N-bromobutanimide → 3-Bromo-7-{[2-chloro-3-(trifluoromethyl)phenyl]carbonyl}-5,6,7,8-tetrahydroimidazo[1,2-a]pyrazine

Participants

Reaction Steps

7-{[2-Chloro-3-(trifluoromethyl)phenyl]carbonyl}-5,6,7,8-tetrahydroimidazo[1,2-a]pyrazine (3.30 g, 10 mmol, Example 1) and NBS (1.869 g, 10.50 mmol) were heated at 110° C. for 2 hr in Toluene (50 ml) and N,N-dimethylformamide (DMF) (10 ml). The mixture was cooled and concentrated in vacuo. The residue was partitioned between ethyl acetate (100 ml) and water (100 ml). The aqueous phase was extracted with ethyl acetate (100 ml). Very bad emulsions were obtained that did not clear using brine, filteration or saturation with salt. Repeated extractions with ethyl acetate (×10) and treatment of the organic extracts with anhydrous sodium sulfate removed the water. The solvents were concentrated in vacuo, and the residue dissolved in chloroform (500 mL), dried over anhydrous sodium sulfate and concentrated to an oil. The crude oil was purified by flash chromatography (Biotage SP4, 40+M, eluting with a 0-100% gradient of [10% 2M NH3/MeOH in DCM]/DCM) to afford product 3-bromo-7-{[2-chloro-3-(trifluoromethyl)phenyl]carbonyl}-5,6,7,8-tetrahydroimidazo[1,2-a]pyrazine (3.1 g, 7.59 mmol, 76% yield), as a beige foam. A 0.180 g sample of this material was further purified by mass-directed automated preparative HPLC and then dissolved in dichloromethane (5 ml) and treated with 4N HCl in dioxane (0.5 ml). The solvents were removed in vacuo and the resulting solid tritruated in diethyl ether to afford 3-bromo-7-{[2-chloro-3-(trifluoromethyl)phenyl]carbonyl}-5,6,7,8-tetrahydroimidazo[1,2-a]pyrazine hydrochloride (0.095 g, 0.213 mmol, 2.135% yield).

Provenance & Evidence