A-Glycosyl halides

In the Koenigs-Knorr method and in the Helferich or Zemplen modifications thereof, a glycosyl halide (bromide or chloride iodides can be produced in situ by the addition of tetraalkylammonium iodide) is allowed to react with a hydrox-ylic compound in the presence of a heavy-metal promoter such as silver oxide, carbonate, perchlorate, or mercuric bromide and/or oxide,19-21 or by silver triflu-oromethanesulfonate22 (AgOTf). Related to this is the use of glycosyl fluoride donors,23 which normally are prepared from thioglycosides.24... 

In the halide-assisted method,25 a glycosyl halide (normally bromide) with a nonparticipating 2-substituent and with the thermodynamically more stable axial orientation at C-l is treated with an excess of the corresponding halide anion by the addition of a soluble tetraalkylammonium salt. This sets up an equilibrium between the axial and the (much less stable) equatorial glycosyl halide. The lat-... 

T. Usui, Y. Tskagi, T. Ikuchiya, and S. Umezawa, Synthesis of 3-0-acetyl-2,6-diazido-4-0-benzyl-2,6-dideoxy-L-idopyranosyl chloride, a glycosyl halide for the synthesis of neomycin B, Carbohydr. Res. 130 165 (1984). 

An example which supports the trans rule is the condensation of 2,5-di-0-benzoyl-3-deoxy-3-phthalimido-/3-D-ribosyl chloride, a glycosyl halide containing the Cl-C2-trans structure, with mercuri derivatives of certain purines only nucleosides of the /3-d type are obtained.202 227... 

Benzyl glycosides may be prepared by the Koeiiigs-Knorr glycoside synthesis from benzyl alcohol plus a glycosyl halide, or from benzyl alcohol and the sugar in the presence of an acid. ... 

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