| Summary: | Acetalization and deacetalation are a pair of routine manipulations to protect and deprotect the 4- and 6-hydroxyl groups of glycosides in the synthesis of glycosyl building blocks. In this study, we found that treatment of SnCl<sub>4</sub> with various carbohydrates containing acetal/ketal groups with the assistance of water in CH<sub>2</sub>Cl<sub>2</sub> led to deacetalization/deketalization products in almost quantitative yields. In addition, for substrates containing both acetal/ketal and <i>p</i>-methoxylbenzyl groups, we also found that the <i>p</i>-methoxylbenzyl group was selectively cleaved by the use of a catalytic amount of SnCl<sub>4</sub>, while the acetal/ketal groups remained. Furthermore, based on this, 4,6-benzylidene glycosides can be conveniently converted to 4,6-OAc or 4-OH, 6-OAc glycosides.
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