312
2
General Synthetic Methods
⊡ Scheme 12
⊡ Scheme 13
Using the Henry reaction [29], addition of nitromethane to the carbonyl group of 5-O-benzoyl1,2-O-isopropylidene-α-D-erythro-ketofuranos-3-ulose 40 took place stereoselectively to give
ribo isomer 41 in almost qunatitative yield ( > Scheme 14). KF was found to be better than
any other bases for this reaction. The absolute configuration of all asymmetric carbon atoms
in 41 was confirmed by single-crystal X-ray crystallographic analysis. The stereoselectivity probably resulted from the steric hindrance of the 1,2-O-isopropylidene group. Several
new C-branched iminosugar derivatives bearing a pyrrole ring, such as 42, were synthesized
from 41.
2.3 Wittig Reaction
Wittig reaction and its variants (e. g., Wadsworth–Emmons, Wittig–Horner, etc) are widely applied in the synthesis of C-branched sugar derivatives. The Wittig reagent reacts with
aldehyde or ketone sugar affording the C=C bond as a potent functional group which could
2
General Synthetic Methods
⊡ Scheme 12
⊡ Scheme 13
Using the Henry reaction [29], addition of nitromethane to the carbonyl group of 5-O-benzoyl1,2-O-isopropylidene-α-D-erythro-ketofuranos-3-ulose 40 took place stereoselectively to give
ribo isomer 41 in almost qunatitative yield ( > Scheme 14). KF was found to be better than
any other bases for this reaction. The absolute configuration of all asymmetric carbon atoms
in 41 was confirmed by single-crystal X-ray crystallographic analysis. The stereoselectivity probably resulted from the steric hindrance of the 1,2-O-isopropylidene group. Several
new C-branched iminosugar derivatives bearing a pyrrole ring, such as 42, were synthesized
from 41.
2.3 Wittig Reaction
Wittig reaction and its variants (e. g., Wadsworth–Emmons, Wittig–Horner, etc) are widely applied in the synthesis of C-branched sugar derivatives. The Wittig reagent reacts with
aldehyde or ketone sugar affording the C=C bond as a potent functional group which could