Synthesis of C-glycosyl compounds by the wittig iodocyclization procedure. Differences from mercuriocyclization

Various sugars were C-glycosylated by treatment with methylenetriphenyl-phosphorane and subsequent iodocyclization of the resulting hept- and hex-enitols. In all cases, a Cglycofuranosyl compound was obtained, except for 3,4,5,7-tetra-O-benzyl-1,2-dideoxy-d-manno-hept-1-enitol which yielded a C-pyranosyl compound. High stereoselectoin, with formation of the 1,2-cis adduct as major product, was observed when an asymmetric center was present in the position adjacent to the double bond.