A solution of anhydrous K2CO3 (249 mg, 1.8 mmol) in tetrahydrofuran (8 ml) and water (12 ml) is degassed with argon and then methyl cis-3-phenoxyacetamido-1-(2,4-dimethoxybenzyl)-4-oxoazetidine-2-carboxylate (150 mg, 0.35 mmol) is added. The reaction is stirred 1.5 hours at room temperature, the organic solvent is evaporated and the aqueous layer is acidified and extracted with methylene chloride. The dried extracts are evaporated to give a solid which is recrystallized from ethyl acetate-hexane to give pure cis-3-phenoxyacetamido-1-(2,4-dimethoxybenzyl)-4-oxoazetidine-2-carboxylic acid, mp 169°-170° (d).
