Formation of septanoses from hexopyranosides via 5,6-exo-glycals

► Dihydroxylation of 5,6-exo-glucal gives 1,6-anhydro-5-keto-sugars. ► A new stable, crystalline, septanosyl chloride has been obtained. ► Unusual ring opening of the 1,6-anhydro-structure gives new septanose derivatives.