From Enamines and Mercaptocarboxylic Acids

From Enamines and Mercaptocarboxylic Acids. In the course of their wider study of the reaction between enamines and thiol adds, Klemmensen et have described a smooth condensation of enamines (312) derived from ethyl acetoacetate and ammonia or methylamine (/.e. ethyl j8-amino-crotonates) with a-mercaptocarboxylic acids (311) to thiazolidinones (313). The cyclization involves the addition of the thiol group, of (311), to the double bond, and amide formation between the amine and acid.  

A synthesis formally not unrelated is the cyclization of adducts of type (315), which arise by the addition of mercaptoacetic acid to Schiff s bases (314) they are ring-closed to 2,3-disubstituted thiazolidin-4-ones (316) and subsequently oxidized to the 1,1-dioxides (317).  

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