Thioglycosides combination

Takeuchi, K, Tamura, T, Jona, H, Mukaiyama, T, A novel activating agents of disarmed thioglycosides, combination of trityl tetrakis(pentafluorophenyl)borate, iodine and 2,3-dichloro-5,6-dicyano-/7-benzoquinone (DDQ), Chem. Lett., 692-693, 2000. 

Scheme 5.1 Mechanism of thioglycoside activation (a) by thiophiles X1 such as /V-bromosuccinimicle (NBS), 11,12 methyl triflate,13 dimethyl(methylthio)sulfonium triflate (DMTST),14 phenylselenyl triflate (PhSeOTf),17,18 iV-iodosuccinimide/triflic acid (MS/TfOH),19 20 and iodonium di-sym-collidine perchlorate (IDCP)21 (b) by tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBPA,+)25 and (c) via anomeric sulfoxides.26 The stereochemical outcome of these glycosylations follows the same general trends as with many other glycosyl donor/promoter combinations (m-CPBA = mcta-chloroperbenzoic acid).

Unlike the other N5 modifications described previously, a 5-azido thioglycoside was found to be less reactive than the simple amide as is clear from the measured relative reactivity values (RRVs) (Fig. 5.4) [59], However, it was subsequently reported by Teruaki Mukaiyama and coworkers that a 5-azido sialyl fluoride was more reactive than both the corresponding acetamide and the V,V-diacctyl derivatives toward activation with the combination of SnCl4 and AgB(C6F5)4, although this may be a consequence of the differing anomeric stereochemistries employed [60],... 

---