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Ph-I
Pd(OAc)
2
(2.5 mol%)
PPh
3
(10 mol%)
125°C
Ph
H
MeMgCl / TMEDA
61%(C3 :C2=14 :1)
N
N
Mg
H
dioxane, 65°C
Cl
Ph
N
125°C
Ph-B r
Pd(OAc)
2
(2.5 mol%)
IMes (2.5 mol%)
N
H
96%(C3 :C2=67 :1)
Scheme 4.46 C3 arylation of indole.
NN
Mes
Mes
NN
NN
N
Adm
Mes
Adm
Mes
NN
Cl
Pd
Cl
O
Mes
Pd(I
2
)PPh
3
Mes
Pd(I
2
)PPh
3
N
N
Pd(I
2
)PPh
3
70a
70b
70c
70d
Figure 4.32 Precatalysts studied for the direct arylation of SEM-protected azoles.
comparison with the Pd-PPh
3
system and bromobenzene gave better results
than iodobenzene (Scheme 4.46).
They then studied the arylation of SEM-protected azoles.
146
The activities
of four different catalysts exhibiting different steric and electronic properties
(70, Figure 4.32) were probed in the reaction between SEM-protected indoles
and iodobenzene. Precatalyst 70d was the most active in the coupling.
However, because its synthesis was low yielding, the scope of the reaction
was studied using 70a, the second most active precatalyst. The reaction oc-
curred at 125 1C in DMA in the presence of CsOAc as the base. Catalyst
loadings ranged from 0.15 to 5 mol%. Thus, a range of N-containing het-
erocycles were selectively arylated in various positions and globally in good
yields. Iodides were found to be better coupling partners than bromides
(Scheme 4.47).
In 2010, Sames and co-workers also investigated the reactivity of complex
70a for the C5 arylation of SEM-protected imidazoles.
147
The complex was
active, but less ecient than the system combining Pd(OAc)
2
and P(nBu)Ad
2
(Scheme 4.48).
In 2006, Sanford and co-workers developed a system for the selective C2
arylation of indoles at room temperature.
148
The reaction took place in AcOH
using 5 mol% of [Pd(IMes)(OAc)
2
] as the precatalyst (Scheme 4.49). In this
case, no aryl halide was used in the reaction. Instead, a hypervalent iodine
salt was used as the arylating agent. The reaction proceeded smoothly under
mild conditions (r.t.-60 1C), affording the expected 2-arylated indoles in
good yields. Two examples of pyrroles were also reported.
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