Levoglucosan (1,6-anhydro-β-D-glucopyranose) is a bicyclic anhydro sugar in which the C1 anomeric and C6 hydroxyl are linked through an internal ether bridge, locking the pyranose in the ¹C₄ (or alternative) chair. It is the principal pyrolysis product of cellulose and is widely used as a biomarker for biomass-burning aerosols in atmospheric chemistry, as a starting material for chiral synthesis and oligosaccharide building blocks in carbohydrate chemistry, and as a model compound in glycoside chemistry.