The synthesis of the (-)-antipodes of the natural products nojirimycin (+)-1 and mannojirimycin (+)-2 has been carried out by stereocontrolled reduction of the thiazole ketone 7 as a common key intermediate. This ketone was in turn obtained from the L-serine derived aldehyde 3 by two convergent routes involving carbonylolefination and dihydroxylation processes. Moreover, 3-deoxy derivatives of (-)-1 and (-)-2 have been prepared from 3 and the lithium enolate of 2-acetylthiazole followed by stereocontrolled reduction of the resultant aldol.