16. Anomeric Anhydro Sugars

Anomeric anhydro sugars are sugar derivatives where the anomeric carbon participates in an acetal linkage with two of the hydroxyl groups of the sugar. They are essentially intramolecular glycosides, and their bicyclic nature provides a powerful conformational constraint that greatly influences their reactivity. This chapter reviews the occurrence, properties, formation, and reactions of anomeric anhydro sugars. Particular emphasis is placed on 1,2- and 1,6‑anhydropyranoses, including conformational aspects and ring‐opening reactions. Epoxide‐containing 1,6‑anhydro sugars (Černý epoxides) are briefly reviewed, and the formation and some reactions of the 1,6‑anhydro sugar enone, levoglucosenone, is covered. An overview is given of the use of 1,2‑anhydro sugar as glycosyl donors. Also discussed are the formation and reactions of anomeric anhydro sugars containing nitrogen, sulfur, or selenium.