1,4-Dioxane → 3-Amino-5-bromo-1-methyl-1,2-dihydropyridin-2-one

To a solution of 5-bromo-3-(diphenylmethyleneamino)-1-methylpyridin-2(1H)-one (3.82 g, 10.4 mmol) in ethyl acetate (10 mL) was added 4 MHCl/dioxane (7.8 mL, 31.3 mmol). The reaction mixture was stirred for 0.5 h and concentrated under reduced pressure. The residue was washed with tert-butyl methyl ether and filtered. The solid was dissolved in ethyl acetate (10 mL) and water (10 mL). The pH of the resulting mixture was adjusted to between 7 and 8 by adding K2CO3 gradually. The water phase was separated and extracted with dichloromethane for three times. The combined organic layer was concentrated under reduced pressure to afford 325a as a yellow solid (1.1 g, 52%). MS-ESI: [M+H]+ 202.9.