Electrochemical glycosylation - Carbohydrate Chemistry: Chemical and Biological Approaches - page 168

2.3 Electrochemical activation of Se- and Te-glycosides
The groups of Balavoine and Lubineau reported in one of their joint
publications the first electrochemical activation of selenoglycosides. 12
They found that the oxidation potentials of the perbenzylated phenyl
selenoglucoside 68 was lower than that of the corresponding thiogluco-
side 15 (1.36 V vs. 1.50 V), and the same trend was observed also for the
peracetylated derivatives 69 and 16 (1.35 V vs. 1.67 V). They anticipated
that this behaviour would facilitate the use of sugar protecting groups
more prone to oxidation. However, it was pointed out that similar low
oxidation potentials can be reached and even surpassed by phenyl thio-
glycosides bearing one or more methoxy groups onto the aromatic ring
(see section 2.2).
Two years later, Yamago, Yoshida and co-workers described the first
electrochemical activation of another member of the chalcogenoglyco-
side family, the telluroglycoside. 25 As expected, the oxidation potentials
of the latter compounds are in the 0.6-0.9 V range, well below the values
found for the corresponding selenoglycosides. The glycosylation re-
actions were carried out in a divided cell using variously p-substituted
phenyl telluroglucosides and two aliphatic alcohols (cyclohexanol,
3-phenyl-1-propanol) and one sugar alcohol as the acceptors. Indeed, the
coupling between 72 and 73 gave the corresponding disaccharides 74 in
moderate yield as a mixture of anomers.
In a subsequent article, 26 the same authors found that better yields
of simple O-glycosides as well as disaccharides could be obtained by
performing the electrochemical activation of telluroglycosides in an un-
divided cell. Thus, the reaction of the acceptor 73 with 75 (1 equiv.),
the tetra-O-benzoylated analogue of 72, afforded the corresponding
disaccharide in 90% yield as the pure b- D anomer. In the same paper
an extensive study was reported on the selective activation of S-, Se-, and
Te-glycosides taking advantage of their significantly different oxidation
potentials, which can be finely tuned both by the para-substituent of