reaction with arenediazo-
nium salts.
Universita` di Bari, via Amendola 173, 70126 Bari
Received August 5, 1999
In tr od u ction
Palladium-catalyzed cross-coupling reactions between
organometallic reagents and electrophilic aromatic part-
ners represent a powerful synthetic tool for carbon-
carbon bond formation.1 Besides aryl halides and tri-
flates, arenediazonium salts have been employed as
electrophiles for palladium-catalyzed cross-coupling reac-
tions with stannyl derivatives.2 Related processes also
involving arenediazonium salts are represented by pal-
ladium-catalyzed reactions with alkenes,3 or with germyl
derivatives,4 carboxylation,5 formylation,6 and carbony-
lation7 reactions.
Recently, Geneˆt and co-workers8 have reported the
cross-coupling reaction between arenediazonium tet-
rafluoroborates and aryl or alkenyl boronic acids8a or
potassium trifluoroborates8b in the presence of catalytic
amounts of palladium(II) acetate. The process appears
of special interest since it occurs under mild conditions
and in the absence of both base and ligand. After the
work of the Geneˆt group, similar results involving boronic
acids have been reported also by Sengupta and Bhatta-
charyya.9
Resu lts a n d Discu ssion
* To whom correspondence should be addressed.
(1) Farina, V. In Comprehensive organometallic chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford,
1995; vol. 12, pp 161-240. Naso, F.; Marchese, G. In The chemistry of
functional groups, supplement D: The chemistry of halides, pseudo-
halides and azides; Patai, S., Rappoport, Z., Eds.; New York: Wiley,
1983; pp 1353-1449. Naso, F. Pure Appl. Chem. 1988, 60, 79.
(2) Kikukawa, K.; Kono, K.; Wada, F.; Matsuda, T. J . Org. Chem.
1983, 48, 1333.
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Ku¨hlein, K. Tetrahedron Lett. 1994, 35, 8773. Sengupta, S.; Bhatta-
charyya, S. J . Chem. Soc., Perkin Trans. 1 1993, 1943. Sengupta, S.;
Sadhukhan, S. K.; Bhattacharyya, S.; Guha, J . J . Chem. Soc., Perkin
Trans. 1 1998, 407. Yong, W.; Hongwen, H.; Zhuangyu, Z. Synthesis
1991, 967. Kikukawa, K.; Nagira, K.; Wada, F.; Matsuda, T. Tetrahe-
dron 1981, 37, 31. Kikukawa, K.; Meamura, K.; Kiseki, Y.; Wada, F.;
Matsuda, T. J . Org. Chem. 1981, 46, 4885. Akiyama, F.; Miyazaki,
H.; Kaneda, K.; Teranishi, S.; Fujiwara, Y.; Abe, M.; Taniguchi, H. J .
Org. Chem. 1980, 45, 2359. Brunner, H.; Le Cousturier de Courcy, N.;
Geneˆt, J . P. Tetrahedron Lett. 1999, 40, 4815.
Alkenylsilanes 1a -c and (1E,3E)-1,4-bis(trimethylsi-
lyl)-1,3-butadiene 1d were subjected to reaction with
boron trichloride in methylene chloride solution to per-
form the easy ipso-borodesilylation described above. After
removal of the solvent, the intermediates deriving from
the transmetalation step were used directly in a cross-
coupling procedure, adding the solvent (dioxane), pal-
ladium acetate as the catalyst, and diazonium tetraflu-
oroborates 2a -e to the crude product. The results,
reported in Table 1 (entries 1-8), clearly show that, in
contrast with the direct aryldesilylation of vinylsilanes
(10) Kikukawa, K.; Ikenaga, K.; Wada, F.; Matsuda, T. Chem. Lett.
1983, 1337. Kikukawa, K.; Ikenaga, K.; Wada, F.; Matsuda, T. J .
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L.; Demoute, J . P.; Geneˆt, J . P. Bull. Soc. Chim. Fr. 1996, 133, 1095.
b) Darses, S.; Geneˆt, J . P.; Brayer, J . L.; Demoute, J . P. Tetrahedron
Lett. 1997, 38, 4393. Darses, S.; Michaud, G.; Geneˆt, J . P. Tetrahedron
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1989, 45, 5621.
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(14) (a) Farinola, G. M.; Fiandanese, V.; Mazzone, L.; Naso, F. J .
Chem. Soc. Chem. Commun. 1995, 2523. (b) Babudri, F.; Farinola, G.
M.; Fiandanese, V.; Mazzone, L.; Naso, F. Tetrahedron 1998, 54, 1085.
