- Secondary amine salt catalyzed controlled activation of 2-deoxy sugar lactols towards alpha-selective dehydrative glycosylation
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A new organocatalytic glycosylation method exploiting the lactol functionality has been disclosed. The catalytic generation of glycosyl oxacarbenium ions from lactols under forcible conditions via weakly Br?nsted-acidic, readily available secondary amine salts affects the diastereoselective glycosylation of 2-deoxypyranoses and furanoses. This operationally simple iminium catalyzed activation of 2-deoxy hemi-acetals is a potential alternative to the existing cumbersome methods that need specialized handling. The mechanisms for this unique transformation and kinetic/thermodynamic effects have been discussed based on both experimental evidence and theoretical studies.
- Ghosh, Titli,Mukherji, Ananya,Srivastava, Hemant Kumar,Kancharla, Pavan K.
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supporting information
p. 2870 - 2875
(2018/05/03)
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- α-Selective organocatalytic synthesis of 2-deoxygalactosides
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Alpha rules: A thiourea acts as an efficient organocatalyst for the glycosylation of protected galactals to form oligosaccharides containing a 2-deoxymonosaccharide moiety (see scheme). The reaction is highly stereoselective for α-linkages and proceeds by way of a syn-addition mechanism. Copyright
- Balmond, Edward I.,Coe, Diane M.,Galan, M. Carmen,McGarrigle, Eoghan M.
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supporting information
p. 9152 - 9155
(2012/10/29)
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- Synthesis of positional thiol analogs of β-D-galactopyranose
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Approaches toward the synthesis of thio-β-D-galactose derivatives are described. These compounds were prepared from the parent carbohydrates: D-galactose, methyl β-D-galactoside and methyl β-D-glucoside, respectively. It was found that not only the strategies of protecting group introduction and selective deprotection, but also the choices of solvent and nucleophilic reagent concentration were crucial to allow the efficient introduction of sulfur at different positions of the galactose ring. The effects from the solvent, the nucleophilic reagent concentration, and the protecting group patterns have been investigated. The results clearly show that ester protecting groups play highly important roles for the synthesis of thio-containing carbohydrates, requiring nonpolar solvents to suppress the neighboring group participation. For the Lattrell-Dax (nitrite-mediated) inversion reaction, employed in the synthetic route to the 2-thio-β-D- galactoside, intramolecular nucleophilic attack, as well as stronger stereospecific ester activation, are necessary to overcome hindrance from 4,6-O-benzylidene protection. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Pei, Zhichao,Dong, Hai,Caraballo, Remi,Ramstroem, Olof
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p. 4927 - 4934
(2008/03/14)
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- A mild and efficient approach for the regioselective silyl-mediated protection-deprotection of C-4 hydroxyl group on carbohydrates
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A regioselective route is reported, which makes the free 4-OH group of hexopyranoses and derivatives easily and rapidly available. This protocol shows high efficiency on intermediates, such as 1a, which contain a TIPS protective group at C-6 and necessarily a benzoyl group at C-4. Treatment of 1a with TBAF cleaves the TIPS protecting group and gives rise to an intramolecular migration of the benzoyl group at C-4 to the less crowded C-6 position.
- Graziani, Andrea,Passacantilli, Pietro,Piancatelli, Giovanni,Tani, Simona
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p. 3857 - 3860
(2007/10/03)
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