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N-(2,4-dimethoxybenzyl)glycine is prepared by the reaction of glycine with 2,4-dimethoxybenzaldehyde in the presence of sodium hydroxide, reduction with palladium-on-carbon in methanol and subsequent neutralisation with 2 N hydrochloric acid. The aqueous solution obtained is concentrated. 41.9 g of this mixture of N-(2,4-dimethoxybenzyl)-glycine and sodium chloride are stirred at 110° C. for 1.5 hours in 300 ml of dimethyl sulphoxide with 23.18 g (142 mmol) of isatoic acid anhydride. The mixture is poured into ca 2 liters of water and stirred for 0.5 hour. The separated crystals are filtered off under suction, washed with water and dried. After recrystallisation from ethyl acetate, there is obtained 3,4-dihydro-4-(2,4-dimethoxybenzyl)-2H-1,4-benzodiazepine-2,5(1H)-dione of melting point 151°-152.5° C.

1. customThe aqueous solution obtained
2. concentrationis concentrated
3. filtrationThe separated crystals are filtered off under suction
4. washwashed with water
5. customdried
6. customAfter recrystallisation from ethyl acetate