Influence of Various Silyl Protecting Groups on Stereoselective 2-Deoxyrhamnosylation.

The influence of various silyl protecting groups on 2-deoxyrhamnosylation using 2-deoxyrhamnosyl acetates, thioglycosides, and ( p -methoxyphenyl)vinylbenzoate (PMPVB) donors has been presented. C -Glycosylation reactions reveal that tert -butyldimethylsilyl (TBDMS), triisopropylsilyl (TIPS), and tert -butyldiphenylsilyl (TBDPS) silyl protected rhamnosyl oxocarbenium ions have no facial selectivity except for the conformationally ( 4 H 3 ) locked tetraisopropyldisiloxane (TIPDS) protected rhamnose donor, which provides complete α-selectivity. However, TBDPS protected rhamnosyl donors are found to be superior protecting groups for α-stereoselective O -glycosylation reactions with various acceptors. The observed results are found consistent across donors and donor activation conditions. Most importantly, the study was conducted at room temperature unlike the other energy-intensive low-temperature studies and was bound to have more practical utility. The outcomes have been explained using kinetic and thermodynamic analyses.