New and simple one-step cobalt-catalyzed preparation of functionalized arylstannanes from the corresponding aryl bromides or iodides

Article abstract of DOI:10.1039/b417326k

The process for the preparation of functionalized arylstannanes from the corresponding aryl bromides or iodides was described. The corresponding arylstannane was detected by gas chromatography using an internal standard alkane. The two-step coupling react

Full text of DOI:10.1039/b417326k

View Article Online / Journal Homepage / Table of Contents for this issue
C O M M U N I C A T I O N
New and simple one-step cobalt-catalyzed preparation of
functionalized arylstannanes from the corresponding aryl bromides
or iodides
Corinne Gosmini* and Jacques Pe´richon
Laboratoire d’Electrochimie, Catalyse et Synthe`se Organique, UMR 7582, Universite´ Paris
12-CNRS, 2 Rue Henri Dunant, 94320, Thiais, France. E-mail: gosmini@glvt-cnrs.fr;
Fax: 01 4978 1148; Tel: 01 4978 1139
Received 22nd September 2004, Accepted 15th November 2004
First published as an Advance Article on the web 7th December 2004
A variety of functionalized arylstannanes are obtained
in moderate to excellent yields by a one-step chemical
procedure from corresponding halides and tributylstannyl
chloride via cobalt catalysis.
to enhance the yield of the organozinc species and decrease
the formation of the byproducts, especially ArH. After the
formation of the organozinc compound, 1 equiv. of Bu3SnCl
was added to the solution at room temperature. The mixture
was stirred for 30 min. Hydrolysis with NH4Cl followed by
diethyl ether extraction gives crude arylstannane in good yields.
Purification by column chromatography (silica gel, pentane)
gives the arylstannanes in 80% yield.
It seemed interesting to develop a convenient method for
the one step synthesis of arylstannanes from aryl bromides or
iodides. This procedure follows the protocol already described
but after the usual preliminary step of 5 min of stirring with
0.3 equiv. of allyl chloride, the aryl halide (1 equiv.) and the
tributylstannyl chloride are added simultaneously in acetonitrile
at room temperature. The mixture is stirred until total con-
sumption of the aryl bromide is achieved. The corresponding
arylstannane is detected by GC using an internal standard
(alkane). An inert atmosphere is not required. If the medium
is heated at 50 ◦C after introduction of ArBr and Bu3SnCl, the
reaction proceeds faster and similar results are obtained (eq. 2).
The Stille coupling of aromatic rings requires the formation
of arylstannanes.1 This arises from the growing availability of
organostannanes, their broad spectrum of tolerated functional
groups and their stability towards moisture and air. The most
common procedure is generally the transformation of an aryl
halide to an organometallic reagent (Grignard,2 lithium3 or
zinc4) and its reaction with trialkylstannyl chloride R3SnCl
(R = Me or Bu) which yields the corresponding arylstannane.
However, the main difficulty with this method is the preliminary
preparation of the organometallic reagent when the aromatic
ring bears reactive functional substituents (COR, CN. . .).
Alternatively, some functionalized arylstannanes can be directly
prepared from aromatic halides by palladium catalyzed reaction
of an excess of hexabutylditin with aryl halides ArX (X = Br,
I).5 Recently and given the growing interest of arylzinc species
in chemical synthesis, a convenient method for the preparation
of aromatic organozinc species has been discovered in our
laboratory.6 The versatility and simplicity of the original method
are based on the direct activation of aryl bromides or iodides
by low-valent cobalt(I) species arising from the reduction of
cobalt(II) halide by zinc dust in acetonitrile.
In the course of our work on the cobalt-catalyzed preparation
of organometallic compounds, the current paper deals with a
method of preparation of functionalized arylstannanes from
the corresponding arylzinc species. In fact, arylzinc species can
neither be stored for a long time nor isolated. Furthermore,
they have to be rapidly engaged in coupling reactions after
their formation to avoid the formation of the symmetrical
biaryl due to the presence of the cobalt in solution. We first
verified that the two-step coupling reaction of aryl bromides and
tributylstannyl chloride led to corresponding arylstannanes at
room temperature without further addition of a catalyst (eq.1).
1)AllylCl 0.3 eq
CH CN, CF CO H
2
3
3
CoBr2 + Zn −−−−−−−−→ ArSnBu3
(2)
2)ArBr 1 eq
Bu SnCl 1.1 eq
3
◦
50
C
0.1eq 1.5eq
We consequently applied this method to various aromatic
bromides or iodides bearing electron-donating or electron-
withdrawing groups in the para, meta and ortho series. The
resulting products have been isolated and results are reported
in Table 1.
Table 1 One-step synthesis of arylstannanes from ArX (X = Br, I) at
50 ◦
C
Aryl bromide
Reaction time/h
Isolated yield (%)a of ArSnBu3
1)AllylCl 0.3 eq
4-MeOPhBr
4-MeOPhI
2-MeOPhBr
3-MeOPhBr
4-(Me)2NPhBr
4-ClPhBr
2-EtOCOPhBr
4-EtOCOPhBr
4-MeCOPhBr
4-F3CPhBr
4-HCOPhBr
2-NCPhBr
0.5
0.5
1
1.5
4
1.5
1.5
1
2
24
1
1
1
96
CH CN, CF CO H
2
3
3
Bu SnCl 1 eq,r.t.
3
CoBr2 + Zn −−−−−−−−→ ArZnBr −−−−−−−→ ArSnBu3 (1)
78 (Ar–Ar = 20%)
2)ArBr 1 eq
82
85
61
63
88
90
78
56
66
60
75
96
0.1 eq 1.5eq
The behaviour of our arylzinc compounds, synthesized via
cobalt catalysis in acetonitrile, towards Bu3SnCl is similar
to traditional behaviour. For example, p-MeOC6H4SnBu3 and
p-EtOCOC6H4SnBu3 have been readily synthesized in two
step sequences from the corresponding aryl bromides and
Bu3SnCl, using the reaction conditions detailed elsewhere for
the preparation of ArZnBr: 0.1 equiv. of CoBr2, 1.5 equiv.
of zinc dust activated by 50 ll of trifluoroacetic acid and a
1.5 M aryl bromide concentration. Prior to the addition of aryl
bromide in acetonitrile, a 5 min preliminary step was carried out
using 0.3 equiv. of allyl chloride (3 equiv. vs. cobalt) in order
3-NCPhBr
4-NCPhBr
0.6
a Based on initial ArX. All products gave satisfactory 1H, 13C NMR and
mass spectra.
2 1 6
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 6 – 2 1 7
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

