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

A strategy allowing the straightforward synthesis of 1- C -phosphonomethyl and 1- C -phosphonodifluoromethyl iminosugars is reported. Conversion of sugar lactams to the corresponding imines with Schwartz's reagent followed by their reaction with LiCH 2 P(O)(OEt) 2 and LiCF 2 P(O)(OEt) 2 stereoselectively afforded the 1,2- cis and 1,2- trans 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- C -phosphonomethyl iminosugars.