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A mixture consisting of 5.52 g of potassium carbonate in 20 ml of water and 160 ml of 1,2-dichloroethane is brought to reflux and 15.5 mmole of N-sulfonyl benzyloxycarbonylthreonine amide, O-mesylate, tetrabutylammonium salt is added in 20 ml of 1,2-dichloroethane (20 ml used as a rinse). After refluxing for 30 minutes, the mixture is poured into a separatory funnel, diluted with 50 ml of water and 100 ml of methylene chloride and the phases split. The resulting organic phase is dried over sodium sulfate and concentrated to yield crude (3S-trans)-3-benzyloxycarbonylamino-4-methyl-2-oxo-1-azetidinesulfonic acid, tetrabutylammonium salt. The crude azetidinone is treated in 250 ml of ethanol with 0.8 g of 5% palladium on charcoal catalyst and hydrogen is bubbled through the solution. After 90 minutes the mixture is filtered through Celite with 50 ml of ethanol used as a rinse. The addition of 1.2 ml of formic acid to this solution causes an immediate precipitation of the title zwitterion which is filtered after stirring for 1 hour to yield, after drying at 10-1 torr for 1 hour, 1.1 g of product. A second crop of product is obtained upon concentration of the filtrate and addition of more formic acid to give 1.3 g of the title zwitterion.

1. customis bubbled through the solution
2. filtrationAfter 90 minutes the mixture is filtered through Celite with 50 ml of ethanol
3. additionThe addition of 1.2 ml of formic acid to this solution
4. customan immediate precipitation of the title zwitterion which
5. filtrationis filtered
6. customto yield
7. customafter drying at 10-1 torr for 1 hour
8. customA second crop of product is obtained upon concentration of the filtrate and addition of more formic acid
9. customto give 1.3 g of the title zwitterion