The invention provides a novel compound of Formula II which is useful in the preparation of imipenem monohydrate of Formula I, wherein R1 is a p-nitrobenzyl or p-methoxybenzyl group; and R2 and R3 may be identical to or different from each other and are each independently a C.sub.1-6alkyl or aryl group, or a derivative thereof, and a process for preparing the compound of Formula II by coupling (5R,6S) p-nitrobenzyl-3-(diphenylphosphono)-6-[(1R)-1-hydroxyethyl]-1-azabicyclo[- 3.2.0]hept-2-ene-7-one-2-carboxylate with 2-aminoetahnethiol hydrocloride in the presence of a base, followed by a reaction with a ketone. Further, the invention provides a process for preparing the compound of Formula I by reacting a compound of Formula II with isopropylformimidate or benzylformimidate in the presence of a base, followed by hydrogenation, separation and crystallization. ##STR00001##