(c) Naso, F. In Current Trends in Organic Chemistry; Scolastico, C.,
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10.1021/jo9912451 CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/11/2000

Notes
J . Org. Chem., Vol. 65, No. 5, 2000 1555
Sch em e 1
Exp er im en ta l Section
Silica gel 60 (particle size 0.040-0.063) for flash column
chromatography and aluminum sheets with silica gel 60 F254
for TLC were used. GC analyses were performed on a gas
chromatograph equipped with a SE-30 (methylsilicone, 30 m ×
2) Ar-X, Pd (PPh3)4,
base, benzene
1
0.25 mm i.d.) capillary column. H NMR spectra were recorded
in CDCl3 at 500 MHz and at 200 MHz using the residual CHCl3
as the standard. To obtain reproducible results, it is recom-
mended that commercial 1 M solutions of BCl3 in methylene
chloride be stored under nitrogen in a freezer over anhydrous
Na2CO3. 1,4-Dioxane and benzene were distilled from benzophe-
none ketyl immediately prior to use. Dichloromethane was
distilled over phosphorus pentoxide immediately prior to use.
All reactions were performed under a nitrogen atmosphere.
Arenediazonium tetrafluoroborates were generally prepared
from commercial aromatic amines according to published meth-
ods.19 If necessary, the salts were purified by several recrystal-
lizations from acetone/diethyl ether and could be stored for
several weeks at -4 °C.
Sch em e 2
(E)-Stilben e (3a ). Typ ica l P r oced u r e. A 1 M methylene
chloride solution of BCl3 (2.3 mL, 2.3 mmol) was added dropwise
under a nitrogen atmosphere to a stirred solution (5 mL) of the
vinylsilane 1a (0.30 g, 1.7 mmol) in dichloromethane at 0 °C.
The reaction was monitored by GC until no more vinylsilane
was detected (a small amount of protodesilylated product was
present). After reaction completion, as detected by GC analysis
(2 h), the solvent was removed under vacuum and the residue
dissolved in anhydrous dioxane. The catalyst, Pd(OAc)2 (0.02 g,
0.089 mmol), and phenyl diazonium tetrafluoroborate 2a (0.27
g, 1.40 mmol) were then added. The resulting suspension was
stirred at room temperature for 24 h. After completion, the
reaction was quenched with water (15 mL), and the resulting
mixture was extracted thrice with ethyl acetate (3 × 15 mL).
The combined organic extracts were washed with water and
dried over anhydrous sodium sulfate, and the solvent was
evaporated at reduced pressure. The residue was purified by
column chromatography on silica gel (petroleum ether as eluent);
0.20 g (80% yield) of 3a were recovered (mp 123-124 °C from
ethanol; lit. 124-125 °C20).
with arenediazonium salts, our protocol allows a stereo-
selective and regioselective arylation of vinylsilanes af-
fording the cross-coupling products with various arene-
diazonium tetrafluoroborates, in acceptable to good yields.
The nature of the arenediazonium tetrafluoroborate
substituent does not exert a significant influence on the
reactions of these substrates: similar yields are obtained
either with electron-withdrawing (nitro) or electron-
donating (methoxy or methyl) groups.
When the methodology is extended to the bis-silylated
system 1d (entries 9-11), the cross-coupling also occurs
in a chemo- and stereoselective fashion, involving only
one of the two trimethylsilyl groups, thus providing an
alternative route to the synthesis of trimethylsilyl dienes.
The chemoselectivity of the ipso-borodesilylation process,
involving only one of the two trimethylsilyl groups of 1d ,
may be ascribed to the electron-withdrawing effect of the
boron group on the conjugated system,15 which renders
more difficult the electrophilic substitution of the second
trimethylsilyl group.
(E)-4-Bromostilbene (3b ),21 (E)-4-methylstilbene (3c),20,22
(E)-4-bromo-4′-methylstilbene (3d ),23(E)-4-methoxy-4′-methyl-
stilbene (3e),24,25(E)-4-methyl-4′-nitrostilbene (3f),26(E)-4,4′-di-
methylstilbene (3g),23 (E)-1-(2-naphthyl)-2-phenylethene (3h ),27
(1E, 3E)-1-phenyl-4-trimethylsilyl-1,3-butadiene (3i),28 (1E, 3E)-
1-(4-nitrophenyl)-4-trimethylsilyl-1,3-butadiene (3j),29 (1E, 3E)-
4-(4-methylphenyl)-1-trimethylsilyl-1,3-butadiene (3k )14b were
1
characterized comparing their physical properties and H NMR
Reactions involving arenediazonium tetrafluoroborates
containing a bromine substituent (entries 2, 4) display
high chemoselectivity, leading to bromo intermediates
which can be used in further stepwise cross-coupling
reactions. In fact, we have performed the sequential
cross-coupling reaction on 4-bromoarenediazonium tet-
rafluoroborate 2b as shown in Scheme 3. The bromo-
stilbene 3d was then allowed to couple with the styryl-
silane 1a according to our procedure,14a,b which, when
halides are involved as substrates, requires the use of a
Pd(0)-phosphine complex as catalyst. The unsymmetri-
cal distyryl derivative 4a was formed in the reaction.
spectra with those reported in the literature.
