Preparation of diversely protected 2-azido-2-deoxyglycopyranoses from

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 protect- ing groups present: sodium azide and diphenyldiselenide in the presence of (diacetoxyiodo)benzene for per- acetylated 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 com- patibility 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- l -enitol and its 6-0-acety I, 6-0-allyl, 6-0-benzyl, and 6-0-tert-butyldimethylsilyl derivatives as well as with 1,s-anhydro-4,6-0-benzylidene-2-deoxy-d-lyxo- hex-1-enitol and its 3-0-acetyl and 3-0-benzyl derivatives, which were transformed into phenyl2-azido-2- deoxy-a-d-selenogalactopyranoside derivatives in good yield. In the second step, hydrolysis of these selenogly- cosi&s afforded diversely protected glycopyranoses in high yield. Peracetylated derivatives were hydrolyzed in the presence of N-iodosuccinimide, whereas mercury trifluoroacetate was employed for 3,4-0-isopropylidene, 4,6-0-benzylidene, and perbenzylated derivatives. In some cases the two steps can be canied out without iso- lation of the intermediate selenoglycoside. protected 2-azido-2-deoxy derivatives of galactose and glu- group, 2-azido-2-deoxyglycopyran~Syl donors are generally cose are extensively used for the synthesis of biologically used as reactive intermediates. ~~~~~di~~ on the leaving