Hydrogen Bromide → 8-Chloroimidazo[1,2-a]pyrazine

Participants

Reaction Steps

Bromoacetaldehyde diethyl acetal (200 mL, 1.3 mol) and a solution of 48% HBr (48 ml) are heated at reflux for 1.5 hours, then poured onto a suspension of NaHCO3 (100 g) in propan-2-ol (1.6 L). The resulting solid is filtered off and 2-amino-3-chloropyrazine (51.8 g, 0.4 mol) is added to the solution then heated to reflux, during which time a clear solution forms which precipitates over 2 hours. The reaction mixture is cooled and allowed to stand overnight, and the solid may be collected by filtration and washed with propan-2-ol and Et2O. The solid is added to a saturated solution of NaHCO3 (500 mL) and DCM (1 L). The aqueous layer is separated from the organic solvent and re-extracted with DCM (2×250 mL). The organic layers are combined and dried over MgSO4, filtered and evaporated to dryness, to afford a light brown solid. The propan-2-ol and Et2O liquors from washing the filter cake, are evaporated to give a pale brown solid which is washed with a saturated solution of NaHCO3 and extracted with DCM (X 3). The two solids were combined to afford compound 8-chloro-imidazo[1,2-a]pyrazine (59.1 g, 96%).

Provenance & Evidence