310
2
General Synthetic Methods
⊡ Scheme 7
⊡ Scheme 8
uct of the Aldol-Cannizzaro reaction can be further transformed into locked nucleic acid
(LNC) [23] containing other functional groups, such as ethenyl [24], ethynyl [25], and so
on [26] ( > Scheme 10).
2.2.3 Nitroaldol Condensations (Henry Reaction)
Condensation of aldehyde or ketone with nitroalkane, bearing an α-hydrogen, stereoselectively enables the formation of a new carbon–carbon bond under mild basic conditions with the
generation of a β-nitroalcohol, which is called nitroaldol condensation or the Henry reaction
( > Scheme 11). This is a good method for preparing the branch-chain sugars containing nitrogen, since it provides a polyhydroxylated carbon framework with multiple stereogenic centers
as well as the possibility for transformation of the nitro group to other functional groups. Many
natural or unnatural azasugars have been obtained through this reaction for the development
of new glycosidase inhibitors in recent years.
Bols [27] reported an improved synthesis of isofagomin 32 and noeuromycin 34 from D-arabinose in six and seven steps, respectively. As shown in > Scheme 12, Henry reaction of
ketone sugar 29 gave the nitromethane adduct benzyl 4-deoxy-4-C-nitromethylene-D-arabi-
2
General Synthetic Methods
⊡ Scheme 7
⊡ Scheme 8
uct of the Aldol-Cannizzaro reaction can be further transformed into locked nucleic acid
(LNC) [23] containing other functional groups, such as ethenyl [24], ethynyl [25], and so
on [26] ( > Scheme 10).
2.2.3 Nitroaldol Condensations (Henry Reaction)
Condensation of aldehyde or ketone with nitroalkane, bearing an α-hydrogen, stereoselectively enables the formation of a new carbon–carbon bond under mild basic conditions with the
generation of a β-nitroalcohol, which is called nitroaldol condensation or the Henry reaction
( > Scheme 11). This is a good method for preparing the branch-chain sugars containing nitrogen, since it provides a polyhydroxylated carbon framework with multiple stereogenic centers
as well as the possibility for transformation of the nitro group to other functional groups. Many
natural or unnatural azasugars have been obtained through this reaction for the development
of new glycosidase inhibitors in recent years.
Bols [27] reported an improved synthesis of isofagomin 32 and noeuromycin 34 from D-arabinose in six and seven steps, respectively. As shown in > Scheme 12, Henry reaction of
ketone sugar 29 gave the nitromethane adduct benzyl 4-deoxy-4-C-nitromethylene-D-arabi-