ENANTIOPURE 2-THIOXOTETRAHYDRO-1,3-O,N-HETEROCYCLES FROM CARBOHYDRATES .3. ENANTIOPURE C-4 CHIRAL OXAZINE-2-THIONES AND OXAZOLIDINE-2-THIONES FROM 3-DEOXY-3-ISOTHIOCYANATO SUGARS

The synthesis of 3-deoxy-3-isothiocyanato derivatives of D-glucose, D- allose, and D-galactose is reported. The intramolecular cyclization of partially or fully unprotected 3-deoxy-3-isothiocyanates has been fou nd to proceed with total stereocontrol, the outcome of the reaction be ing governed by the sugar configuration. Bicyclic enantiopure C-4 (and C-5) chiral tetrahydrooxazine- and oxazolidine-2-thiones have been pr epared in this way. An unexpected nucleophilic addition of the gamma-o xo group to the NCS group has been observed in the case of the fully u nprotected D-gluco derivative, leading to the formation of a 4-(trihyd roxypropyl)tetrahydrooxazine-2-thione.