Chemistry Reference
In-Depth Information
[RhCl(C
2
H
4
)
2
]
2
(5 mol%)
P[
C
HC
Ar
p-
(CF
3
)C
6
H
4
]
3
(20 mol%)
TEMPO (4 equiv)
dioxane/
t
BuOH (10/1)
9h, 130 °C
+
ArB(OH)
2
N
N
4equiv
S
S
OEt
N
N
Ph
Ph
N
Ph
EtO
+
N
N
50%
18%
87%
82%
32%
Scheme 12.55 Rh-catalyzed N-atom-directed C-H arylation using TEMPO as
oxidant.
C
N
ArB(OH)
2
Ar
L
2
Rh
I
TEMPO
(TEMPO)B(OH)
2
L
L
2
Rh
I
Ar
C
L(OPMET)ArRh
II I
2TEMPO
N
TEMPOH
L
2
(TEMPO)
2
Rh
III
Ar
HC
L(TEMPO)
2
ArRh
III
N
N
HC
L
Figure 12.15 Rh-catalyzed direct C-H arylation using TEMPO as oxidant.
thiophene ring. For 2-phenylpyridine, again mono- and diarylation were
observed (Scheme 12.55).
It was proposed that TEMPO oxidizes the L
2
Rh
I
Ar species to
L
2
(TEMPO)
2
Rh
III
Ar with the generation of TEMPO anion. This TEMPO anion
act as a base and promotes base-assisted C-H activation. A successive re-
ductive elimination was proposed to account for the formation of the desired
arylated product and regeneration of Rh species (Figure 12.15).
83
Furthermore, in the case of Rh-catalyzed direct arylation, acid
chlorides
84
and acid anhydrides
85
were also used as coupling partner. In
2008, Zhao and Yu reported the C-H arylation of benzo[h]quinoline with a
variety of acid chlorides in the presence of
[Rh(COD)Cl]
2
as catalyst
(Scheme 12.56).
84
It was suggested that acid chlorides, after a successive oxidative addition
and decarbonylation, form an arylRh
III
chloride species, which is respon-
sible for the direct C-H arylation of benzo[h]quinoline. The same reaction
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