a copper catalyst. This method was quite impressive since palladium-based catalytic systems failed to produce compound 11 [14].
4 CuI/L-Proline/[Bmim][BF 4 ] Ionic Liquids with
Aryl/Heteroaryl Bromides
Room temperature ionic liquids (RTILs) are a class of nonmolecular ionic solvents.
The intrinsic properties of RTILs such as low vapor pressure, high polarity,
solubility of metal salts, and reusability have made them more attractive candidates
for solvents in the last two decades [15]. Bao et al. reported the use of RTILs in C–N
bond forming reactions of aryl/heteroaryl bromides with imidazoles and
benzimidazoles using a combination of CuI and L-proline at 105–115
C in the
presence of K 2 CO 3 to give the coupled products in good yields. They found the use
of RTILs, for example, [Bmim]BF 4 gave slightly improved yields over bench top
organic solvents (Table 1).
The scope of the method was thoroughly explored using a variety of aryl
bromides with imidazole, and the selected examples are listed in Table 2. In most
cases, good yields of products were obtained, except in the case of o-substituted
N
NH
O
OH
Benzolactam V8
HN
CO 2 H
HO 2 C
N
tBu
(intermediate for
SB-214857)
1
2
CO 2 H
OH
N
H
I
(intermediate for
martinellic acid)
3
NH OH
(intermediate for
iprodione)
4
N
N
(intermediate for
Linezolid)
5
O
O
O
OTHP
N
(intermediate for
Toloxatone)
6
O
O
OTHP
N
(intermediate for
Isooncinotine)
7
N
O
O
OBn
( )
6
8
NBoc
(intermediate for
U86192)
Br
MeO
Br
NH 2
9
N
CF 3
H 2 N
(intermediate for
AMN107)
N
N
O
HO
10
(intermediate for
AG3433)
11
F
N
O
O
Ph
NHPr
O
Fig. 1 Selected precursors for biologically important molecules involving copper-catalyzed C–N
formation
122
M.L. Kantam et al.