The cyclo-condensation of silyl 2-mercaptoalkanoates and arylmethyleneamines proceeded with high stereoselectivity to give alternatively both the cis-and trans-2, 5-disubstituted 4- thiazolidinones, some of which are known as anti-platelet activating factor-active drugs. The use of the piperidine catalyst and no catalyst showed very high cis-stereoselectivity (cis/trans= 10/1—50/1) during the reaction. On the other hand, the trans-selective reaction ...