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P. 211
Novel
compounds
containing
1,3,4--oxadiazole…
2.1.3.
Synthesis
of
Mannich
bases
containing
[1,3,4]
oxadiazole
and
pyrazol--3
one
nuclei
(IX)
a. 5--methyl--
4--(4|--substituted
phenyl
hydrazono)--2--(5--thioxo--[1,3,4]
oxadiazole--2--yl--methyloxyphenyl)--2,4--dihydro--pyrazol--3--one
(VIII)
A
mixture
of
V
(19.9
g,
0.1
mol),
KOH
(5.5
g,
0.1
mol),
ethanol
(100
mL)
and
carbon
disulphide
(6.02
mL,
0.1
mol)
was
refluxed
in
a
water
bath
till
the
evolution
of
hydrogen
sulphide
is
ceased.
The
excess
of
alcohol
was
removed
by
distillation.
The
reaction
mixture
was
cooled
to
room
temperature,
poured
into
ice
cold
water
and
neutralized
with
dilute
hydrochloric
acid.
The
precipitate
so
formed
was
filtered,
washed
with
water,
dried
and
recrystallized
from
ethanol--dioxane
mixture
(1:1)
to
give
VIII.
b. 5--methyl--4--(4|--substituted
phenyl
hydrazono)--2--[5--thioxo--4--
[alkyl/phenyl/heterocyclic
amino
methyl]--4,5--dihydro--[1,3,4]
oxadiazol--
2--yl--methyl]--2,4--dihydro--pyrazol--3--ones
(IX)
A
mixture
of
VIII
(0.01
mol)
in
ethanol
and
dioxane
(20
mL)
was
treated
with
formaldehyde
(40%,
1.5
mL).
Appropriate
amine
(0.01
mol)
in
ethanol
(10
mL)
was
added
to
the
reaction
mixture
and
stirred
over
night.
The
precipitated
Mannich
base
was
filtered,
dried
and
recrystallized
from
ethanol--DMF
mixture
(1:1).
The
reaction
sequence
is
outlined
in
Scheme
3.
R NH N CH3 EtOH R NH N CH3
O N O N
KOH + CS2 N
N
(V) H (VIII) N
R O C N NH2 O NH
O O S
EtOH - dioxane /
HCHO
NH N CH3 R NH N CH3
O N R1R2NH / EtOH O N
N N
(VIII) N (IX) N R1
O NH R2
O N N
OS
OS
NHR1R2
=
morpholinyl,
piperazinyl,
N--methylpiprazinyl;
R1
=
--H,
R2
=
p--Tolyl,
p--anisyl,
p--
fluorophenyl,
p--chlorophenyl,
p--bromophenyl,
p--nitrophenyl;
R1
=
R2
=
ethyl
or
phenyl.
Scheme
3.Synthesis
of
Mannich
bases
containing
[1,3,4]
oxadiazole
and
pyrazol--3--one
moiety.
205
