Hydrochloric Acid → 6-fluoro-2-methyl-3-[(3S,9aR)-octahydropyrazino[2,1-c][1,4]oxazin-3-yl]benzonitrile hydrochloride

tert-butyl(3S,9aR)-3-(3-cyano-4-fluoro-2-methylphenyl)hexahydropyrazino[2,1-c][1,4]oxazine-8(1H)-carboxylate (1-17C) (158.8 g, 423.0 mmol) was suspended with 318 mL of 2-propanol. The resulting slurry was treated with HCl solution in 2-propanol (5.5 M, 1000 mL, 5499 mmol), and the mixture was heated to 50° C. for 2 hours. The mixture was concentrated to remove approximately 400 mL of 2-propanol, then was cooled to rt and agitated overnight. The mixture was filtered to collect the solid product and the wet cake was washed with 50 mL of 2-propanol. The filter cake was dried under vacuum for two days at 40° C. with nitrogen bleed to afford the title compound.