The 2-(hydroxymethyl)penem (I) is transformed into the corresponding mesylate (II), which is then condensed with sarcosinamide (III), to afford adduct (IV). The O-silyl group of (IV) is removed by treatment with tetrabutylammonium fluoride, yielding alcohol (V). Finally, the allyl ester group of (V) is cleaved in the presence of palladium and triphenylphosphine to furnish the target carboxylic acid.

The 2-(hydroxymethyl)penem (I) is transformed into the corresponding mesylate (II), which is then condensed with sarcosinamide (III), to afford adduct (IV). The O-silyl group of (IV) is removed by treatment with tetrabutylammonium fluoride, yielding alcohol (V). Finally, the allyl ester group of (V) is cleaved in the presence of palladium and triphenylphosphine to furnish the target carboxylic acid.

The 2-(hydroxymethyl)penem (I) is transformed into the corresponding mesylate (II), which is then condensed with sarcosinamide (III), to afford adduct (IV). The O-silyl group of (IV) is removed by treatment with tetrabutylammonium fluoride, yielding alcohol (V). Finally, the allyl ester group of (V) is cleaved in the presence of palladium and triphenylphosphine to furnish the target carboxylic acid.

In a related method, the 4-acetoxy-azetidinone (I) is reacted with 2-chlorothioacetic acid (II) in the presence of ZnI2 to give the (chloroacetylthio)azetidinone (III). Nitrogen acylation in (III) by means of allyl oxalyl chloride produces (IV), which undergoes ring closure to the penem (V) in the presence of triethyl phosphite in boiling toluene. Displacement of chloride (V) with sarcosinamide (VI) yields adduct (VII). After desilylation of (VII) to (VIII) by means of tetrabutylammonium fluoride, palladium-catalyzed allyl ester cleavage leads to the title compound.