alpha-glucosaminide synthesis: exercising stereocontrol at C1 or C2 via torsional effects or DeShong nucleophiles

The synthesis of alpha-glucosaminides may be carried out by installing synt hons for the cis-related C1 and C2 functionalities in either order. When th e C2 azide is installed first, cc-glycosidation can be induced by using a 4 ,6-O-benzylidene ring to provide torsional control of anomeric selectivity. In the alternative option, the C1 linkage can be established by use of an n-pentenyl-manno-1,2-orthoester, the C2-oxygen of the resulting alpha-manno side being replaced with inversion by use of DeShong's hypervalent silicon azide. (C) 2000 Elsevier Science Ltd. All rights reserved.