The bifunctional catalytic efficacy
of alumina-supported gold nanoparticles
(Au/Al
2
O
3
) was investigated for the synthesis
of a series of 2-amino-3-aryl-imidazopyridines through the chemoselective
reduction of the corresponding 2-nitro-3-aryl-imidazo[1,2-
a
]pyridines in high isolated yields. This highly efficient
protocol was initially applied for the synthesis of 2-nitro-3-aryl
imidazo[1,2-
a
]pyridines via the reaction between
2-aminopyridine and nitroalkenes catalyzed by the present catalytic
system Au/Al
2
O
3
. Moreover, the heterogeneous
surface γ-Al
2
O
3
was also found to catalyze
this pathway in a comparable manner. However, only Au/Al
2
O
3
was further proved as the appropriate catalytic system
for the selective transfer hydrogenation of the synthesized 2-nitro
imidazopyridine derivatives into the corresponding 2-amino-3-aryl
imidazo[1,2-
a
]pyridines using NaBH
4
as
a hydrogen-donor molecule. In addition, the one-pot two-step reaction
between nitroalkenes and aminopyridines in the presence of Au/Al
2
O
3
–NaBH
4
provided directly the
fast and facile synthesis of 2-amino-3-aryl imidazopyridines, highlighting
a useful synthetic application of the catalytic protocol.
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