Iodine-hexamethyldisilane (HMDS)-mediated anomerization of peracetylated 1,2-trans-linked alkyl and aryl glycosides

Stereocontrolled Synthesis of Phenolic α-d-Glycopyranosides

“…The resulting 2-naphthyl 6-O-TBDPS-α-D-galactopyranoside was stable in the presence of 50 mol% of MeOTf and only a trace of anomerization was detected by NMR spectroscopy (~19:1 α/β) over 72 hours contrary to the case of the α-an β-D-phenyl glycopyranosides of peracetylated sugars which are converted into anomeric mixtures in the presence of Lewis acids to varying degrees. 13,25,26 Excellent yields and selectivities were observed in the case of N-Cbz-tyrosine methyl ester (Table 1, entry 12; Table 2, entry 10). This is a good example of direct and highly stereoselective α-glycosidation with tyrosine in the absence of protecting groups such as benzyl ethers.…”

Hexamethyldisilane

“…15 Indeed the in situ formation of Me 3 SiI species leads to the anomerization step by ring opening of a silylated carbohydrate intermediate.…”

“…(F) Hexamethyldisilane/I 2 as a Precursor of TMSI: Malik et al demonstrated that the hexamethyldisilane-iodine system mediated anomerization of alkyl glycoside in quantitative yield. 15 Indeed the in situ formation of Me 3 SiI species leads to the anomerization step by ring opening of a silylated carbohydrate intermediate.…”

Halogenation and anomerization of glycopyranoside by TESH/bromine and BHQ/bromine

“…For environmentally friendly synthesis, preparation of anhydrous hydrogen halide in situ can provide a convenient and inexpensive reagent in the preparation of glycosyl halide. Anhydrous HI can be generated by mixing solid iodine with triethylsilane [ 23,24 ] or thiolacetic acid [ 25 ] and applied in preparation of glycosyl halide. In connection with those studies, we attempted to supplement and intact the production of glycosyl halide by TESH/halogen and BHQ/Bromine.…”