(R)-hydroxyethyl)-2-[(cis-l-oxo-3-thiolanyl) thio]-2-penem-3-carboxylic acids 1 and 2. This synthetic pathway provided in high yield enantiopure thioacetate intermediates 15 and 19. To accommodate the fragile side chain sulfoxide moiety of the targeted@-lactams, standard penem synthetic methodology waa modified to facilitate the conversion of 15 and 19 to 1 and 2. The reactive chloroamtidinone 4b was utilized to generate key azetidinone ...