Synthesis of 1,2‐ cis ‐Configurated Glycosylphosphonates

A synthesis of 1,2‐ cis ‐configurated, non‐isosteric phosphonate analogues of aldose‐1‐phosphates is described. Treatment of 1‐ O ‐acyl‐glycoses 1 , 7 , 13 , and 19 with trialkyl phosphite in the presence of trimethylsilyl trifluoromethanesulfonate gave the 1,2‐ cis ‐configurated glycosylphosphonates 2 , 4 , 8 , 10 , 14 , 16 , 20 , and 22 as the major anomers and the 1,2‐ trans ‐configurated glycosylphosphonates 3 , 5 , 9 , 11 , 15 , 17 , 21 , and 23 as the minor anomers. The 1,2‐ cis ‐configurated phosphonates 4 , 10 , 16 , and 22 were deprotected to give the (β‐ D ‐glucopyranosyl)phosphonate 6 , the (β‐ D ‐mannopyranosyl)phosphonate 12 , the (β‐ D ‐ribofuranosyl)phosphonate 18 , and the (β‐ D ‐arabinofuranosyl)phosphonate 24 , respectively, in high yields. The preferred formation of 1,2‐ cis ‐configurated phosphonates is explained by postulating an equilibrium between the anomeric phosphonium‐salt intermediates (such as 25 and 26 ) and a stabilization of the cis ‐configurated salts through formation of a pentacoordinated species (such as 28 ).