LETTER
1137
Palladium-Catalyzed Coupling Reaction of Alkenylgalliums with Aryl Halides
P
alladium-Cat
a
alyze
d
Cou
t
pling R
o
eaction shi Mikami, Hideki Yorimitsu, Koichiro Oshima*
Department of Material Chemistry, Graduate School of Engineering, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
Fax +81(75)7534863; E-mail: oshima@fm1.kuic.kyoto-u.ac.jp
Received 16 February 2002
yield. Moreover, the use of Pd2(dba)3 CHCl3 (1.0 mol%)
Abstract: Treatment of aryl halides with alkenylgallium dichlor-
and (o-tolyl)3P (4 mol%) improved the yield of 3a (94%).
ide, prepared from GaCl3 and alkenylmagnesium bromide, in the
presence of a catalytic amount of palladium provided cross-coup-
1-(1-Methylethenyl)-3-methoxybenzene 4a was produced
as byproduct in 6% yield.4
ling products in good yields.
Key words: alkenylgallium, coupling reaction, aryl halide, palladi-
um
Table 1 Effect of Ligand on the Coupling Reaction in the Presence
of Pd2(dba)3 CHCl3
OMe
GaCl2
Many organometallic reagents, including magnesium,
3a
OMe
1a
aluminium, boron, silicon, zinc, and tin compounds, have
proven to be highly useful for the transition-metal cata-
lyzed cross-coupling reaction with alkenyl halides and
aryl halides.1 Among them, organoboron compounds have
been extensively studied because of their unique reactivi-
ties and easy accessibility and handling.2 In contrast, the
related reaction of gallium compounds are not yet well de-
veloped,3 although boron and gallium belong to the same
group in the periodic table. Here we wish to describe pal-
ladium-catalyzed cross coupling reaction of alkenylgalli-
um with aryl halides bearing several functional groups.
0.5 mol% Pd2(dba)3•CHCl3
THF/DMSO
+
+
OMe
I
4a
2a
Yield
Liganda
none
3a (%)
54
16
60
54
8
4a (%) 2a (%)
-
34
71
24
38
80
59
40
20
-
n-Bu3P
-
Alkenylgallium compounds were prepared from gallium
trichloride and the corresponding alkenylmagnesium bro-
mides in THF. We picked up the reaction of 3-iodoanisole
(2a) with 1-propenylgallium (1a) as a model reaction
(Scheme 1). At first the effect of cosolvent on the reaction
of 1a with 2a in the presence of a catalytic amount of
PdCl2(PPh3)2 was studied. Cosolvents employed (THF–
cosolvent = 1:3) and the yields of the coupling product 3a
are as follows: without cosolvent, 14%; HMPA, 18%;
NMP, 33%; DMF, 32%; DMSO, 45%. Thus, DMSO gave
the highest yield of 3a among many cosolvents.
(c-C6H11)3P
4
7
-
Ph3P
(2,4,6-trimethoxyphenyl)3P
[3,5-bis(trifluoromethyl)phenyl]3P
(2-furyl)3P
26
45
71
94
32
11
9
-
3
3
6
-
(o-tolyl)3P
(o-tolyl)3Pb
Pd/C
60
80
78
91
45
cat.
Pd
+
I
Ph2PCH2PPh2
Ph2PCH2CH2PPh2
Ph2P(CH2)3PPh2
Ph2P(CH2)4PPh2
-
GaCl2
OMe
OMe
1a
2a
3a
-
Scheme 1
4
-
Next
we
examined
several
ligands,
using
37
5
Pd2(dba)3 CHCl3 as a precatalyst for the reaction of 1a
with 2a in a mixed solvent THF–DMSO. The results are
shown in Table 1. Among many monodentate and biden-
tate phosphine ligands examined, (o-tolyl)3P gave the best
result and the coupling product 3a was obtained in 71%
a The amounts of ligands were 2 mol% for monodentate ligands and 1
mol% for bidentate ligands. b Pd2(dba)3 CHCl3 (1.0 mol%) and
(o-tolyl)3P (4 mol%) were used.
Having optimized reaction conditions in hand, we exam-
ined a variety of aryl iodides and bromides bearing several
functional groups in the coupling reaction with alkenyl-
gallium dichloride as shown in Table 2. Several com-
ments are worth noting. (1) Aryl iodides having electron-
Synlett 2002, No. 7, 01 07 2002. Article Identifier:
1437-2096,E;2002,0,07,1137,1139,ftx,en;Y06002ST.pdf.
© Georg Thieme Verlag Stuttgart · New York
ISSN 0936-5214