Bicyclic azasugar glycomimetics structurally related to the polyhydroxy-indolizine and -piperidine series incorporating a stereoelectronically controlled pseudoanomeric axial hydroxy group have been prepared by tautomeric rearrangement of cyclic thiocarbamate precursors; preliminary enzyme inhibition tests show an increased selectivity towards yeast α-glucosidase for the α-D-glucopyranose analogue as compared with castanospermine or nojirimicin.