Synthesis of Glycosylphosphine Oxides and Related Compounds

The benzyl‐protected glycosyl acetates 1 , 6 , 11 , and 15 react with MeOPPh 2 under catalysis by TMSOTf to yield diastereoselectively the glycosylphosphine oxides 2 , 3 , 8 , 12 , 13 , and 16 , with a strong preference for the 1,2‐ cis ‐configurated anomers. Hydrogenolysis of the major products gave the crystalline, unprotected phosphine oxides 4 , 9 , 14 , and 17 , of which 4 was transformed in to the acetate 5 , and 9 into the benzoate 10 . The benzylated phosphine oxides 4 , 8 , 12 , and 16 were reduced with Cl 3 SiH in the presence of a tertiary amine to form the phosphines 18 , 21 , 24 , and 26 , which were transformed into the phosphine sulfides 19 , 22 , 25 , and 27 . Moreover, 18 and 21 , were characterized as the borane adducts 20 , and 23 . The structure of the (arabinofuranosyl)phosphine oxide 12 , the corresponding sulfide 25 , and of the borane complex 20 were established by X‐ray analysis. According to NMR spectroscopy, the equatorial pyranosylphosphine oxide 8 , the sulfide 22 , and the borane complex 23 adopt a 4 C 1 conformation. The axial phosphine oxide 2 is a flattened 4 C 1 , the sulfide 19 exists as a B 2,5 , and the borane complex 20 is a flattened 4 C 1 in the solid sate and a B 2,5 in solution. Thus, the conformational behavior of these α‐ D ‐glucopyranose derivatives reflects the steric requirement of the P‐substituents.