Efficient one-pot synthesis of 2-hydroxyethyl per-O-acetyl glycosides

A class of stereo-isomerically-pure alkanediol monoglycosides, 2-hydroxyethyl per- O -acetyl pyranosides ( IIIa-IIIf ), was conveniently prepared by a one-pot reaction of per- O -acetylated pyranoses ( Ia-If ) and 2-( tert -butyldimethylsilyloxy)ethanol ( II ) with catalysis by BF 3 ·OEt 2 . The α -( IIIa ) or β -linked glycosides ( IIIb-IIIf ) with 1,2- trans -configuration were obtained from glycosyl donors with participation of the neighbouring 2- O -acetyl group. BF 3 ·OEt 2 , along with hydrogen fluoride released from BF 3 ·OEt 2 under the experimental conditions used, facilitates the subsequent de-protection of siloxane to successfully afford 2-hydroxyethyl per- O -acetyl-pyranosides.