Dissecting Tin-Based Activation and Anomerization Pathways in Carbohydrate Chemistry

Area of Science:

• Carbohydrate Chemistry
• Organometallic Chemistry
• Computational Chemistry

Background:

• Tin-based Lewis acids are crucial catalysts in glycosylation reactions.
• The exact mechanism of tin promoters in these transformations remains unclear.
• Understanding tin's role is vital for developing efficient synthetic strategies.

Purpose of the Study:

• To elucidate the mechanistic role of Sn(IV) promoters in glycosylation.
• To investigate the interaction between tin promoters and glycosyl donors.
• To clarify the influence of tin on anomerization processes.

Main Methods:

• ¹¹⁹Sn Nuclear Magnetic Resonance (NMR) spectroscopy to probe tin species.
• Density Functional Theory (DFT) calculations to model reaction pathways.
• Comparison of experimental and computed ¹¹⁹Sn chemical shifts for structural validation.

Main Results:

• Evidence for the formation of stable ion pairs between glycosyl oxocarbenium ions and tin counterions.
• ¹¹⁹Sn NMR chemical shifts confirm the coordination environment of tin species.
• DFT calculations support a detailed mechanism for anomerization involving C-O bond cleavage and rotation.

Conclusions:

• Tin promoters actively participate in glycosylation by forming ion pairs with key intermediates.
• The study provides structural insights into tin coordination during the reaction.
• A refined mechanism for tin-mediated anomerization is proposed, aiding Lewis acid design.