Thiazolidine‐2,4‐dicarboxylic acid and its esters: Synthesis, in solution behaviour and regioselective cyclocondensation

Thiazolidine‐2,4‐dicarboxylic acid 2 was obtained as a diastereoisomeric mixture from the condensation of glyoxylic acid with L(‐) R ‐cysteine 1 . In solution behaviour studies suggested that the reaction proceeded through an acid catalyzed epimerization mechanism. The methyl esterification of 2 was stereoselective, which can be explained by an interconversion of 2a via a ring seco intermediate. Condensation of the dimethyl ester 3 or the dissymmetric diester 4 with phenyl isocyanate gave rise to the same hydantoin 5 . N ‐acylation of diesters 3 or 4 followed by the reaction with benzylamine was regioselective leading to bicyclic derivatives 8‐10 .