20. De novo Synthesis of Monosaccharides

Recent approaches to asymmetric total synthesis of monosaccharides and derivatives are reviewed. They imply biochemical methods or chemical methods, or combinations of both. Aldoses, alditols, deoxysugars, aminodeoxymonosaccharides, and their analogues are considered, including aza- and thiosugars (with nitrogen and sulfur in the pyranose or furanose ring). Most common monosaccharides have three to six carbon‐chains, but examples of long-chain and branched-chain carbohydrates will also be described. Organization of the review is based on the synthetic methodology rather than on the types of targeted sugar, starting with aldolase‐catalyzed aldol reactions of achiral precursors, and the now popular amino-acid‐catalyzed aldol and Mannich reactions. Chain elongations of small aldose derivatives with one, two, three, or four carbons remain very useful approaches as they allow one to reach a large structural and stereochemical diversity. Other methods apply Diels–Alder or hetero-Diels–Alder additions. Enantiomerically pure monosaccharides have been derived from achiral alkene, diene, and triene derivatives. Almost any targeted natural or non-natural sugar and derivative can be obtained in a few synthetic steps from inexpensive starting materials.