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 was promoted by Ti(O-i-Bu)4 and Al(O-s-Bu)3 catalysts (cis/trans = 1/8—1/25). Both reactions were conducted with higher cis- and trans-selectivities as compared with those of the alkyl 2-mercaptoalkanoates under