Chemistry Reference
In-Depth Information
Pd(OAc)
2
(ref 55) or CuI (ref 54)
Heterocyclearene
C-2 arylation
N
Het
N
H
Y
Y
(Y=O,NR)
[RhCl(CO)
2
]
2
(ref 56)
C-2 arylation
ArBr
Me
N
Ar
Me
N
H
O
NHAr
O
NHAr
Pd(OAc)
2
/PCy
3
(ref 51)
ArBr
Ar
directed C-3 arylation
H
N
N
Pd(OAc)
2
(5 mol%)
phen (15 mol%)
Cs
2
CO
3
,140
H
R
1
non-directed C-3
arylation
R
R
1
+
°
C
R
N
X
N
Scheme 12.31
Selective arylation in the pyridine ring.
C-H activation
I
H
OAc
Pd
IV
OAc
O
N
N
PhI
H
Pd
L
N
Pd
II
N
H
3
C
N
O
N
Ph
N
Ph
N
coordination
OAc
H
trans
effect
H
Pd
II
N
N
OAc
OAc
OAc
N
I
Cs
2
CO
3
H
Pd
II
N
Pd
II
N
N
N
N
H
Pd
OAc
CsI
AcOH
H
N
N
N
Figure 12.11 Mechanism of non-directed C3 arylation.
H
H
H
H
3
3
3
4
5
N
N
N
H
H
N
N
N
H
H
pyrazole
2H Indazole
1H Indazole
C3 (2H)>>C3 (1H)
C5>C4>>C3
Figure 12.12 Reactivity pattern of pyrazole and indazole.
of Pd around different positions of pyridine. Notably, the C3 position is
statistically favored as two equivalent carbons are available. Thus, proper
orientation between the p-system of the pyridine ring and Pd leads to C-H
bond cleavage.
Other than pyridines, site-selective direct arylations of indazoles, 1,2,3-
triazole (C5),
61
thiophene (C2),
62
benzothiophene (C5),
62
pyrrole (C5),
62,63
thiazole (C2, C4 and C5),
62,64
oxazole, benzoxazole (C2),
65
imidazole (C5)
62
and pyrazoles have also been reported (Figure 12.12).
66
In particular,
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