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Efficient syntheses of thiadiazoline and
thiadiazole derivatives
X
H
(CH3CO)2O
Ar
N
Ar
N
N
N
O
S
N
S
H
O
N
N
H
H
N
N
N
O
R
Y
R = C6H5 or H
R
X = COCH3
N N
O
FeCl3
Ar
S
N
N
O
R
N
H
O
Tetrahedron, 2005, November, 61, 10917-10925.
Y = COCH3 or H
3-Aryl-4-formylsydnone 4'-phenylthiosemicarbazones
and 3-aryl-4-formylsydnone thiosemicarbazones are
precursors of 3-aryl-4-heterocyclic sydnones.
S
H2N
N
N
H
H
Ar
2a
N
H
O
1a-1d
O
O
3a-3d
S
N
N
N
N
O
Ar
H2N
N
H
2b
S
H
NH2
N
N
H
H
O
S
H
Ar
N
N
N
O
3e-3h
O
N
N H
H
H
Thiosemicarbazones 3a-d reacted with acetic anhydride to
give monoacetyl-substituted thiadiazolines 5a-d and
diacetyl-substituted thiadiazolines 6a-h.
S
H
Ar
N
N
N
O
3a-3d
O
5a-5d
H
H
+
75 o C
H3C
O
CH3
O
CH3
N
S
N
N
18-20 h
4a
Ar
N
N
O
O
O
H
O
O
H
N
75
N
H
o
C
25-27 h
CH3
N
Ar
N
S
N
O
6a-6d
O
O
N
N
CH3
Figure 1. ORTEP drawing of compound 4-Acetyl-2-phenylamino-5(3-phenylsydnon-4-yl)-4,5-dihydro-[1,3,4]thiadiazole (5a).
Figure 2. ORTEP drawing of compound 4-Acetyl-2-phenylamino-5[3-(4-ethoxyphenyl)sydnon-4-yl]-4,5-dihydro-[1,3,4]thiadiazole (5d).
Figure 3. ORTEP drawing of compound 4-Acetyl-2-(N-phenylacet
amido)-5-(3-phenylsydnon-4-yl)-4,5-dihydro-[1,3,4]thiadiazole (6a).
However, thiosemicarbazones 3e-h produced
only diacetyl-substituted thiadiazolines 6e-h.
S
H
N
Ar
N
N
O
O
N
N
H
H
O
H
+
H3C
O
O
4a
3e-3h
O
H
60 o C
7-9 h
CH3
N
Ar
N
S
N
O
6e-6h
O
O
N
N
H
CH3
CH3
Figure 3. ORTEP drawing of compound 4-Acetyl-2-acetamido-5-[3(4-methoxyphenyl)- sydnon-4-yl]-4,5-dihydro-[1,3,4]thiadiazole (6g).
The mechanism of reaction of compounds 3 with acetic anhydride.
H
O
S
..
N
Ar
N
N
O
O
N
N
H
H
R
O
H3C
O
H3C
H
O
CH3
H
N
Ar
OAc
R
N
N
N
S
N
H
O
O
3a-3h
O
H
N
Ar
-HOAc
N
S
N
O
5a-5h
O
CH3
O
O
O
H
N
CH3
N
Ar
N
H
R
H3C
O
fast or slow
CH3
N
N
S
N
O
6a-6h
O
H3C
N
R
+ HOAc
O
Compounds 3a-h could also undergo self-cyclization
by the oxidation of ferric chloride to yield the
corresponding thiadiazoles 7a-h.
S
H
Ar
N
N
N
O
3a-3h
O
N
N
N
H
H
R
FeCl3
EtOH/ H2O
N
N
Ar
S
N
N
O
R
H
O
7a-7h
3a, 3e: Ar = C6H5; 3b, 3f: Ar = p-CH3C6H4; 3c, 3g: Ar = p-CH3OC6H4;
3d, 3h: Ar = p-C2H5OC6H4; 3a-3d: R = C6H5; 3e-3h: R = H
Figure 5. ORTEP drawing of 2-amino-5-(3-phenylsydnon-4-yl)[1,3,4]thiadiazole (7e).
The mechanism of reaction of compounds 3 with ferric chloride
S
H
Ar
N
N
N
N
N
H
H
R
Ar
[O]
N
N
N
N
.
N
R
H
O
O
O
O
S
H
3
N
.
N
N
Ar
S
N
H
N N
R
- H.
H
Ar
S
N
O
7
O
H
O
O
S
H
Ar
N
N
N
N
H
N
N
N
N
.
R
O
O
R