4
Table 5
Sulfated polyborate catalyzed synthesis of unsymmetrical 1,3-disubstituted ureas under solvent-free condition.a, 61
Entry
N
(R1)
-phenylureas
Amines
(R2)
Time
(h)
Yieldb
(%)
M.P. °C
Lit.
Obs.
1
2
3
4
5
H
C6H5
1
93
91
87
94
89
236-238
222-223
149-150
167-168
167-168
238-24047
217-21958
148-15059
168-16958
166.5-167.560
H
4-CH3-C6H4
(C6H5)-(CH3)-CH
C6H5-CH2
C6H5-CH2
1
H
1.5
0.75
1
H
4-CH3O
a Reaction conditions: N-phenylurea (1 mmol), urea (1.2 mmol), and sulfated polyborate (10 wt %), b Isolated yield.
161.
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off. The filtrate was evaporated under vacuum to recover the
catalyst. Recovered catalyst was recycled for four times with no
significant loss in catalytic activity.
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In conclusion, we have developed an efficient, simple and
expeditious method for the synthesis of (un)symmetrical ureas
and benzimidazolones by reaction of amines, OPDA with urea or
N-phenylurea catalyzed by sulfated polyborate under metal-free
conditions. Due to the mild reaction conditions, wide substrates
scope, good to excellent yields and easy work-up procedure, the
present protocol has edge over the other methods.
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Acknowledgements
Authors are grateful to University Grants Commission, India
for their financial support.
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