Table 1. Optimization of the Conditions for Stereoselective α-Glycosidation of l-QuiN3 Using 14 as a Model Acceptor.
| entry | donor | solvent | activation method | yielda | α:βb |
|---|---|---|---|---|---|
| 1 | 6a | CH2Cl2 | NIS, TfOH 0 °C | 87 | 3:1 |
| 2 | 6a | CH2Cl2:Et2O (1:1) | NIS, TfOH 0 °C | 85 | 8:1 |
| 3 | 6a | Tol | NIS, TfOH 0 °C | 84 | 3:1 |
| 4 | 6a | Tol:dioxane (1:1) | NIS, TfOH 0 °C | 77 | 5:1 |
| 5 | 6a | THF | NIS, TfOH 0 °C | 78 | 2:3 |
| 6 | 6a | CH2Cl2:Et2O (1:1) | TolSCl AgOTf −78 °C to rt | 87 | 1:1 |
| 7 | 6a | CH2Cl2:Et2O (1:1) | TolSCl, AgOTf −40 °C to rt | 88 | 15:1 |
| 8 | 6b | CH2Cl2:Et2O (1:1) | TMSOTf 0 °C | 85 | 5:1 |
| 9 | 6c | CH2Cl2 | TMSOTf thiophene 0 °C | 83 | 12:1 |
a
Isolated yields (%).
b
α:β anomeric ratios were determined by 1H NMR analysis of reaction mixtures.