S-Glycosylation
3.5
687
tives is usually straight-forward using participating protecting groups. However, also the construction of 1,2-cis compounds is usually performed using acetyl protecting groups, but then
starting from 1,2-trans halogeno sugars employing conditions favoring S N 2-type reactions to
give the 1,2-cis products. The anomeric thiol can either be isolated (with the concomitant
problem of disulfide formation) and is then often activated as the thiolate during the coupling with the electrophile using, e. g., sodium hydride, or the cleavage and activation can be
accomplished in situ. The displacement reaction is performed using an aprotic polar solvent
or a phase-transfer reagent and non-polar solvents. Activation through complete deacetylation
⊡ Scheme 56
⊡ Scheme 57
⊡ Scheme 58
⊡ Scheme 59
⊡ Scheme 60
3.5
687
tives is usually straight-forward using participating protecting groups. However, also the construction of 1,2-cis compounds is usually performed using acetyl protecting groups, but then
starting from 1,2-trans halogeno sugars employing conditions favoring S N 2-type reactions to
give the 1,2-cis products. The anomeric thiol can either be isolated (with the concomitant
problem of disulfide formation) and is then often activated as the thiolate during the coupling with the electrophile using, e. g., sodium hydride, or the cleavage and activation can be
accomplished in situ. The displacement reaction is performed using an aprotic polar solvent
or a phase-transfer reagent and non-polar solvents. Activation through complete deacetylation
⊡ Scheme 56
⊡ Scheme 57
⊡ Scheme 58
⊡ Scheme 59
⊡ Scheme 60