274
2
General Synthetic Methods
dro ring. The most reactive are oxiranes and oxetanes, with oxolane (THF) and oxane (THP)
derivatives being much less reactive. Selected examples of the representative derivatives: their
synthesis and reactivity, from each group will be presented.
2 Anomeric Anhydrosugars: Synthesis and Reactions
Anomeric anhydrosugars represent a class of molecules that can be regarded as intramolecular glycosides. The glycosydic bond may engage the terminal alcohol of a sugar molecule
(1,6-anhydropyranoses, 1,6-anhydrofuranoses, etc.) or any other atom (1,2-, 1,3-anhydrosugars etc.). The most representative are 1,6- and 1,2-anhydro-sugars; others are less common and
have rather limited synthetic potential [3].
2.1 1,6-Anhydrosugars
2.1.1 1,6-Anhydrohexopyranoses
The most common 1,6-anhydrosugars are anhydro-aldopyranoses, which are formal derivatives of 6,8-dioxabicyclo[3.2.1]octane; less common are anhydro-aldofuranoses.
1,6-Anhydro-β-D-glucopyranose (levoglucosan), the most representative example of this class
of compounds, was first isolated in pure form in 1894 by Tanret upon treatment of naturally
occurring phenolic glycoside with barium hydroxide [2]. This compound is now conveniently
obtained by pyrolysis of starch or cellulose and its production is covered by many patents.
Other 1,6-anhydrosugars with different configurations, such as mannosan or galactosan, may
be prepared by pyrolysis of mannan ivory nut meal or α-lactose [2,3].
Generally, treatment of a sugar with a free hydroxyl group at the C-6 position possessing
a good leaving group at the anomeric position (halogen, azide, tosylate etc.) with a strong base
affords 1,6-anhydropyranoses [3]. Another method consists of a selective activation of a terminal hydroxyl group; this procedure is applicable for most 1,6-anhydro-pyranoses. FraserReid and co-workers described a large-scale synthesis of 1,6-anhydro-D-gluco- and D-mannopyranoses from free sugars by selective activation of the terminal position with tosyl chloride
2
General Synthetic Methods
dro ring. The most reactive are oxiranes and oxetanes, with oxolane (THF) and oxane (THP)
derivatives being much less reactive. Selected examples of the representative derivatives: their
synthesis and reactivity, from each group will be presented.
2 Anomeric Anhydrosugars: Synthesis and Reactions
Anomeric anhydrosugars represent a class of molecules that can be regarded as intramolecular glycosides. The glycosydic bond may engage the terminal alcohol of a sugar molecule
(1,6-anhydropyranoses, 1,6-anhydrofuranoses, etc.) or any other atom (1,2-, 1,3-anhydrosugars etc.). The most representative are 1,6- and 1,2-anhydro-sugars; others are less common and
have rather limited synthetic potential [3].
2.1 1,6-Anhydrosugars
2.1.1 1,6-Anhydrohexopyranoses
The most common 1,6-anhydrosugars are anhydro-aldopyranoses, which are formal derivatives of 6,8-dioxabicyclo[3.2.1]octane; less common are anhydro-aldofuranoses.
1,6-Anhydro-β-D-glucopyranose (levoglucosan), the most representative example of this class
of compounds, was first isolated in pure form in 1894 by Tanret upon treatment of naturally
occurring phenolic glycoside with barium hydroxide [2]. This compound is now conveniently
obtained by pyrolysis of starch or cellulose and its production is covered by many patents.
Other 1,6-anhydrosugars with different configurations, such as mannosan or galactosan, may
be prepared by pyrolysis of mannan ivory nut meal or α-lactose [2,3].
Generally, treatment of a sugar with a free hydroxyl group at the C-6 position possessing
a good leaving group at the anomeric position (halogen, azide, tosylate etc.) with a strong base
affords 1,6-anhydropyranoses [3]. Another method consists of a selective activation of a terminal hydroxyl group; this procedure is applicable for most 1,6-anhydro-pyranoses. FraserReid and co-workers described a large-scale synthesis of 1,6-anhydro-D-gluco- and D-mannopyranoses from free sugars by selective activation of the terminal position with tosyl chloride