Further Anomeric Esters
3.3
557
⊡ Scheme 74
(Ref. [89])
a catalytic amount of SnCl 4 -AgClO 4 or Cp 2 HfCl 2 -2AgClO 4 promoted decarboxylation of an
1-O-carbonate sugar to afford the α-glycoside stereoselectively ( > Scheme 73) [86]. At the
same time, they reported the synthesis of mixed β-carbonates of acyl-protected sugar and their
decarboxylative glycosylations promoted by TMSOTf [87] or Hf(OTf) 4 [88] and obtained the
β-glycosides stereoselectively.
On the other hand, Mukai et al. reported a glycosylation reaction based on the alkyneCo 2 (CO) 6 complex, thus O-protected glycopyranose possessing 4-(O-protected-glycosyl)6-phenyl-5-hexynoate residue at an anomeric position was converted to the corresponding
cobalt complex, which on exposure to TMSOTf afforded the product disaccharide in good
yield via the internal delivery of the glycosyl acceptor ( > Scheme 74) [89].
⊡ Scheme 75
(Ref. [90])
3.3
557
⊡ Scheme 74
(Ref. [89])
a catalytic amount of SnCl 4 -AgClO 4 or Cp 2 HfCl 2 -2AgClO 4 promoted decarboxylation of an
1-O-carbonate sugar to afford the α-glycoside stereoselectively ( > Scheme 73) [86]. At the
same time, they reported the synthesis of mixed β-carbonates of acyl-protected sugar and their
decarboxylative glycosylations promoted by TMSOTf [87] or Hf(OTf) 4 [88] and obtained the
β-glycosides stereoselectively.
On the other hand, Mukai et al. reported a glycosylation reaction based on the alkyneCo 2 (CO) 6 complex, thus O-protected glycopyranose possessing 4-(O-protected-glycosyl)6-phenyl-5-hexynoate residue at an anomeric position was converted to the corresponding
cobalt complex, which on exposure to TMSOTf afforded the product disaccharide in good
yield via the internal delivery of the glycosyl acceptor ( > Scheme 74) [89].
⊡ Scheme 75
(Ref. [90])