L-Tartaric acid → D-Tartaric acid

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73.6 g (0.34 mol) of cis-8-benzyl-2,8-diazabicyclo[4.3.0]nonane, as a solution in 111 ml of dimethylformamide, are added dropwise, at 80° to 90° C., to a solution of 102.9 g (0.685 mol) of L(+)-tartaric acid in 343 ml of dimethylformamide. Seeding with [R,R]-8-benzyl-2,8-diazabicyclo[4.3.0]nonane L-tartrate takes place, and the mixture is cooled slowly down to an internal temperature of 18° C. The crystals are filtered off with suction, and the filtrate is seeded with [S,S]-8-benzyl-2,8-diazabicyclo[4.3.0]nonane L-tartrate and stirred until crystallisation is complete. (After concentrating and liberating the base as described under method I, [S,S]-8-benzyl-2,8-diazabicyclo[4.3.0]nonane D-tartrate can be obtained from the mother liquor by purification with D(-)-tartaric acid.) Subsequently, filtration takes place with suction, and the sediment is washed with dimethylformamide and isopropanol and air-dried. The crystals are recrystallised from 88% strength ethanol. 52 g of [S,S] -8-benzyl-2,8-diazabicyclo[4.3.0]nonane L-tartrate trihydrate are obtained.

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