Helferich glycosylation

Other references related to the Fischer-Helferich glycosylation are cited in the... 

This reaction is related to the Helferich Glycosylation, Hilbert-Johnson Reaction, and Koenigs-Knorr Reaction. 

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... 

U. Aich and D. Loganathan, Zeolite-catalyzed Helferich-type glycosylation of long-chain alcohols. Synthesis of acetylated alkyl 1, 2-trans glycopyranosides and alkyl 1, 2-cis C2-hydroxy-glycopyranosides, Carbohydr. Res., 342 (2007) 704-709. 

The application of diazo coupling is somewhat limited by the availability of the p-aminophenyl glycosides, particularly of those of the oligosaccharides. Their precursors, the p-nitrophenyl glycosides, are usually obtained by the condensation of a per-O-acetylated glycosyl halide with p-nitrophenol in ethanol (Michael reaction)19,20 or by the reaction of a per-O-acetylated sugar with p-nitrophenol in the presence of a Lewis acid catalyst (Helferich reaction).21 p-Nitrobenzyl 1-thioglycosides have also been prepared by the condensation of the... 

By glycosylation of 19 with the halide 20 following Helferich conditions (HgBr2, HgO), a typical but acceptable amount of the desired a-glycoside 21 (40%) of a 2,6-dideoxy sugar in the L-series was obtained which represents the A-B disaccharide unit of aclacinomycin A [8],... 

One of the first syntheses of nucleosides was reported by Fischer and Helferich and involved condensation of the silver salts of both 2,6,8-trichloropurine and 2,8-dichloroadenine with 2,3,4,6-tetra-O-acetyl-a-D-glucopyranosyl bromide to form glycosyl derivatives.These nucleosides were fully characterized much later. 

After Fischer and Helferich, as well as Koenigs and Knorr, introduced the use of the heavy-metal salts of a purine to direct the glycosylation reaction to N9, Todd and co-workers adapted Fischer s silver salt method for the coupling of 2,8-dichloroadenine with 2,3,5-tri-O-acetyl-D-ri-bofuranosyl bromide to provide an intermediate blocked nucleoside that was converted to both adenosine and guanosine4 ... 

The introduction by Davoll and Lowy of the chloromercurio derivatives of purines, in place of the silver salts, represents a significant improvement in technique. Adenosine (1) and guanosine (2) were obtained in sufficient yield via 5 and 6, respectively. The introduction of 2,3,5-tri-(2-benzoyl-D-ribofuranosyl chloride even increased the glycosylation yields.The heavy-metal salts are usually insoluble in hydrocabons. Therefore, the Fischer-Helferich-Davoll-Lowy condensation is a heterogeneous reaction. 

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