Hydrogenolysis of benzyl 2,3-anhydro-α-D-allopyranoside (4) in tetrahydrofuran over palladium–charcoal afforded crystalline 2,3-anhydro-α-D-allopyranose (6a). When dissolved in water this sugar underwent rapid mutarotation to give an equilibrium mixture containing mainly the α-pyranose (6a)(41%) and the β-furanose (6d)(42%), together with the β-pyranose (6b) and the α-furanose (6c)(5 and 12%, not individually assigned). 2,3-Anhydro-D-ribose, as an equilibrium mixture (13), has been prepared by hydrogenolysis of benzyl 2,3-anhydro-α-D-ribopyranoside (12). 2-O-Methylsulphonyl-α-D-mannopyranose (18) has been prepared and shown to give 1,6-anhydro-β-D-glucopyranose (20) with base.