724
3
Chemical Glycosylation Reactions
⊡ Scheme 43
⊡ Scheme 44
Studies of hetero Diels–Alder condensation that used enantiopure substituted aldehydes found
that the catalyzed additions had a high and predictable stereoselectivity [231]. The synthesis
of N-acetylneuraminic acid 130 [232] from diene 127 and (S)-selenoaldehyde 128, which is
shown below, illustrates this point ( > Scheme 44).
A brand-new methodology for synthesizing glycals from noncarbohydrate precursors, one
based on cyclization of acetylenic alcohols, has emerged from the field of metalorganics.
Molybdenum pentacarbonyl-trialkylamine complexes have been found to efficiently catalyze
cyclization of 1-alkyn-4-ols to substituted dihydrofurans [233,234]. This same transformation
has been successfully carried out on asymmetrically substituted alcohols; the furanoid glycals
132, 134, and 135 ( > Scheme 45) so obtained have in turn been used as intermediates in the
synthesis of nucleosides [235].
⊡ Scheme 45
3
Chemical Glycosylation Reactions
⊡ Scheme 43
⊡ Scheme 44
Studies of hetero Diels–Alder condensation that used enantiopure substituted aldehydes found
that the catalyzed additions had a high and predictable stereoselectivity [231]. The synthesis
of N-acetylneuraminic acid 130 [232] from diene 127 and (S)-selenoaldehyde 128, which is
shown below, illustrates this point ( > Scheme 44).
A brand-new methodology for synthesizing glycals from noncarbohydrate precursors, one
based on cyclization of acetylenic alcohols, has emerged from the field of metalorganics.
Molybdenum pentacarbonyl-trialkylamine complexes have been found to efficiently catalyze
cyclization of 1-alkyn-4-ols to substituted dihydrofurans [233,234]. This same transformation
has been successfully carried out on asymmetrically substituted alcohols; the furanoid glycals
132, 134, and 135 ( > Scheme 45) so obtained have in turn been used as intermediates in the
synthesis of nucleosides [235].
⊡ Scheme 45