Acid. -Cycloaddition of divinyl sulfone (II) to the azomethine ylides, generated from imino esters (I) under action of Lewis acids, proceeds stereoselectively to form racemic pyrrolidines (III). Functionalization of the endocyclic nitrogen atom affords the derivatives (V) and (VII). Compounds containing the vinylsulfonyl fragment have an effect on phosphatidylserine-coated platelets. The presence of a small alkyl substituent at the endocyclic nitrogen atom seems to be critical for inhibition of platelet activation. (VIIa) appears to be the most interesting compound for further applications.