Citric Acid → (3S,5R)-1-(tert-butoxycarbonyl)-5-(methoxycarbonyl)piperidine-3-carboxylic acid (1R)-1-phenylethylamine salt

Participants

Reaction Conditions

Reaction Steps

Under a nitrogen stream, quinidine (69.9 g, 0.215 mol) and tetrahydrofuran (200 mL) were charged and the mixture was cooled to −5 to 5° C. tert-Butyl 2,4-dioxo-3-oxa-7-azabicyclo[3,3,1]nonane-7-carboxylate (50.0 g, 0.196 mol) was added at the same temperature, and the used container was washed with tetrahydrofuran (50.0 mL). Methanol (9.41 g, 0.29 4 mol) was added dropwise at −5 to 5° C., and the mixture was stirred at −5 to 5° C. for 2 hr. To the reaction mixture were added ethyl acetate (350 mL) and 20 w/v % aqueous citric acid solution (250 mL), and the mixture was partitioned. The aqueous layer was extracted again with ethyl acetate (125 mL×2). The organic layers were combined and washed successively with 20 w/v % aqueous citric acid solution (250 mL) and water (250 mL×2). The organic layer was concentrated under reduced pressure. To the residue were added ethanol (100 mL) and ethyl acetate (450 mL), the mixture was heated to 60-70° C., and (R)-phenethylamine (23.7 g, 0.196 mol) was added. The mixture was stirred at 50-60° C. for 1 hr, at 20-30° C. for 1 hr and at −5 to 5° C. for 1 hr. The precipitated crystals were collected by filtration, washed with ethanol-ethyl acetate (2:9, 100 mL), and dried under reduced pressure at 50° C. to give (3S,5R)-1-(tert-butoxycarbonyl)-5-(methoxycarbonyl)piperidine-3-carboxylic acid (1R)-1-phenylethylamine salt as a white crystalline powder (55.7 g, yield 69.6%).

Provenance & Evidence