Hypervalent iodine reagents as activators in glycosylation reactions

Glycoconjugates are present in various bioactive natural products and medicianlly important compounds; therefore, the development of novel and efficient glycosylation reactions is an important objective in organic synthesis. Thioglycosides are glycosyl donors that can act as protected glycosides at the anomeric position and can be selectively activated by the appropriate reagents under mild conditions. Although numerous methods employing oxidizing agents as an activator of the thioglycoside are currently available, more versatile approaches are still required to attain higher chemical yield and anomer selectivities. We have found that trivalent hypervalent iodine reagents, such as phenyliodine diacetate (PIDA) and phenyliodine bis(trifluoroacetate) (PIFA), display a much greater reactivity than heavy metal oxidizers or monovalent iodonium species to activate the thioglycosides. We now report novel O- and N-glycosylation reactions of the thioglycosides, activated by a combination of the hypervalent iodine reagent and Lewis acid. [GRAPHICS] .