750
3
Chemical Glycosylation Reactions
⊡ Scheme 23
to the enone of levoglucosenone leads to C-4 methyl-substituted carbohydrates [69,70]. Furthermore, conjugate addition of glycosyl nitronates [71] or thioglycosides [72] with levoglucosenone affords C- or S-linked disaccharides, respectively. The alkene of levoglucosenone
acts as a dienophile in Diels–Alder reactions [73]. Some transformations of levoglucosenone
are summarized in > Scheme 23.
5 Anhydro Sugars Containing Nitrogen, Sulfur, or Selenium
A number of anhydro sugars are known that contain nitrogen, sulfur, or selenium. Tri-O-acetyl
thioglucosan was first prepared in 1963 by Akagi and co-workers by treatment of S-glucosyl dithiocarbonate (21; > Fig. 2) with sodium methoxide [74]. Since that time, numerous
syntheses have been reported that rely on the introduction of a thioester at C-1 or C-6 and
the activation of the alternate position with a halide or sulfonate group [75,76]. Treatment
of a ‘doubly activated’ hexopyranose such as (24) with hydrogen sulfide and triethylamine
⊡ Figure 2
3
Chemical Glycosylation Reactions
⊡ Scheme 23
to the enone of levoglucosenone leads to C-4 methyl-substituted carbohydrates [69,70]. Furthermore, conjugate addition of glycosyl nitronates [71] or thioglycosides [72] with levoglucosenone affords C- or S-linked disaccharides, respectively. The alkene of levoglucosenone
acts as a dienophile in Diels–Alder reactions [73]. Some transformations of levoglucosenone
are summarized in > Scheme 23.
5 Anhydro Sugars Containing Nitrogen, Sulfur, or Selenium
A number of anhydro sugars are known that contain nitrogen, sulfur, or selenium. Tri-O-acetyl
thioglucosan was first prepared in 1963 by Akagi and co-workers by treatment of S-glucosyl dithiocarbonate (21; > Fig. 2) with sodium methoxide [74]. Since that time, numerous
syntheses have been reported that rely on the introduction of a thioester at C-1 or C-6 and
the activation of the alternate position with a halide or sulfonate group [75,76]. Treatment
of a ‘doubly activated’ hexopyranose such as (24) with hydrogen sulfide and triethylamine
⊡ Figure 2