Thioglycosides chemoselective glycosylations

Glycosylation Strategies Using Thioglycosides 4.1.6.1 Chemoselective Glycosylations... 

Codee JDC, Litjens REJN, den Heeten R, Overkleeft HS, van Boom JH, van der Marel GA. Ph2S0/Tf20 a powerful promoter system in chemoselective glycosylations using thioglycosides. Org. Lett. 2003 5 1519-1522. 

The results discussed in this chapter clearly indicated that NIS/TfOH is a valuable promoter system for the chemoselective glycosylation of latent acceptor with active thioglycosyl donors. Furthermore, this study revealed that the amount of triflic acid used was crucial for the selective activation of active thioglycosides over relatively latent thioglycosides. 

Several other examples have been reported in which thioglycosides were used as glycosyl acceptors. Thus, thioglycosides containing free hydroxyls can be coupled chemoselectively with glycosyl bromides and chlorides in the presence of silver triflate or tin(II) chloride-silver perchlorate as the promoter system [12,53,56,162,218-221]. 

The ability to chemoselectively deprotect pent-4-enyl glycosides opens an avenue for a two-step transformation of NPGs into different glycosyl donors. In this context, NPGs can be transformed [50] into thioglycosides 81 [51,52,53], glycosyl trichloroacetimidates 82 [54], and glycosyl chlorides 83 [55] (O Scheme lie). 

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