Glycals in the Stereoselective Synthesis of Triterpene 2-Deoxy-α-l-Glycosides under Conditions of Acidic Catalysis

3β-Hydroxy triterpenes of the oleanane, ursane, and lupane types were successfully glycosylated with acetylated l-glucal and l-rhamnal under conditions of acidic catalysis (anhydrous cation-exchange resin and LiBr). The 2-deoxy- and 2,6-dideoxy-α-l-arabino-hexopyranosides (1−5) were stereoselectively prepared in 83−90% yields, following deacetylation under mild conditions, which led to the target triterpene 2-deoxy-α-l-glycosides (6−10).