462
HETEROCYCLES
N
H
NH 2
phenylhydrazine
O
Me
Me
N
H
N
Me
a phenylhydrazone
H
H
N
N
Me
H
H
N
N
Me
H
H
NH 2
N
Me
H
H
N
Me
NH 2
H
H
N
Me
NH 3
H
N
Me
H
tautomerism
to enamine
cyclic
rearrangement
tautomerism to
enamine (aromatic
amine)
nucleophilic attack of
amine onto imine
(or iminium cation)
− NH 3
elimination
of ammonia
N
H
NH 2
Me
O
Me
H
reagents
Unfortunately, the reaction fails with acetaldehyde
and cannot, therefore, be used to synthesize indole
itself. It is possible to use the ketoacid pyruvic acid
instead and decarboxylate the product to yield indole.
N
H
NH 2
O
Me
CO 2 H
pyruvic acid
N
CO 2 H
H
N
H
− CO 2
heat
indole
HETEROCYCLES
N
H
NH 2
phenylhydrazine
O
Me
Me
N
H
N
Me
a phenylhydrazone
H
H
N
N
Me
H
H
N
N
Me
H
H
NH 2
N
Me
H
H
N
Me
NH 2
H
H
N
Me
NH 3
H
N
Me
H
tautomerism
to enamine
cyclic
rearrangement
tautomerism to
enamine (aromatic
amine)
nucleophilic attack of
amine onto imine
(or iminium cation)
− NH 3
elimination
of ammonia
N
H
NH 2
Me
O
Me
H
reagents
Unfortunately, the reaction fails with acetaldehyde
and cannot, therefore, be used to synthesize indole
itself. It is possible to use the ketoacid pyruvic acid
instead and decarboxylate the product to yield indole.
N
H
NH 2
O
Me
CO 2 H
pyruvic acid
N
CO 2 H
H
N
H
− CO 2
heat
indole