Download (8Mb) - Etheses - Saurashtra University
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3.4 Result and Discussion<br />
It was found that the cyclocondensation of 2-alkylaminopyrimidines with αbromoacetophenones<br />
at 80 °C first led to stable 2-hydroxy-2,3-dihydroimidazo[1,2a]pyrimidinium<br />
bromides. The bicyclic nature of the structures clearly followed from<br />
1 H NMR data, indicating the doublet of doublets of the methylene fragments, as well<br />
as from 13 C NMR spectra.<br />
The 2-hydroxy-2,3-dihydroimidazo[1,2-a]pyrimidinium salts were obtained in good<br />
yields, and only for sterically hindered 2-alkylaminopyrimidines the yields slightly<br />
decreased. Dehydration of the 2-hydroxy-2,3-dihydroimidazo[1,2-a]pyrimidinium<br />
salts was successfully achieved by short (15 min) heating in polyphosphoric acid<br />
(PPA) at 150 °C. The corresponding imidazo[1,2-a]pyrimidinium salts were isolated<br />
and characterized as perchlorates, and in most cases the yields were almost<br />
quantitative. The structures of aromatic salts were completely consistent with their 1 H,<br />
and 13 C NMR data.<br />
The cleavage step was performed under microwave irradiation at 100 °C, using 7<br />
equivalents of hydrazine hydrate. Resulting 2-amino-1H-imidazoles were obtained in<br />
high yields. Using this protocol we have synthesized library of substituted 2aminoimidazole<br />
(Table-1)<br />
No.<br />
Compound<br />
Code<br />
H 2N<br />
N<br />
N<br />
R 1<br />
R 2<br />
R1 R2 Yield % m.p. o C<br />
1 BS-042 cyclododecane H 53 228-230<br />
2 BS-045 cyclooctane H 53 152-154<br />
3 BS-048 cycloheptane H 54 180-182<br />
4 BS-078 cyclohexane H 64 153-155