Abstract: The invention relates to C-glycose compounds of formula (I) where: S? is a monosaccharide radical or a polysaccharide radical derived from a monosaccharide or polysaccharide S; R is a linear or branched alkyl radical; and Z is an ethylenyl CH?CR1(R2) or an acetylenyl C?CR3 radical. The invention also relates to a method for preparing C-glycoside compounds of formula (III), characterized in that the method consists of a step of reacting a sugar (S), in an aqueous solvent or in the absence of a solvent and in the presence of an organic or mineral base (B), with a phosphonate of formula (II) according to the following reaction pattern: Formulas (II), (III).