A fine suspension of 25.18 grams (0.05 mol) of potassium salt of enamine
protected ampicillin and 10.65 grams (0.05 mol) 3-bromophthalide were
reacted in a 1:2 mixture of acetone/ethyl acetate (1,500 ml) for 24 hours.
After filtration the organic layer was washed twice with 250 ml portions of 1 N
sodium bicarbonate and brine, dried over anhydrous magnesium sulfate and
concentrated in vacuo. Addition of ether crystallized the phthalide enamine
protected α-aminophenylacetamido penicillanate in 85% yield.
