2 research outputs found
In(III) Triflate-Mediated Solvent-Free Synthesis and Activation of Thioglycosides by Ball Milling and Structural Analysis of Long Chain Alkyl Thioglycosides by TEM and Quantum Chemical Methods
Conventional
solution-phase synthesis of thioglycosides from glycosyl
acetates and thiols in the presence of InÂ(III) triflate as reported
for benzyl thioglucoside failed when applied to the synthesis of phenolic
and alkyl thioglycosides. But, it was achieved in high efficiency
and diastereospecificity with ease by solvent-free grinding in a ball
mill. The acetates in turn were also obtained by the homogenization
of free sugars with stoichiometric amounts of acetic anhydride and
catalytic InÂ(OTf)<sub>3</sub> in the mill as neat products. Per-<i>O</i>-benzylated thioglycosides on grinding with an acceptor
sugar in the presence of InÂ(OTf)<sub>3</sub> yield the corresponding <i>O</i>-glycosides efficiently. The latter in the case of a difficult
secondary alcohol was nearly exclusive (>98%) in 1,2-<i>cis</i>-selectivity. In contrast, the conventional methods for this purpose
require use of a coreagent such as NIS along with the Lewis acid to
help generate the electrophilic species that actually is responsible
for the activation of the thioglycoside donor in situ. The distinctly
different self-assembling features of the peracetylated octadecyl
1-thio-α- and β-d-galactopyranosides observed
by TEM could be rationalized by molecular modeling