AbstractThe benzyl‐protected glycosyl acetates1,6,11, and15react with MeOPPh2under catalysis by TMSOTf to yield diastereoselectively the glycosylphosphine oxides2,3,8,12,13, and16, with a strong preference for the 1,2‐cis‐configurated anomers. Hydrogenolysis of the major products gave the crystalline, unprotected phosphine oxides4,9,14, and17, of which4was transformed in to the acetate5, and9into the benzoate10. The benzylated phosphine oxides4,8,12, and16were reduced with Cl3SiH in the presence of a tertiary amine to form the phosphines18,21,24, and26, which were transformed into the phosphine sulfides19,22,25, and27. Moreover,18and21, were characterized as the borane adducts20, and23. The structure of the (arabinofuranosyl)phosphine oxide12, the corresponding sulfide25, and of the borane complex20were established by X‐ray analysis. According to NMR spectroscopy, the equatorial pyranosylphosphine oxide8, the sulfide22, and the borane complex23adopt a4C1conformation. The axial phosphine oxide2is a flattened4C1, the sulfide19exists as aB2,5, and the borane complex20is a flattened4C1in the solid sate and aB2,5in solution. Thus, the conformational behavior of these α‐D‐glucopyranose derivatives reflects the steric requirement of the P