PREPARATION OF DIVERSELY PROTECTED 2-AZIDO-2-DEOXYGLYCOPYRANOSES FROM GLYCALS

A new and efficient preparation of diversely protected 2-azido-2-deoxyglycopyranosides from the corresponding glycals is described. The glycals are first transformed into protected phenyl 2-azido-2-deoxy-selenoglycopyranosides by azido-phenylselenylation. Two procedures were employed according to the protecting groups present: sodium azide and diphenyldiselenide in the presence of (diacetoxyiodo)benzene for peracetylated glycals (Procedure A) or trimethylsilyl azide and tetra-n-butylammonium fluoride in the presence of N-phenylselenophthalimide for perbenzylated glycals (Procedure B). A gluco–manno mixture (90%) is obtained from protected d-glucal whereas only the galacto isomer is formed from protected d-galactal (75%). The compatibility of the second procedure with one free hydroxyl group and a variety of protecting groups was verified with 1,5-anhydro-2-deoxy-3,4-O-isopropylidene-d-lyxo-hex-1-enitol and its 6-O-acetyl, 6-O-allyl, 6-O-benzyl, and 6-O-tert-butyldimethylsilyl derivatives as well as with 1...