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Mol Divers
Table 2 Microwave-assisted
synthesis of substituted
2-amino-1H-imidazoles 1
N
Br
N
+
NHR 1
O
R 2
1. MW 80 °C
MeCN 30 min
heating or microwave irradiation led to a mixture of salts 3
and 6 (Table 1). Interestingly, using microwave irradiation at
120 ◦ C for 60 min, we were able to drive the reaction completely
to the formation of the imidazo[1,2-a]pyrimidinium
salt 6 (Table 1, entry 12).
As the transformation of salts 3 into salts 6 is relatively
rapid at the temperatures above 100 ◦ C, the synthesis of
salts 3 was conducted at 80 ◦ C. Treatment of substituted
4
5
N
Br
3
N
N R1 OH
R 2
2. N 2H 4, MW 90 °C
MeCN 10 min
R 1HN
entry 2-aminopyrymidine 4 α–bromoketone 5 product 1 yield
1
2
3
4
5
6
N
N
N
N
N
N
N
N
N
N
N
N
H
N
N
H
NH 2
NH 2
NH 2
Me
Piperonyl
N
H
Pr
Br
Br
Br
Br
Br
Br
O
O
O
O
O
O
OMe
Ph
F
Cl
OMe
Cl
Cl
H 2N
H 2N
H 2N
Me
HN
Piperonyl
Pr
HN
N
N
H
N
N
H
N
N
H
MeO
N
N
H
HN
N
N
H
N
N
H
1{1}
1{2}
1{3}
1{4}
1{5}
1{6}
Ph
F
Cl
OMe
N
N
H
1
R 2
(%) a
2-aminopyrimidines 4 with 15 mol% excess of α-bromoketones
5 in MeCN under microwave irradiation for 30 min
generated the intermediate salts 3 which, in most cases, precipitated
from the reaction mixture upon cooling (Table 2).
Reaction progress was monitored by mass-spectrometry.
In all the cases examined, the reaction appeared to be complete
after 30 min. The cleavage step was performed under
microwave irradiation at 90 ◦ C, using seven equivalents of
Cl
Cl
75
79
88
48
72
70
123