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imidazoles, where the addition of a suitable nitrogen nucleophile is followed by the<br />
elimination of an activated leaving group such as a halogen or alkyl sulfoxide or<br />
sulfone. This method has been applied with limited success to electron-poor<br />
imidazoles or when fluorine is the leaving group. 4,15 An interesting synthetic route to<br />
functionalized 2-AI's, which were difficult to obtain by other methods, has been<br />
achieved using a base catalyzed rearrangement of 3-amino-1,2,4-oxadiazoles. 16<br />
Another type of heterocyclic rearrangement involves the reaction of 2-aminooxazoles<br />
with ammonia or formamide. 17 Most recently, the synthesis of 2-amino-4(5)-(αhydroxyalkyl)imidazoles<br />
has been demonstrated where 2-AI was reacted with<br />
aldehydes under neutral conditions. 18<br />
The microwave-assisted procedure for the synthesis of 1,4,5-substituted 2aminoimidazoles<br />
(Scheme-1) is two-step protocol based on the cyclocondensation of<br />
2-aminopyrimidines and bromocarbonyl compounds at 130-150 °C, followed by the<br />
cleavage of the intermediary imidazo[1,2-a]pyrimidin-1-ium salts with an excess of<br />
hydrazine.<br />
3.2 Reaction Scheme<br />
Scheme-1<br />
N<br />
N<br />
+<br />
N<br />
H<br />
Br O<br />
H<br />
H 2N<br />
N<br />
N<br />
R 1<br />
R 2<br />
R 1<br />
R 2<br />
MeCN<br />
MW<br />
80 °C, 30 min<br />
MeCN<br />
64% N2H4 MW<br />
100 °C, 10 min<br />
Br<br />
N<br />
N<br />
N<br />
N<br />
N R1 OH<br />
R 2<br />
PPA, 150 °C<br />
aq. HClO4 N R 1<br />
R 2<br />
ClO 4