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In the iridium-catalyzed coupling reaction of the 1-position of sugar with borate esters, **strict control of water and oxygen** is necessary. The reasons are as follows:
1. **Iridium catalyst sensitivity**:
- Iridium catalysts (such as [Ir(cod)Cl]₂ or Ir(I) complexes) are easily oxidized by oxygen and deactivated, resulting in decreased reaction efficiency.
- Water will hydrolyze the borate ester (such as B₂pin₂), generating borate by-products, which consume the raw materials and inhibit the reaction.
2. **Stability of sugar-ene substrates**:
- The olefinic bonds of sugar-ene may undergo hydrolysis or oxidation side reactions in the presence of water and oxygen.
**Optimization suggestions**:
- Use **Schlenk technique** or glove box operation to ensure no water or oxygen;
- Add molecular sieves (4Å) or desiccants (such as MgSO₄) to remove water;
- Pre-activate the catalyst (such as heating or adding phosphine ligands). If the result is still not satisfactory, one can try adjusting the ligand (such as dtbpy) or switch to a more stable iridium catalyst system.
