Thioethyl glycosides

Thiophenyl Glycosides and Selenophenyl Glycosides (Different Donors, Common Activator) Changing from thioethyl glycosides to selenophenyl glycosides... 

S. Houdier and P. Vottero, Steric effect of a bulky 6-substituent in the I+-promoted glycosylation with pent-4-enyI and thioethyl glycosides, Carbohydr. Res. 232 349 (1992). 

There has been some degree of success in the glycosylation of latent nitrothio-phenyl glycosides with thioethyl glycosides (Fig. 20),51 but results have not been entirely encouraging to date. 

Other saccharide electrophiles utilized have been an a, 8-unsaturated keto derivative and ethylated thiolevoglucosan. The former yielded in a Michael addition with tetra-O-acetyl-l-thio-/3-D-glucop)Tanose the (1— 4)-linked disaccharide in an excellent yield (O Scheme 59) [183,184]. The latter, when reacted with the sodium salt of the above glucose thiol, gave the (1 6)-linked disaccharide as its thioethyl glycoside (O Scheme 60) [185]. 

Fig. 3 Three levels of anraneric reactivity in thioethyl glycosides...

On the other hand, the reactivity-tuned coupling of selenophenyl donor 92 and thioethyl glycoside 93, mediated by NIS/TMSOTf, proceeded smoothly to give the disaccharide 94 as a single anomer in 77% yield. The Aloe group was selected to control the a-selectivity of the glycosylation reaction. 

The thioethyl glycosides thus produced, could be converted into the mannosides (75—>85, Scheme 16). This overall inversion of configuration at C2 proceeded via an oxidation-reduction sequence to give, exclusively, the mannose derivative. The... 

---