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COOH
O
COOH
N
NH
2
N
COOH
+
-H
2
O
COO
-H
2
O
O
OH
NH
2
N
O
NH
3
H
2-oxoglutaric acid
90%
H
NH
2
N
O
O
OH
.
2 H
2
O
+
NH
2
N
O
OH
O
H
Oxalic acid
100%
H
H
H
NH
2
N
N
N
O
N
N
+
+
N
N
NH
2
N
N
N
O
H
H
H
1,4-dihydroquinoxaline-2,3-dione
H
H
H
O
NH
2
N
N
NH
2
N
-H
2
O
N
O
H/ H
2
O
+
O
O
N
NH
2
N
O
O
N
O
H
H
H
Parabanic acid
-H
2
O
H
H
O
N
N
N
N
O
N
N
N
H
OH
H
O
NH
2
H
H
HH
O
N
N
N
H
2
O
O
N
N
N
H
HO
H
Scheme 1.37 Mechanochemical cascade condensation reaction.
Pyrimidine derivatives were synthesized by the direct condensation of an
equimolar amount of an aldehyde, malononitrile, and thiourea/urea under
ball milling within 40 min (Scheme 1.38).
34
This protocol offers a wide
variety of substituted pyrimidine derivatives in pure form without further
purification and in quantitative yields.
1.3.2 Oxygen-containing Heterocycles
In the last decade, much work has been done in the area of oxygen con-
taining heterocycle synthesis under ball milling. It was observed that use of a
ball mill not only allowed a net enhancement of the reaction yields but also
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