General procedure for the synthesis of 4-dimethylaminopiperidine dihydrochloride from N-Boc-4-dimethylaminopiperidine: 10.0 g of tert-butyl 4-(dimethylamino)piperidine-1-carboxylate (0.044 mol) was dissolved in 60 mL of dichloromethane and cooled in an ice bath. Subsequently, 4 mol/L of HCl/dioxane solution (34.5 mL, 0.138 mol) was slowly added, and stirring was maintained during the dropwise addition. The reaction mixture was continued to be stirred under ice bath conditions for 8 hours. Upon completion of the reaction, a large amount of white solid precipitate was observed to be generated, and the precipitate was collected by filtration and washed with a small amount of cold dichloromethane to remove residual HCl. 6.4 g of the target product, 4-dimethylaminopiperidine dihydrochloride, was finally obtained in 85.3% yield.
