Chemistry Reference
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[RuCl
2
(p-cymene)]
2
(2.5 mol%)
Cs
2
CO
3
(3 equiv), Preligand (5 mol%),
NMP (2mL), 10-20h, 120 °C
Ar
Ar
+
Ar-Br
N
N
1mmol
2 mmol
N
Cl
N
Me
preligand =
Me
MeO
Ph
MeO
Me
Scheme 12.73 Ortho-arylation of 2-phenylpyridine using NHC ligand.
[RuCl
2
(C
6
H
6
)]
2
(5 mol%)
KOPiv (20 mol%)
K
2
CO
3
, solvent, 2-100 °C
Het
Het
Het
+
Het-X
+
N
N
N
S
S
N
S
N
N
N
N
N
N
Me
Me
Me
so lvent
1%
2%
99%
98%
0
100%
H
2
O
62%
38%
NMP
Scheme 12.74 Ortho-arylation of 2-phenylpyridine in water.
the reaction system was found to be compatible with both aryl chlorides and
aryl tosylates.
115,116
Changing the halide partner to tosylate also allowed for better control
of product ratios. Aryl chlorides formedbis-arylatedproduct,whereas
tosylates gave mono-arylated products preferentially. Notably, despite
their increased accessibility and economic advantages, tosylates have not
been used much as coupling partners owing to their decreased reactiv-
ity.
131
Among transition metals, palladium with some unique electron-rich
ligand system is known to react with tosylates. For instance, DPPF ligand
has been used for C-N bond formation even with heterocyclic tosy-
lates.
132,133
In this respect, a few other well-known ecient ligands are
XPhos, SPhos, etc.
134
¨
zdemir and co-workers discovered the NHC complex of Ru
II
for the
arylation of 2-phenylpyridine
in the presence of
carbonate base
(Scheme 12.73).
117
Dixneuf and co-workers later showed that the same reaction can be carried
out in water and better selectivity is shown for diarylation in water than the
organic solvent NMP.
135
Under these conditions, pivalate was found to be a
better ligand than acetate. The reaction proceeds even in the absence of
KOPiv, but less eciently (Scheme 12.74).
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