644
3
Chemical Glycosylation Reactions
⊡ Scheme 75
CB glycosides in the synthesis of α-C-glycosides
5.8 2 -Carboxybenzyl Glycosides as Glycosyl Donors
for C-Glycosylation
Glycosylation of various glycosyl acceptors (NuH or NuTMS, > Scheme 75) with manno- and
gluco- CB glycosyl donors 450 and 454, respectively afforded α-C-glycosides 455, exclusively
or predominantly in good yields [218]. Experimentally these reactions were carried out by
addition of the donor to a solution of the acceptor, DTBMP, and Tf 2 O in CH 2 Cl 2 at −78 °C.
These modified conditions led to increased yields of C-glycosides and minimized the amount
of self-condensed esters 456.
6 O-Heteroaryl Glycosyl Donors
Glycosides of some heterocycles have also been investigated as glycosyl donors.
6.1 2-Pyridyl 2,3,4,6-tetra-O-benzyl-D-glucosides
The first example, reported by Nikolaev and Kochetkov [219], dealt with the use of 2-pyridyl
2,3,4,6-tetra-O-benzyl-β-D-glucoside in glycosylation. This heteroaryl glycoside was prepared by glycosylation of 2(1H)-pyridinone by the corresponding sugar chloride, and was
activated by electrophiles, such as MeOTf and Et 3 O·BF 4 , to give mixtures of cis- and transglycosides.
6.2 O-Hetaryl Glycosides by Schmidt’s Group
Schmidt and co-workers [168,220,221] reported the preparation, and use in glycosylation
reactions of several O-hetaryl glycosides, e. g. 458, conveniently prepared by anomeric
3
Chemical Glycosylation Reactions
⊡ Scheme 75
CB glycosides in the synthesis of α-C-glycosides
5.8 2 -Carboxybenzyl Glycosides as Glycosyl Donors
for C-Glycosylation
Glycosylation of various glycosyl acceptors (NuH or NuTMS, > Scheme 75) with manno- and
gluco- CB glycosyl donors 450 and 454, respectively afforded α-C-glycosides 455, exclusively
or predominantly in good yields [218]. Experimentally these reactions were carried out by
addition of the donor to a solution of the acceptor, DTBMP, and Tf 2 O in CH 2 Cl 2 at −78 °C.
These modified conditions led to increased yields of C-glycosides and minimized the amount
of self-condensed esters 456.
6 O-Heteroaryl Glycosyl Donors
Glycosides of some heterocycles have also been investigated as glycosyl donors.
6.1 2-Pyridyl 2,3,4,6-tetra-O-benzyl-D-glucosides
The first example, reported by Nikolaev and Kochetkov [219], dealt with the use of 2-pyridyl
2,3,4,6-tetra-O-benzyl-β-D-glucoside in glycosylation. This heteroaryl glycoside was prepared by glycosylation of 2(1H)-pyridinone by the corresponding sugar chloride, and was
activated by electrophiles, such as MeOTf and Et 3 O·BF 4 , to give mixtures of cis- and transglycosides.
6.2 O-Hetaryl Glycosides by Schmidt’s Group
Schmidt and co-workers [168,220,221] reported the preparation, and use in glycosylation
reactions of several O-hetaryl glycosides, e. g. 458, conveniently prepared by anomeric