Reaction of Glycals with Organic Peroxides: Synthesis of 2-iodo, 2-Deoxy and 2,3-Unsaturated Glycosides

摘要

Reaction of peroxides with glycals, when carried in the presence of NIS affords2-deoxy-2-iodo-a-glycosides in good yields with predominant trans-diaxial selectivity at rt. Under photolytic conditions in the presence of catalytic eosin Y, the reaction leads to 2-deoxyglycosides or 2,3-unsaturated-a-glyco- sides. NIS plays two roles firstly, to form an iodonium ion with the glycal and secondly to bring about the decomposition of the organic peroxide into an alcohol that reacts with the activated sugar whereas blue LED light and Eosin Y bring about a radical-mediated glycosylation to give the a-2-deoxy glyco- side or 2,3-unsaturated glycosides based on the protecting group at C-3 position of glycals.