832715-51-2

5382-16-1

108-23-6

832715-51-2

General procedure for the synthesis of isopropyl 4-hydroxypiperidine-1-carboxylate from 4-hydroxypiperidine and isopropyl chloroformate: Step 3: Preparation of isopropyl 4-hydroxypiperidine-1-carboxylate (5) To a mixed solution containing 4-hydroxypiperidine (53.8 g, 1.000 eq.), triethylamine (71.8 g, 1.334 eq.) and ethyl acetate (498.8 g) was slowly added pure isopropyl chloroformate (78.0 g, 1.1966 eq.) under stirring conditions, with the rate of addition being controlled to ensure that the temperature of the reaction mixture was maintained between 10°C and 17°C ( achieved by reactor jacket cooling). After addition, the reaction mixture was stirred continuously at 20°C for 18 hours. Subsequently, water (100 g) was added and stirred for 15 minutes, after which phase separation was carried out. Prior to separation of the aqueous layer, the organic phase was washed with two 100 g aqueous solutions of 20 wt% NaCl for 15 min each at a stirring speed of 150 rpm. Finally, after washing the organic phase with water (100 g), the organic phase was concentrated by rotary evaporator under reduced pressure to give a light amber oily product (2) (91.1 g, 92.0% yield) with 96.8% GC purity. The crude product was distilled at 117°C to 120°C and at a pressure of 0.3 to 1.0 torr to give a colorless oily product (2) with 95.7% recovery, collected at 112°C to 119°C.