DIASTEREOISOMERIC AND REGIOISOMERIC BICYCLIC THIOHYDANTOINS FROM CHIRAL 1,3-THIAZOLIDINE-2,4-DICARBOXYLIC ACIDS

Bicyclic thiohydantoins were synthesized in a stereoselective manner b y reacting (2R)/(2S)-diastereoisomer mixtures of 1,3-thiazolidine-2,4- dicarboxylic acids or their dimethyl diesters with PhNCS,5,5-Dimethyl- 1,3-thiazolidine-2, 4-dicarboxylic acid with PhNCS led to a cyclizatio n involving the C=O group at the C(2) center of the thiazolidine ring, while the acid's dimethyl diester gave cyclization involving the C=O group at C(4). In contrast, reactions involving unsubstituted 1,3-thia zolidine-2,4-dicarboxylic acid or its dimethyl diester led to thiohyda ntoins in which the ring closure had taken place only with the COO gro up at C(4). Independently of the direction of the ring closure, all re actions produce exclusively products with the (R)-configuration at C(2 ). The configurational assignments were based on H-1- and C-13-NMR stu dies, and confirmed by X-ray crystallographic analyses.