Silylated 4-oxoazetidine-2-carboxylic acid (I) was converted to the mixed anhydride with isobutyl chloroformate, and then reduced to alcohol (II) with NaBH4. Subsequent Mitsunobu coupling of (II) with mercaptotetrazole (III) provided thioether (IV). Desilylation of (IV) was then achieved by treatment with CsF in MeOH to give (V). Reaction of 4-(trifluoromethyl)benzyl chloride (VI) with methylamine afforded secondary amine (VII). This was reacted with phosgene and diisopropyl ethylamine to produce the carbamoyl chloride (VIII). Finally, condensation of this chloride with azetidinone (V) in the presence of lithium bis(trimethylsilyl)amide furnished the target urea.

Silylated 4-oxoazetidine-2-carboxylic acid (I) was converted to the mixed anhydride with isobutyl chloroformate, and then reduced to alcohol (II) with NaBH4. Subsequent Mitsunobu coupling of (II) with mercaptotetrazole (III) provided thioether (IV). Desilylation of (IV) was then achieved by treatment with CsF in MeOH to give (V). Reaction of 4-nitrobenzyl chloride (VI) with methylamine afforded secondary amine (VII). This was reacted with phosgene and diisopropyl ethylamine to produce the carbamoyl chloride (VIII). Finally, condensation of this chloride with azetidinone (V) in the presence of lithium bis(trimethylsilyl)amide furnished the target urea.