A new route to exo-glycals is described which starts from S-glycoside dioxides and utilises Meyers' variant of the Ramberg-Backlund rearrangement. The methodology is successful with glucose, galactose, mannose, xylose, fucose and ribose derivatives, and has been used to prepare di-, tri- and tetra-substituted alkenes. (C) 1998 Elsevier Science Ltd. All rights reserved.