Stereoselective Synthesis of 1--Diethylphosphonomethyl and -difluoromethyl Iminosugars from Sugar Lactams.

A strategy allowing the straightforward synthesis of 1--phosphonomethyl and 1--phosphonodifluoromethyl iminosugars is reported. Conversion of sugar lactams to the corresponding imines with Schwartz's reagent followed by their reaction with LiCHP(O)(OEt) and LiCFP(O)(OEt) stereoselectively afforded the 1,2- and 1,2- glycosyl phosphonates, respectively, in modest to good yields. Application of this methodology to C-2 orthogonally protected sugar lactams paved the way to 2-acetamido- and 2-deoxy-1--phosphonomethyl iminosugars.