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O
O
OH
[Pd(MeCN)
4
](BF
4
)
2,
L, AMS
O
2,
NMP,50°C, 3-8 h
+DMSO
80°C, 24-48 h
Ar
Ar
65-96%
54-84%
O
SO
3
Na
N
N
MeO
OMe
L
O
AMS
Scheme 9.151
Synthesis of 3-arylphenols via deborylative Heck reaction.
Ph
Ph
Ph
BF
3
K
Cu(OTf)
2,
phen
MnO
2,
DCE , 105°C, 24 h
+
Ph
Ph
85%
Scheme 9.152 Copper(II)-assisted Heck-like alkylation of alkenes'
CO
2
Et
SiMe
2
OH
Pd(OAc)
2
(1 0 mol%)
Cu( OAc)
2,
LiOA c
DMF, 100°C, 44 h
CO
2
Et
n-C
6
H
13
n-C
6
H
13
52%
Scheme 9.153 Example of a desilylative alkenylation reaction.
non-organometallic Pd(II) complexes, organoboron compounds do not need
activation by base. What about organosilicon compounds?
Unfortunately, so far too few data exist. Organosilicon compounds are
more often used in the regular Mizoroki-Heck reaction, where organosilicon
residues compete with hydrogen in the elimination, bringing forward the
problem of selectivity.
419
Organosilicon compounds were shown to take part in oxidative Heck re-
actions by Mori and co-workers,
420
who used silanols, compounds which are
known not to require activation by fluoride to take part in transmetallation
with organopalladium species, which is taken advantage of in a special
cross-coupling method (the Hiyama-Denmark reaction).
421
The transme-
tallation with more reactive Pd(II) complexes takes place readily to allow the
oxidative Heck procedure, which was performed either stoichiometrically in
a very simple system containing only Pd(OAc)
2
or using a cupric salt as
terminal oxidant (Scheme 9.153).
The reactions were rather slow and gave modest yields. A rhodium-cata-
lysed version of this reaction was discovered,
421
but no more interest in the
method was evident for many years.
This underexplored method was recently revisited by Cheng and co-
workers, who used trimethoxysilanes, which are easily activated by fluoride
anion to enter the Heck process using 1,10-phenanthroline as ligand and
AgF as both reoxidant and fluoride source.
422
The method was applicable not
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