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1-Thioglycosides activators

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). 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).
As iodine is a milder thioglycoside activator than IDCP, we have been able to directly monitor iodine-promoted thioglycoside activation, epimerization, and gly-cosylation reactions by H NMR spectroscopy.41,44 We have been able to show that... [Pg.48]

Given that we find iodine to be a relatively mild promoter for thioglycoside activation, we have investigated its reaction with a panel of thioglycosides of varying reactivity (Fig. 21).53 We also have made a systematic study of the ability of iodine-based promoters to effect activation of a latent nitrothiophenyl galac-toside in an attempt to ascertain the relative reactivity of the various promoter systems we have studied (Fig. 22).53 It is clear that the cheap, readily available promoters we have reported vary in their reactivity by several orders of magnitude. [Pg.51]

The common promoters of thioglycoside activation are summarized in Table 4.3. [Pg.124]

Halonium ions are another type of electrophile used for thioglycoside activation. The use of NBS, originally introduced by Hanessian for the synthesis of simple glycosides from a 2-pyridinyl... [Pg.124]

Fukase, K, Nakai, Y, Kanoh, T, Kusumoto, S, Mild but efficient methods for stereoselective glycosylation with thioglycosides activation by [A-phenylselenophthalimide-Mg(C104)2] and [PhI0-Mg(C104)2], Synlett, 84-86, 1998. [Pg.179]

Fukase, K, Hasuoka, A, Kinoshita, I, Aoki, Y, Kusumoto, S, A stereoselective glycosidation using thioglycosides, activation by combination of A-bromosuccinimide and strong acid salts. Tetrahedron, 51, 4923-4932, 1995. [Pg.179]

Cura, P, Aloui, M, Kartha, K P R, Field, R A, Iodine and its interhalogen compounds versatile reagents in carbohydrate chemistry XII. Tuning promoter reactivity for thioglycoside activation, Synlett, 1279-1280, 2000. [Pg.180]

Kallin, E, Lonn, H, Norberg, T, Glycosidations with thioglycosides activated by suUuryl chloride trifluoromethanesulfonic acid — synthesis of a human-blood group-B trisaccharide glycoside, Glycoconjugate J., 5, 3-8, 1988. [Pg.180]

Scheme 31. Thioglycoside activation with a sulfenyl chloride/silver triflate combination. Scheme 31. Thioglycoside activation with a sulfenyl chloride/silver triflate combination.
Scheme 2.71 Principle of "orthogonal glycosidic activation on a polymer (e.g. polyethylene glycol) support, lb facilitate purification, a hydrophobic tag (e.g. 2-(trimethylsilyl)ethyl) is introduced [158]. Conditions A are for thioglycoside activation, conditions B for activation of glycosyl fluorides. Scheme 2.71 Principle of "orthogonal glycosidic activation on a polymer (e.g. polyethylene glycol) support, lb facilitate purification, a hydrophobic tag (e.g. 2-(trimethylsilyl)ethyl) is introduced [158]. Conditions A are for thioglycoside activation, conditions B for activation of glycosyl fluorides.
Oxathiolanes may be synthesised from aldehydes and mer-captoethanol using NBS as a catalyst the reverse reaction is also possible in aqueous acetone.Glycosidation can be achieved using thioglycosides activated by NBS and a catalytic amount of strong acid salts. 43... [Pg.49]

Dithioacetal, Trithioorthoester, and Thioglycoside Activation. DMTSF provides a chemoselective reagent for dithioacetal activation in the presence of electron-rich alkenes. This bond-forming procedure complements the TiCLj mediated reaction between acetals and sUyl enol ethers demonstrated hy Mukaiyama. The generation of ketone precursors through dithioacetal carban-ion (acyl anion equivalents) chemistry further amplifies the significance of DMTSF activation. [Pg.220]

Thioglycoside Activation. A thioglycoside was successfully converted into a glycosyl fiuoride with DMTSF ... [Pg.221]

S,0-Acetals Including Thioglycosides. Activation of 5,0-acetals with DMTSF in the presence of intramolecular silyl enol ethers affects cyclization (eq 26). As expected the activation is completely selective for the thiol group... [Pg.223]


See other pages where 1-Thioglycosides activators is mentioned: [Pg.53]    [Pg.208]    [Pg.317]    [Pg.234]    [Pg.235]    [Pg.268]    [Pg.118]    [Pg.415]    [Pg.45]    [Pg.45]    [Pg.129]    [Pg.328]    [Pg.545]    [Pg.292]    [Pg.328]    [Pg.545]    [Pg.189]    [Pg.179]    [Pg.136]   
See also in sourсe #XX -- [ Pg.101 ]




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