Fazadon,Duncan Flockhart,UK,1976
(a) 1-Acetamido-3-methyl-2-phenylimidazo[1,2-a]pyridinium bromide - A
mixture of 2-(2-acetylhydrazino)pyridine (2 g) and 2-bromopropiophenone
(2.84 g), in ethanol (10 ml) was heated in an open flask in a bath at 160°C to
170°C until the ethanol had evaporated; the residual melt was then heated for
a further 0.25 hour. After cooling, the residual gum was triturated with
acetone and the resulting solid (2.8 g) recrystallized from ethanol-ether giving
the bromide as colorless prisms, MP 232°C to 234°C.
(b) 1-Amino-3-methyl-2-phenylimidazo[1,2-a]pyridinium bromide - A solution
of the acetamido compound (2.78 g) in 24% hydrobromic acid (12 ml) was
boiled under reflux for 1 hour. The solution was then evaporated under
reduced pressure and the residue dissolved in methanol. Addition of ether
precipitated the bromide which crystallized from ethanol as colorless prisms,
MP 243°C to 244°C (1.7 g).
(c) 1,1'-Azobis[3-methyl-2-phenyl-1H-imidazo[1,2-a]pyridinium]dibromide - A
warm (50°C) solution of the N-amino compound (0.6 g) in water (10 ml) was
treated with saturated bromine water (70 ml) and the precipitated orange
solid filtered off and washed with water. The orange solid was sucked dry and
then boiled with acetone (30 ml) until the suspended solid became yellow.
Absolute acetone (10 ml) was then added and the solution filtered giving the
dibromide (0.57 g) which crystallized from water as the yellow dihydrate, MP
215°C to 219°C (softened at 196°C).
