156
2
General Synthetic Methods
⊡ Scheme 65
Two bonds are missing in the first compound
⊡ Scheme 66
Anomeric O-alkylation via 1,2-O-stannylene acetals
derivatives, the use of DMAP as the base gave an α/β ratio similar to the starting 1-OH
derivative. In contrast, formation of the β-anomer was favored using 1,4-dimethyl piperazine
( > Scheme 67b) [385,386,387].
The reverse situation, in which the phenol acts as the nucleophile attacking activated carbohydrate hemiacetals, has also found several practical applications preparing O-aryl glycosides [388]. However, this situation implies an attack at the anomeric carbon and not at the
anomeric oxygen.
3.1.2 Anomeric O-Dealkylation
On treatment with aqueous acid, glycosides are hydrolyzed to give the corresponding alcohol
and the reducing sugar. Solvolysis of glycosidic bonds is one of the most general and important
reactions in carbohydrate chemistry and so the literature on the acid hydrolysis of O-glycosidic
2
General Synthetic Methods
⊡ Scheme 65
Two bonds are missing in the first compound
⊡ Scheme 66
Anomeric O-alkylation via 1,2-O-stannylene acetals
derivatives, the use of DMAP as the base gave an α/β ratio similar to the starting 1-OH
derivative. In contrast, formation of the β-anomer was favored using 1,4-dimethyl piperazine
( > Scheme 67b) [385,386,387].
The reverse situation, in which the phenol acts as the nucleophile attacking activated carbohydrate hemiacetals, has also found several practical applications preparing O-aryl glycosides [388]. However, this situation implies an attack at the anomeric carbon and not at the
anomeric oxygen.
3.1.2 Anomeric O-Dealkylation
On treatment with aqueous acid, glycosides are hydrolyzed to give the corresponding alcohol
and the reducing sugar. Solvolysis of glycosidic bonds is one of the most general and important
reactions in carbohydrate chemistry and so the literature on the acid hydrolysis of O-glycosidic