Stereoselektive synthese von α-glucosiden mit 1,1′ -diacetal-struktur

Reaction of ($\text{1b}$) and ($\text{1d}$) with the acetal ($\text{2a}$) in presence of trimethylsilyl trifluoromethanesulfonate at ?70° C gives the α-glucosides ($\text{3a}$) and ($\text{4a}$), whereas ($\text{1a}$) and ($\text{1c}$) lead to the β-glucosides ($\text{4c}$) and ($\text{4b}$). At 0° C reaction of ($\text{1a}$) with the acetals ($\text{2b-g}$) gives exclusively the α-glucosides ($\text{3b-g}$).