Direct synthesis of the isosteric phosphono analogues of α-L-rhamnose 1-phosphate and β-L-fucose 1-phosphate

The isosteric phosphono analogue of α-L-rhamnose 1-phosphate has been stereoselectively synthesized by reaction of 2,3,5-tri-O-benzyl-L-rhamnose with tetraethyl methylenediphosphonate and sodium hydride in diglyme, followed by deprotection with iodotrimethylsilane. To synthesize stereoselectively the isosteric phosphono analogue of β-L-fucose 1-phosphate, 2,3,5-tri-O-benzyl-L-fuconolactone was treated with lithiated dimethyl methylenephosphonate, and the 3,4,5-tri-O-benzyl-1,7-dideoxy-1-(phosphonodimethyl)-L-galactoheptulopyranose obtained was stereoselectively reduced with triethylsilane and boron trifluoride etherate to afford the dimethyl (2,3,4-tri-O-benzyl-β-L-fucopyranosyl)methanephosphonate which was finally deprotected with iodotrimethylsilane.