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With aq. sodium hydroxide; In 1,2-dimethoxyethane; aqueous sodium hydroxide;
(a) Allyl 4-benzyloxycarbonylaminopiperidine-4-carboxylate. 4-Amino-1-tert-butoxycarbonylpiperidine-4-carboxylic acid (18.0 g) was dissolved in 0.03M aqueous sodium hydroxide (750 mL), and 1,2-dimethoxyethane (100 mL). The pH was adjusted to 9.5 with dilute hydrochloric acid, and the suspension was added to an ice-cold solution of N-(benzyloxycarbonyloxy)succinimide (28.8 g) in 1,2-dimethoxyethane (100 mL). The pH was kept at 9.5 by addition of aq. sodium hydroxide, and the mixture was stirred at room temperature. More N-(benzyloxycarbonyloxy)succinimide (3 g) was added after 7 h, then stirring continued overnight. After evaporation to remove the 1,2-dimethoxyethane, the aqueus residue was extracted with ether then acidified to pH 4 and extracted with ethyl acetate. This extract was washed with dilute hydrochloric acid, water and brine, dried and evaporated. Trituration of the oily residue gave 4-benzyloxycarbonylamino-1-tert-butoxycarbonylpiperidine-4-carboxylic acid (23 g).
In sodium hydroxide; 1,2-dimethoxyethane;
(a) Methyl 4-benzyloxycarbonylamino-1-tert-butoxycarbonylpiperidine-4-carboxylate. 4-Amino-1-tert-butoxycarbonylpiperidine-4-carboxylic acid (18.0 g) was dissolved in 0.03M aqueous sodium hydroxide (750 ml), and 1,2-dimethoxyethanol (DME, 100 ml). The pH was adjusted to 9.5 with dilute hydrochloric acid, and the suspension was added to an ice-cold solution of N-(benzyloxycarbonyloxy)succinimide (28.8 g) in DME (100 ml). The pH was kept at 9.5 by addition of aqueous sodium hydroxide, and the mixture was stirred at room temperature. More N-(benzyloxycarbonyloxy)succinimide (3 g) was added after 7 hours, then stirring was continued overnight. After evaporation, the aqueous residue was extracted with ether then acidified to pH4 and extracted with ethyl acetate. This extract was washed with dilute hydrochloric acid, water and brine, dried and evaporated. Trituration of the oily residue gave 4-benzyloxycarbonylamino-1-tert-butoxycarbonylpiperidine-4-carboxylic acid (23 g).