View Article Online
These results show that this original method gives the expected
arylstannane in good to excellent yields. The byproduct is only
the reduction product in the case of aryl bromides, contrary
to the two-step procedure where the homocoupling product is
detected in small amounts. With more reactive compounds such
as aromatic iodides, the homocoupling product is also formed
in the one-step procedure. However, as already described in the
formation of the arylzinc species formed by cobalt catalysis in
acetonitrile, no organostannanes could be detected from the
chlorobenzene which did not react. This confirms that Co(I) is
not reactive towards aryl chloride. Then, bromochlorobenzene
led to the mono arylstannane (4-ClPhSnBu3). It can be pointed
out that the position of the substituent has again a slight
influence on the yields as revealed in the cases of bromoanisole
or bromobenzoate (except in the case of bromobenzonitrile).
In the following series of experiments, we have tried to apply
this method to heteroaromatic halides. Unfortunately, results
were disappointing with bromopyridines and bromothiophenes
at 50 ◦C. All the reactant was converted into the reduction
compound with bromopyridine or 2-bromothiophene. In the
case of 3-bromothiophene, poor yields were obtained under
these conditions (28%). However, the thienylstannane can be
generated from 2 and 3-bromothiophenes in good to excellent
yield when the reaction is conducted at room temperature. The
stannane species are obtained in 45 and 80% yield, respectively.
2-Thienyl bromide, which is more reactive, gives a large amount
of the reduction product. However, bromopyridines always led
to the reduction product even if the reaction was carried out
at room temperature. This last behaviour was expected and is
consistent with the fact that these products are not converted
into the corresponding zinc species.
In summary, we have established that readily available cobalt
halide, zinc dust and tributyl stannyl chloride are convenient for
the facile preparation of arylstannanes from the corresponding
aryl bromides (or iodides) in acetonitrile. The transmetalation
between arylzinc species formed in the medium and tributyl
stannyl chloride occurs in a single operation and makes this new
chemical method an excellent alternative to classical routes.
References
1 J. K. Stille, Angew. Chem., Int. Ed. Engl., 1986, 25, 508; V. Farina, Pure
Appl. Chem., 1996, 68, 73; P. Espinet and A. M. Echavarren, Angew.
Chem., Int. Ed., 2004, 43, 4704.
2 T. Hayashi and M. Ishigedani, Tetrahedron, 2001, 57, 2589.
3 C. Earbon and G. Seconi, J. Chem. Soc., Perkin Trans. 2, 1976, 925;
B. Iddon and B. L. Lim, J. Chem. Soc., Perkin Trans. 1, 1983, 271; H.
Gilman and S. D. Rosenberg, J. Am. Chem. Soc, 1953, 2507.
4 P. Knochel and R. D. Singer, Chem. Rev., 1993, 93, 2117; X. Zhu, B. E.
Blough and F. I. Caroll, Tetrahedron Lett., 2000, 41, 9219.
5 M. Kosugi, K. Shiminu, A. Ohtani and T. Migita, Chem. Lett., 1981,
829; M. Kosugi, T. Ohya and T. Migita, Bull. Chem. Soc. Jpn., 1983,
56, 3855.
6 H. Fillon, C. Gosmini and J. Pe´richon, J. Am. Chem. Soc., 2003,
125, 3867; I. Kazmierski, C. Gosmini, J. M. Paris and J. Pe´richon,
Tetrahedron Lett., 2003, 44, 6417.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 6 – 2 1 7
2 1 7