Catching elusive glycosyl cations in a condensed phase with HF/SbF₅ superacid

Area of Science:

• Carbohydrate Chemistry
• Organic Chemistry
• Physical Chemistry

Background:

• Glycosyl cations are crucial intermediates in glycosylation reactions.
• Their high reactivity and short lifespan in organic media have prevented direct observation and structural studies.

Purpose of the Study:

• To generate and stabilize glycosyl cations in a condensed phase.
• To investigate the three-dimensional structure of these transient species.
• To understand the influence of glycosyl cation structure on glycosylation stereochemistry.

Main Methods:

• Utilized liquid hydrofluoric acid-antimony pentafluoride (HF/SbF5) superacid as a stabilizing medium.
• Employed Nuclear Magnetic Resonance (NMR) spectroscopy for structural analysis.
• Performed complementary computational studies to aid structural elucidation.
• Used deuteration to probe the impact of cation structure on reaction outcomes.

Main Results:

• Successfully generated and stabilized glycosyl cations from peracetylated 2-deoxy and 2-bromoglucopyranose.
• Determined the three-dimensional structure of stabilized glycosyl cations using NMR and computations.
• Demonstrated that cation structure significantly influences the stereochemical outcome of glycosylation.

Conclusions:

• The use of HF/SbF5 superacid allows for the unprecedented stabilization and structural characterization of glycosyl cations.
• This work provides direct evidence for the role of glycosyl cation structure in controlling glycosylation stereochemistry.
• The findings advance the understanding of fundamental carbohydrate chemistry and reaction mechanisms.