This invention relates to a process for the removal of an allyl or allyloxycarbonyl group from an allyl or allyloxycarbonyl group protected compound (such as an allylic ester, carbonate, carbamate, O-allyl derivatives or N-allyl derivatives), which comprises contacting the allyl or allyloxycarbonyl group protected compound with a sulfinic acid compound, in the presence of a palladium catalyst in a reaction-inert solvent. Preferably, the sulfinic acid compound is represented by the formula:X--SO.sub.2 M (I)wherein X is C.sub.1-20 alkyl, substituted C.sub.1-20 alkyl (wherein the substituent(s) are independently halo, nitro, sulfo, oxo, amino, cyano, carboxy, hydroxy or moieties derived therefrom), phenyl, substituted phenyl (wherein the substituent(s) are independently C.sub.1-3 alkyl, halo nitro, sulfo, oxo, amino, cyano, carboxy, hydroxy, acetamido or moieties derived therefrom), furyl or thienyl; and M is hydrogen, an alkali metal or ammonium salt residue. Of these, most preferred sulfinic acid compound is lithium p-toluenesulfinate, sodium p-toluenesulfinate, potassium p-toluenesulfinate, p-toluenesulfinic acid, ammonium p-toluenesulfinate, lithium benzenesulfinate, sodium benzenesulfinate, potassium benzenesulfinate, benzenesulfinic acid or ammonium benzenesulfinate. This invention is well suited to a process for the conversion of an allyl ester of 5R,6S-6-(1R-hydroxyethyl)-2-(1R-oxo-3S-thiolanylthio)-2-penem-3-carboxylic acid to 5R,6S-6-(1R-hydroxyethyl)-2-(1R-oxo-3S-thiolanylthio)-2-penem-3-carboxylic acid.