Download (8Mb) - Etheses - Saurashtra University

2.4 Results and discussion:
Initially careful investigation of the formation and dehydratation of salt (3) resulting
in the formation of salt (4) under conventional heating conditions as well as upon
microwave irradiation has been studied. As a proof of concept, the condensation of 2methylaminopyrimidine
(1, R1 = Me) and α-phenacylbromide (2, R2 = Ph) was
studied (Table 1). A sealed vial containing a solution of the starting compounds in
acetonitrile was conventionally heated with an oil bath (Table 1, No-1-6) or irradiated
with microwaves (Table 1, No-7-12) at different temperatures for 30−60 min. The
formation of the 2-hydroxy salt (3) was faster under microwave irradiation and this
compound was obtained in 88% yield within 30 min. Further increase of the
temperature up to 120 °C using conventional heating or microwave irradiation led to a
mixture of salts (3) and (4) (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 (4) (Table 1, No-12).
N
N N R N
N
Br O
R1 N N +
1 + N
H H R Br
N
2
OH
1 2 3 R2 R Conditions
Br
1
(R1 = Me, R2 = Ph)
4 R2 No. Conditions Time (min) T (°C) 3 (yield %) b 4 (yield %) b
1
30 80 64 0
2 60 80 77 0
3 30 100 81 Traces
Conventional
4 60 100 85 Traces
5 30 120 68 17
6 60 120 53 28
7
30 80 88 0
8 60 80 85 0
9 Microwave 30 100 48 33
10 60 100 45 35
11 30 120 12 79