PURPOSE: To provide a new compound useful as a synthetic intermediate for carbapenem antibiotic substances such as thienamycin.

CONSTITUTION: This compound is expressed by formula I (R1 to R3 are each a 1-4C alkyl) such as p-nitrobenzyl 2-diazo-3-t-butyldimethylsilyoxy-3-butenoate. The compound can be produced by reacting a p-nitrobenzyl diazoacetoacetate intermediate of formula II with a triorganosilyl triflate silylation agent of formula III (preferably t-butyldimethylsilyl trifluoromethylsufonate) in an inert organic solvent such as THF in the presence of an organic base (preferably a 1-4C trialkylamine) preferably at 0-5°C. The intermediate of the formula II is produced e.g. by reacting ethyl acetoacetate with p-nitrobenzyl alcohol in toluene and reacting the resultant p-nitrobenzyl acetoacetate with a toluene sulfonylazide in the presence of triethylamine.