(1S,4S,5S)-4-Bromo-6-oxabicyclo[3.2.1]octan-7-one

Used as Edoxaban impurity.

(1S)-Cyclohex-3-ene-1-carboxylic acid (II) (5 g) was dissolved in dichloromethane (25 mL). To this solution, N-bromosuccinimide (1.1 mole) was added at room temperature. In two lots, calcium oxide (0.25 mole) was charged to the Suspension. The reaction mixture was stirred at 20 to 25°C for 1 hour and filtered. The bed was washed with dichloromethane (10 mL). The washings were combined with the filtrate, and the solvent was recovered under vacuum at 35 to 40 °C. Deionized water (50 mL) was charged to the solid, heated to 50 °C, stirred for 10 minutes, and filtered. The bed was washed with deionized water (10 mL) and suction dried. The solid was dried under vacuum at 45-50 °C to get (1S,4S,5S)-4-Bromo-6-oxabicyclo[3.2.1]octan-7-one. Yield: 61%