Chemistry Reference
In-Depth Information
are converted into symmetrical N,N
0
-diarylureas 1089 in 40-85% yield upon mi-
crowave irradiation of a 2:1 molar mixture of the selected amine and urea 1088 for
4 min [786].
O
O
2 equiv. ArNH
2
microwave irr. 4 min
Ar
NN
Ar
H
2
N
2
HH
40-85 %
1088
1089
Cyclic ureas 1092 and 1094 can be prepared in satisfactory yields (54 and 77%, re-
spectively) by condensation of N,N
0
-dialkylureas of type 1090 with glyoxal 1091 or
of urea 1088 with a-functionalized carbonyl compounds 1093, followed by hydro-
genolysis or removal of water [787-789].
O
H
H
O
O
O
1091
H
3
C
Red
H
3
C
NN
CH
3
CH
3
NN
HH
54 %
1092
1090
O
h
O
O
H
H
1093
NN
H
2
N
2
77 %
1088
1094
N-Alkylation of ureas represents a further useful method for the selective synthesis
of N,N,N
0
,N
0
-tetrasubstituted ureas, including cyclic ones. Thus, N,N
0
-divinylpro-
pyleneurea 1097 is prepared in 89% yield by the addition of vinyl propionate 1096
over a period of 15 min to a mixture of propyleneurea and dimethylaminopyridine
(DMAP) at 95
C and refluxing for 5.5 h [790].
O
O
O
OEt
1096
NN
HN
NH
DMAP, 95 °C, 5.5 h
89 %
1095
1097
