A series of fluorine and non-fluorine-substituted C-glucosylidenes (exo-glucals) has been synthesized via a modified Julia olefination. The deprotected exo-glucals were prepared in five steps from commercially available D-gluconolactone. The evaluation of this original family of compounds against a panel of glycosidases showed a highly specific in vitro activity towards mammalian β-glucosidase depending on the double bond substituents.