Chemistry Reference
In-Depth Information
OMe
MeO
OH
Br
[R h( CO D)
2
Cl] (10 mol%)
P(NMe
2
)
3
(30 mol%)
Cs
2
CO
3
(1.7 equiv)
toluene, reflux,18h
OH
+
a
OMe
MeO
OH
OMe
1.5 equiv
b
combined yield 62%
a:b = 50:3
OMe
Scheme 12.59 Rh-catalyzed ortho-arylation of unsubstituted phenol using P(NMe
2
)
3
as ligand.
Ph
[Rh(COD)
2
Cl](2.5mol%)
P(NMe
2
)
3
(20mol%)
K
2
CO
3
(2 equiv)
Cs
2
CO
3
(2 equiv)
toluene, 100 °C, 20h
Br
Me
OH
Me
OH
Me
OH
+
+
Ph
Ph
63%
22%
Scheme 12.60 Rh-catalyzed ortho-arylation of substituted phenol using P(NMe
2
)
3
as
ligand.
Me
OH
Me
Br
[Rh(COD)Cl]
2
(5 mol%)
ClP
i
Pr
2
(10 mol%)
Cs
2
CO
3
(1.7 equiv)
toluene, reflux, 18h
Me
OH
Me
Me
Me
Me
+
Me
Me
Me
91%
1.2 equiv
Me
Me
OH
Br
[Rh(COD)Cl]
2
(5 mol%)
ClP
i
Pr
2
(10 mol%)
Cs
2
CO
3
(1.7 equiv)
toluene, reflux, 18h
OH
Me
+
Me
Me
Me
2equiv
26%
Scheme 12.61 Rh-catalyzed ortho-arylation of phenols with a chlorophosphine
ligand.
12.3.3 C-H Functionalization Without Chelating Mechanism
Heteroarenes without a pendent directing group were arylated using Rh in
2004 by Bergman and co-workers.
90
Aryl iodides were used as the coupling
partner in the presence of a catalytic amount of [Rh(coe)
2
Cl]
2
and PCy
3
lig-
and. A variety of nitrogen- and oxygen-containing heteroarenes underwent
arylation with good to moderate yields (Scheme 12.62).
90
An N-heterocyclic carbene (NHC) resulting from the tautomerization of
nitrogen-containing heteroarenes was proposed as a plausible intermediate.
In the catalytic cycle, the benzimidazole substrate coordinates to the metal
center, forming an Rh
I
-NHC complex, which oxidatively combines with the
aryl iodide. Finally, arylated heteroarene and HI are released via reductive
elimination (Figure 12.17).
90
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