402
2
General Synthetic Methods
metathesis protocol [156,157,158,159]. Under basic conditions, silyl-group shifts occur in
a 6-deoxy-6,6,6-trifluorosugar 192 and form a pyranoside derivative [160]. Acetolysis of the
methyl glycoside 194 mainly affords the piperidine 195 [161]. Azasugar ethyl thioglycoside 197, a new type of azasugar derivative, can be stereoselectively prepared from suitable
glycosylenamine 196, through anhydroazasugar derivatives. The thioethoxy group is introduced through a highly stereoselective substitution. The attack of EtSH was 100% stereoselective [162,163] ( > Scheme 44).
The protected 5-ulose derivative 198 can be converted into the piperidine 199 by reductive amination [164]. The 5-O-sulfonyllactol 200 is reductively transformed into the azasugar 201 by
way of oxime formation [165]. Reductive deprotection of the aminodeoxylactol derivative 202
affords the N-substituted piperidine 203 [166]. The unsaturated alcohol, readily obtained from
the lactol 204 and Grignard reagent, cyclizes into the C-glycoside 206 [167]. The lactol 207 is
converted into the unsaturated dithioacetal, which cyclizes slowly to give 208 on storage [168]
( > Scheme 45).
⊡ Scheme 45
2
General Synthetic Methods
metathesis protocol [156,157,158,159]. Under basic conditions, silyl-group shifts occur in
a 6-deoxy-6,6,6-trifluorosugar 192 and form a pyranoside derivative [160]. Acetolysis of the
methyl glycoside 194 mainly affords the piperidine 195 [161]. Azasugar ethyl thioglycoside 197, a new type of azasugar derivative, can be stereoselectively prepared from suitable
glycosylenamine 196, through anhydroazasugar derivatives. The thioethoxy group is introduced through a highly stereoselective substitution. The attack of EtSH was 100% stereoselective [162,163] ( > Scheme 44).
The protected 5-ulose derivative 198 can be converted into the piperidine 199 by reductive amination [164]. The 5-O-sulfonyllactol 200 is reductively transformed into the azasugar 201 by
way of oxime formation [165]. Reductive deprotection of the aminodeoxylactol derivative 202
affords the N-substituted piperidine 203 [166]. The unsaturated alcohol, readily obtained from
the lactol 204 and Grignard reagent, cyclizes into the C-glycoside 206 [167]. The lactol 207 is
converted into the unsaturated dithioacetal, which cyclizes slowly to give 208 on storage [168]
( > Scheme 45).
⊡ Scheme 45