β-L-Rhamnosylation and β-D-Mannosylation Mediated by 4-O-Ester Groups in Weakly Nucleophilic Environment

Eq-4-O-acyl group directed β-rhamnosylation and β-mannosylation are achieved in carborane or BARF anion formed weakly nucleophilic environment with the assistance of a 2,3-orthocarbonate group. The 4-O-acyl group plays a critical role in directing the β-selectivity, and the weakly coordinating anion is essential to amplify this direction. The orthocarbonate group could be readily removed with 1,3-propanediol in the presence of BF3.Et2O.