Syn th esis of 1-(4-Meth yl-tr a n s-styr yl)-4-tr a n s-styr ylben -
zen e (4a ). A 1 M dichloromethane solution of BCl3 (1.5 mL, 1.5
(15) Glogowski, M. E.; Williams, J . L. R. J . Organomet. Chem. 1981,
218, 137.
(16) Fouquey, C.; Lehn, J . M.; Maltheˆte, J . J . Chem. Soc., Chem.
Commun. 1987, 1424.
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Mu¨llen, K., Wegner, G., Eds.; Wiley-VCH: Weinheim, 1998; pp 449-
478.
(18) Harrison, M. G.; Friend, R. H. In Electronic Materials: The
Oligomer Approach; Mu¨llen, K., Wegner, G., Eds.; Wiley-VCH: Wein-
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Tiek, M., J . Am. Chem. Soc. 1991, 113, 8012.
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Chem. 1975, 96, 237.
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2 1975, 329.
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(24) Dubois, J . E.; Ruasse, M. F. J . Org. Chem. 1973, 38, 493.
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Payard, M.; Bonnafous, R.; Tisne-Versailles, J . Eur. J . Med. Chem.
1994, 29, 87.
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247.
Con clu sion s
In conclusion, our procedure opens the access to the
use of vinyl and polyenyl silanes in highly regio- and
stereoselective cross-coupling reactions with arenedi-
azonium tetrafluoroborates. Furthermore, the possibility
of employing the unsaturated silanes in sequential cross-
coupling reactions with bromoarene diazonium salts
enlarges the synthetic potential of these versatile sub-
strates. Indeed, the preparation of conjugated structures
of interest in the field of liquid crystals16 and of NLO17
and electroluminescent materials18 can be easily envis-
aged.
(27) Li, S.-W.; Zhou, Z.-L.; Huang, Y.-Z.; Shi, L.-L. J . Chem. Soc.,
Perkin Trans. 1 1991, 1099.
(28) Ni, Z.-J .; Yang, P.-F.; Ng, D. K. P.; Tzeng, Y.-L.; Luh, T.-Y. J .
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1556 J . Org. Chem., Vol. 65, No. 5, 2000
Notes
Ta ble 1. F or m a l Cr oss-cou p lin g Rea ction s of Vin ylsila n es w ith Ar en ed ia zon iu m Tetr a flu or obor a tes
a
Yields refer to purified isolated products
Sch em e 3
mmol) was slowly added under nitrogen to a stirred dichlo-
romethane solution (3 mL) of 1a (0.15 g, 0.85 mmol) at 0 °C.
After reaction completion (2 h), the solvent was removed under
vacuum and the residue dissolved in anhydrous benzene/ethanol

Notes
J . Org. Chem., Vol. 65, No. 5, 2000 1557
(2/1, 15 mL). Bromostilbene 3d (0.22 g, 0.85 mmol) and the
catalyst Pd(PPh3)4 (0.03 g, 0.026 mmol) were then added, and
the mixture was stirred for a few minutes. A 2 M solution of
NaOH (0.9 mL) was slowly dropped while stirring. The mixture
was then refluxed for 24 h until no more 3d was present (GC
analysis). The reaction was quenched with water, and the
resulting mixture was extracted with dichloromethane. The
solvent was then evaporated at reduced pressure. The crude
product 4a was purified by chromatography on silica gel
(petroleum ether/dichloromethane 6/4 as eluent) to give 0.20 g
of a white solid (78% yield), mp 276-277 °C from chlorobenzene
(lit. 276 °C30).
Scientifica e Tecnologica, Rome, by the University of
Bari (National Project “Stereoselezione in Sintesi Or-
ganica. Metodologie ed Applicazioni”), and by Consiglio
Nazionale delle Ricerche, Rome (National Project “Pro-
getto Finalizzato Materiali Speciali per Tecnologie
Avanzate II”).
Su p p or tin g In for m a tion Ava ila ble: Characterization
data are available for compounds 3i-k and 4a . This material
is available free of charge via the Internet at http://pubs.acs.org.
J O9912451
Ack n ow led gm en t. This work was financially sup-
ported by Ministero dell′ Universita` e della Ricerca
(30) Schmitt, J .; Comoy, P.; Boitard, J .; Suquet, M. Bull. Soc. Chim.
Fr. 1956, 636.